Multi-scale Relationships Between Coarse Woody Debris and Presence/Absence of Western Hemlock in the Oregon Coast Range

Abstract

Western hemlock (Tsuga heterophylla) is a key structural component of old-growth forests in the Pacific Northwest, typically providing a multi-layered canopy and contributing to the diversity of tree ages. Forest managers are looking for ways to promote the establishment of hemlock in the hope of accelerating the development of old growth characteristics. This study examines the relationship between the abundance of coarse woody debris (CWD) and the establishment of western hemlock at two different scales: microsite-level and stand-level within the Oregon Coast Range. We use hierarchical logistic regression models to explore this relationship at the microsite-level, and further, whether this relationship itself depends upon the overall amount of CWD available in the stand. We find a significant association between the amount of CWD and hemlock establishment at the microsite-level, but the association does not seem to depend on the total amount of CWD available in the stand. This suggests that hemlock is not able to use alternative substrates for recruitment when CWD is not available. In turn, these results suggest that CWD can be used to help predict the presence of hemlock saplings in a stand, and that management practices that increase the amount of CWD in forest stands should be considered as potentially beneficial to hemlock establishment.