THE EFFECTS OF BLISTER RUST ON POSTFIRE REGENERATION OF WHITEBARK-PINE - THE SUNDANCE BURN OF NORTHERN IDAHO (USA)

In the northern Rocky Mountains, whitebark pine (Pinus albicaulis) is rapidly declining as a result of previous five exclusion policies, mou ntain pine beetle (Dendroctonus ponderosae) outbreaks, and white pine blister rust (Cronartium ribicola). Blister rust is potentially the mo st destructive agent, killing seedlings, cone-bearing branches, and, e ventually, mature trees. We examined densities of whitebark pine regen eration and the incidence and severity of blister-rust infection of se edlings and saplings in the 25-year-old Sundance Burn in the Selkirk R ange of northern Idaho, an area heavily infected by blister rust. We f ound that the mean regeneration density of whitebark pine was signific antly lower than that of two other comparably aged burns in western Mo ntana. The low density was attributed to the severe damage to the seed source on the brim perimeter, resulting from previous infestation of mountain pine beetle and blister rust. Overall, 29% of the whitebark p ine regeneration in the Sundance Burn was infected by blister rust. Ag e and height of seedlings were important predictors of incidence of in fection, and height was the most important predictor of severity of in fection. Thus, as seedlings grow larger, they present a bigger target to airborne blister-rust spores. Because of the lack of seed productio n in the adjacent forest and expected mortality, regeneration of white bark pine in the Sundance Burn will be slow In areas of northern Idaho and northwestern Montana affected by blister rust and pine beetle, pr escribed fires for managing whitebark pine ecosystems should be restri cted to small areas or should require plantings of rust-resistant seed lings.