Abstract
Whitebark pine (Pinus albicaulis. Engelm.) is vulnerable to a number of threats including an introduced pathogen (Cronartium ribicola J.C. Fisch.), epidemic levels of native mountain pine beetle (Dendroctonus ponderosae Hopkins), fire suppression, and climate change. To describe the structure of whitebark pine populations in two national parks in the southern Cascades (Crater Lake, Oregon, USA (CRLA) and Lassen Volcanic, California, USA (LAVO) National Parks), we surveyed trees in 30 × 50 × 50 m plots in both parks. We used these plots to describe the extent of white pine blister rust (the disease caused by Cronartium ribicola), mountain pine beetle occurrence, and to elucidate factors influencing the presence of pests and pathogens, cone production, and canopy kill. In each plot, we recorded data related to tree health, including symptoms of blister rust and mountain pine beetle, and reproductive vigor (cone production). In both parks, encroachment from other species, particularly mountain hemlock (Tsuga mertensiana (Bong.) Carrière), was negatively associated with cone production. In CRLA, water stress was a good predictor of blister rust infection and cone production. For CRLA and LAVO, the presence of mountain pine beetle and blister rust was associated with higher canopy kill for whitebark pine. Lastly, we found evidence for a pest-pathogen interaction, mountain pine beetle attack was greater for trees that showed symptoms of blister rust infection in CRLA. Our results indicate that whitebark pine populations in the southern Cascade Range are experiencing moderate levels of blister rust infection compared with other sites across the species range, and that competition from shade-tolerant species may result in an additional threat to whitebark pine in both parks. We present our findings in the context of park management and situate them in range-wide and regional conservation strategies aimed at the protection and restoration of a declining species.
Highlights
Five-needle white pines (Family Pinaceae, Genus Pinus, Subgenus Strobus), and in particular whitebark pine (Pinus albicaulis Engelm.), limber pine (P. flexilis James), and foxtail pine (P. balfourianaBalf.), are described as keystone or foundational species in upper subalpine and treeline forests [1,2,3].At these higher elevations, five-needle pines are often dominant species and are thought to serve key ecosystem functions, including modulating springtime snowmelt, moderating local environments allowing for establishment of shade-tolerant species, and, during mast years producing large seed crops critical to wildlife, such as Clark’s nutcrackers (NucifragaColumbiana Wilson) [4,5]
Given that the rate of blister rust incidence in Lassen Volcanic National Park (LAVO) is comparable to Crater Lake National Park (CRLA), whitebark pine in LAVO may be increasingly susceptible to mountain pine beetle infestation and mortality in the future
Our study provides a baseline assessment of whitebark pine populations in CRLA and LAVO
Summary
Five-needle white pines (Family Pinaceae, Genus Pinus, Subgenus Strobus), and in particular whitebark pine (Pinus albicaulis Engelm.), limber pine (P. flexilis James), and foxtail pine (P. balfourianaBalf.), are described as keystone or foundational species in upper subalpine and treeline forests [1,2,3].At these higher elevations, five-needle pines are often dominant species and are thought to serve key ecosystem functions, including modulating springtime snowmelt (thereby increasing summer water availability), moderating local environments allowing for establishment of shade-tolerant species, and, during mast years producing large seed crops critical to wildlife, such as Clark’s nutcrackers (NucifragaColumbiana Wilson) [4,5]. Whitebark pine is impacted by increasing populations of the native mountain pine beetle (Dendroctonus ponderosae Hopkins), competition with encroaching vegetation (such as mountain hemlock, Tsuga mertensiana (Bong.) Carrière) due to fire exclusion [8], and changing climate [5,9]. These factors, acting singly or in combination, are likely to change the structure, function, and composition of these high elevation forests
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