Disturbance Departure and Fragmentation of Natural Systems in the Interior Columbia Basin

Hann, Wendel J.; Wisdom, Michael J.; Rowland, Mary M. 2003. Disturbance departure and fragmentation of natural systems in the interior Columbia basin. Res. Pap. PNW-RP-545. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 19 p. We integrated landscape data from science assessments of the interior Columbia basin (basin) into one variable that functions as a robust index of departure from native conditions. This variable, referred to as the disturbance departure and fragmentation index, is a spatially explicit measure of landscape quality and resiliency. Primary causes of departure and fragmentation include fire exclusion, timber harvest, mining, oil and gas development, livestock grazing, invasive species, road networks, and the interface of these activities with agricultural and urban development. We derived four classes of the disturbance departure and fragmentation index: very high, high, moderate, and low. Very high departure and fragmentation was associated with low-elevation subwatersheds dominated by agricultural and urban lands. High departure and fragmentation was found in subwatersheds containing a mix of agricultural lands with low-elevation forests, woodlands, or rangelands. Subwatersheds with moderate departure and fragmentation were associated with lowto mid-elevation forests, woodlands, or rangelands in public ownership. Subwatersheds with low departure and fragmentation typically occurred at higher elevations, on public lands within or near wilderness areas, roadless areas, or national parks. Because the disturbance departure and fragmentation index represents the composite effects of management activities that do not mimic native or natural processes, the index appears useful as a planning tool for integrated restoration of wildland landscapes.