![]() ![]() ![]() ![]() ![]() Moreover, most field studies and model-based assessments of vegetation responses to climate have focused on changes associated with natality and growth, which are inherently slow processes for woody plants-even though the most rapid changes in vegetation are caused by mortality rather than natality ( 13). Previous studies of woody ecotones document landscape-scale shifts in vegetation as occurring only over relatively long (decades to millennia) periods ( 8– 12). Persistent vegetation shifts are most clearly detected in the distributions and abundances of long-lived woody plants, namely, trees and shrubs ( 7). The responses of vegetation to variations in climate are expected to be most rapid and extreme at ecotones, the boundaries between ecosystems ( 2– 5), with semiarid ecotones considered to be among the most sensitive ( 6). The rapidity and the complex dynamics of the persistent shift point to the need to represent more accurately these dynamics, especially the mortality factor, in assessments of the effects of climate change.ĭistributions of vegetation across landscapes depend on climate, perhaps best illustrated by the wholesale movement of plant species across geographic and topographic gradients during the last deglaciation ( 1). Forest patches within the shift zone became much more fragmented, and soil erosion greatly accelerated. Here we report the most rapid landscape-scale shift of a woody ecotone ever documented: in northern New Mexico in the 1950s, the ecotone between semiarid ponderosa pine forest and piñon–juniper woodland shifted extensively (2 km or more) and rapidly (<5 years) through mortality of ponderosa pines in response to a severe drought. However, current models do not adequately provide for such rapid effects-particularly those caused by mortality-largely because of the lack of data from field studies. These shifts are expected to be most rapid and extreme at ecotones, the boundaries between ecosystems, particularly those in semiarid landscapes. In coming decades, global climate changes are expected to produce large shifts in vegetation distributions at unprecedented rates. ![]()
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