Spatial simulation of historical landscape patterns in coastal forests of the Pacific Northwest

Concerns about the fragmentation of Pacific Northwest forests are based on the assumption that these landscapes historically contained large, contiguous patches of old growth. However, this supposition appears to conflict with disturbance history research, which shows that wildfire was an important component of pre-settlement forest ecosystems. To better quantify historical forest patterns, a spatial simulation model of wildfire and forest succession was used to simulate pre-settlement landscape dynamics in the Oregon Coast Range, U.S.A. The model was parameterized to simulate fire regimes over 1000 years prior to Euro-American settlement using data from paleoecological, dendro-ecological, and historical sources. A simple fire-spread algorithm produced mosaics of variable fire severity and allowed simulated fires to be calibrated to match the shapes of real fires. The simulated landscape was spatially heterogeneous and highly dynamic. Old growth was the dominant patch type occupying a median of 42% of the total area. The relatively long fire return intervals, highly skewed fire size distributions, and mixed severities characteristic of the historical fire regime generated a landscape mosaic with large (>100 000 ha) patches of old-growth forest, although smaller patches (<100 ha) were the most numerically abundant. Both small and large patches of old forest have important ecological roles in a dynamic ecosystem, and future landscape management efforts should consider the implications of altering these historical patterns.