As temperatures rise and droughts become more severe in the Southwest, trees are increasingly up against extremely stressful growing conditions, especially in low to middle elevations, University of Arizona researchers report in a study soon to be published in the Journal of Geophysical Research Biogeosciences.
Lead author Jeremy Weiss, a senior research specialist in the UA department of geosciences, said: "We know the climate in the Southwest is getting warmer, but we wanted to investigate how the higher temperatures might interact with the highly variable precipitation typical of the region."
Weiss' team used a growing season index computed from weather data to examine limits to plant growth during times of drought.
"The approach we took allows us to model and map potential plant responses to droughts under past, present and future conditions across the whole region," explained Julio Betancourt, a senior scientist with the U.S. Geological Survey who co-authored the study along with Jonathan Overpeck, co-director of the UA Institute of the Environment. Betancourt holds adjunct appointments in the UA department of geosciences, the UA School of Geography and Development, the UA School of Natural Resources and the Environment and the UA Laboratory of Tree-Ring Research.
"Our study helps pinpoint how vegetation might respond to future droughts, assuming milder winters and hotter summers, across the complex and mountainous terrain of the Southwest," Betancourt said.
For this study, the researchers used a growing season index that considers day length, cold temperature limits and a key metric called vapor pressure deficit to map and compare potential plant responses to major regional droughts during 1953-56 and 2000-03.
A key source of plant stress, vapor pressure deficit is defined as the difference between how much moisture the air can hold when it is saturated and the amount of moisture actually present in the air. A warmer atmos
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University of Arizona