Harvest Retention Survivorship of Endangered Whitebark Pine Trees

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.

Detection of standing retention trees in boreal forests with airborne laser scanning point clouds and multispectral imagery

“…Key tree‐level attributes that affect the value of a retention tree include tree species, size and condition, that is, dead, weakened or living, and on a within‐tree level, the presence of tree‐related microhabitats (as defined by Larrieu et al, 2018). Of particular importance are large trees rich in microhabitats (Bütler et al, 2013), dead trees that play a key role in the protection of saproxylic species, including rare and red‐listed species (Gustafsson et al, 2020), and certain tree species that are otherwise considered ecologically valuable (Koch Widerberg et al, 2018; Lundström et al, 2013; Murray et al, 2021). Besides tree‐level attributes, the positioning of retention trees plays a crucial role in the effectiveness of retention trees, both within a stand (e.g.…”