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Climatic Limits on Foliar Growth During Major Droughts in the Southwestern USA | CLIMAS

Climatic Limits on Foliar Growth During Major Droughts in the Southwestern USA

TitleClimatic Limits on Foliar Growth During Major Droughts in the Southwestern USA
Publication TypeArticles
Year of Publication2012
AuthorsWeiss, J, Betancourt, J, Overpeck, JT
JournalJournal of Geophysical Research: Biogeosciences
ISBN Number2156-2202
Keywords0426 Biosphere/atmosphere interactions, 1616 Climate variability, 1630 Impacts of global change, 1812 Drought, 1926 Geospatial, drought, elevational gradient, foliar growth limits, low temperature, southwestern USA, vapor pressure deficits

Pronounced droughts during the 1950s and 2000s in the American Southwest provide
an opportunity to compare mesoscale ecosystem responses to anomalously dry conditions before and during the regional warming that started in the late 1970s. This year-round warming has produced fewer cool season freezes, losses in regional snowpack, an 8-10 day advance in spring onset, and hotter summers, all of which should affect vegetation differently across seasons and elevations. Here, we examine indices that represent climatic limits on foliar growth for both drought periods and evaluate these indices for areas that experienced tree mortality during the 2000s drought. Relative to the 1950s drought, warmer conditions during the 2000s drought decreased the occurrence of temperatures too low for foliar growth at lower elevations in winter and higher elevations in summer. Higher vapor pressure deficits (VPDs), largely driven by warmer temperatures in the more recent drought, were more limiting to foliar growth from spring through summer at lower and middle elevations. At many locations where tree mortality occurred during the 2000s drought, low-temperature constraints on foliar growth were extremely unlimiting, whereas VPD constraints were extremely limiting from early spring through late autumn. Our analysis shows that in physiographically complex regions such as the Southwest, seasonality and elevational gradients are important for understanding vegetative responses to warming. It also suggests that continued  warming will both increase the degree to which
VPD limits foliar growth during future droughts and expand its reach to higher elevations
and other seasons.