Document: MIC-3-65-11

Examining current forest patterns in the context of historical dynamics: An example from the Pacific Northwest.

WIMBERLY, M.C.* and T.A.SPIES

USDA Forest Service, Corvallis, OR 97331 USA ¹

Abstract:
Studies of historical landscapes play an important role in ecological assessments, providing baselines to compare with current conditions and setting potential targets for landscape restoration. These assessments must recognize that the assumption of a steady-state landscape is unrealistic and instead quantify a range of possible historical conditions. We used a spatial simulation model of wildfire regimes to estimate historical landscape patterns in the Oregon Coast Range. We modeled landscape dynamics over the past 3,000 years based on fire regime parameters derived from paleoecological, dendroecological, and historical research. The model accounted for spatial and temporal variation in fire frequency and severity, as well as the influences of wind, topography, and fuel accumulation on fire spread. Multiple simulation runs were used to generate probability distributions of landscape pattern under the historical disturbance regime, and these results were compared with several estimates of present-day spatial patterns. Measurements of current landscape patterns were obtained using classified Landsat TM images of forest composition and structure. The amount and spatial pattern of old-growth forests varied considerably in our historical simulations. Old growth typically covered from 30-70% of the landscape, much of which was concentrated in one or more large patches > 100,000 ha in size. Current estimates of total old growth area (< 5% of the landscape) and patch sizes (< 100 ha) were both lower than expected under the historical disturbance regime, even when past landscape variability and uncertainty in our current landscape measurements were taken into account.

Keywords: disturbance, landscape dynamics, old growth

This abstract is being presented at: 11:15 AM in session:
Oral Session #58: Landscape Ecology.