Click here to download the posters, below, which were presented by CECS Co-Director, Roger Bales, Co-PI, Martha Conklin, and colleague, Christine Ma, at the “Forests in Flux: How Science Can Inform Policy” event in Fall 2019. These posters describe:
- The effects of thinning treatments on forest water use and watershed health;
- The effects of wildfire on forest water balance; and
- The predictions of drought resilience and vulnerability.
Science Lecture Series
Click here to listen to the talk “Predicting mountain-ecosystem response to disturbance through scaling subsurface water-storage capacity” by CECS Co-Director Roger Bales, of UC Merced.
Presentation overview: The historical, widespread forest disturbance by wildfire and drought-induced tree mortality in the Sierra Nevada is accompanied by changes in the partitioning of precipitation between evapotranspiration and runoff. We use assessments of these historical evapotranspiration to project changes in water balance from forest management, and to assess forest vulnerability to drought. We determined annual spatial patterns of evapotranspiration using a top-down statistical model, correlating measured annual evapotranspiration from eddy-covariance towers across California with NDVI (Normalized Difference Vegetation Index) measured by satellite, and with annual precipitation. The study area was the Yuba and American River watersheds, two densely forested watersheds in the northern Sierra Nevada. Wildfires resulted in significant post-fire reductions in evapotranspiration for at least 5 years (as much 150-200 mm yr-1), and in some cases for more than 20 years. Rates of recovery in post-wildfire evapotranspiration confirm the need for follow-up forest treatments at intervals of 5-20 years to sustain lower evapotranspiration. Using the metric of cumulative precipitation minus evapotranspiration (P-ET) during multi-year dry periods, we found that forests in the study area showed little evidence of past moisture stress; however, more-severe or sustained drought periods will push some lower-elevation forests in the area studied toward the cumulative P-ET thresholds previously associated with widespread forest mortality in the southern Sierra Nevada.