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Wednesday, April 11 • 11:30am - 11:45am
FOREST LANDSCAPE PROCESSES: Regional Variation in Landscape-level Forest Biomass Trends Before and During a Multi-year Drought

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AUTHORS: David M. Bell*, USDA Forest Service; Matthew J. Gregory; Oregon State University; Robert E. Kennedy, Oregon State University; John J. Battles, University of California at Berkley; Brandon M. Collins, University of California at Berkley; David S. Saah, University of San Francisco; Robert A. York, University of California at Berkley

ABSTRACT: Future increases in the prevalence of drought may alter forested landscapes globally, indicating a need to monitor the magnitude and distribution of forest ecosystem change across scales. 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. First, we used the Landsat-based detection of Trends in Disturbance and Recovery (LandTrendr) to identify forest disturbances and extract fitted spectral trajectories based on annual time-series of 30-m multispectral satellite imagery from Landsat 5, 7, and 8. Second, we incorporated fitted Landsat imagery from LandTrendr and US Forest Service Forest Inventory and Analysis plot data into a nearest neighbor imputation framework to generate 30-m predictions of AGB across all forest lands. We then used model-based techniques to estimate AGB means and confidence intervals for 6349 landscape-level hexagons (8672 ha) distributed across the study area. At the landscape-level, model precision was high, with coefficients of variation in AGB estimates being less than 5% in hexagons with more than 4300 ha of forest. During the study period, landscapes accumulating AGB (i.e., positive change) decreased from 80% of hexagons (1990-1994) to 50% of hexagons (2011-2016). From 2011-2016, annual rates of change in AGB decreased in 66% of landscapes compared to the previous two decades (1990-2010). In some cases, these changes resulted in a shift from accumulating to losing live tree biomass. Areas diverging most strongly during 2011-2016 experienced numerous large wildfires and episodes of drought-induced tree mortality, especially during 2015 and 2016. These results imply that the multi-year drought in California beginning in 2012 may have contributed to a substantial shift in landscape ecosystem function.

Wednesday April 11, 2018 11:30am - 11:45am CDT
Spire Parlor