Microrefugia May Explain Rapid Spread of Forests After Last Glacial Maximum

Tree Migration-Rates: Narrowing the Gap between Inferred Post-Glacial Rates and Projected Rates

Authors:

1. Angelica Feurdean (a,b)
2. Shonil A. Bhagwat (c,d,e,f)
3. Katherine J. Willis (d,e)
4. H. John B Birks (c,g,h)
5. Heike Lischke (i)
6. Thomas Hickler (a,j)

Affiliations:

a. Senckenberg Research Institute and Natural History Museum and Biodiversity and Climate Research Center, Frankfurt am Main, Germany

b. Romanian Academy “Emil Racoviţă” Institute of Speleology, Cluj Napoca, Romania

c. Department of Geography, The Open University, Milton Keynes, United Kingdom

d. School of Geography and the Environment, University of Oxford, Oxford, United Kingdom

e. Long-Term Ecology Laboratory, Biodiversity Institute, Department of Zoology, University of Oxford, Oxford, United Kingdom

f. Biodiversity Institute, Oxford Martin Institute, Department of Zoology, University of Oxford, Oxford, United Kingdom

g. Department of Biology, University of Bergen, Bergen, Norway

h. Environmental Change Research Centre, University College London, London, United Kingdom

i. Dynamic Macroecology, Landscape Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland

j. Biodiversity and Climate Research Centre and Senckenberg Gesellschaft für Naturforschung and Goethe University, Frankfurt am Main, Germany

Abstract:

Faster-than-expected post-glacial migration rates of trees have puzzled ecologists for a long time. In Europe, post-glacial migration is assumed to have started from the three southern European peninsulas (southern refugia), where large areas remained free of permafrost and ice at the peak of the last glaciation. However, increasing palaeobotanical evidence for the presence of isolated tree populations in more northerly microrefugia has started to change this perception. Here we use the Northern Eurasian Plant Macrofossil Database and palaeoecological literature to show that post-glacial migration rates for trees may have been substantially lower (60–260 m yr–1) than those estimated by assuming migration from southern refugia only (115–550 m yr–1), and that early-successional trees migrated faster than mid- and late-successional trees. Post-glacial migration rates are in good agreement with those recently projected for the future with a population dynamical forest succession and dispersal model, mainly for early-successional trees and under optimal conditions. Although migration estimates presented here may be conservative because of our assumption of uniform dispersal, tree migration-rates clearly need reconsideration. We suggest that small outlier populations may be a key factor in understanding past migration rates and in predicting potential future range-shifts. The importance of outlier populations in the past may have an analogy in the future, as many tree species have been planted beyond their natural ranges, with a more beneficial microclimate than their regional surroundings. Therefore, climate-change-induced range-shifts in the future might well be influenced by such microrefugia.