Vegetation synchronously leans upslope as climate warms

Ecologists have long sought to understand how vegetation re- lates to climate (1, 2). Such knowledge underlies effective mitigation and adaptation to contempo- rary climate change (3). Warming tem- peratures associated with anthropogenic increases in greenhouse gases have led ecologists to predict that vegetation gra- dients will ‘‘march’’ up the hill as cli- mate envelopes shift with elevation, at a lag that scales with species’ generation times (4, 5). This prediction derives from the hypothesis that low-temperature constraints relax in association with warming climate, resulting in more fa- vorable conditions for establishment and growth at the leading edge of a species’ range (e.g., the upper elevation bound- ary on a mountain) (6, 7). Because of competition and change in plant-available water, the trailing edge is expected to track the leading edge (5) with the cen- tral tendency expected to concurrently ‘‘march’’ upslope. This type of response has important implications for predict- ing and mitigating climate change impacts, particularly for vegetation span- ning elevation gradients. If, rather than collectively moving with climate change, responses of dominant species assem- bled along an elevation gradient are highly individualistic, there is greater potential for more novel, nonanalog veg- etation assemblages.