Recent tree mortality and recruitment in mature and old-growth forests in western Washington

• DOI: 10.1016/j.foreco.2014.10.008
• Publication Date: 2014-11-07T04:00:26Z
• Authors: Steven A. Acker; John R. Boetsch; Mignonne Bivin; Lou Whiteaker; Carla Cole; Tom Philippi
• Keywords: Tsuga; Western Hemlock; Thuja

Abstract Tree mortality is a fundamental driver of forest ecosystems and occurs both in catastrophic events and as a chronic process. Persistent changes in the rate of chronic or background mortality can dramatically alter the structure and composition of forests stands. Tree recruitment is the complement to tree mortality, combining with mortality to determine changes in tree density and species composition. The purpose of this study is to ascertain trends of mortality and recruitment in mature and old-growth forests in western Washington state, U.S.A. We used a set of permanent plots established in units of the National Park System spanning the environmental gradient of forests in these parks (from near sea-level to 1800 m elevation). Duration of observation was five years for most plots and two or three years for a small number of plots. Principal tree species on the plots were Picea sitchensis, Tsuga heterophylla, Pseudotsuga menziesii, Thuja plicata, Abies lasiocarpa, and Abies amabilis. Tree mortality was evaluated annually; recruitment was recorded at the end of the study. For small (dbh 12.7–76.1 cm) and large (dbh >76.1 cm) trees, annual mortality pooled across all elevations, parks, plots, and years was 1% for unmanipulated, old-growth forests in the Pacific Northwest.