Vegetation synchronously leans upslope as climate warms

Ecologists have long sought to understand how vegetation relates to climate (1, 2). Such knowledge underlies effective mitigation and adaptation to contemporary climate change (3). Warming temperatures associated with anthropogenic increases in greenhouse gases have led ecologists to predict that vegetation gradients will “march” up the hill as climate 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 favorable conditions for establishment and growth at the leading edge of a species' range (e.g., the upper elevation boundary 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 central tendency expected to concurrently “march” upslope. This type of response has important implications for predicting and mitigating climate change impacts, particularly for vegetation spanning elevation gradients. If, rather than collectively moving with climate change, responses of dominant species assembled along an elevation gradient are highly individualistic, there is greater potential for more novel, nonanalog vegetation assemblages. Several types of plant distribution responses to contemporary changes in climate have been documented, such as truncation of species' ranges at lower boundaries via tree mortality (8, 9), range-wide decreases in species abundance, either in response to extreme events (10) or due to increased background rates of mortality without increases in recruitment (11), and increases in the mean elevation in the distribution …