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In Mitteleuropa kommen innerhalb der Gattung Diphasiastrum neben drei Ausgangsarten (D. alpinum, D. complanatum, D. tristachyum) drei Taxa hybridogenen Ursprungs vor (D. x issleri = D. alpinum x D. complanatum; D. x oellgaardii = D. alpinum x D. tristachyum; D. x zeilleri = D. complanatum x D. tristachyum). Alle sechs Taxa sind diploid. Die homoploiden Hybriden unterscheiden sich sowohl morphologisch als auch hinsichtlich ihres Kern-DNA-Gehaltes deutlich voneinander und nehmen eine intermediäre Stellung zwischen ihren Elternarten ein. Daher ist zu vermuten, dass es genetische Schranken für Rückkreuzungen gibt. Außer den regelmäßig auftretenden diploiden Hybriden konnten drei sehr seltene triploide Diphasiastrum-Hybriden nachgewiesen werden. Auf Grund ihres Kern-DNA-Gehaltes und der Morphologie kann auf folgende Kombinationen geschlossen werden:
Diphasiastrum alpinum x D. x issleri (Genomformel AAC),
Diphasiastrum alpinum x D. x oellgaardii (Genomformel AAT),
Diphasiastrum complanatum ssp. complanatum x D. x issleri (Genomformel ACC).
Es kann vermutet werden, dass diese triploiden Hybriden durch eine Kreuzbefruchtung zwischen einem diploiden Gametophyten, entstanden aus einer Diplospore, und einem haploiden Gametophyten hervorgegangen sind. Diplosporen könnten auch zur Vermehrung der diploiden Hybriden mittels Sporen beitragen; allerdings sind sie bei Flachbärlappen noch nicht experimentell eindeutig nachgewiesen. Bisherige Untersuchungen dreier genetischer Marker (cp, RPB, LFY) sowie die Ergebnisse einer AFLP-Analyse legen jedoch eine überwiegende de-novo-Entstehung durch primäre Kreuzungsereignisse nahe.
Die drei Elternarten unterscheiden sich hinsichtlich ihrer genetischen Diversität erheblich. Während von D. alpinum mindestens zwei genetische Linien existieren, ist D. tristachyum offensichtlich wenig variabel. Die größte genetische Vielfalt weist D. complanatum auf, für das eine sexuelle Reproduktion durch flowzytometrische Untersuchungen der gametophytischen Generation nachgewiesen werden konnte. Auch die Hybriden sind genetisch nicht einheitlich, was für unabhängige Entstehungsereignisse spricht.
Die Vertreter der Gattung Diphasiastrum weisen einen ausgeprägten Pioniercharakter auf und können Lebens-räume mit frühen Sukzessionsstadien erfolgreich besiedeln. Hier bilden sie durch ihr klonales Wachstum flächig ausgedehnte Bestände (Klone) aus. Diese können, längerfristig geeignete Standortbedingungen vorausgesetzt, ein Alter von vielen Jahrzehnten bis zu mehreren Hundert Jahren erreichen. Mit ihren staubfeinen Sporen sind Flachbärlappe auch zur Besiedlung von Gebieten, die von bestehenden Vorkommen weiter entfernt sind, mittels Langstreckentransport durch die Luft befähigt.
Flachbärlappe sind obligate Dunkelkeimer mit sich über mehrere Jahre erstreckenden Entwicklungszyklen. Die heterotrophen unterirdisch lebenden Gametophyten benötigen für Ihre Entwicklung Mykorrhizapilze. Funde von Gametophyten des Alpen-Flachbärlapps boten die Möglichkeit, den assoziierten Mykorrhizapilz morphologisch und genetisch zu untersuchen. Dieser wurde als zur Sebacinales-Gruppe B (Agariomycota) zugehörig identifiziert. Diese Pilzgruppe ist auch als Mykorrhizapartner von Ericaceen (Heidekrautgewächse) bekannt. Da keine Hinweise auf eine Mykorrhizierung des sporophytischen Bärlapp-Gewebes gefunden wurden, ist die Beziehung zwischen Pilz und Bärlapp möglicherweise nicht symbiotischer sondern parasitischer Natur. Der mykoheterotrophe Bärlapp-Gametophyt würde in diesem Fall epiparasitisch auf Vertretern der Ericaceen leben. Dies würde die regelmäßige Vergesellschaftung von Flachbärlappen mit verschiedenen Heidekrautgewächsen erklären. Eine ericoide Mykorrhiza bei Bärlappen, bestehend aus einem Netzwerk zwischen Ericaceen, Mykorrhizapilzen und Bärlapp-Gametophyten, wurde zuvor nicht beobachtet.
Die aktuelle Verbreitung der Flachbärlappe ist in den meisten Landesteilen Deutschlands und auch in einigen anderen Regionen Mitteleuropas weitgehend bekannt. Ihre früheren Arealbilder sind hingegen erst für Teilgebiete geklärt, was auf ihre schwierige Bestimmbarkeit und der über Jahrzehnte in der botanischen Literatur bestehenden taxonomischen Verwirrung zurückzuführen ist. Die frühere Verbreitung konnte auf der Basis kritischer Herbarrevisionen bislang für Niedersachsen und Bremen, Nordrhein-Westfalen, Thüringen und Teilgebiete Hessens und Bayerns rekonstruiert werden.
Die standortökologischen Ansprüche der Flachbärlapp-Sippen sind für Deutschland und einige Regionen angrenzender Länder hingegen gut untersucht. Es werden Sandböden mit unterschiedlich hohen Lehm- und Tonanteilen besiedelt, die relativ humusreich sind und größere Skelettanteile aufweisen können. Die Böden sind trocken bis frisch, reagieren sehr stark bis stark sauer (pH-Werte zwischen 2,9 und 4,5) und sind nährstoffarm (Stickstoffgehalte im Mittel zwischen 0,12 % und 0,25 %). Hinsichtlich ihrer Lichtansprüche unterscheiden sich die Flachbärlapp-Taxa erheblich. D. complanatum, D. tristachyum und ihre Hybride D. x zeilleri besiedeln recht heterogene Wuchsorte und sind sowohl an halbschattigen als auch lichtreichen Standorten zu finden (relativer Lichtgenuss meist zwischen 20 % und 80 %). D. alpinum und seine Hybriden D. x issleri und D. x oellgaardii bevorzugen dagegen offene Wuchsorte mit einem relativen Lichtgenuss zwischen 80 % und 100 %.
Die allermeisten Vorkommen von Flachbärlappen sind in Mitteleuropa heute an Sekundärstandorten anthropogenen Ursprungs zu finden. Primärstandorte stellen außerhalb des Alpenraumes die große Ausnahme dar. Die Vergesellschaftung der Flachbärlappe ist gut dokumentiert. Neben verschiedenen von Nadelhölzern dominierten Wald- und Forstgesellschaften (Leucobryo-Pinetum, Cladonio-Pinetum, Vaccinio myrtilli-Piceetum) treten sie in verschiedenen Vegetationstypen des Offenlandes mit lückiger und kurzrasiger Struktur auf (Vaccinio-Callunetum, Genisto anglicae-Callunetum, Violion- und Nardion-Gesellschaften, Festuca nigrescens-Agrostis capillaris-Bestände).
Die Flachbärlappe sind seit Jahrzehnten von einem dramatischen Bestandsrückgang betroffen und werden daher in den meisten nationalen Roten Listen Mitteleuropas als stark gefährdet oder sogar als vom Aussterben bedroht geführt. Hauptgrund ist das fast vollständige Verschwinden ihrer ehemaligen Lebensräume durch Aufgabe traditioneller Nutzungsformen und Änderungen in der forstlichen Bewirtschaftung. Die zunehmende Eutrophierung durch die ständig intensiver werdende Landwirtschaft stellt einen sukzessionsbeschleunigenden Faktor dar und bedingt, dass die Verweildauer eines Bestandes an einem Sekundärstandort ohne pflegende Eingriffe mittlerweile auf maximal 10 bis 15 Jahre gesunken sein dürfte. Allerdings lassen sich die Bestände durch das regelmäßige manuelle Entfernen bzw. Eindämmen pflanzlicher Konkurrenten stützen und ihre Überlebensdauer damit deutlich erhöhen, wie Erfahrungen im Rahmen diverser Artenhilfsprogramme in verschiedenen Teilen Deutschlands gezeigt haben. Auch die Flachbärlapp-Hybriden bilden langlebige und flächig ausgedehnte Klone aus und können fernab einer oder sogar beider Elternarten auftreten. Unabhängig von ihrer noch ungeklärten generativen Reproduktionsfähigkeit verhalten sie sich wie unabhängige Arten und sollten daher naturschutzfachlich auch als solche bewertet werden.
Der starke Rückgang sowie eine hohe internationale Verantwortlichkeit Deutschlands für einige Diphasiastrum-Taxa, speziell für D. x issleri und D. x oellgaardii, zeigen die dringende Notwendigkeit für gezielte Artenhilfsprogramme für diese faszinierende Pflanzengruppe.
Forests are ecologically important ecosystems, for example, they absorb CO2 from the
atmosphere, mitigate climate change, and constitute habitats for the majority of terrestrial
flora and fauna. Currently, due to increasing human pressure, forest ecosystems are
increasingly subjected to changing environmental conditions, which may alter forest growth
to varying degrees. However, how exactly different tree species will respond to climate
change remains uncertain and requires further comprehensive studies performed at different
spatial scales and using various tree-ring parameters.
This dissertation aims to advance the knowledge about tree-ring densitometry and
tree responses to climate variability and extremes at different spatial scales, using various
tree species. More specifically, the following aims are pursued: (i) to obtain and compare
wood density data using different techniques, and to assess variability among laboratories
(Chapter I). (ii) To investigate microsite effects on local and regional Scots pine (Pinus
sylvestris L.) responses to climate variability (Chapter II) and extremes (Chapter III),
using ring width (RW) and latewood blue intensity (LBI) parameters. (iii) To give a general
site- and regional-scales overview of Scots pine, pedunculate oak (Quercus robur L.), and
European beach (Fagus sylvatica L.) RW responses to climate variability (Chapter IV). (iv)
To discuss the challenges which may result from compiling tree ring records from different
(micro)sites into large-scale networks. The study area comprises nine coastal dune sites, each
represented by two contrasting microsites: dune ridge and bottom (Chapters II and III), and
310 different sites within the south Baltic Sea lowlands (Chapter IV).
The dissertation confirms that sample processing and wood density measuring are
very important steps, which, if not performed carefully, may result in biases in growth trends,
climate-growth responses, and climate reconstructions. The performed experiment proved
that the mean levels of different wood density-related parameters are never comparable due
to different measurement resolutions between various techniques and laboratories. Further,
the study revealed substantial biases using data measured from rings of varying width due
to resolution issues, where resolution itself and wood density are lowered for narrow rings
compared to wide rings (Chapter I).
The (micro)site-specific investigation showed that, depending on the species,
different climate variables (temperature, precipitation, or drought) constitute important
factors driving tree growth across investigated locations (Chapters II and IV). However,
there is evidence that the strength and/or direction of climate-growth responses differ(s)
between microsite types (Chapter II) and across sites (Chapter IV). Moreover, climategrowth
responses are non-stationary over time regardless of the tree species and tree-ring
parameter used in the analysis (Chapters II and IV). There are also differences in RW and
LBI responses to extreme events at dune ridge and bottom microsites (Chapter III).
The regional-scale investigations revealed that climate-growth responses (strength
and non-stationarity) are quite similar to those observed at the local scale. However,
compiling RW or LBI measurements into regional networks to study tree responses to
extreme events led to weakened signals (Chapter III).
The findings presented in Chapters II and IV suggest that the strength, direction,
and non-stationary responses are very likely caused by several climatic and non-climatic
factors. The mild climate in the south Baltic Sea region presumably does not constitute a
leading limiting growth factor, especially for Scots pine, whose distribution extends from
southern to northern Europe. Thus, the observed climate-growth responses are usually of
weak to moderate strength. In contrast, for other species reaching their distribution limit at
the Baltic coast, the climatic signal can be very strong. However, the observed findings also
result from the effects of microsite conditions, and potentially other factors (e.g.,
management, stand dynamic), which all together alter the physiological response of the tree
at a local scale. Although climate at the south Baltic Sea coast is mild, extreme climate events
may occur and affect tree growth. As demonstrated (Chapter III), extreme climate events
affected tree growth across dune sites, however, to varying degrees. The prominent
differences in tree responses to extreme climate events were significant at the local scale but
averaged out at the regional scale. This is very likely associated with observed microsite
differences, where each microsite experiences different drivers and dynamics of extreme
growth reductions.
This dissertation helped to demonstrate that integrating local tree-ring records into
regional networks involves a series of challenges, which arise at different stages of research.
In fact, not all possible challenges have been discussed in this dissertation. However, it can
be summarized that several steps performed first at the local scale are very important for the
quality and certainty of climate-growth responses, tracking tree recovery after extreme
events, and potential climate reconstructions at the larger scale. Among them, identification
of microsite conditions, sample preparation, and measurement, examination of growth
patterns and trends, and identification of a common limiting growth factor are very
important. Otherwise, the compilation of various tree-ring data into a single dataset could
lead to over- or underestimation of the results and biased interpretations.
Coastal sand dunes near the Baltic Sea are a dynamic environment marking the boundary between land and sea and oftentimes covered by Scots pine (Pinus sylvestris L.) forests. Complex climate-environmental interactions characterize these ecosystems and largely determine the productivity and state of these coastal forests. In the face of future climate change, understanding interactions between coastal tree growth and climate variability is important to promote sustainable coastal forests. In this study, we assessed the effect of microsite conditions on tree growth and the temporal and spatial variability of the relationship between climate and Scots pine growth at nine coastal sand dune sites located around the south Baltic Sea. At each site, we studied the growth of Scots pine growing at microsites located at the ridge and bottom of a dune and built a network of 18 ring-width and 18 latewood blue intensity chronologies. Across this network, we found that microsite has a minor influence on ring-width variability, basal area increment, latewood blue intensity, and climate sensitivity. However, at the local scale, microsite effects turned out to be important for growth and climate sensitivity at some sites. Correlation analysis indicated that the strength and direction of climate-growth responses for the ring-width and blue intensity chronologies were similar for climate variables over the 1903–2016 period. A strong and positive relationship between ring-width and latewood blue intensity chronologies with winter-spring temperature was detected at local and regional scales. We identified a relatively strong, positive influence of winter-spring/summer moisture availability on both tree-ring proxies. When climate-growth responses between two intervals (1903–1959, 1960–2016) were compared, the strength of growth responses to temperature and moisture availability for both proxies varied. More specifically, for the ring-width network, we identified decreasing temperature-growth responses, which is in contrast to the latewood blue intensity network, where we documented decreasing and increasing temperature-growth relationships in the north and south respectively. We conclude that coastal Scots pine forests are primarily limited by winter-spring temperature and winter-spring/summer drought despite differing microsite conditions. We detected some spatial and temporal variability in climate-growth relationships that warrant further investigation.
Coastal dunes near the Baltic Sea are often stabilized by Scots pine forests and are characterized by a mild climate. These ecosystems are affected by water shortages and might be influenced by climate extremes. Considering future climate change, utilizing tree rings could help assess the role of climate extremes on coastal forest growth. We used superposed epoch analysis to study Scots pine responses to droughts and cold winters, with focus on frequency, timing, and duration. We measured ring widths (RW) and latewood blue intensity (LBI) on samples extracted from trees growing at dune ridge and bottom microsites at the south Baltic Sea. At the regional scale, we observed some similarities in tree responses to both extremes between RW and LBI within the same microsite type and region. At the local scale, RW and LBI were more frequently influenced by cold winters than droughts. RW and LBI from dune ridges were more frequently influenced by droughts than RW and LBI from dune bottoms. LBI from both microsites was more often influenced by droughts than RW. RW and LBI from both microsites were similarly often influenced by cold winters. At both scales, the response time of RW and LBI after droughts predominantly lagged by one year, while cold winters were recorded in the same year. The typical duration of growth reductions after both extremes was one year for both RW and LBI. Our study indicates that Scots pine from the Baltic Sea region is sensitive to climate extremes, especially cold winters.
Agriculture in the populated islands of the Galapagos Archipelago, a protected area due to its unique biodiversity, has been detrimental to its conservation but highly required to meet food necessities. A potential solution to make agricultural farming more sustainable is adopting water-saving technologies (WSTs). Therefore, this study aimed to test the effectiveness of using WSTs such as Groasis Waterboxx® in three of the most valuable crops in the islands through participatory research with the involvement of a group of farmers from the Floreana and Santa Cruz islands and explore a possible transition to more sustainable agricultural practices. Capsicum annuum, Cucumis sativus and Solanum lycopersicum were cultivated using Groasis Waterboxx® and compared to conventional irrigation practices (drip-irrigated controls) to assess the variability of productivity, the number of fruits and individual fruit weight (IFW). In addition, differences in plant traits were analyzed by crop, and island. Results suggested that WSTs such as Groasis Waterboxx® may provide on-farm benefits regarding the yields of the studied traits. From this study, it is difficult to determine whether participation in such a research study will permanently change irrigation practices. However, the participant’s responses to the study suggest an increase in their understanding of the use and benefits of WST.
Die mitteleuropäischen Flachbärlappe (Gattung Diphasiastrum) sind in Deutschland alle hochgradig gefährdet und können ohne geeignete Artenhilfsmaßnahmen hier nicht dauerhaft überleben. In der vorliegenden Arbeit werden die Grundlagen für ein Artenhilfsprogramm geschaffen, indem die Reproduktionsbiologie untersucht worden ist und die ökologischen Ansprüche und Gefährdungsursachen ermittelt wurden, um entsprechende Hilfsmaßnahmen für die Arten zu entwickeln.
Um Rückschlüsse auf das Reproduktionssystem der Eltern- und Hybridarten zu erhalten, wurde die genetische Diversität ermittelt. Dabei kam das fingerprinting-Verfahren AFLP zum Einsatz, womit Arten und genetisch verschiedene Individuen voneinander abgegrenzt werden können. Verwendet wurden die beiden Primer-Kombinationen EcoRI-AAG / VspI-CT und EcoRI-ACT / VspI-CAG. Die größte genetische Diversität der Elternarten weist D. complanatum auf, die überwiegend durch echte Fremdbefruchtung (outcrossing) entsteht, während die genetische Diversität der beiden anderen Elternarten D. alpinum und D. tristachyum gering ist und nur knapp oberhalb einer definierten Fehlerrate liegt. Die Proben der Hybridarten unterscheiden sich so stark voneinander, dass davon ausgegangen werden muss, dass dies immer wieder neu entstehende F1-Hybriden sind, wenngleich die Unterschiede bei D. oellgaardii vergleichsweise gering aufgrund der geringen genetischen Diversität der Elternarten D. alpinum und D. tristachyum ist.
Die Sporenproduktion in den Sporenständen wurde unter anderem direkt durch Zählung von Sporen in den Sporangien unterm Stereomikroskop und Zählung der Sporangien in den Sporenständen ermittelt. Sporangien von L. clavatum enthalten demnach 27735 (± 7492) Sporen pro Sporangium, 105,2 (± 3,7) Sporangien pro Sporenstand und hochgerechnet etwa 2,1 bis 3,8 Millionen Sporen pro Sporenstand.
Die terminale Fallgeschwindigkeit liegt für L. clavatum bei 2,16 (± 0,11) cm*s-1 und für D. complanatum bei 2,25 (± 0,10) cm*s-1. Die Sporen haben einen Durchmesser von 29,5 (± 2,0) μm bzw. 32,3 (± 2,5) μm. Die gemessene Geschwindigkeit liegt deutlich unter der theoretischen und lässt sich damit erklären, da Sporen keine perfekten Kugeln sind und aufgrund ihrer stark reliefierten Oberfläche Turbulenzen erzeugt werden, die den Fall verlangsamen.
Die Anzahl der in Entfernungen bis 200 m zu einer sporenbildenden Population fliegenden Sporen wurde mithilfe von vertikalen klebenden Sporenfallen bei D. complanatum, D. tristachyum und L. clavatum bestimmt. Nur für die Population von L. clavatum mit 11358 reifen Sporenständen auf kleiner Fläche wurden weitere Berechnungen durchgeführt. Folgende Funktion beschreibt die Anzahl der durch die Luft fliegenden Sporen in einer Höhe von etwa 40 cm über dem Boden in Abhängigkeit zur Entfernung x: f(x) = 45878*x-2,302 (R² = 0,9979). Es konnten selbst in 200 m Entfernung noch einzelne Sporen an den Sporenfallen nachgewiesen werden. Da die maximale theoretische Ausbreitungsdistanz bei nur knapp 130 m liegt, selbst wenn ein konstant horizontal wehender Wind von 100 km/h angenommen wird, müssen aufwärtsgerichtete Luftströmungen eine entscheidende Rolle bei der Fernausbreitung spielen.
Die Ansiedlungsversuche wurden im Thüringer Schiefergebirge am Grünen Band bei Brennersgrün (D. alpinum und D. tristachyum) und im Pöllwitzer Wald (D. complanatum) durchgeführt. Als Vergleichsart wurde wieder L. clavatum verwendet. Die Sprossverpflanzungen verliefen insgesamt erfolgreich mit einer Überlebensrate von 8% für D. alpinum, 17% für D. complanatum, 8% für D. tristachyum und 22% für L. clavatum. Der jährliche Rhizomzuwachs liegt bei 0,5 cm, 13,3 (± 1,8) cm, 7,5 cm bzw. 9,1 (± 4,0) cm für die entsprechenden Arten.
Die Vegetationsbedeckung vorher abgeplaggter Flächen liegt zwischen 39 und 53% nach zwei Jahren, jedoch mit großen Unterschieden selbst zwischen benachbarten Flächen und wird hauptsächlich durch ein schnelles Mooswachstum bestimmt.
Nach etwa fünf Monaten sind keine Sporen auf sterilem Nährstoffmedium gekeimt, obwohl diese unterschiedlich behandelt wurden, zum Beispiel mit Rauchgas, Hitze, konzentrierter Schwefelsäure oder durch Mörsern. Auch die Keimungsversuche an den Wuchsorten waren nach 2,5 Jahren erfolglos. Eine Erklärung kann ein Dormanzstadium unbekannter Dauer vor der Keimung sein.
Der Anzahl der jährlich gebildeten vertikalen Sprossbüschel wurde indirekt für je eine Population für D. zeilleri (2,5/Jahr) und D. issleri (2,0/Jahr) bestimmt, indem der Quotient aus der Anzahl der Sprossbüschel an der längsten Rhizomverbindung und dem bekannten Alter des Standorts ermittelt worden ist. Die Zugehörigkeit von Rhizomstücken zu einem Klon wurde mit der AFLP-Methode abgesichert. Die meisten Populationen in Deutschland werden demnach mehrere Jahrzehnte alt, jedoch ohne beobachtete Verjüngung über Prothallien. Eine Erklärung könnten die immer noch sehr geringen pH-Werte in den Unterböden von 3,6 (± 0,24) sein, die giftige Al3+-Ionen pflanzenverfügbar machen.
Zusammenfassung
Der Iran besitzt zwölf UNESCO-Biosphärenreservate, die reich an einmaligen Natur- und Kulturschätzen und hohem menschlichen Potenzial aus verschiedenen ethnischen Gruppen sind. Die ersten neun Biosphärenreservate wurden frühzeitig mit den ersten Biosphärenreser-vaten der Welt im Jahr 1976 gegründet, die auch gleichzeitig andere Kategorien der Schutz-gebiete im Iran wie Nationalparks, geschützte Lebensräume für Wildtiere und Naturschutzge-biete beinhalten und bis heute unter ihrem alten Status verwaltet werden. Damit entsprechen sie nicht den aktuellen internationalen Anforderungen an Biosphärenreservate und besteht die Gefahr, dass diese Gebiete in baldiger Zukunft ihre natürlichen und kulturellen Werte verlie-ren und irreversibel beschädigt werden.
Diese Studie untersucht und bewertet die zwei exemplarisch ausgewählten iranischen Bio-sphärenreservate Golestan und Dena unter Berücksichtigung der UNESCO-Kriterien, unter anderem die Ziele und Grundlagen der Sevilla-Strategie und der Internationalen Leitlinien für das Weltnetz der Biosphärenreservate (1995). Das Biosphärenreservat Golestan wurde im Jahr 1976 gegründet und ist somit eines der ältesten Biosphärenreservate des Irans. Bei dem im Jahre 2010 gegründeten Biosphärenreservat Dena, handelt es sich um das jüngste Biosphä-renreservat im Iran zu Beginn der Studie.
Beide Schutzgebiete sind gebirgig und beinhalten die wichtigsten Waldökosysteme mit einer großen Biodiversität. Das Biosphärenreservat Golestan befindet sich im Nordosten des Irans im östlichsten Teil des Elburs-Gebirge und Dena liegt im zentralen Zagros-Gebirge im Westiran.
Für den methodischen Ansatz dieser Studie wurde ein Methodenmix aus qualitativen Elemen-ten: Oral History, Interviews, offenen Fragen und Teilnehmender Beobachtung und quantita-tiven Elementen: SWOT-Analyse (engl. Akronym für Strengths (Stärken), Weaknesses (Schwächen), Opportunities (Chancen) und Threats (Bedrohungen) und Auswertung der Fra-gebögen mit Hilfe des statistischen Programms SPSS20 angewendet.
Die untersuchten Gruppen bestanden gemäß der jeweiligen Analyse aus Experten des De-partments für Umwelt (DoE) in Teheran, den Provinz-Umweltschutzbehörden von Golestan und Kohgiluye und Boyer Ahmad, Akademikern, der Nationale Commission for UNESCO in Teheran, Zeitzeugen, lokaler Bevölkerung, Rangern, Umwelt-NGOs (engl. Non-Governmental Organization), dem Tourismus-Sektor und den Umwelt-Medien.
Die Ergebnisse in dieser Studie zeigen, dass die Entwicklung der iranischen Biosphärenreser-vate seit ihrer Gründung 1976 bis heute von den Veränderungen der wirtschaftlichen, politi-schen und gesellschaftlichen Situation des Irans und demzufolge von den Veränderungen in der Organisationsstruktur des Departemants für Umwelt (DoE) und der Prioritätensetzung in Bezug auf die Gesetze zu Umwelt- und Naturschutz beeinflusst wurden.
Überdies stellen die Ergebnisse dar, dass in den beiden untersuchten Biosphärenreservaten Golestan und Dena hinsichtlich der internationalen UNESCO-Kriterien und Richtlinien ver-gleichsweise ähnliche Defizite und Mängel bestehen:
• fehlende nationale Rechtsstruktur für die Biosphärenreservate im Iran,
• fehlender Managementplan für Biosphärenreservate und somit auch schwaches Mana-gementsystem der Biosphärenreservate,
• Mangel an Kenntnissen über Biosphärenreservate,
• beschränkte Beteiligung an den Angelegenheiten der Biosphärenreservate seitens aller untersuchten Gruppen – von der lokalen Bevölkerung bis hin zu den staatlichen Ent-scheidungsträgern und
• ungenügende Zusammenarbeit zwischen Staat und Interessengruppen in diesen Gebie-ten.
Ebenso wurde in dieser Studie versucht, konkrete Lösungsansätze zur Verwirklichung der Ziele der Biosphärenreservate bzw. der Verbesserung ihrer aktuellen Situation zu empfehlen.
In diesem Zusammenhang ist es erforderlich, dass Gesetze für die Biosphärenreservate auf nationaler Ebene definiert und die vorhandenen Biosphärenreservate im Iran gründlich nach internationalen Kriterien untersucht und mit einem systematischen Managementplan auf wis-senschaftlicher Grundlage verwaltet werden. Des Weiteren benötigen diese Gebiete für ihre Funktionalität eine Erhöhung und Verbesserung der Kenntnisse über die Biosphärenreservate der aktiven Personen, sowie der Kooperation und Kommunikation zwischen allen zuständigen Behörden und Interessengruppen. Hiermit soll allen sozialen, kulturellen, geistigen und wirt-schaftlichen Anliegen der Interessengruppen, vor allem aber der lokalen Bevölkerung, Rech-nung getragen werden, entsprechend dem weltweiten Ansatz der UNESCO-Biosphärenreservate.
Winter warming is ecologically more relevant than summer
warming in a cool-temperate grassland
(2019)
The cultivation of common reed (Phragmites australis) is one of the most promising practices of paludiculture on fen peatlands. This highly productive grass has a high adaptation capacity via high levels of genetic diversity and phenotypic plasticity. In this study, a reed experimental site established on a degraded fen in 1996/97 with a mixture of monoclonally (meristematically propagated plantlets) and polyclonally (pre-grown seedlings) planted plots was investigated by microsatellite genotyping. All nine genotypes of the monoclonal planted plots were recovered and could be genetically characterized; invasion by other genotypes was negligible. Similarly, the polyclonal plots sustained high clonal diversity with no prevalence of a single genotype. The growth characteristics of the five quantitatively investigated genotypes significantly differed from each other (α = 0.05): dry biomass per stem 5–18 g, panicles per m2 20–60, average stem diameter 3.5–6 mm, height 170–250 cm. Similarly, the persistence of genotypes at the planted plots and their invasiveness (ability to invade neighboured plots) varied. These results show that common reed stands are extremely persistent even if established with genotypes that are likely not to be locally adapted. Their genetic structure remained stable for at least 24 years regardless of the planting density (1, 4, and 10 plants per m2). Our results indicate that farmers may be able to maintain favourable genotypes for many years, thus the selection and breeding of common reed as a versatile crop for rewetted peatlands is a promising objective for paludiculture research.
Numerous insertions of mitochondrial DNA in the genome of the northern mole vole, Ellobius talpinus
(2024)
Background
Ellobius talpinus is a subterranean rodent representing an attractive model in population ecology studies due to its highly special lifestyle and sociality. In such studies, mitochondrial DNA (mtDNA) is widely used. However, if nuclear copies of mtDNA, aka NUMTs, are present, they may co-amplify with the target mtDNA fragment, generating misleading results. The aim of this study was to determine whether NUMTs are present in E. talpinus.
Methods and results
PCR amplification of the putative mtDNA CytB-D-loop fragment using ‘universal’ primers from 56 E. talpinus samples produced multiple double peaks in 90% of the sequencing chromatograms. To reveal NUMTs, molecular cloning and sequencing of PCR products of three specimens was conducted, followed by phylogenetic analysis. The pseudogene nature of three out of the seven detected haplotypes was confirmed by their basal positions in relation to other Ellobius haplotypes in the phylogenetic tree. Additionally, ‘haplotype B’ was basal in relation to other E. talpinus haplotypes and found present in very distant sampling sites. BLASTN search revealed 195 NUMTs in the E. talpinus nuclear genome, including fragments of all four PCR amplified pseudogenes. Although the majority of the NUMTs studied were short, the entire mtDNA had copies in the nuclear genome. The most numerous NUMTs were found for rrnL, COXI, and D-loop.
Conclusions
Numerous NUMTs are present in E. talpinus and can be difficult to discriminate against mtDNA sequences. Thus, in future population or phylogenetic studies in E. talpinus, the possibility of cryptic NUMTs amplification should always be taken into account.
Da Feuchtgebiete nicht wie reguläres Ackerland genutzt werde können, werden sie oft als Ödland betrachtet und daher für Ackerbau trockengelegt. Diese sehr einseitige Perspektive auf Feuchtgebiete übersieht die vielfältigen Ökosystemleistungen, die es Menschen und Natur zur Verfügung stellt. Einige dieser Leistungen sind das Speichern und die Reinigung von Abwasser, die Bereitstellung von Lebensmitteln und Rohmaterialien, die lokale Klimaregulierung und die Nutzung als Habitat. Viele dieser Leistungen werden von der Natur „umsonst“ bereitgestellt und haben keinen monetären Wert auf traditionellen Märkten. In China bedecken Feuchtgebiete 8% der Gesamtfläche, sind aber in einer bedrohlichen Situation, auch wenn in den letzten Jahren einige Teile erfolgreich restauriert werden konnten. In den vergangenen 50 Jahren gingen mehr als 20% der Feuchtgebiete durch Verschmutzung, Wasserableitung und -aufstauung, Nutzbarmachung, Trockenlegung und Übernutzung der Resourcen verloren. Die Wasserressourcen und Feuchtgebiete – besonders in Nord- und Nord-Ost-China sind bedroht, da sie in ariden oder semi-ariden Regionen liegen. Feuchtgebiete stellen gleichwohl wichtige Ökosystemdienstleistungen für die genannte Region zur Verfügung und tragen signifikant und in vielfältiger Weise zu lokalem Lebensunterhalt bei, z. B. durch Nahrungs- und Rohstoffbereitstellung. Ziel dieser Arbeit war es, zu einer ökonomisch-ökologischen Bewertung des Gemeinen Schilfs (Phragmites australis) am Wuliangsuhai See zu kommen, in dem Schilf in großen Mengen vorkommt und lokal relevant ist. Schilf wurde an einem Fallbeispiel in der Inneren Mongolei, China, untersucht, ein Teil des Forschungsprojektes “Sustainable Water Management and Wetland Restoration in Settlement of Arid Central Asia” war, welches in der Inneren Mongolei, China, durchgeführt wurde. Meine Arbeit beeinhaltete vielfältige Apsekte: Zuerst wurde eine detaillierte Literaturanalyse durchgeführt, um die kommerzielle Nutzung von Schilf weltweit zu untersuchen. Es konnten vielfältige Verwertungen ausgemacht werden, viele lokal und nur in kleinem Maßstab (z. B. Nahrung), einige andere innovativ und/oder noch im Experimentierstadium (z. B. Ethanol). Im Bezug auf den Wuliangsuhai See kann geschlussfolgert werden, dass nur große, “einfache” Lösungen in Frage kommen. Besonders der Einsatz als Rohstoff zur Verfeuerung und als Baumaterial scheint erfolgversprechend. Daran anschließend wurde die Biomasseproduktivität am Wuliangsuhai See mit Hilfe zweier Feldkampagnen erhoben und dann auf den gesamten See projiziert. Diese Daten waren entscheidend, da sie Basis waren, um die totale verfügbare Biomasse sowie auch den Einfluss der Schilfernte auf das Nährstoff-Budget abzuschätzen, da ein erheblicher Anteil an Nährstoffen jährlich durch die Ernte dem See entzogen wird. Nach der Bestimmung der verfügbaren Schilfressourcen wurde deren Verwendung durch qualitative Interviews untersucht und mit dem „Netchain Approach“ dargestellt. Die verschiedenen Interessengruppen, die in das Schilfgeschäft involviert sind, sowie deren Einkommen wurden skizziert. Es wurde deutlich, dass die Verwertung zur Papierproduktionen aus einer Vielzahl von Gründen kaum profitabel ist. Basierend auf dieser Erkenntnis wurden vier verschiedene Szenarien für eine innovative Schilfenergienutzung am Wuliangsuhai See analysiert und bewertet. Die Schilfenergienutzung ist unter bestimmten Voraussetzungen profitabel, aber nur schwer wettbewerbsfähig gegenüber günstiger und lokal verfügbarer Kohle. Abschließend wurde der Wuliangsuhai See in einen umfassenderen Ausblick eingeordnet, welche auch das Bewässerungssystem stromaufwärts miteinschloss. Vier Szenarien beleuchteten, wie heutige Entscheidungen die Zukunft des Sees beeinflussen. Diese Arbeit präsentiert die folgenden Haupteinsichten und Empfehlungen für das Management des Wuliangsuhai Sees: 1. Ein übergreifendes Konzept für den Wuliangsuhai See ist nötig, welches auch das gesamte Hetao Bewässerungsgebiet miteinbezieht. 2. Der See ist in dieser sehr trockenen Gegend einzigartig und sollte nicht nur für die Bereitstellung von Marktgütern, sondern auch für „Nicht-Markt-Leistungen“, wie die Abwasserreinigung, beachtet werden. 3. Die Restorationsleistung der Schilfernte konnte in dieser Publikation gezeigt werden und sollte bei zukünftigen Managemententscheidungen berücksichtigt werden. 4. Die lokale Schilfökonomie wird von verschiedenen Seiten herausgefordert. Dennoch scheint auch die lokale Schilfenergienutzung kaum profitabel. 5. Aufgrund der hohen Relevanz der Schilfökonomie für die lokale Ökonomie und Ökologie sollte die Regierung die Seeverwaltung unterstützen. Zusammenfassend konnten die vielfältigen sozialen, ökologischen und ökonomischen Werte von Schilf am Wuliangsuhai See aufgezeigt werden. Da nur geringe Informationen vorhanden waren, stellt dies den ersten umfassenden Überblick dar und soll Entscheidungsträgern ermöglichen, auf diesen Informationen basierend Entscheidungen für die Zukunft des Sees zu treffen.
Tree growth in northern and upper treeline ecotones of the circumpolar boreal forest is
generally limited by temperature, i.e., trees grow generally more under warm, and less under
cold climatic conditions. Based on the assumption that this relationship between tree growth
and climate is linear and stable through time, dendroclimatologists use tree rings as natural
archives to reconstruct past temperature conditions. Such tree-ring based reconstructions,
together with other natural archives (e.g., ice cores and pollen), constitute our understanding of
past climatic conditions that reach beyond modern instrumental records.
However, a steadily increasing amount of studies reports a recent reduction or loss of the
summer temperature signal for several species and sites of the boreal forest. Such a reduction
of temperature sensitivity results in temporally unstable climate-tree growth relationships,
which challenges the work of dendroclimatologists by potentially leading to miscalibrations of
past climatic conditions. On the upside, this shift in the trees’ climate sensitivity might point to
a shift in tree growth-limiting factors and thus serve as an early indicator of climate change
impacts. There is evidence that this recent reduction in temperature sensitivity might be caused
by the observed strong temperature increase at high latitudes, and thus temperature-induced
drought stress. Other potential drivers and amplifiers of this phenomenon are differing microsite
conditions (dry vs. wet soils) and factors inherent to trees, like genetic properties or age
effects.
In this PhD thesis, I systematically assessed the effects of frequently discussed drivers of
unstable climate-tree growth relationships (climate change, micro-site effects, genetical
predisposition) on two representative species of the boreal forest, white spruce in North
America and Scots pine in Eurasia, across various temporal and spatial scales. I used classical
(tree-ring width) and more novel (wood density, quantitative wood anatomy)
dendrochronological proxies to unravel the effects from annual to sub-monthly resolution.
More precisely, in chapter I, white spruce clones were compared to non-clones at two treeline
sites in Alaska to test whether their growth patterns differ, and whether white spruce clones are
generally suitable for dendroclimatic assessments. Clonal reproduction is frequent at treeline
due to harsh conditions, but might lead to competition among individuals due to the close
proximity among each other, which in turn might obscure their climatic signal. Second, I tested
the effect of warmer and drier climatic conditions on the summer temperature signal of Scots
pine in Eurasia (chapter II) and on the growing season moisture signal of white spruce in North
America (chapter III), respectively. Temperature-induced drought stress is expected to be the
most important driver of unstable climate-growth relationships in the boreal forest. I included
several sites across latitudinal (50-150 km) and longitudinal (1,000-2,200 km) gradients to
cover large parts of the species’ distribution ranges. Since Scots pine covers a wide range of
ecological habitats, I additionally tested the effect of dry and wet micro-site conditions on the
summer temperature signal of Scots pine in chapter II. Finally, in chapter IV, a systematic
literature review was carried out in order to investigate the distribution of unstable climategrowth
relationships in global tree-ring studies, and the usage of such series in climate
reconstructions. Furthermore, the scientific impact of these potentially inaccurate climate
reconstructions was assessed.
In this PhD project, warmer and drier climatic conditions led to temporally unstable climate
signals in both Scots pine (chapter II) and white spruce (chapter III), as expected. Unstable
climate-growth relationships were found for all tested tree-ring proxies and at all sites in North
America, and at most sites in Eurasia. Micro-site effects (chapter II) and clonal growth
(chapter I) had no significant effect on the climate sensitivity and high-frequency variability
of the tested species, but affected absolute growth. The review (chapter IV) revealed that the
phenomenon of unstable climate-growth relationships is globally widespread, and occurs
independent of tree species, geographic location, and tree-ring and climate proxies. While
reconstructions inferred from these unstable relationships are frequent and respective papers
have a high impact, the tree-ring community seems to increasingly recognize the challenge of
unstable climate-growth relationships.
With these findings, this PhD project helped to shed more light on the frequency, underlying
drivers, and the impact of unstable climate-growth relationships in boreal forest trees, as well
as underlying reaction processes in trees. Above all, this PhD project suggests that the loss of
climate sensitivity is caused by a change of growth limiting factors: temperature limitation
seems to be suspended in warmer and drier years for Scots pine in Eurasia, and moisture
limitation first arises under warm/dry conditions for white spruce in North America. Due to
plastic growth responses in trees, the general assumption in dendroclimatology – that climategrowth
relationships are stable through time – seems to be incompatible with the principle of
limiting factors (one factors is always most growth limiting).
To improve the validity of future climate reconstructions, statistical approaches considering
synchronously or changing climatic limiting factors need to be promoted, along with attempts
to select the best responding trees from a dataset. Furthermore, a better understanding of nonclimatic
factors potentially affecting tree growth (e.g., age, disturbance, soil parameters) is
needed. A growth reduction of mature and dominant white spruce trees sampled in this PhD
project seems likely under future warming conditions, with series of wood cells being valuable
early indicators of climate change effects in white spruce. However, inferences cannot be
extended to the entire stand due to the applied sample design. Projected climate warming will
probably lead to a further reduction of the summer temperature signal in trees of the northern
boreal forest, while wider consequences for forest growth and productivity are unclear.
Tree growth at northern boreal treelines is generally limited by summer temperature, hence tree rings serve as natural archives of past climatic conditions. However, there is increasing evidence that a changing summer climate as well as certain micro-site conditions can lead to a weakening or loss of the summer temperature signal in trees growing in treeline environments. This phenomenon poses a challenge to all applications relying on stable temperature-growth relationships such as temperature reconstructions and dynamic vegetation models. We tested the effect of differing ecological and climatological conditions on the summer temperature signal of Scots pine at its northern distribution limits by analyzing twelve sites distributed along a 2200 km gradient from Finland to Western Siberia (Russia). Two frequently used proxies in dendroclimatology, ring width and maximum latewood density, were correlated with summer temperature for the period 1901–2013 separately for (i) dry vs. wet micro-sites and (ii) years with dry/warm vs. wet/cold climate regimes prevailing during the growing season. Differing climate regimes significantly affected the temperature signal of Scots pine at about half of our sites: While correlations were stronger in wet/cold than in dry/warm years at most sites located in Russia, differing climate regimes had only little effect at Finnish sites. Both tree-ring proxies were affected in a similar way. Interestingly, micro-site differences significantly affected absolute tree growth, but had only minor effects on the climatic signal at our sites. We conclude that, despite the treeline-proximal location, growth-limiting conditions seem to be exceeded in dry/warm years at most Russian sites, leading to a weakening or loss of the summer temperature signal in Scots pine here. With projected temperature increase, unstable summer temperature signals in Scots pine tree rings might become more frequent, possibly affecting dendroclimatological applications and related fields.
The frequency of sudden, strong warming events is projected to increase in the future. The effects of such events on spring phenology of trees might depend on their timing because spring warming has generally been shown to advance spring budburst while fall and winter warming have been shown to delay spring phenology. To understand the mechanism behind timing-specific warming effects on spring phenology, I simulated warming events during fall, mid-winter and at the end of winter and quantified their effects on bud dormancy depth and subsequently on spring leaf out. The warming events were carried out in climate chambers on tree seedlings of Betula pendula and Fagus sylvatica in October, January, and February. Control seedlings were kept at photoperiod and temperature matching the daily fluctuating field conditions. Warmed seedlings were kept 10°C warmer than the control seedlings for 10 days during the respective warming periods. Warming in October increased bud dormancy depth and decreased spring leaf-out rate only for F. sylvatica, whereas warming in February reduced bud dormancy depth and advanced spring leaf-out rate only for B. pendula. Neither bud dormancy depth nor spring leaf out rate were affected by January warming. The results indicate that warming-induced changes in bud dormancy depth may explain species- and timing-specific warming effects on spring phenology. The extent to which the timing of bud dormancy phases is species-specific will influence among-species variation in future spring leaf out times.
The onset of the growing season in temperate forests is relevant for forest ecology and biogeochemistry and is known to occur earlier with climate change. Variation in tree phenology among individual trees of the same stand and species, however, is not well understood. Yet, natural selection acts on this inter-individual variation, which consequently affects the adaptive potential to ongoing environmental changes. Budburst dates of 146 mature individuals of Fagus sylvatica, the dominant natural forest tree of central Europe, were recorded over 12 years in one forest stand of 1 ha in the Müritz National Park, Germany. The tree-specific location, topographical differences, as well as social status, were measured to explain the inter-individual variation in budburst. Furthermore, inter-individual differences in bud dormancy were quantified. Additional phenology and weather data across Germany from 405 sites over a 25-year period was used to put the insights from the single stand into perspective. Consistent phenological ranking over the years with respect to early and late flushing trees was observed within the single forest stand, with 23 trees consistently flushing 3–6 days earlier and 22 trees consistently flushing 3–10 days later than the median. Trees flushing consistently early varied most in their spring budburst dates and were less dormant than late-flushing trees already in mid-winter. The higher variation in earlier flushing trees was best explained by a slower warming rate during their budburst period in the observed stand as well as across Germany. Likewise, years with a lower warming rate during the budburst period were more variable in budburst dates. The rate of warming during spring time is crucial to accurately project future within-species variation and the resulting adaptive potential in spring phenology of dominant forest tree species.
Stoffflüsse in Makrophytensystemen: Ein Vergleich zwischen Küstenlagunen der südlichen Ostsee
(2017)
In früheren Jahrzehnten verschlechterte sich der ökologischen Zustand von zahlreichen inneren Küstengewässern der Ostsee durch die Eutrophierung, was z. B. zu intensiven Algenblüten führte. Submerse Makrophyten können den ökologischen Zustand von Süßgewässern verbessern, denn sie unterstützen z. B. die Sedimentation von suspendiertem Material und verringern die Resuspension. Zudem reduzieren sie indirekt das Phytoplankton, weil sie Zooplankton einen Prädationsschutz bieten und somit die Beweidung des Phytoplanktons durch das Zooplankton fördern. Es ist möglich, dass diese Rückkopplungsmechanismen in Brackgewässern weniger effektiv sind. Das Zooplankton ist anders zusammengesetzt und beweidet dadurch weniger effektiv das Phytoplankton. Außerdem wird es selbst, innerhalb der Makrophyten, durch bestimmte Fische und Invertebraten gefressen. In der vorliegenden Arbeit, wurden die Interaktionen zwischen submersen Makrophyten und ihrer abiotischen und biotischen Umgebung in zwei verschiedenen Küstengewässern der südlichen Ostsee untersucht: Vitter Bodden (mesotroph, Makrophyten-dominiert) und Darß-Zingster Boddenkette (DZBK, eutroph bis stark eutroph, Phytoplankton-dominiert). Die folgenden Parameter wurden von Juni bis September 2013 (Vitter Bodden) und von März bis November 2014 (DZBK) gemessen: Lichtattenuation, Konzentration von Gesamt-suspendiertem Material (TSM), von Chlorophyll a (Chl a), von Gesamt-Phosphor (TP) und von Gesamt-Stickstoff (TN). Zudem wurden die Verhältnisse TP zu TN und Chl a zu TP bestimmt. Der Beweidungsdruck des Zooplanktons auf das Phytoplankton wurde sowohl für den Tag als auch für die Nacht berechnet, in dem das jeweilige Zooplankton ausgezählt, die Biomasse und die Beweidungsrate berechnet wurde. Im Vitter Bodden wurde die Zusammensetzung der Makrophyten bestimmt, sowie ihr Bedeckungsgrad und ihr Anteil an der Wassersäule (PVI) in einer Wassertiefe <1 m geschätzt. In der DZBK wurde die Biomasse der Makrophyten bis in eine Wassertiefe von 1,9 m bestimmt. Die Tiefenverbreitung der Makrophyten war im Vitter Bodden nicht Licht-limitiert, aber in der DZBK, da sich dort der Hauptanteil der Makrophytenbiomasse nur bis in eine Wassertiefe von 1 m befand. In der DZBK hatte das Phytoplankton einen großen Anteil an der Lichtattenuation und limitierte dadurch vermutlich die Lichtverfügbarkeit nicht nur für die Makrophyten sondern auch für sich selbst. Aufgrund der TN zu TP Verhältnisse war das Phytoplankton in der DZBK P-limitiert, während es im Vitter Bodden durch beide Nährstoffe gleichzeitig limitiert war. Die Beweidung durch das Zooplankton konnte zeitweise vermutlich das Phytoplankton im Vitter Bodden reduzieren, aber nicht in der DZBK. Der Bedeckungsgrad der Makrophyten war hoch, aber sie hatten eine flache Wachstumsform und daher nur einen geringen PVI. Zusammenfassend kann gesagt werden, dass der vermutlich hohe Wasseraustausch mit der Ostsee und der fehlende Eintrag aus Fließgewässern verantwortlich für die hohe Lichtverfügbarkeit im Vitter Bodden sind. Ein möglicher Einfluss der Makrophyten auf Wassertrübung, Nährstoffe, Phytoplankton und Zooplankton wurde vermutlich durch diesen Wasseraustausch maskiert. Im Gegensatz dazu gab es keine Effekte der Makrophyten auf Nährstoffe in der Wassersäule, sowie auf Phytoplankton und Zooplankton in der DZBK, da die Makrophyten nur auf die Randbereiche der Bodden beschränkt sind. Da Sedimentation und Resuspension hauptsächlich die Wassertrübung beeinflussen, wurde in einem weiteren Teil der vorliegenden Arbeit ermittelt, in wie weit Wind-induzierte Wellen die Sedimentationsraten beeinflussen, wenn sie unmittelbar sedimentiertes Material wieder resuspendieren. Zu diesem Zweck wurden zwei verschiedene Sedimentationsfallen verwendet: Zylinderfallen (ZF) und Tellerfallen (TF). Die TF wurden in dieser Studie das erste Mal an einem Wellen-exponiertem Standort verwendet. Sie erlaubten, dass unmittelbar sedimentiertes Material wieder resuspendiert werden konnte, was die ZF nicht konnten. Sedimentationsraten wurden mit beiden Fallentypen in einer Wassertiefe zwischen 0,9 m und 1,6 m bestimmt. Die Wellenexposition wurde berechnet, indem die halbe Oberflächenwellenlänge (λ/2) durch die Wassersäule oberhalb der Fallen (dF) dividiert wurde. Eine hohe Wellenexposition war definiert als (λ/2) / dF >1. Die Sedimentationsraten in beiden Fallentypen waren von der Wellenexposition beeinflusst. Jedoch in gegensätzlicher Weise. Bei hoher Wellenexposition sedimentierte ein geringerer Anteil des TSM pro Stunde auf den TF als bei geringer Wellenexposition, während in den ZF ein größerer Anteil sedimentierte. Daher wurde die Sedimentationsrate bei hoher Wellenexposition mit den ZF überbestimmt. Die verwendeten TF sind ein viel versprechendes Mittel um Sedimentationsraten in flachen, Wellen-exponierten Orten abzuschätzen, denn sie reflektieren den unmittelbaren Einfluss von Wellenbewegungen auf die Sedimentation von suspendiertem Material.
Over thousands of years, peatlands around the world have accumulated carbon (C) stocks of global importance. Drainage for agriculture, forestry and peat extraction has transformed many peatlands from long-term sinks into strong sources of carbon dioxide (CO2). Peat extraction is worldwide responsible for about ten percent of drained peatlands and is mainly carried out in northern countries and Eastern Europe. In Belarus, 0.3 Mha of peatlands are drained for peat extraction, which is twelve percent of the country's peatland area. From 2006 to 2013, 21,333 ha of this area have been rewetted to protect these peatlands from fire and further degradation, reduce their greenhouse gas (GHG) emissions, turn them back into C sinks and promote biodiversity. A further 260,000 ha are no longer used for peat extraction and their rewetting would be a great benefit for nature conservation and climate protection.
Rewetting of abandoned peat extraction areas usually leads to inundation of large areas where not adapted plants die and new species establish, depending on water level and nutrient conditions. Beavers, of which there are many in Belarus, also play an important role in the rewetting of peatlands. They dam up ditches in drained and rewetted peatlands, thus contributing to water level increases and vegetation changes. The aim of this PhD thesis was to investigate the impact of inundation on vegetation and GHG emissions in formerly extracted fens in Belarus, to determine the role of water level in this process, and to study whether such fens develop back into C sinks with an almost neutral GHG balance within one or two decades after rewetting (Papers II and III). Also the potential of beaver activities for peatland restoration was assessed (Paper III).
Two very different fens, rewetted after peat extraction, were chosen as study areas. The first one, Giel'cykaŭ Kašyl, is a former flood mire and was rewetted with water from the Jasiel'da River in 1985. During the study period 2010–2012 this site was a shallow lake (~ 1 m deep) dominated by very productive, tall reed. Shallower areas along the edges had a partly floating vegetation cover of cattail (Typha latifolia, T. angustifolia) and sedges (Carex elata, C. vesicaria). The second fen, Barcianicha, is fed by groundwater. Rewetting from 1995 onwards resulted in water levels at or slightly above surface and a lower nutrient availability compared to Giel'cykaŭ Kašyl'. This was reflected in the establishment of mesotrophic communities of Eriophorum angustifolium and Carex rostrata. Phragmites australis stands, which were also dominant here, were shorter and less productive than in Giel'cykaŭ Kašyl'. The southern area of Barcianicha was not used for peat extraction and has not been rewetted. Until 2009 vegetation of this part was characterized by forbs (Urtica dioica) and wet meadows (Agrostis stolonifera). From autumn 2009, a beaver dam in the main drainage ditch caused flooding of these areas and led to diverging vegetation development depending on water levels.
Within the framework of this doctoral thesis annual fluxes of CO2, methane (CH4) and nitrous oxide (N2O) and the development of water levels and vegetation were monitored for two years at nine sites and evaluated (Papers II and III). Three of the sites, respectively, were located (a) in Giel’cykaŭ Kašyl’, flooded in 1985, (b) in the central area of Barcianicha, which was rewetted in 1995, and (c) in the southern part of Barcianicha, which was flooded by beavers end of 2009. GHG measurements were carried out with manual chambers from August 2010 to September 2012. Annual net CO2 exchange rates (NEE) were modeled based on light response curves of gross primary production (GPP) and on temperature response curves of ecosystem respiration (Reco), which were determined every third to fourth week by alternating measurements with transparent (cooled) and opaque chambers (both with fan) along the daily amplitude of photosynthetically active radiation (PAR) and temperature. Annual CH4 emissions were calculated mainly based on the temperature response of CH4 fluxes over the course of the year, based on biweekly (in summer) to monthly (in winter) repeated single measurements with opaque chambers (without fan). This was done, although all longer rewetted sites were dominated by aerenchymatic plants whose gas transport during the vegetation period may change over the course of the day and can be influenced by shading. This might apply to the six longer rewetted sites, two of which were dominated by Phragmites australis, and the others by Typha latifolia, Carex elata, Carex rostrata or Eriophorum angustifolium. For these six sites therefore studies on the daily course of CH4 release and the influence of chamber shade were conducted, covering 8–24 hours and lasting at least from sunrise to afternoon. Also the extent to which flux rates were affected by a lack of chamber headspace mixing by fans was investigated in the mentioned studies (Papers I and II).
The daytime course of CH4 emissions showed a pronounced dynamic for Phragmites australis in both fens, with minimum release during the night and maximum during the day (Paper I). The other sites in contrast did not show a significant diurnal CH4 flux dynamic (Paper II). Lack of headspace mixing by fans as compared to chambers with fan resulted in a slight underestimation of CH4 emissions at very high chambers (220 and 250 cm), as used for Phragmites australis in Giel'cykaŭ Kašyl', while there was no difference at lower chambers (≤185 cm), as used for the other sites. Opaque chambers resulted for sites dominated by Typha latifolia and Carex elata in significantly (1.2 times and 1.1 times, respectively) lower CH4 fluxes compared to transparent chambers. For the other sites, opaque chambers did not significantly reduce CH4 emissions. This result was unexpected, especially for Phragmites australis, as PAR out of all parameters tested had the strongest influence on CH4 emissions from both reed sites, and clouds directly led to reduction of their emissions. Presumably the gas flow in the reed shoots located within opaque chambers was maintained by shoots outside the chamber that were connected to the enclosed shoots by rhizomes (Paper I). The investigations showed that single measurements between 9 a.m. and 6 p.m. with opaque chambers without fan, as performed for the determination of annual CH4 fluxes, resulted for Carex rostrata and Eriophorum angustifolium in estimates similar to the daily mean, but for Phragmites australis in estimates that were rather above the daily mean. Annual CH4 fluxes from Phragmites australis could therefore be slightly overestimated. CH4 fluxes from Typha latifolia and Carex elata during the vegetation period were corrected by a factor of 1.2, although darkness inside of opaque chambers matters only at day, not at night. Daily and annual CH4 fluxes from these sites have been therefore most likely slightly overestimated, too.
Water saturation and the establishment of adapted vegetation were the most important conditions for the restoration of C sinks (gaseous CO2 and CH4 fluxes) in the investigated peatlands. The only site with falling water levels in summer and thus temporarily aerated peat was the beaver flooded forbs (Urtica dioica) site at Barcianicha. This site was a very strong CO2 emitter and the only significant N2O source of the entire study (Paper III). All other sites were permanently wet, had much lower CO2 emissions or were even net C sinks (Papers II and III). Establishment of adapted vegetation depended on inundation depth and time since rewetting. For example, within one year the meadow site in Barcianicha shallowly flooded by beaver was colonized by Carex rostrata and other adapted helophytes and developed into a CO2 sink, while the deeper flooded site at the same meadow initially attracted only Chara and some individuals of Alisma plantago aquatica and remained a moderate CO2 source. However, the results of the longer rewetted sites show, that also deeply (~ 1 m) flooded fen areas can become densely populated with mire plants in the course of 25 years and develop into net C sinks. Highest annual C uptake in both fens was achieved by the reed sites. Eriophorum angustifolium and Carex rostrata in mesotrophic Barcianicha were smaller C sinks. Typha latifolia and Carex elata in the eutrophic Giel'cykaŭ Kašyl', on the other hand, released CO2, presumably because the high and fluctuating water levels imposed stress to the plants, and because the large supply of nutrients and dead plant material allowed for strong heterotrophic respiration (Paper II). The simultaneously high CH4 emissions made Typha latifolia and Carex elata major sources of GHG. CH4 emissions from Phragmites australis in Giel'cykaŭ Kašyl' were even higher, but due to extremely high CO2 uptake the site was only a small net GHG source. CH4 emissions in Barcianicha were much lower and comparable to undisturbed sedge fens. The difference between Giel'cykaŭ Kašyl' and Barcianicha was mainly due to the different nutrient supply and the related productivity of the plants. Important conclusions are that stable inundation is an appropriate measure for restoration of the C sink of formerly extracted fens, but nutrient input with water needs to be stopped or reduced in order to decrease CH4 production. If this is not possible, establishment of Phragmites australis and other strong C sinks could help to compensate for the climate impact of high CH4 emissions from eutrophic sites.
The effect of the beaver dam on the development of the southern part of Barcianicha depended not only on the initial situation but mainly on the water level. Under optimal conditions, it led to the rapid establishment of adapted mire plants, the restoration of a C sink and a significant reduction of GHG emissions. However, this situation in the shallowly flooded meadow was achieved by chance. In comparison to planned rewetting measures, which aim to raise the water level evenly over the entire peatland, beavers dam ditches in order to improve their immediate habitat, thus influencing water levels only up to a certain distance, but rarely over the entire peatland. Nevertheless, beaver activity is of high value both for mire conservation projects, where existing dams are supplemented by beaver dams, and for abandoned, drained peatlands, like former peat extraction areas in Belarus, many of which at least partially have been rewetted by beavers.
Environmental activism, defined as a range of difficult pro-environmental behaviors, is analyzed within the conceptual framework of Significance Quest Theory (SQT). In Study 1, 40 interviews were carried out on two groups of people in the European Union: Committed Actors for Nature (CANs, n = 25) versus Committed Actors for Society (CASs, n = 15). Results demonstrated that Significance Quest (SQ) motivates each group to be strongly committed to their chosen action and the main difference between them being in their ideology (pro-social vs. pro-environmental). In Study 2 (N = 131), the relationship between SQ and intention to enact difficult pro-environmental behaviors was assessed. Results suggested that the higher the SQ, the higher the tendency to enact difficult pro-environmental behaviors, but not average or easy ones. Moreover, the higher the pro-environmental ideology, the stronger the indirect effect of SQ on difficult behavior through willingness to sacrifice.
Abstract
Aim
Distribution ranges of temperate tree species are shifting poleward and upslope into cooler environments due to global warming. Successful regeneration is crucial for population persistence and range expansion. Thus, we aimed to identify environmental variables that affect germination and seedling establishment of Europe's dominant forest tree, to compare the importance of plasticity and genetic variation for regeneration, and to evaluate the regeneration potential at and beyond the southern and northern distribution margins.
Location
Europe.
Time period
2016–2018.
Major taxa studied
European beech (Fagus sylvatica (L.)).
Methods
We investigated how germination, establishment and juvenile survival change across a reciprocal transplantation experiment using over 9,000 seeds of beech from 7 populations from its southern to its northern distribution range margins.
Results
Germination and establishment at the seedling stage were highly plastic in response to environmental conditions. Germination success increased with warmer and declined with colder air temperature, whereas establishment and survival were hampered under warmer and drier conditions. Germination differed among populations and was positively influenced by seed weight. However, there was no evidence of local adaptation in any trait.
Main conclusions
The high plasticity in the early life‐history traits found irrespective of seed origin may allow for short‐term acclimatization. However, our results also indicate that this plasticity might not be sufficient to ensure the regeneration of beech in the future due to the low survival found under dry and hot conditions. The future climatic conditions in parts of the distribution centre and at the rear edge might thus become limiting for natural regeneration, as the likelihood of extreme heat and drought events will increase. By contrast, at the cold distribution margin, the high plasticity in the early life‐history traits may allow for increasing germination success with increasing temperatures and may thus facilitate natural regeneration in the future.
Abstract
Aim
Climate limits the potential distribution ranges of species. Establishment and growth of individuals at range margins is assumed to be more limited by extreme events such as drought or frost events than in the centre of their range. We explore whether the growth of beech is more sensitive to drought towards the dry distribution margin and more sensitive to frost towards the cold distribution margin. Furthermore, we aim to gain insight into the adaptive potential of beech towards both the dry and cold distribution margins.
Location
European gradient from the dry (Spain) to the cold (Poland, Sweden) distribution margin of beech.
Taxon
European beech (Fagus sylvatica L.).
Methods
We applied a range‐wide dendroecological study to analyse spatial and temporal trends in climate–growth relationships. We further investigated negative growth anomalies and growth synchrony towards the range margins.
Results
We found beech to be drought sensitive across its whole range, except at the dry distribution margin. Furthermore, sensitivity to winter temperature was not found in the centre or at the cold distribution margin, but at the southern distribution margin. Growth synchrony was lower at the dry than at the cold distribution margin.
Main conclusions
Beech seems to be adapted to drought at the dry distribution margin with a high adaptive potential indicated by the lowest growth synchrony along the gradient. At the cold distribution margin, cold events in winter and spring were less important for growth than drought. Still, the importance of spring frost for beech growth appears to increase in recent decades. Considering a projected north‐eastward shift of the distribution range, beech is likely facing drought stress in combination with spring frost risk at the cold margin which could lead to a hampered range expansion.
Species have to cope with climate change either by migration or by adaptation and acclimatisation. Especially for long-living tree species with a low seed dispersal capacity (e.g. European beech, hereafter called beech), the in situ responses through genetic adaptation and phenotypic plasticity play an important role for their persistence. Beech, the dominant climax tree species in Central Europe, shows a high drought sensitivity and its distribution range is expected to shift northwards. On the other hand, projected northward shifts need to be taken with caution, as some studies suggest a sensitivity of beech to frost events in winter and spring. However, studies on the growth performance of cold-marginal beech populations are still rare. Previous studies on beech populations found local adaptation to drought and phenotypic plasticity in fitness-related traits as well as phenological traits. However, studies on the regeneration of beech under natural conditions are yet missing, although germination and establishment of young trees are a very first selective bottleneck and are crucial for tree population persistence and for successful range shifts.
This PhD-thesis aimed to identify the potential of plasticity and local adaptation in the important early life-history traits germination, establishment after the 1st year, and survival after the 2nd year in a reciprocal transplantation experiment at 11 sites across and even beyond the distribution range of beech (Manuscript 1). Moreover, this thesis investigated the climate sensitivity and the adaptation potential of beech populations by conducting dendroecological studies along a large climatic gradient across the distribution range (Manuscript 2) and along a strong winter temperature gradient towards the cold distribution margin in Poland (Manuscript 3). In addition, the impact of local climatic singularities was studied in a local study at the southern margin (Manuscript 4).
Warm and dry conditions limited natural regeneration, which was indicated by very low survival of young trees, even though germination rates increased with increasing temperature (Manuscript 1). This was also the case in parts of the distribution centre due to the hot and dry conditions in 2018. Although the transplantation experiment revealed high plasticity in the early life-history traits, this plasticity might thus not buffer against climate change under dry conditions. Local adaptation was not detected for any of these traits along the climatic gradient. In contrast, the results of the dendroecological study across the gradient (Manuscript 2) hint towards an adaptation potential of adult trees to drought at the southern margin. Thus, adult trees seemed to be adapted to drought at the southern margin, whereas tree growth in the distribution centre was sensitive to drought. These results indicate that parts of the centre may become ecologically marginal with increasing drought frequency in times of climate change. Interestingly, Manuscript 4 shows that beech growth was positively influenced by frequent fog immersion at the southern distribution margin in north-eastern Spain. This study underlines the importance of local climatic singularities, as they may allow marginal populations to grow in climate refugia in an otherwise unfavourable climate.
At the cold distribution margin, the study in Manuscript 1 found a remarkably higher survival of young trees in Sweden than in Poland. Moreover, the dendroecological studies revealed that beech was hampered by both drought at the cold-dry margin (Manuscript 2) and by winter cold at the cold-wet margin in Poland (Manuscript 3). All these results highlight the importance to study climate sensitivity of adult trees and the response of early life-history traits at the cold margin with a more differentiated view comparing cold-dry against the cold-wet populations and growing conditions. However, the high plasticity of the early life-history traits may allow for an increasing germination rate with climate warming at the northern margin and may thus facilitate natural regeneration there. In contrast, the dendroecological studies suggest that adult trees at the cold distribution margin may suffer either from drought or from winter cold and that the risk for spring frost may increase. Thus, the often-predicted compensation of dry-marginal population decline by a northward range expansion should be discussed more critically.
In conclusion, my PhD thesis provides new knowledge about the potential of natural regeneration and about climate sensitivity of adult trees across the distribution range of beech. Moreover, it underlines the importance to study both the young tree stages as well as adult trees to assess the performance and vulnerability of tree species under climate change, as both showed differences in their response to changing environmental conditions.
Against the background of post-socialist transition and nationwide economic growth in Azerbaijan this dissertation analyses the utilisation of rangeland resources by mobile pastoralists in Azerbaijan. The study was motivated by the initially scarce knowledge about pastoralism in Azerbaijan and concerns about declining pasture condition due to growing livestock numbers. The study was guided by three research objectives, which were addressed cumulatively in five publications. The first objective aims at analysing the development of pastoralism in the transition period in comparison to developments in the pastoral sectors of other post-socialist countries. Secondly, the study addresses socio-economic causes of inappropriate pasture management by pastoralists. Finally, in an application-oriented research process recommendations for improving the management of pastoral farms and pasture governance were developed in order to mitigate inappropriate pasture management. For addressing these objectives the study frames the management of rangelands as a complex natural resource management system, in which the environment, users, governance structures, and the socio-political context are closely linked. Within this framework, the study focused especially on pastoral farms using a farm economics approach and on pasture governance with employing institutional economic theories. Regarding the methodology, a case study approach in four study regions was chosen in order to deal with the ex-ante limited information about Azerbaijani pastoralism and the explanatory aim of research.
Diversified livelihoods combining farming, livestock keeping and non-farm income arecharacteristic of many rural households worldwide. For the Central Asian and Caucasian region,livestock keeping is especially important in terms of land use and socio-cultural heritage. We contributeto the literature with data from the under-researched Caucasus region and investigate: (i) the extent ofdiversification in smallholder households; (ii) the role of livestock keeping in diversification; (iii) theinfluence of household-specific and location-specific variables and diversification on householdincome. Based on a dataset of 303 households, we calculate contribution margins for the mainagricultural activities, household income, and diversification indices and analyze the influence ofdiversification, asset and location variables on household income with a regression model. Householdincome is generally diversified and a combination of four income sources (crops, livestock, poultry/beesand social benefits) was the most frequent. The econometric analysis shows that higher householdincomes are positively correlated with higher household land and livestock assets, the presence ofnon-farm work and social benefit income sources and with an increasing specialization as measuredby the diversification index. For enhancing rural household incomes and slowing down rural-urbanmigration, the development of non-farm job opportunities is recommended.
Im Manu Nationalpark im südöstlichen Tieflandregenwald Perus leben die Matsiguenka der Dorfgemeinschaften Tayakome und Yomibato. Zur Erwirtschaftung dringend benötigter Basisgüter begannen sie im Jahr 1997 mit dem Bau einer Touristenherberge. Die vorliegende Studie untersucht das tradierte Wirtschaftssystem dieser Dorfgemeinschaften und die Einflüsse neuer Wirtschaftsformen, insbesondere der Herberge sowie des Nationalparks. Bisher brachte die Herberge nicht die von den Matsiguenka erwünschten wirtschaftlichen Erfolge, so dass sie zur Deckung ihrer Grundbedürfnisse weiterhin auf Spenden verschiedener Organisationen angewiesen sind. Die Einflüsse durch die Herberge auf das sehr traditionelle Wirtschaftssystem der Matsiguenka sind bisher gering. Da Tourismus derzeit die einzige Möglichkeit darstellt, von den Matsiguenka erwünschte Einkommen zu erzielen, und sich gleichzeitig stabilisierend auf das Wirtschaftssystem der Matsiguenka auswirken kann, stellt die Beteiligung im Tourismusgeschäft eine Chance für eine nachhaltige Entwicklung im Nationalpark Manu dar. Um diese Ziele zu erreichen, ist aber die verstärkte Zusammenarbeit mit Tourismusunternehmen und Nationalparkverwaltung erforderlich. Außerdem müssen an den aktuellen Wissensstand der Matsiguenka angepasste Beteiligungsformen gefunden werden. Hierfür bietet sich die Ausbildung eines Co-Managementsystems in der touristischen Zone des Nationalparks an, an dem die Nationalparkverwaltung, die Matsiguenka sowie die Tourismusunternehmen beteiligt sind.
Baltic coastal lagoons are severely threatened by eutrophication. To evaluate the impact of eutrophication on macrophytobenthos, we compared the seasonal development in macrophytobenthic composition, biomass and production, water column parameters (light, nutrients), phytoplankton biomass and production in one mesotrophic and one eutrophic German coastal lagoon. We hypothesized that light availability is the main driver for primary production, and that net primary production is lower at a higher eutrophication level. In the mesotrophic lagoon, macrophytobenthic biomass was much higher with distinct seasonal succession in species composition. Filamentous algae dominated in spring and late summer and probably caused reduced macrophytobenthic biomass and growth during early summer, thus decreasing vegetation stability. Light attenuation was far higher in the eutrophic lagoon, due to high phytoplankton densities, explaining the low macrophytobenthic biomass and species diversity in every season. Areal net primary production was far lower in the eutrophic lagoon. The “paradox of enrichment” hypothesis predicts lower production at higher trophic levels with increased nutrient concentrations. Our results prove for the first time that this hypothesis may be valid already at the primary producer level in coastal lagoons.
Forest ecosystems around the world and especially boreal forests, are facing
drastically changing climatic conditions. It is known that these changes could
challenge their functionality and vitality. Still, the exact impact is not fully
understood, as tree growth is a complex process and depends on countless
environmental and genetic factors. To estimate the effects of climate change
on tree growth and forest development precisely, we must learn more about
tree growth itself. A comprehensive approach is needed where trees and
forests are investigated on different scales and levels of detail, ranging from
global studies to studies on single individuals.
In this dissertation, I follow such a comprehensive approach, using the
North American conifer white spruce as an example. I present three papers
in the form of three chapters in which my co-authors and I studied the
growth and anatomy of white spruce (Picea glauca [Moench] Voss) and how
it is influenced by environmental, climatic, and genetic factors.
We used diverse approaches and methods on different spatial scales, ranging from
investigations on the landscape to the local scale. We established three paired
plots with forest and treeline sites (two cold-limited and one drought-limited).
as well as one additional forest site. In the first chapter, we concentrated
on the genetic diversity of white spruce within and between populations at
all study sites throughout Alaska. The genetic investigations were combined
with analyses on the individual growth response of trees to climatic conditions
to find whether genetic similarities or spatial proximity caused similarities
in growth and climatic sensitivity. In the second chapter, we studied the
direct and indirect effects of environmental conditions on the xylem tissue
of white spruce. We analyzed the impact of precipitation, temperature, and
tree height on four xylem anatomical traits in trees growing at the three
treelines. The investigated traits represented the main functions of xylem
tissue (i.e., water transport and structural support). In the third chapter,
we investigated similar xylem anatomical traits at one cold-limited treeline.
We compared xylem anatomy and annual increment between genetic groups
and individuals and between spatial groups to investigate whether spatial or
genetic grouping influenced the anatomy and growth of white spruce.
We found an overall high gene flow and high genetic diversity in white
spruce. However, the sensitivity of the growth and anatomical traits of white
spruce was driven mainly by spatial rather than genetic effects and differed
between study sites. Trees from the drought-limited site were more sensitive
towards precipitation and a moisture index, while trees from the cold-limited
sites were more sensitive towards temperature. A strong direct effect of tem-
perature was primarily found in latewood traits related to the structural sup-
port of the tree. Earlywood traits related to water transport, however, were
influenced mainly by tree height. Tree height itself was potentially affected
by diverse abiotic and biotic factors (e.g., (micro)climate, soil conditions,
and competition). Thus, traits related to water transport were indirectly
influenced by environmental conditions. Genetic effects in xylem anatomical
traits were found in the earlywood hydraulic diameter and latewood den-
sity, whereas in general, primarily spatial rather than genetic grouping was
influencing the anatomy of white spruce.
Overall, white spruce showed to be a genetically diverse species with a
high gene flow. The effects of spatial proximity and spatial grouping on the
sensitivity and anatomy of white spruce indicate high phenotypic plastic-
ity. This high phenotypic plasticity combined with the vast genetic diversity
translates into an immense potential for the species to adjust (phenotypically)
and possibly adapt (genetically) to changing conditions. Thus, in terms of
climate change, white spruce may be a rather persistent species that manages
to cope with the drastic changes. Though additional work might be needed to
draw a more solid conclusion, the presented work shows how a comprehensive
study approach can help to interpret and understand the growth and ecology
of a tree species. It may be an inspiration for future studies to broaden their
approaches and to use comprehensive methods on different levels of detail to
not only observe trees but to explore and understand them.
Direct and Indirect Effects of Environmental Limitations on White Spruce Xylem Anatomy at Treeline
(2021)
Treeline ecosystems are of great scientific interest to study the effects of limiting environmental conditions on tree growth. However, tree growth is multidimensional, with complex interactions between height and radial growth. In this study, we aimed to disentangle effects of height and climate on xylem anatomy of white spruce [Picea glauca (Moench) Voss] at three treeline sites in Alaska; i.e., one warm and drought-limited, and two cold, temperature-limited. To analyze general growth differences between trees from different sites, we used data on annual ring width, diameter at breast height (DBH), and tree height. A representative subset of the samples was used to investigate xylem anatomical traits. We then used linear mixed-effects models to estimate the effects of height and climatic variables on our study traits. Our study showed that xylem anatomical traits in white spruce can be directly and indirectly controlled by environmental conditions: hydraulic-related traits seem to be mainly influenced by tree height, especially in the earlywood. Thus, they are indirectly driven by environmental conditions, through the environment’s effects on tree height. Traits related to mechanical support show a direct response to environmental conditions, mainly temperature, especially in the latewood. These results highlight the importance of assessing tree growth in a multidimensional way by considering both direct and indirect effects of environmental forcing to better understand the complexity of tree growth responses to the environment.
Xylem Anatomical Variability in White Spruce at Treeline Is Largely Driven by Spatial Clustering
(2020)
The ecological function of boreal forests is challenged by drastically changing climate conditions. Although an increasing number of studies are investigating how climate change is influencing growth and distribution of boreal tree species, there is a lack of studies examining the potential of these species to genetically adapt or phenotypically adjust. Here, we sampled clonally and non-clonally growing white spruce trees (Picea glauca [Moench] Voss) to investigate spatial and genetic effects on tree ring width and on six xylem anatomical traits representing growth, water transport, mechanical support, and wood density. We compared different methods for estimating broad sense heritability (H2) of each trait and we evaluated the effects of spatial grouping and genetic grouping on the xylem anatomical traits with linear models. We found that the three different methods used to estimate H2 were quite robust, showing overall consistent patterns, while our analyses were unsuccessful at fully separating genetic from spatial effects. By evaluating the effect size, we found a significant effect of genetic grouping in latewood density and earlywood hydraulic diameter. However, evaluating model performances showed that spatial grouping was a better predictor than genetic grouping for variance in earlywood density, earlywood hydraulic diameter and growth. For cell wall thickness neither spatial nor genetic grouping was significant. Our findings imply that (1) the variance in the investigated xylem anatomical traits and growth is mainly influenced by spatial clustering (most probably caused by microhabitat conditions), which (2) makes it rather difficult to estimate the heritability of these traits in naturally grown trees in situ. Yet, (3) latewood density and earlywood hydraulic diameter qualified for further analysis on the genetic background of xylem traits and (4) cell wall thickness seems a useful trait to investigate large-scale climatic effects, decoupled from microclimatic, edaphic and genetic influences.
This dissertation evaluates the effects of site conditions and livestock grazing on the vegetation of Azerbaijan’s winter pastures. We improved methods to estimate grazing intensity in vast rangelands and enhanced an approach to detect discontinuities in vegetation changes along environmental gradients. All analyses use field data from the semi-arid rangelands of Gobustan and Jeiranchel, at the foothills of the Greater Caucasus mountains. The data set comprises 313 vegetation relevés, each sized 100 m², based on a pre-stratification using topographical parameters. Additionally, we included data from farm transects and exclosure experiments. For each plot, selected site and soil variables were determined. VEGETATION AND SITE CONDITIONS: By means of cluster analysis, we derived 16 vegetation types with a total of 272 vascular plant species. Our vegetation classification, which is closely linked to site conditions, is an important groundwork for adapted rangeland management and monitoring. The study areas are dominated by semi-deserts with a high coverage of dwarf shrubs, and the mean number of vascular plant species was found to be about 28 per 100 m². According to ordination analysis (NMDS), species composition changes primarily along the altitudinal gradient, gradually proceeding from the Salsola nodulosa semi-deserts of the lowest parts (below 300 m a.s.l.) to the Salsola ericoides and Artemisia lerchiana semi-deserts of the upper regions (300–650 m a.s.l.). Soil salinity and carbonate concentration decrease as altitude increases. A second gradient reflects grazing intensity. One plant community that is typically found on intensively grazed sites in the vicinity of farmyards stands apart from the rest, which are subject to lower grazing and trampling pressures. A third factor that differentiates plant communities is the sand concentration of the soils. Additionally, communities that occur on steep slopes differ from communities that occur on level terrain. EXCLOSURE EXPERIMENTS: Exclosure experiments revealed that short-time abandonment of grazing leads to an increase in the number of annual species, in vegetation coverage, and in the heights of forbs and grasses. Clipping experiments indicated that the herbaceous species show hardly any compensatory growth in response to grazing. ESTIMATING GRAZING INTENSITY: A recurrent theoretical problem in rangeland research is the spatial modelling of grazing intensity around grazing hotspots like farms or watering places, the so called piospheres. In a widely used approach, grazing intensity is assumed to decrease in direct proportion to the distance from a hotspot. The resulting response patterns, which relate characteristics of the vegetation or site conditions to grazing intensity, are often nonlinear, and have been interpreted as indicating threshold changes or diff erent state-and-transitions along grazing gradients. However, we show that these ‘thresholds’ are usually geometrical artefacts. Taking into account the concentric structure of grazing hotspots, we suggest a new approach that approximates grazing intensity as the ratio of the total number of livestock kept at the farm to the distance between a given plot and the hotspot centre. Our approach is a simple yet significant improvement over current approaches because it enables us to merge or compare data from different sampling sites and because the approximation is in direct proportion to other grazing indicators like dung density or soil salinity. SPECIES TURNOVER PATTERNS: Combining our new grazing pressure model with species presence/absence data, we modelled vascular plant species responses, patterns of species richness and species turnover along grazing gradients on farm transects in Gobustan. The derived typical species response pattern along the finite grazing gradient is a sigmoid decrease. Species richness declines monotonically with increasing grazing intensity and thus conforms to generally acknowledged assumptions on the relationship between species richness and grazing pressure in semi-arid rangelands. Species turnover along the gradient was calculated using the slopes of species response curves. At first sight, the resulting pattern gives evidence for a discontinuous change. However, it ranges within the 95 % confidence interval of a null model based on assumptions of the individualistic continuum concept. Thus, species composition seems to change continuously along grazing gradients in Gobustan. This new null model approach can probably be adapted and applied to all ecological gradients and is useful for the validation of individualcontinuum or community concepts.
Plant roots influence many ecological and biogeochemical processes, such as carbon, water and nutrient cycling. Because of difficult accessibility, knowledge on plant root growth dynamics in field conditions, however, is fragmentary at best. Minirhizotrons, i.e. transparent tubes placed in the substrate into which specialized cameras or circular scanners are inserted, facilitate the capture of high-resolution images of root dynamics at the soil-tube interface with little to no disturbance after the initial installation. Their use, especially in field studies with multiple species and heterogeneous substrates, though, is limited by the amount of work that subsequent manual tracing of roots in the images requires. Furthermore, the reproducibility and objectivity of manual root detection is questionable. Here, we use a Convolutional Neural Network (CNN) for the automatic detection of roots in minirhizotron images and compare the performance of our RootDetector with human analysts with different levels of expertise. Our minirhizotron data come from various wetlands on organic soils, i.e. highly heterogeneous substrates consisting of dead plant material, often times mainly roots, in various degrees of decomposition. This may be seen as one of the most challenging soil types for root segmentation in minirhizotron images. RootDetector showed a high capability to correctly segment root pixels in minirhizotron images from field observations (F1 = 0.6044; r2 compared to a human expert = 0.99). Reproducibility among humans, however, depended strongly on expertise level, with novices showing drastic variation among individual analysts and annotating on average more than 13-times higher root length/cm2 per image compared to expert analysts. CNNs such as RootDetector provide a reliable and efficient method for the detection of roots and root length in minirhizotron images even from challenging field conditions. Analyses with RootDetector thus save resources, are reproducible and objective, and are as accurate as manual analyses performed by human experts.
AbstractArchetype analysis is a promising approach in sustainability science to identify patterns and explain mechanisms shaping the sustainability of social-ecological systems. Although considerable efforts have been devoted to developing quality standards and methodological advances for archetype analysis, archetype validation remains a major challenge. Drawing on the insights from two international workshops on archetype analysis and on broader literature on validity, we propose a framework that identifies and describes six dimensions of validity: conceptual; construct; internal; external; empirical; and application validity. We first discuss the six dimensions in relation to different methodological approaches and purposes of archetype analysis. We then present an operational use of the framework for researchers to assess the validity of archetype analysis and to support sound archetype identification and policy-relevant applications. Finally, we apply our assessment to 18 published archetype analyses, which we use to describe the challenges and insights in validating the different dimensions and suggest ways to holistically improve the validity of identified archetypes. With this, we contribute to more rigorous archetype analyses, helping to develop the potential of the approach for guiding sustainability solutions.
The recent developments in artificial intelligence have the potential to facilitate new research methods in ecology. Especially Deep Convolutional Neural Networks (DCNNs) have been shown to outperform other approaches in automatic image analyses. Here we apply a DCNN to facilitate quantitative wood anatomical (QWA) analyses, where the main challenges reside in the detection of a high number of cells, in the intrinsic variability of wood anatomical features, and in the sample quality. To properly classify and interpret features within the images, DCNNs need to undergo a training stage. We performed the training with images from transversal wood anatomical sections, together with manually created optimal outputs of the target cell areas. The target species included an example for the most common wood anatomical structures: four conifer species; a diffuse-porous species, black alder (Alnus glutinosa L.); a diffuse to semi-diffuse-porous species, European beech (Fagus sylvatica L.); and a ring-porous species, sessile oak (Quercus petraea Liebl.). The DCNN was created in Python with Pytorch, and relies on a Mask-RCNN architecture. The developed algorithm detects and segments cells, and provides information on the measurement accuracy. To evaluate the performance of this tool we compared our Mask-RCNN outputs with U-Net, a model architecture employed in a similar study, and with ROXAS, a program based on traditional image analysis techniques. First, we evaluated how many target cells were correctly recognized. Next, we assessed the cell measurement accuracy by evaluating the number of pixels that were correctly assigned to each target cell. Overall, the “learning process” defining artificial intelligence plays a key role in overcoming the issues that are usually manually solved in QWA analyses. Mask-RCNN is the model that better detects which are the features characterizing a target cell when these issues occur. In general, U-Net did not attain the other algorithms’ performance, while ROXAS performed best for conifers, and Mask-RCNN showed the highest accuracy in detecting target cells and segmenting lumen areas of angiosperms. Our research demonstrates that future software tools for QWA analyses would greatly benefit from using DCNNs, saving time during the analysis phase, and providing a flexible approach that allows model retraining.
Vegetation dynamics on abandoned terraces of Sicily: the course and driving factors of succession
(2007)
Secondary succession processes have been widely studied in Europe for some agroecosystems, but not for terraced ones. The first part of the present study focuses on a description of the plant communities involved in secondary succession processes on Sicily (Italy) a) from a floristic and structural point of view and b) from a species diversity point of view. In order to obtain these results, 129 vegetation relevés (sensu Braun-Blanquet) were made on abandoned terraces in five of the main terraced areas of Siciliy: 1) the Aeolian Islands, 2) Pantelleria Island, 3) Mt. Etna, 4) the Palermo Mts. and 5) the Hyblaean Plateau. Only abandoned vineyards or grain crop fields were selected as sample plots, always 50 m2-sized. The results of biodiversity evaluation by t-tests and ANOVA showed that vascular plant diversity is linked to disturbance regime and to abiotic factors (especially geological substrate). Especially grazing increases species richness. Moreover, it was found that on limestone species richness is higher than on volcanic substrates. Vegetation relevés were also analysed with DCA and TWINSPAN. The resulting 14 sample plot groups (= clusters) were then used to check the dynamic relations. From a floristic point of view, plant communities involved in secondary succession processes on Sicilian terraces are quite different between and within the five study areas. This is mainly due to different substrate and bioclimatic conditions. Moreover, vegetation is strongly influenced by abandonment age and disturbance status. If no disturbance biases succession, then plant communities evolve rather rapidly (30-50 years) to maquis communities. If frequent fires or intense grazing occur, secondary succession is blocked in a "steady state". The second part of the present study focuses on the colonization mechanisms of old fields by woody species. In a first section, the existence of 1) the neighbourhood effect and 2) the safe-site effect are checked by analyzing 51 transect relevés, made up of 357 subplot relevés (1x1m). The transects were made in target fields 1) with older neighbour (i.e. old succession stage characterized by maquis communities) and 2) with older neighbour absent within a 100 m-distance. All woody species individuals were counted, recording if they grew within the influence of a potential safe site (former crop plants of vine and the terrace wall base). Data evaluation by Kruskal-Wallis ANOVA and Mann-Whitney Rank Sum confirmed the existence of the two effects. Moreover, it was shown that animals as dispersal vectors strongly influence these effects. For the neighbourhood effect, seed dispersal distance is the crucial point, while for the safe site effect 1) passive facilitation (i.e. animals tend to create heterogeneous seed rain patterns because they frequent certain microhabitats more often than others) and 2) active facilitation (i.e. the positive influence of an existing woody or herbaceous plant individual on the establishment or the growth of another one) are crucial. The second section describes the performance of establishment of Quercus ilex L. in different microsites of terraced old fields. In November 2004, acorns were buried on a North-facing slope and on a South-facing slope in five different microsites: 1) under vine plants, 2) at wall bases, 3) under the canopies of isolated shrubs, 4) between small rock accumulations and 5) in open spaces (i.e. outside of any of the previously named microsites). In monthly checks, seedling emergence, survival, height and leaf number were recorded. Moreover, in April and July were measured air temperature and air humidity in the different microsites. Overall emergence rate was 52.4% (n = 1,020). More seedlings emerged on the South-facing slope (S; 59.8%) than on the North-facing slope (N; 45.0%). Emergence was higher when acorns were buried under vine plants and at the wall base than in other microsites of the old fields. At the end of the experiment (September 2006), 45.3% of all emerged seedlings were still alive (29.2% on N, 58.9% on S). Survival was higher in general on the South-facing slope, and higher under vine plants and at the wall base than in the open spaces of the old fields. From literature, it is known that seed vitality, seed germination and seedling survival of Quercus ilex are favoured by shady, wet and fresh conditions. The temperature and air humidity measurements showed that at the wall base, under vine plants and under isolated shrubs environmental conditions are milder than in open spaces. However, even if temperature and relative air humidity seem to play an important role for Quercus ilex seedling emergence and survival, they did not unambiguously explain the differences between the safe site types. A factor of major importance is probably soil moisture. As a last part, the present study discusses what does the obtained results mean for terrace landscape conservation and biodiversity management.
Due to climate change, economically important crop plants will encounter flooding periods causing hypoxic stress more frequently. this may lead to reduced yields and endanger food security. As roots are the first organ to be affected by hypoxia, the ability to sense and respond to hypoxic stress is crucial. At the molecular level, therefore, fine-tuning the regulation of gene expression in the root is essential for hypoxia tolerance. Using an RnA-Seq approach, we investigated transcriptome modulation in tomato roots of the cultivar ‘Moneymaker’, in response to short- (6 h) and long-term (48 h) hypoxia. Hypoxia duration appeared to have a significant impact on gene expression such that the roots of five weeks old tomato plants showed a distinct time-dependent transcriptome response. We observed expression changes in 267 and 1421 genes under short- and long-term hypoxia, respectively. Among these, 243 genes experienced changed expression at both time points. We identified tomato genes with a potential role in aerenchyma formation which facilitates oxygen transport and may act as an escape mechanism enabling hypoxia tolerance. Moreover, we identified differentially regulated genes related to carbon and amino acid metabolism and redox homeostasis. Of particular interest were the differentially regulated transcription factors, which act as master regulators of downstream target genes involved in responses to short and/or long-term hypoxia. Our data suggest a temporal metabolic and anatomic adjustment to hypoxia in tomato root which requires further investigation. We propose that the regulated genes identified in this study are good candidates for further studies regarding hypoxia tolerance in tomato or other crops
Abstract
Climate change will lead to more frequent and severe drought periods which massively reduce crop production worldwide. Besides drought, nitrogen (N)‐deficiency is another critical threat to crop yield production. Drought and N‐deficiency both decrease photosynthesis and induce similar adaptive strategies such as longer roots, reduction of biomass, induction of reactive oxygen species (ROS), and antioxidative enzymes. Due to the overlapping response to N‐deficiency and drought, understanding the physiological and molecular mechanisms involved in cross‐stresses tolerance is crucial for breeding strategies and achieving multiple stress resistance and eventually more sustainable agriculture. The objective of this study was to investigate the effect of a mild N‐deficiency on drought stress tolerance of tomato plants (Solanum lycopersicum L., cv. Moneymaker). Various morphological and physiological parameters such as dry biomass, root length, water potential, SPAD values, stomatal conductance, and compatible solutes accumulation (proline and sugar) were analyzed. Moreover, the expression of ROS scavenging marker genes, cytosolic ASCORBATE PEROXIDASES (cAPX1, cAPX2, and cAPX3), were investigated. Our results showed that a former mild N‐deficiency (2 mM NO3−) enhances plant adaptive response to drought stress (4 days) when compared to the plants treated with adequate N (5 mM NO3−). The improved adaptive response was reflected in higher aboveground biomass, longer root, increased specific leaf weight, enhanced stomatal conductance (without reducing water content), and higher leaf sugar content. Moreover, the APX1 gene showed a higher expression level compared to control under N‐deficiency and in combination with drought in the leaf, after a one‐week recovery period. Our finding highlights a potentially positive link between a former mild N‐deficiency and subsequent drought stress response in tomato. Combining the morphological and physiological response with underlying gene regulatory networks under consecutive stress, provide a powerful tool for improving multiple stress resistance in tomato which can be further transferred to other economically important crops.
Forests are and have been of major importance to cover a variety of societal needs. Today the demands on forests are ever increasing with sequestering carbon and balancing the climate, to name only a few. To cover those requirements forests need vital, productive, and sustainable. A difficult concept as such as the understanding of a healthy forest varies greatly. Nevertheless, forests still have to produce a sufficient amount of yield while threatened by changing climate conditions. These are predicted to bring extended and more intense drought periods as well as a higher frequency of storms and the promotion of secondary disturbances like insects calamities to also rise. In this complex situation of high and versatile demand the focus is on the allocation of the “right” forest. Forest management is requested to balance the needs of humans against those of wildlife against those of the trees themselves. To gain the respective knowledge on species responses and provenance growth, now and in the future research gaps need to be closed. All factors influencing tree growth and therefore ultimately yield need to be understood and special focus needs to be on the interactions within the forest ecosystem. One of the parameters in understanding aggregated tree growth is the dynamic of growth. This can be visualised by dendroecological methods, providing a picture of growth within the individual years. Growth dynamics are dependent on multiple factors, some, like soil being preconditioning and other like climate causing short-term responses. In this thesis I focus on the influence of climate on annual tree growth using a new approach of daily climate data to calculate climate-growth correlations. This method has the advantage of representing tree processes better than the former approach of using monthly means. Furthermore the program enables the user to feed climate scenarios and therefore estimate future growth. To gather information on species as well as provenance differences to provide advice to foresters I used different trials in Britain and Germany. On the British site different oak species were planted while the German sites are stocked with various spruce provenances. For the latter we additionally used stable carbon isotope analysis to calculate intrinsic water use efficiency. The climate-growth correlations revealed differences between the oak species with a generally higher linkage to precipitation than temperature. While the differences are clear, the question of thresholds and the role of extreme events became apparent in this work. VII Abstract Assessing the impact of extreme events using dendrometer data revealed little differences in the response to short term events of the three investigated species, oak, beech, and pine. We were able to pick up stimulus-response-relationships and as a novel result no species-specific responses were found when focusing on such a small time frame. The provenance trials offered the opportunity to investigate the potential of the use of daily climate data more closely. The two contrasting sites planted with six spruce provenances each gave an insight on the adaptive potential of provenances as well as an indication on the response times. Depending on the proceeding environmental and the local climate conditions decisions have to be made on the species or provenance selection. This thesis provides a method as well as insight on the behaviour of the important European species beech, oak, pine, and spruce. It, however, highlights the limitations such methods have for large scale estimates. While general trends on the response to specific soil factors can be used, the climatic responses, be it thresholds or climate-growth correlations can only be seen within the ecological context of their sampling region.
Global change, amongst others characterized by increasing temperatures, altered precipitation patterns, an increase of extreme climatic events and continued atmospheric depositions of pollutants, is expected to severely impact forest ecosystems worldwide. The complex interplay between different factors acting upon tree growth, combined with regional patterns in climatic change calls for a region specific evaluation of the possible consequences on forest ecosystems. For northeastern Germany regional climate models identify a rise in temperatures and a change in precipitation patterns. Drier summers and wetter winters together with an increase in extreme weather events are seen as the most pronounced changes that will occur during the 21st century. In this thesis I analysed past growth rates and climate-growth relationships in different stands of beech (Fagus sylvatica L.) and oak (Quercus robur L.) along a gradient of decreasing precipitation in a space for time approach. Special attention was paid to the influence of summer drought, soil waterlogging and the importance of site conditions in modulating the reactions to these climatic stressors. Departing from these retrospective analyses, future growth trends are modelled for beech, oak and Scots pine (Pinus sylvestris L.), based on projections of a regional climate model until the year 2100. Furthermore, I studied the influence of sudden and extreme shifts in hydrological conditions on the growth of oaks in a drained peatland that was subject to catastrophic rewetting. All analyses of this thesis are based on ring-width and wood anatomical features applying a variety of dendrochronological methods. The gradient approach revealed similar climate-growth relationships for beech and oak on drought exposed, sandy sites, where water availability during early summer was the main growth-limiting factor for both species. Decreasing precipitation rates towards the East are associated with higher drought susceptibility, especially for beech. As a result, competitive superiority of beech over oak decreases. In a drier future the competitive balance between the two species may shift (rank reversal). During the past decades beech has shown larger interannual growth variability and a higher number of growth depressions. These changes might indicate that increasing temperatures and climatic variability are already affecting its growth patterns and climate sensitivity. This is in line with the prospective modelling approach. According to our models, growth trends will turn negative for beech and oak towards the end of the 21st century, with beech showing the highest growth reduction (23% compared to the reference period 1971-2000). For pine, modelled growth rates show only minor changes. Whereas beech and oak shared a high common signal on the dry sites, the two species differed in high frequency ring patterns on the wet sites. On poorly drained, loamy soils beech, with its superficial root system, suffered from summer droughts. In contrast, on these sites ring-width of pedunculate oak was not correlated to summer moisture conditions resulting in differing interannual ring patterns between dry and wet sites. Wet periods with high soil water saturation did not have a negative influence on the growth of either species. Such a lack of response is not surprising for oak, which is generally known as rather tolerant to soil waterlogging, but it indicates an unexpectedly high tolerance of beech to stagnating wetness. Using the natural laboratory of an oak forest that suffered a catastrophic flooding I could show that slower grown trees that had likely been suppressed displayed a higher adaptive capacity compared with bigger, dominant trees. Many of the previously dominant individuals died within 18 years after the event. Trees that survived the groundwater rise displayed a typical ring pattern: growth was suppressed for a few years, but afterwards recovered and even surpassed previous growth rates, most likely as a result of competition release. The sudden hydrological change left a clear imprint in ring patterns and wood anatomical features in both the dying and the surviving trees. This differentiated imprint may be helpful for a better interpretation of growth patterns found in subfossil bog oaks, an important climate proxy of the Holocene. The insights gained from this thesis support existing concerns about drought induced growth decline for oak, but especially for beech. Changes in precipitation patterns might lead to wetter conditions during winter, but these will likely have only little effect on growth. Both s show rather high resilience to stagnating wetness. More likely, it are extreme events like prolonged droughts or heavy rainfalls that might breach thresholds in the ability of the two species to cope with too much or too little water. Such extreme events thus pose a strong risk to the future growth performance of both oak and beech.
In micro-densitometry of wood it is standard procedure to extract resin and other soluble compounds before X-ray analysis to eliminate the influence of these extractives on wood-density. Dendrochemical studies using X-ray fluorescence analysis on the other hand are commonly conducted without previous extraction. However, it is well known that translocation processes of elements during heartwood formation in trees or (temporal) differences in sap content of wood samples can influence dendrochemical element profiles. This might bias environmental signals stored in time series of element concentrations in wood proxies. We hypothesize that metals tightly bound to cell walls show a more robust proxy potential for environmental conditions than easily translocated ones. To eliminate the noise of these soluble substances in wood elemental time series, their extraction prior to analysis might be necessary. In our study we tested the effect of different solvents (water, alcohol, and acetone) and different extraction times on elemental time series of three tree species with differing wood structure (Pinus sylvestris; Quercus robur and Populus tremula). Micro-XRF analysis was conducted on nine replicates per species using an ITRAX-Multiscanner. A set of elements commonly detected in wood (S, Cl, K, Ca, Ti, Mn, Fe, and Ni) was analysed at high resolution before and after several extraction runs. Besides lowering their levels, extraction did not significantly change the temporal trends for most elements. However, for some elements, e.g., Potassium, Chlorine or Manganese, especially the water extraction led to significant decreases in concentrations and altered temporal trends. Apparently the dipole effect of water produced the strongest extraction power of all three solvents. In addition we observed a dependency of extraction intensity from wood density which differed between wood types. Our results help in interpreting and evaluating element profiles and mark a step forward in establishing dendrochemistry as a robust proxy in dendro-environmental research.
AbstractUsing measurements from high resolution monitoring of radial tree-growth we present new data of the growth reactions of four widespread broadleaved tree-species to the combined European drought years 2018 and 2019. We can show that, in contrast to field crops, trees could make better use of the winter soil moisture storage in 2018 which buffered them from severe drought stress and growth depressions in this year. Nevertheless, legacy effects of the 2018 drought accompanied by sustained low soil moisture conditions (missing recharge in winter) and again higher than average temperatures and low precipitation in spring/summer 2019 have resulted in severe growth reductions for all studied tree-species in this year. This highlights the pivotal role of soil water recharge in winter. Although short term resistance to hot summers can be high if sufficient winter precipitations buffers forest stands from drought damage, legacy effects will strongly impact tree growth in subsequent years if the drought persists. The two years 2018 and 2019 are extreme with regard to historical instrumental data but, according to regional climate models, resemble rather normal conditions of the climate in the second half of the 21st century. Therefore the observed strongly reduced growth rates can provide an outlook on future forest growth potential in northern Central Europe and beyond.
Aim
Climate change challenges temperate forest trees by increasingly irregular precipitation and rising temperatures. Due to long generation cycles, trees cannot quickly adapt genetically. Hence, the persistence of tree populations in the face of ongoing climate change depends largely on phenotypic variation, that is the capability of a genotype to express variable phenotypes under different environmental conditions, known as plasticity. We aimed to quantify phenotypic variation of central Europe's naturally dominant forest tree across various intraspecific scales (individuals, mother trees (families), populations) to evaluate its potential to respond to changing climatic conditions.
Location
Europe.
Time Period
2016–2019.
Major Taxa Studied
European beech (Fagus sylvatica L.).
Methods
We conducted a fully reciprocal transplantation experiment with more than 9000 beech seeds from seven populations across a Europe-wide gradient. We compared morphological (Specific Leaf Area), phenological (leaf unfolding) and fitness-related (growth, survival) traits across various biological scales: within single mother trees, within populations and across different populations under the contrasting climates of the translocation sites.
Results
The experiment revealed significant phenotypic variation within the offspring of each mother tree, regardless of geographic origin. Initially, seedling height growth varied among mother trees and populations, likely due to maternal effects. However, the growth performance successively aligned after the first year. In summary, we observed a consistent growth response in different beech populations to diverse environments after initial maternal effects.
Main Conclusions
The study strikingly demonstrates the importance of considering intraspecific variation. Given the surprisingly broad spectrum of phenotypes each mother tree holds within its juvenile offspring, we conclude that Fagus sylvatica might have the potential for medium-term population persistence in face of climate change, provided that this pattern persists into later life stages. Hence, we also suggest further investigating the inclusion of passive adaptation and natural dynamics in the adaptive management of forests.
The “East German National Park Programme” of 1989/1990 was considered a coup de main, resulting in the immediate protection of 4.5% of the GDR’s territory. The authors of this programme later described the approach and its success as “using a window of opportunity during the transition phase of state and nation.” This leads to the question whether a state’s transformation period constitutes a preferred time frame and momentum for spatial conservation success.
Conservation efforts in Azerbaijan showed a similar success as the East German National Park Programme. In a country with the highest biodiversity in Europe, increasing the share of protected land from 5.0 % in 2001 to 10.3% in 2015 constitutes a remarkable achievement. Thus, the country became an interesting case study regarding the question whether “hot moments for conservation” exist in times of political and governmental changes, and if spatial success in nature conservation can be linked to political transformation. This thesis attempts to identify how the protected area (PA) network in Azerbaijan could be expanded by 100%, what achievements were made, and what conditions still need to be met for the quantitative and qualitative improvement of the PA network. To this end, I consider this increase under landscape-ecological, historical and institutional aspects. The local culture and political pre-sets in the country present additional issues for analysing the past 25 years of nature conservation in Azerbaijan.
Carbon dioxide (CO2) is one of the most important factors of the Earth’s carbon cycle. Peatlands are well-known to be a long term sink for atmospheric carbon dioxide. Under changing environmental conditions, the carbon balance and hence the CO2 fluxes can be significantly changed, and peatlands may even become a significant atmospheric carbon source. To be able to predict the changes in climatic conditions and their effects on ecosystems, it is important to understand the contemporary CO2 exchange of the ecosystems. Many studies on peatland CO2 fluxes have been conducted in the boreal zone of North America and Scandinavia. Still little scientific evidence is available from peatland ecosystems of boreal Russia. This dissertation presents the detailed investigation of CO2 dynamics and the relevant processes and environmental factors from the boreal peatland site Ust-Pojeg (61°56'N, 50°13'E) in Komi Republic, northwest Russia. On the small spatial scale (microform), the investigated peatland was characterised by high variability in vegetation composition and coverage as well as in water table level which resulted in large variability in CO2 fluxes not only between the microform types but also within one microform type. The cumulative flux over the investigation period for the different microforms ranged from strong CO2 sources to CO2 sinks. An area-weighted estimate for the entire peatland showed that it was a CO2 source for the investigation period, which was characterised by average conditions in terms of precipitation and temperature. The CO2 fluxes were measured at different scales: by the closed chamber method at the microform scale and by the eddy covariance technique at the ecosystem scale. Three different upscaling methods were used to compare the fluxes. Irrespective of the upscaling methods, the discrepancies between the estimates based on the upscaled chamber measurements and estimates based on measurements by the eddy covariance technique were high. The high spatial heterogeneity of the vegetation and the water table level and thus of the CO2 fluxes were recognised as reasons for high potential errors when upscaling CO2 fluxes from the microform to the ecosystem level. Large discrepancies were also observed in comparison between measured CO2 fluxes and CO2 estimates based on the mechanistic ecosystem model LPJ-GUESS. Insufficient model forcing may have led to errors in the timing of the onset and the end of the growing season, and the modelled vegetation did not always reproduce the observed vegetation. These two factors may have led to the discrepancies in the model-measurement comparison. Although the closed chamber technique is widely used for measurements of CO2 fluxes between ecosystems and the atmosphere, the errors which might occur during the measurement itself or which are associated with the used measurement devices as well as the flux calculation from chamber-based CO2 concentration data are still under discussion. The study showed that the CO2 fluxes measured by the closed chamber method can be overestimated during low-turbulence nighttime conditions and can be seriously biased by inappropriate application of linear regression for the flux calculation. The methodological studies were conducted at the boreal peatland Salmisuo in eastern Finland (62°46'N, 30°58'E). The methods developed in this dissertation could contribute significantly to improved CO2 flux estimates. VI
Whether mice are an appropriate model for S. aureus infection and vaccination studies is a matter of debate, because they are not considered as natural hosts of S. aureus. We previously identified a mouse-adapted S. aureus strain, which caused infections in laboratory mice. This raised the question whether laboratory mice are commonly colonized with S. aureus and whether this might impact on infection experiments. Publicly available health reports from commercial vendors revealed that S. aureus colonization is rather frequent, with rates as high as 21% among specific-pathogen-free mice. In animal facilities, S. aureus was readily transmitted from parents to offspring, which became persistently colonized. Among 99 murine S. aureus isolates from Charles River Laboratories half belonged to the lineage CC88 (54.5%), followed by CC15, CC5, CC188, and CC8. A comparison of human and murine S. aureus isolates revealed features of host adaptation. In detail, murine strains lacked hlb-converting phages and superantigen-encoding mobile genetic elements, and were frequently ampicillin-sensitive. Moreover, murine CC88 isolates coagulated mouse plasma faster than human CC88 isolates. Importantly, S. aureus colonization clearly primed the murine immune system, inducing a systemic IgG response specific for numerous S. aureus proteins, including several vaccine candidates. Phospholipase C emerged as a promising test antigen for monitoring S. aureus colonization in laboratory mice. In conclusion, laboratory mice are natural hosts of S. aureus and therefore, could provide better infection models than previously assumed. Pre-exposure to the bacteria is a possible confounder in S. aureus infection and vaccination studies and should be monitored.