Retention of needles and seeds on logs in Picea sitchensis – Tsuga heterophylla forests of coastal Oregon and Washington

Abstract

Logs are a major seedbed in Picea sitchensis – Tsuga heterophylla forests; therefore, the interception and retention of seeds on these surfaces is a potential limitation on tree recruitment. The ability of log surfaces within Picea – Tsuga forests to retain needles and seeds was studied at Cascade Head Experimental Forest, Oregon. Moss- and litter-covered surfaces retained many (48–98%) of the seeds and needles placed on them, but rotten wood, sound wood, and bark of Tsuga heterophylla, Picea sitchensis, and Pseudotsuga menziesii retained few (0–8%). Examination of logs mapped in five Picea sitchensis – Tsuga heterophylla stands in Oregon and Washington indicated a mean projected log cover of 9.9%. Thin (<5 cm) and thick (>5 cm) moss mats were the most abundant log surfaces and covered 59 and 25% of the logs, respectively. Analysis of data on seedbed coverage, retentive characteristics, and seedbed-specific seedling survival indicated approximately 1% of a seed cohort would survive the 1st year on log surfaces.