Widespread mortality of trembling aspen (Populus tremuloides) throughout interior Alaskan boreal forests resulting from a novel canker disease
Fig 7
Modeling canker incidence among ecoregions.
Probability of canker infection for different ecoregions as a function of DBH of an aspen tree (A), mean stand-level aspen DBH, a surrogate for stand age (B), and aspen basal area (C). Probabilities were calculated by fixing all other variables as mean values using the following equation derived from a mixed-effects logistic regression model incorporating site as a random effect: Logit (π) = log (π/(1- π)) = –0.761–0.177*DBH– 0.023*Relative Aspen Density + 0.092*Aspen Basal Area + 0.106*Mean Aspen DBH– 1.413*CK– 3.263*CR– 0.358*RM + 0.692*TKL– 0.736*NOM. Ecoregion β values are computed relative to YTU which does not appear in the model and has a log(odds) = the intercept when all other factors are 0. Contrasts derived from logistic models indicated the following differences in canker incidence among ecoregions; TKLa, YTUab, RMbc, NOMabc, CKcd, CRd, where ecoregions with different letters are significantly different at P < 0.05. Ecoregion abbreviations follow Fig 4.