PLEA Network

17 May 2017, Nature, Trees in eastern US head west as climate changes. Breaking from the general poleward movement of many species, flowering trees take an unexpected turn. Ecologists have long predicted that climate change will send plants and animals uphill and towards the poles in search of familiar temperatures. Such movements have increasingly been documented around the world. But a study now shows that changing rainfall patterns may be driving some tree species in the eastern United States west, not north. Songlin Fei, a forest ecologist at Purdue University in West Lafayette, Indiana, and his colleagues tracked the shifting distributions of 86 types of trees using data collected by the US Forest Service’s Forest Inventory and Analysis Program during two periods: from 1980 to 1995 and between 2013 and 2015 for all states. They found more species heading west than north, probably partly because of changing precipitation patterns, the team reported on 17 May in Science Advances¹. “That was a huge surprise for us,” says Fei. This study suggests that, in the near-term, trees are responding to changes in water availability more than to temperature changes, he says. The team measured shifts in the centres of abundance for the 86 types of tree and found that over the past 30 years or so, 34% showed statistically significant poleward shifts at an average rate of 11 kilometres per decade. Forty-seven per cent made statistically significant westward shifts at an even faster rate — 15.4 kilometres per decade. Hardly any types of tree moved south or east. A new direction Most of the trees that shifted west were angiosperms, or flowering trees. Northbound trees were usually gymnosperms, which are mostly conifers in North America. Increased precipitation in the central United States could be one explanation for the angiosperms’ westward movement, says Fei. The increase in moisture is still subtle enough that only the more drought-tolerant and faster-growing flowering trees, which have more-efficient and robust vascular systems, can take advantage for now. Read More here