Whitebark pine and white pine blister rust in the Rocky Mountains of Canada and northern Montana

In 2003-2004, we examined 8031 whitebark pine (Pinus albicaulis Engelm.) trees and 3812 seedling-establishment sites in 170 plots for mortality and incidence of white pine blister rust (Cronartium ribicola A. Dietr.). We found blister rust in all but four plots (98%), and 57% of all trees assessed for blister rust were either already dead or showed signs of blister rust infection. Mean percentage of trees infected was highest in the southern Canadaa-aUnited States border area (similar to 73%), decreasing to a low in the northern region of Banff National Park, Alberta (similar to 16%), and then rising (similar to 60%) in the northern end of the study area in Jasper National Park, Alberta. Stands with higher infection, mortality, and canopy kill of trees and higher presence of rust on seedlings tended to be located on the western side of the Continental Divide. In the eight stands in Waterton Lakes National Park, Alberta, that had been previously assessed in 1996, infection levels increased from 43% to 71%, and mortality increased from 26% to 61%, whereas no change was apparent in Glacier National Park, Montana, stands. The impacts of high mortality and infection levels, high crown kill, and reduced regeneration potential, suggest that the long-term persistence of whitebark pine in the southern part of the study area is in jeopardy.