| Landscape-level disturbance effects vary with climate, geomorphology, topography, soils, and vegetation. Patches minimally affected by successive disturbance events may be thought of as "refugia." Refugia harbor plant and animal species that would be missing if subjected to the characteristic disturbance regime of the surrounding matrix. The goals of this research were to predict the probability of pre-settlement late-successional fire refugia from physiographic and topographic variables and to quantify changes to forest structure and composition resulting from alteration of the natural disturbance regimes by fire suppression and high grade logging.; Plots taken in nine randomly selected sub-drainages across a 187 square mile landscape were evaluated using three criteria to identify potential refugia plots: different disturbance regime from surrounding matrix; different structure from surrounding matrix; and the presence of late-successional trees whose ages predated Euro-American settlement and fire suppression. Classification and Regression Tree Analysis (CART) and logistic regression were used to model late-successional fire refugia as a function of physiographic and topographic variables. The best predictors of refugial status were aspect, topography, and elevation.; Age and diameter class frequency distributions were used to analyze changes in forest composition and structure since Euro-American settlement. Amounts of all tree species increased, but the greatest increases were for shade tolerant species that are characteristically intolerant of fire. Concurrent with changes in species composition were changes in forest structure that put these forests at risk to large scale insect, pathogen, and fire disturbances. |
