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Evaluating changes in drought resistance across California ecosystems

Date: December 22, 2016

Using satellite imagery, this study identifies California ecosystems that are most resistant to drought


Background

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.

Spatial patterns in self- calibrating Palmer Drought Severity Index (scPDSI) in 2014 across California. The gray area denotes trends in scPDSI with latitude and longitude. Negative values indicate drier conditions.
Spatial patterns in self- calibrating Palmer Drought Severity Index (scPDSI) in 2014 across California. The gray area denotes trends in scPDSI with latitude and longitude. Negative values indicate drier conditions.
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).

Key Findings

  • 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.        

Featured Publications

Malone, Sparkle L. ; Tulbure, Mirela G. ; Perez-Luque, Antonio J. ; Assal, Timothy J. ; Bremer, Leah L. ; Drucker, Debora P. ; Hillis, Vicken ; Varela, Sara ; Goulden, Michael L. , 2016


Principal Investigators: 
External Partners: 
Mirela G. Tulbure, The University of New South Wales, Sydney, Australia

Antonio J. Pérez-Luque, University of Granada, Granada Spain

Timothy J. Assal, United States Geological Survey, Fort Collins, Colorado

Leah L. Bremer, Stanford University, Stanford, California

Debora P. Drucker, Campus Unicamp, Campinas, Brazil

Vicken Hillis, University of California-Davis, Davis, California

Sara Varela, Leibniz Institute for Evolution and Biodiversity Science, Berlin, Germany

Michael L. Goulden, University of California-Irvine, Irvine, California