Understory plant establishment on old-growth stumps and the forest floor in western Washington

Coarse woody debris (CWD) provides an important regeneration niche for many tree species, but its role in understory plant establishment has not been well studied. To examine the role of CWD in understory plant establishment, we compared woody vegetation and ferns occurring on 50 paired stump and ground plots (substrates) in a coniferous and a deciduous forest (sites) in Olympia, WA. Plant species richness, evenness, and diversity were similar across substrates and sites. However, Bray-Curtis ordinations revealed clear separation between stump and ground vegetation at each site. Vaccinium parvifolium and Gaultheria shallon dominated stump vegetation, while Rubus ursinus and Polystichum munitum were major components of ground vegetation. V. parvifolium and G. shallon co-occurred on both substrates at the coniferous site, but not at the deciduous site where Rubus spectabilis dominated ground vegetation, probably because of higher light intensity. In areas where R. spectabilis is dominant, elevated CWD microsites may increase local species richness by providing refugia for species unable to persist under the R. spectabilis canopy. (C) 2001 Elsevier Science B.V. All rights reserved.