Changes in blister rust infection and mortality in whitebark pine over time

Abstract

Whitebark pine (Pinus albicaulis Engelm.), a keystone species in subalpine ecosystems of western North America, is under threat across its range from white pine blister rust, mountain pine beetle, fire exclusion, and climate change. Loss of whitebark pine is predicted to have cascading effects on many ecosystem services. We remeasured 115 whitebark pine plots in the Canadian Rocky Mountains to determine whether infection and mortality rates from blister rust were changing over time and (or) latitude. Average rust infection of trees among plots increased from 42% in 2003–2004 to 52% in 2009, while mortality increased from 18% to 28%. In eight plots that have been measured three times, infection increased from 43% of live trees in 1996 to 70% in 2003 and 78% in 2009. Mortality increased from 26% to 65% in the same time period. Overall, infection and mortality have increased 3%/year over the 13 years of the study. Incidence of infection and mortality was highest among plots in the southern part of the study area, particularly on the western side of the Continental Divide. The slowing rates of infection and mortality that we found suggest that some level of natural selection may already be occurring in areas with high levels of both.