Abstract
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 beetle, fire exclusion, and climate change. We monitored whitebark pine in permanent plots in two national parks three times between 2004 and 2016. The proportion of live trees showing evidence 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. The percent of live infected and dead whitebark pine increased with south and east aspects and mortality decreased with elevation. Annualized mortality rates calculated for the entire study period were 1.5% in Mount Rainier National Park and 2.3% in North Cascades National Park Service Complex. Although these rates decreased between the first time period (2004–2009) and the second time period (2009–2016), the prevalence of infected and dead whitebark pine increased across all park landscapes over time and increased in smaller diameter whitebark pine trees.
Highlights
Whitebark pine is a keystone species in high-elevation areas of western North America due to its influence on biodiversity, ecosystem structure, and hydrologic cycles [1,2]
When whitebark pine trees growing in a clump, we trees for evidence of mountain pine beetle and recorded beetles as present if we found pitch tubes, followed the stem to the ground to determine if stems were individual trees or multi-stemmed exit holes, or following visible galleries on dead trees after bark off.greater
Subalpine larch (Larix lyallii) grows only in whitebark pine were recorded in both parks
Summary
Whitebark pine is a keystone species in high-elevation areas of western North America due to its influence on biodiversity, ecosystem structure, and hydrologic cycles [1,2]. C. Fisch) that was first documented in western North America in 1910 [3,4]. The fungus requires an alternate host to complete its life cycle including several species of Ribes, Castilleja, and Pedicularis, which are all widely distributed in the subalpine ecosystems [5]. In addition to WPBR, other factors implicated in the species’ decline include changing fire regimes, mountain pine beetle (Dendroctonus ponderosae Hopkins), and warming climates [6,7,8,9,10]. Whitebark pine is Forests 2018, 9, 244; doi:10.3390/f9050244 www.mdpi.com/journal/forests
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