Coarse woody debris (CWD) is an important structural and functional component of forest ecosystems and provides unique habitat for many plant and animal species. Although the importance of CWD on understorey species diversity has been recognized, the effects of CWD substrate species and decay class on understory vegetation communities as a whole have received little attention. We examined the effects of CWD decay class and substrate species on understory vegetation communities in the central boreal forest of Canada. To cover a wide range of CWD decay classes and substrate species, we sampled fire-origin boreal forest stands that varied in terms of canopy composition and stand age. Vegetation on CWD was sampled by visually estimating the percent cover of each species within a 0.10 x 0.50 m quadrat, laid lengthwise on each sampled CWD log.
Results/Conclusions
We found that percent cover, diversity, and composition of understory vegetation differed significantly with both CWD decay class and substrate species. Percent cover increased along the decompositional gradient in all CWD substrate species, and was highest on the most advanced decay classes of Populus spp. Species richness increased continuously with decay class on broadleaf CWD, but the increase reached a maximum at decay class 4 on conifer CWD; at a given decay class species richness was higher on the CWD of conifers species than broadleaf species. Multivariate analysis indicated that understory species composition differed among decay classes and substrate species. Indicator species analysis showed distinct understorey species affiliations to substrate species at advanced decay classes. Understorey species composition on the CWD of Pinus banksiana showed particularly pronounced changes a dominance of lichens on decay classes 2 and 3, followed by mosses and vascular species on decay classes 4 and 5. These results emphasize the need for forest management to conserve diverse CWD decay classes and substrate species in order to maintain understory plant diversity and function in the boreal forest.