Thermophilic Tree Species Reinvade Subalpine Sweden–Early Responses to Anomalous Late Holocene Climate Warming

Abstract

ABSTRACTConsistent with general predictions and earlier empirical studies, it appears that recent climate warming has started to affect large-scale biogeographical patterns in northern Sweden. Long-term, systematic monitoring in permanent altitudinal belt transects reveals spread of broadleaved thermophilic tree species with quite different life histories into the subalpine forest belt. Saplings of Quercus robur, Ulmus glabra, Acer platanoides, Alnus glutinosa, and Betula pendula have responded to altered climatic conditions by jump-dispersal in the order of 50–300 km northwards and 500–800 m upwards. Thereby, they have reinvaded elevations where they grew during the warmest phase of the Holocene, 9500–8000 years ago, but were subsequently extirpated by Neoglacial cooling. Confined to the past 15 years or so, these unique observations are consistent with background climatic data, i.e. warming of all seasons. The results contribute to more realistic vegetation models by stressing that at least certain plant species are able to track climate warming without substantial migration lag.