Pollen-inferred millennial changes in landscape patterns at a major biogeographical interface within Europe
Abstrakt
We compiled pollen spectra from 112 sites distributed across various landscapes for six time-periods from the Late Glacial to the present. Compositional patterns were assessed by principal coordinates analyses (PCoA) with a sensitivity analysis based on a bootstrap technique.
Site PCoA scores were interpolated geographically and correlated with palaeoclimatic models. Results: Consistently over the last 15,000 years, the first ordination axis sorted samples according to the proportion of deciduous temperate trees, while the second axis consistently followed an altitudinal gradient that coincided with temperature.
The principal gradient was more important than the altitudinal gradient except for the Late Glacial and Bronze & Iron Ages, when both gradients were of similar importance. The fine-grained pattern in the present mountain landscape was formed as late as during early modern colonization.
Main conclusions: Since the Late Glacial, the landscape has been differentiated into temperate, continental and cold regions. This finding supports the hypothesis that refugia are a key factor for understanding current biogeography in Central Europe.
The Late Glacial occurrence of temperate trees is unlikely to be explained only by gradual migrations from southern Europe. Humid but relatively warm mountains hence might have acted as glacial refugia of temperate forest species, while lowlands and leeward basins might have acted as post-glacial refugia of steppe grasslands.
The strong contrast between forested (temperate) and more open continental landscapes during the Early Holocene seems to correspond with recent diversity patterns. Our results highlight the relevance of integrating past landscape trajectories into modern biogeographical models.