Survey methods
We conducted this study over the course of three summers (2016 – 2018). We counted Tsuga heterophylla and Picea sitchensisseedlings in 166 randomly placed 1 m x 1 m plots on the forest floor (n = 52) and 1 m x nurse log diameter on nurse logs (defined as >30 cm diameter and at least 2 m in length; nurse log diameter ranged from 30 to 104 cm; n = 114). For a subset of the nurse log plots (n = 86) and forest floor plots (n = 12), bryophyte composition was surveyed using the point-intercept method. Percent canopy cover was measured as a potential confounding factor using a densiometer placed in the center of each plot. Bryophyte depth was measured (cm) using a caliper in the center of each plot. Because Harmon & Franklin (1989) found that seedlings that receive less than 0.6% of light (< 12.5 µmol/m2/sec) would not be able to survive, and seedling survival was reduced with high moss biomass (an indicator of moss depth), we also measured light irradiance with a photometer in 50 pairs under and beside thick bryophyte mats focusing on the predominant moss in the forest, Hylocomium splendens . Decay class of each nurse log for each plot was measured using the kick test, which included three levels of decay classes: 1 = bark still intact upon contact, 2 = some to various debris falls upon contact, 3 = foot completely in log, several pieces fragmented off of the log (modified from Christy & Mack, 1984; Sollins, Cline, Verhoeven, Sachs, & Spycher, 1987, and Fogel, Ogawa, and Trappe, unpublished report ). These classes correlate with the age of the nurse log so we used them as an indicator of nurse log age (Harmon, 1989b).