Multi-year drought altered regional disturbance dynamics in California and Oregon

Bell, David M; Bell, David M; Bell, David M

Monday, August 12, 2019: 2:50 PM

M109/110, Kentucky International Convention Center

ABSTRACT WITHDRAWN

David M Bell, Pacific Northwest Research Station, USDA Forest Service, Corvallis, OR, Matthew J. Gregory, Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR, Robert Kennedy, Geography, Environmental Sciences, and Marine Resource Management, Oregon State University, Corvallis, OR, John J. Battles, Department of Environmental Science, Policy, and Management, University of California, Berkeley, Berkeley, CA, Brandon Collins, Center for Fire Research and Outreach, UC Berkeley, Berkeley, CA, David S. Saah, Environmental Science, Spatial Informatics Group LLC and University of San Francisco, San Francisco, CA and Robert A. York, UC Berkeley Center for Forestry, Blodgett Forest, Georgetown, CA

David M Bell, USDA Forest Service; Matthew J. Gregory, Oregon State University; Robert Kennedy, Oregon State University; John J. Battles, University of California, Berkeley; Brandon Collins, UC Berkeley; David S. Saah, Spatial Informatics Group LLC and University of San Francisco; Robert A. York, Blodgett Forest

Background/Question/Methods

Future increases in the prevalence of drought may alter forested landscapes globally. In recent decades, forest disturbances associated with multiple, consecutive drought years have become increasingly common. However, the consequences of these multi-year droughts for forest landscape biomass stocks are not yet fully appreciated. In particular, how does landscape aridity influence forest landscape sensitivity to drought. In this research, our objectives were to (1) assess regional changes in disturbance rates and aboveground live forest biomass during the 2011-2016 drought in California and Oregon and (2) examine whether changes were associated with aridity (climatic water deficit [CWD] 1990-2010) and drought magnitude (CWD 2016-2011 – CWD 1990-2010). For this research, we leveraged an integrated disturbance and vegetation mapping approach to map annual live tree aboveground biomass (AGB) across all forest lands in California and western Oregon from 1990-2016.

Results/Conclusions

During the study period, landscapes accumulating AGB (i.e., positive change) decreased from 80% (1990-1994) to 50% (2011-2016) of 8600-ha hexagons. Forested areas experiencing the greatest magnitude shifts in AGB change during 2011-2016 compared to 1990-2010 also experienced numerous large wildfires and episodes of drought-induced tree mortality, with annual disturbance rates increasing by >15% across large portions of southern California where the most extreme drought magnitudes were observed. Changes in disturbance rates during the drought increased with aridity and drought magnitude (R² = 0.32). Within landscapes experiencing >5% increase in disturbance rates during the drought, magnitude of AGB losses in disturbed forests increased with drought magnitude (R² = 0.16). Our results indicate that multi-year drought, especially in semi-arid forest landscapes, contributed to increased disturbance rates and elevated AGB losses. Therefore, multi-year drought has the potential to alter disturbance and ecosystem dynamics, potentially presaging forest decline in moisture-limited environments.

COS 4-5 - Multi-year drought altered regional disturbance dynamics in California and Oregon