Coastal Landscape Analysis and Modeling Study

Characterizing historical fire regimes and landscape dynamics of Coast Range forests

Michael C. Wimberly and Thomas A. Spies, Pacific Northwest Research Station, USDA Forest Service

Forest landscape patterns in the Oregon Coast Range have changed considerably since the arrival of Euro-American settlers in the 19th century. Extensive timber harvesting has reduced amounts of old forests and increased fragmentation in the current landscape. These widespread changes have led to concern for the viability of populations of many native species. Because of limited knowledge and resources, developing and implementing individual management plans for every species is not feasible. An alternative approach involves managing for forest patterns and dynamics similar to the historical range of variability that existed in pre-settlement landscapes. This type of management is essentially a “coarse-filter” method, which assumes that maintaining a range of forest types similar to historical distributions will sustain most of the native species that depend on these habitats.

Better assessments of historical landscape patterns and dynamics are needed to provide a baseline for comparing current conditions, and to possibly serve as a basis for developing new forest management strategies. Most historical landscape assessments to date have not considered the spatial and temporal variability characteristic of natural systems, instead focusing on single points in recent time or assuming steady-state conditions. However, the assumption of a static or equilibrium landscape is unrealistic in ecosystems characterized by large, infrequent disturbances Large wildfires, for example, were ubiquitous in pre-settlement Coast Range forests. These disturbances created a shifting mosaic in which the amounts and spatial patterns of seral stages continually fluctuated. It is therefore necessary to characterize a range of possible landscape patterns over a long time period rather than simply estimate static conditions.

We developed the Landscape Age-Class Dynamics Simulator (LADS), to examine historical variability in the amounts of forest seral stages in the Pacific Northwest. This computer model simulates pre-settlement fire regimes using parameters derived from dendroecological, paleoecological, and historical studies. Results to date have emphasized the sensitivity of landscape variability to the spatial scale of analysis and showed that current amounts of old forest in the Oregon Coast Range province are lower than expected under the pre-settlement disturbance regime (Wimberly et al. 2000). We are currently developing an enhanced version of the LADS model that is sensitive to topography, as well as spatial and temporal variability in vegetation and climate (Wimberly, in review). This new simulator will be linked with models of plant and animal populations to study the responses of various species to changes in the disturbance regime.The animation at right illustrates predicted landscape dynamics from a single model run, encompassing the 3000 years prior to Euro-American settlement. Because the model is stochastic, this simulation should be viewed as a general representation of landscape patterns and dynamics rather than a precise prediction of landscape characteristics at any given point in time.

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Wimberly, M. C., Spies, T. A., Long, C. J., and Whitlock, C., 2000. Simulating historical variability in the amount of old forests in the Oregon Coast Range. Conserv. Biol. 14: 167-180.

Wimberly, M. C., in review. Spatial simulation of dynamics landscape mosaics under historical fire regimes.


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