Spatial and Temporal Patterns in Forest Harvest, Fire, and Pest/Pathogen Disturbance for Western and Eastern Oregon

Abstract:

The disturbance regime in temperate zone forests is a function of both human interventions ─ such as thinning and harvesting ─ and background events, including wildfire and outbreaks of pests and pathogens. Forest management requires a good understanding of the relative magnitude and trends in these disturbances, but the inherent spatial heterogeneity in their distribution and the large size of the relevant domains makes monitoring a challenge. Satellite remote sensing offers various tools to address this challenge, and in this study we employed 25 years of Landsat data (1986-2010) to characterize the disturbance regime over forested areas in the state of Oregon, U.S.A. Segmentation of the temporal trajectory of a spectral vegetation index over the study interval was used to specify the year, duration, and intensity of disturbances for each Landsat pixel. Attribution was to Harvest/Thinning, Fire, and Other (mostly pests and pathogens). The western side of the state had a larger proportion of its area disturbed over the study interval (29% vs. 23% for Eastern Oregon). The incidence of Harvest/Thinning there greatly exceeded the incidence of Fire and Other disturbance. In the more xeric eastern OR, the incidence of Fire was greater than the incidence of Harvest/Thinning or Other. The annual area harvested or thinned increased from the 1990s to the 2000s in western Oregon, but decreased in eastern Oregon. In both cases, the area burned increased. These observed patterns in disturbance will be input to a spatially-distributed biogeochemistry model to evaluate related impacts on the carbon and hydrologic cycles.