The recent occurrence of drought in California provided an important opportunity to examine drought response across ecosystem classes (forests, shrublands, grasslands, and wetlands), which is essential to understand how climate influences ecosystem structure and function. The study looked at data from 2002 to 2014 across all natural areas in California and determined which ecosystems and areas are most drought resistant.
The study resulted from a unique training program hosted by the National Center for Ecological Analysis and Synthesis at University of California-Santa Barbara. A subset of participants collaborated to examine drought effects across California using remote-sensing satellite data to help understand ecosystem vulnerability to drought. This effort was led by RMRS Research Ecologist, Dr. Sparkle Malone.
The team quantified ecosystem resistance (i.e. the ability to maintain function under drought conditions) to drought by comparing changes in satellite-derived estimates of water-use efficiency (WUE).
Water-use efficiency (WUE) = net primary productivity [NPP]/evapotranspiration [ET]) under baseline and drought conditions (ΔWUE = WUE2014 − baseline WUE).
Baseline WUE varied across California (0.08 to 3.85 g C/mm H2O) and WUE generally increased under severe drought conditions in 2014.
Strong correlations between the change in WUE, precipitation, and leaf area index indicate that ecosystems with a lower average leaf area index (i.e., grasslands) also had higher rates of carbon-uptake efficiency under limited water/drought conditions.
Systems with a baseline WUE ≤ 0.4 exhibited a decline in WUE under drought conditions, suggesting that a baseline WUE ≤ 0.4 might be indicative of low drought resistance – or higher vulnerability to drought conditions.
Drought severity, precipitation, and WUE were identified as important drivers of shifts in ecosystem classes over the study period.
These findings have important implications for understanding climate change effects on primary productivity and carbon sequestration across ecosystems and how this may influence ecosystem resistance in the future. Results can be used by California land managers to understand drought vulnerability and to assess the probability of ecosystem-type conversions.