@phdthesis{Theuerkauf2014,
  author    = {Martin Theuerkauf},
  title     = {Fine scaled vegetation patterns in the Lateglacial and Early Holocene of NE Germany – Novel GIS based approaches},
  journal    = {Kleinr{\"a}umige Vegetationsmuster im Sp{\"a}tglazial und Fr{\"u}hholoz{\"a}n in Nordost-Deutschland – Neue GIS basierte Ans{\"a}tze},
  url       = {https://nbn-resolving.org/urn:nbn:de:gbv:9-002100-7},
  year      = {2014},
  abstract  = {The pollen record is a powerful proxy to reconstruct past terrestrial vegetation, but quantifying plant abundances is strongly limited because plants produce pollen in different amounts and pollen is dispersed differently. Further complications arise from the use of percentage data. Finally, a pollen grain deposited at a site may have arrived from proximate or distant sources, which implies that a single pollen sample may reflect very different vegetation scenarios. Present thesis suggests improving quantitative reconstructions of past vegetation by refined calibration of the pollen-vegetation relationship (paper I) and application of the downscaling approach (papers II-IV). Paper I primarily addresses the questions of pollen production and dispersal by calibrating the pollen-vegetation relationship. Data analysis employs the common extended R-value (ERV) approach and a new data-model comparison method, which appears more suitable than the ERV approach. For the first time PPEs have been calculated using three contrasting pollen dispersal options, including a Lagrangian stochastic (LS) model. The study proves that the underlying pollen dispersal model is a crucial parameter in PPE calculations and that the calculations with the LS model produce more reliable and realistic PPEs. Papers II to IV address quantitative reconstructions of past vegetation. Using the newly developed downscaling approach, the three studies explore fine scaled vegetation patterns in NE Germany during the Late Glacial and early Holocene. The main assumption of the downscaling approach is that the present day pattern of abiotic site conditions (e.g. the pattern of soil substrates) existed, at least to a large extend, also during the study periods. The basic principle of the approach is to test, whether pollen deposition in sites across a landscape is correlated to that site pattern. The first application of the approach (paper II) has shown a close correlation between PINUS pollen percentages and the distance weighted abundance of sandy soils and between BETULA pollen percentages and the distance weighted abundance of morainic till during the Aller{\o}d period, indicating that pine and birch formed rather separate stands on either substrate type. The cooling of the Younger Dryas induced significant changes in the vegetation of NE Germany. By combining pollen percentage and pollen accumulation rate data paper III identified a sharp vegetation boundary between the Mecklenburg and Brandenburg area at about 53 °N. The downscaling approach, here used with pollen accumulation rate data, suggests that in the North small tree stands could only exist in sheltered positions. The sharp vegetation boundary is possibly related to a climatic gradient and the southern permafrost limit, which itself may result from the formation of sea ice on the North Atlantic north of 53°N during winter. The warming of the Holocene again allowed the expansion of forests in the study area. Paper IV uses high resolution pollen (accumulation rate) data to study the successive forest formation, including the immigration of hazel, and explores vegetation patterns and composition during these successive stages using the extended downscaling approach. This approach addresses the problems related to differential pollen production, dispersal and the use of percentage data by applying simulations. It reveals that initially pine and birch established, as during the Aller{\o}d period, in largely separate stands with pine dominating on sandy soils and birch dominating on fine grained soils. Also open rich vegetation persisted, possibly due to seasonal drought, mainly on fine grained soils. Hazel later mainly spread on sites that received additional wetness from ground or surface water; it did not enter pine dominated forests on well drained sandy soils. Overall, the early Holocene vegetation of the study area was sharply differentiated by soil humidity and fertility. To conclude, present thesis has revealed vegetation patterns and species site preferences in NE Germany during three periods of the Lateglacial and early Holocene. The results improve our understanding of vegetation history in northern Central Europe, specifically for periods of rapid climate change. The approaches applied are flexible with respect to the type and quality of pollen data used and may be implemented using standard software packages.},
  language  = {en}
}