TRANSITION PROBABILITIES: Whitebark Pine and Blister Rust in the Greater Yellowstone Ecosystem

Whitebark Pine (Pinus albicaulis) plays an integral role in the Greater Yellowstone Ecosystem (GYE). It has been often referred to as a keystone species due to the extensive changes that the ecosystem would undergo if the species were to be lost. Attributed to white pine blister rust (Cronartium ribicola) infection and mountain pine beetles (Dendroctonus ponderosae), the decline of the whitebark population in the GYE over the last few decades led to the establishment of the Interagency Whitebark Pine Monitoring Program in 2004. Using data collected by the program from 2008 through 2016, we focused on white pine blister rust infections, using mixed logistic regression to model the probability of transitioning from no infection to a canopy infection (Model 1) and modeling the probability of transitioning from a canopy infection to a bole infection (Model 2). Explanatory variables included elevation, aspect, tree size, and a time variable the length of time the tree remained uninfected (Model 1) or the length of time the tree remained canopy infected (Model 2). We found that the length of time the tree remined uninfected and tree size were the most useful predictors in the probability of transitioning from no infection to a canopy infection; while the length of time the tree remained canopy infected and elevation were the most useful predictors in the probability of transitioning from a canopy infection to a bole infection.