PARENT SESSION
Poster Session #65: Global Change.
Friday, August 9. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Assessing ecosystem responses to changes in drought duration and intensity.

DAYEM, KATHERINE^*,1, BRESHEARS, DAVID¹, ALLEN, CRAIG², ¹ Los Alamos National Laboratory, Los Alamos, NM² US Geological Survey, Jemez Mountains Field Station, Los Alamos, NM

ABSTRACT- Extreme climate events such as drought are expected to increase in frequency and intensity in coming years as climate change progresses. Previous studies document how drought can cause rapid, persistent, landscape-scale changes in vegetation through plant mortality. However, ecosystem responses to variation in drought intensity and duration are not well understood. Field experiments evaluating the effects of drought are generally limited to one or two treatments and duration of a few years. We evaluated ecosystem responses to drought using FOREST-BGC, a forest biogeochemistry model. First we evaluated ecosystem responses such as soil water content and plant water potential in response to a drought in the 1950s that led to tree mortality. This drought occurred in the southwest United States caused extensive die-off of ponderosa pine, resulting in a 2 km shift of the forest-woodland ecotone in less than 5 years. This initial simulation was used to determine thresholds for ecosystem responses leading to tree mortality. We then conducted a set of simulations to quantify ecosystem responses to variation in drought duration (3 mo. to >10 years) and intensity (100% to 0% of normal precipitation). Our results, which map relationships between drought and ecosystem responses, identify the threshold conditions at which tree mortality may occur and contribute to an improved understanding of the potential impacts of drought on tree mortality and landscape-scale vegetation dynamics.

KEY WORDS: drought, plant mortality, global change, vegetation dynamics