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Forest Disturbance Across the Conterminous United States from 1985-2012: The Emerging Dominance of Forest DeclineEvidence of shifting dominance among major forest disturbance agent classes regionally to globally has been emerging in the literature. For example, climate-related stress and secondary stressors on forests (e.g., insect and disease, fire) have dramatically increased since the turn of the century globally, while harvest rates in the western US and elsewhere have declined. For shifts to be quantified, accurate historical forest disturbance estimates are required as a baseline for examining current trends. We report annual disturbance rates (with uncertainties) in the aggregate and by major change causal agent class for the conterminous US and five geographic subregions between 1985 and 2012. Results are based on human interpretations of Landsat time series from a probability sample of 7200 plots (30 m) distributed throughout the study area. Forest disturbance information was recorded with a Landsat time series visualization and data collection tool that incorporates ancillary high-resolution data. National rates of disturbance varied between 1.5% and 4.5% of forest area per year, with trends being strongly affected by shifting dominance among specific disturbance agent influences at the regional scale. Throughout the time series, national harvest disturbance rates varied between one and two percent, and were largely a function of harvest in the more heavily forested regions of the US (Mountain West, Northeast, and Southeast). During the first part of the time series, national disturbance rates largely reflected trends in harvest disturbance. Beginning in the mid-90s, forest decline-related disturbances associated with diminishing forest health (e.g., physiological stress leading to tree canopy cover loss, increases in tree mortality above background levels), especially in the Mountain West and Lowland West regions of the US, increased dramatically. Consequently, national disturbance rates greatly increased by 2000, and remained high for much of the decade. Decline-related disturbance rates reached as high as 8% per year in the western regions during the early-2000s. Although low compared to harvest and decline, fire disturbance rates also increased in the early- to mid-2000s. We segmented annual decline-related disturbance rates to distinguish between newly impacted areas and areas undergoing gradual but consistent decline over multiple years. We also translated Landsat reflectance change into tree canopy cover change information for greater relevance to ecosystem modelers and forest managers, who can derive better understanding of forest-climate interactions and better adapt management strategies to changing climate regimes. Similar studies could be carried out for other countries where there are sufficient Landsat data and historic temporal snapshots of high-resolution imagery.
Document ID
20170003248
Document Type
Reprint (Version printed in journal)
Authors
Cohen, Warren B. (Forest Service Corvallis, OR, United States)
Yang, Zhiqiang (Oregon State Univ. Corvallis, OR, United States)
Stehman, Stephen (Syracuse Univ. NY, United States)
Schroeder, Todd (Forest Service Ogden, UT, United States)
Bell, David M. (Forest Service Corvallis, OR, United States)
Masek, Jeffrey (NASA Goddard Space Flight Center Greenbelt, MD United States)
Huang, Chengquan (Maryland Univ. College Park, MD, United States)
Meigs, Garrett W. (Vermont Univ. Burlington, VT, United States)
Date Acquired
April 7, 2017
Publication Date
October 30, 2015
Publication Information
Publication: Forest Ecology and Management
Volume: 360
ISSN: 0378-1127
Subject Category
Earth Resources and Remote Sensing
Report/Patent Number
GSFC-E-DAA-TN41000
Funding Number(s)
CONTRACT_GRANT: NNH11AR29I
Distribution Limits
Public
Copyright
Other