Fig. 5

Regression tree results for fir-pine ratio (FPR) for all trees (>15.2 cm DBH) in (a) historical and (b) modern datasets. Inset histograms show distribution of density data, with bin colors in histograms corresponding to box colors in regression trees. Smaller FPR values indicate dominance by pine species; larger values indicate fir dominance. Explanatory variables were selected from the best-fit model (Additional file 1: Table S1, model 6), and included elevation (m), slope aspect (southwest or northeast; aspect), mean annual precipitation (mm; precip), and mean annual climatic water deficit (mm; deficit)