Abstract
Whitebark pine (Pinus albicaulis Engelm.) is a widely distributed high-elevation species in western North America that is threatened primarily by an introduced disease and other disturbances. In British Columbia, this tree is a component of harvested forests, yet knowledge of post-harvest survivorship and factors that promote successful retention is lacking. Our objectives are to describe the temporal attrition of retained mature whitebark pine trees and to identify factors that likely influence survivorship during the critical initial post-harvest period. We assessed five separate harvest units in southeastern British Columbia. Dendrochronological investigation revealed that retained trees experienced high annual mortality rates (3–16%) across harvest sites during the initial five-year post-harvest period. By eight years post-harvest, retention survivorship ranged from 17–80%. After eight years post-harvest, mortality rates drastically declined. The preponderance of fallen stems oriented towards the northeast suggests that storm system events arriving from the Pacific Ocean are the most significant drivers of blowdown. We estimate that survivorship is positively associated with shorter tree heights and longer crown lengths, a lack of disease cankers, a greater presence of rodent wounding, and higher numbers of surrounding retained trees. We found little effect based on slope and aspect. As these trees are an endangered species, harvest operations should be practiced cautiously in associated forests. We recommend carefully selecting retention trees, ensuring an adequate number of neighbor trees, and orienting retention patches to avoid predominant storm wind directions.
Highlights
Whitebark pine (Pinus albicaulis Engelm.), which is widely distributed at higher elevations in western North America, affords notable ecological and cultural services
In southeastern British Columbia (BC) and neighboring Alberta, Smith and others [7] estimated that blister rust infections were rising in the region, with tree mortality levels increasing from 26% to 65% between 1996 and 2009
We suggest that winter storms and approaching fronts of coastal low-pressure systems are the most significant drivers of blowdown for whitebark pine stands in the southern interior region
Summary
Whitebark pine (Pinus albicaulis Engelm.), which is widely distributed at higher elevations in western North America, affords notable ecological and cultural services. This tree is a renowned habitat asset for a variety of wildlife, including grizzly bears (Ursus arctos horribilis Ord), foxes (Vulpes vulpes Linnaeus), and Clark’s nutcrackers (Nucifraga columbiana Wilson), which consume the large nutrient-rich seeds [1,2,3]. In 2012, whitebark pine was listed as an endangered species, becoming the only designated tree in western Canada [5]. Blister rust is evident throughout most of its range, this region, including the adjoining Northern Rocky Mountains of USA, is the most heavily impacted [7,8,9]
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