Using historical data to determine the interactive effects of historical land-cover changes and recent environmental changes on herb-layer plant diversity in temperate forests

土地覆盖变化被认为是对生物多样性最重要的威胁之一。在温带欧洲的许多地区，18世纪和19世纪发生了广泛的土地覆盖变化，当时发生了大规模的森林砍伐，随后发生了农业放弃和重新造林。有理由相信，这些历史上的土地覆盖变化正在造成今天森林草本层植被的延迟反应，因为分别偿还了古代和后农业森林碎片的灭绝债务和殖民信用。然而，关于温带森林中灭绝债务和殖民信用的规模的知识非常有限。可能由于缺乏足够的历史基准数据，他们的薪酬水平就更不为人所知了。在对历史上的土地覆盖变化做出反应的同时，森林植物物种需要对最近的环境变化做出反应。大量的调查研究表明，由于冠层覆盖变化、大气沉积、鹿食活动增强和气候变暖，草本层群落正在发生变化。然而，到目前为止，大多数研究都是单独处理这些驱动因素，而忽略了它们之间以及它们与历史土地覆盖变化遗留问题之间的相互作用。通过这个研究项目，我们将解决这些重要的知识差距。我们的主要目标是(a)分别量化古代和农业后森林碎片的灭绝债务和殖民信贷的规模；(b)确定在过去五十年中，灭绝债务和殖民信贷的偿还程度；(c)确定历史土地覆盖变化的遗留影响与近期环境变化之间的重要相互作用。这项研究将在德国东部约3600平方公里的普里格尼茨地区进行，该地区拥有特殊的历史数据。18世纪末和19世纪末的历史地形图将重建该地区的土地利用历史。然后，历史和当今的景观配置可以与森林碎片中当今草本层物种多样性联系起来，以量化灭绝债务和殖民信用。此外，还将对分布在该地区落叶林中的至少200个1960年以来的半永久性植被样地进行重新调查，以量化物种多样性、森林群落之间的区系分化程度（β多样性）和功能组成的变化。利用场地条件和物种表现特征的测量，我们将能够将观察到的物种多样性和组成的变化归因于历史土地覆盖变化和最近环境变化的相互作用。

Land-cover changes are considered one of the most important threats to biodiversity. In many parts of temperate Europe, extensive land-cover changes occurred during the 18th and 19th century, when massive forest clearance for agriculture, followed by agricultural abandonment and reforestation took place. There is reason to believe that these historical land-cover changes are causing delayed responses in the forest herb layer vegetation today, as extinction debt and colonisation credit in ancient and post-agricultural forest fragments, respectively, are paid. However, knowledge on the magnitudes of extinction debt and colonisation credit in temperate forests is very limited. Even less is known about the degree to which they are being paid, probably due to a lack of adequate historical baseline data. Simultaneously to their response to historical land-cover changes, forest plant species need to respond to more recent environmental changes. Numerous resurvey studies have shown that herb layer communities are changing due to canopy cover changes, atmospheric deposition, enhanced deer browsing and climate warming. However, most studies so far handled these drivers separately, while neglecting their interactions both among each other and with the legacies of historical land-cover changes. With this research project, we will address these important knowledge gaps. Our main objectives are (a) to quantify the magnitude of extinction debt and colonisation credit in ancient and post-agricultural forest fragments, respectively; (b) to determine to which degree extinction debt and colonisation credit have been paid over the last five decades; and (c) to identify important interactions between the legacy effects of historical land-cover changes and recent environmental changes. The study will be conducted in the c. 3600 km² Prignitz region in eastern Germany, for which exceptional historical data are available. Historical topographical maps from the late 18th and late 19th century will allow to reconstruct the land-use history of the region. The historical and present-day landscape configuration can then be related to the present-day herb layer species diversity in forest fragments to quantify extinction debt and colonisation credit. Moreover, at least 200 semi-permanent vegetation plots from c. 1960, distributed across the deciduous forests of the region will be resurveyed to quantify changes in species diversity, the degree of floristic differentiation among forest communities (beta diversity) and functional composition. Using both measurements of site conditions and species performance traits we will be able to attribute the observed changes in species diversity and composition to the interactive effects of historical land-cover changes and recent environmental changes.