Whitebark Pine in the Northern Cascades: Tracking the Effects of Blister Rust on Population Health in North Cascades National Park Service Complex and Mount Rainier National Park

Whitebark pine (Pinus albicaulis Engelm.) is a key component of subalpine and alpine ecosystems in the northern Cascades. The species survival is threatened by white pine blister rust, mountain pine beetles, fire exclusion, and climate change. Trees were monitored in permanent plots in two national parks three times between 2004 and 2016. The proportion of trees showing signs of blister rust infection increased in North Cascades National Park Service Complex from 32% in 2004 to 51% in 2016 and from 18% to 38% in Mount Rainier National Park. Mortality increased from 7% to 21% in North Cascades National Park Service Complex and 38% to 44% in Mount Rainier National Park. Annual mortality rates were calculated for three time periods: 2004-2009, 2009-2015/2016, and 2004-2015/2016. Mortality rates, annualized across the entire study period, were 1.47% in Mount Rainier National Park and 2.27% in North Cascades National Park Service Complex; these rates decreased between the first time period and the second, which could reflect blister rust resistance. Signs of mountain pine beetle were rare and limited to a few trees in individual plots. Although reproductive trees were found in most stands, densities were low and regeneration was dominated by subalpine fir.