Patterns of bryophyte diversity in humid coastal and inland cedar–hemlock forests of British Columbia

Abstract

Mosses and hepatics (bryophytes) are the most diverse and abundant understorey vegetation within the Coastal Western Hemlock (CWH) and Interior Cedar–Hemlock (ICH) zones of British Columbia. This study intensively sampled bryophytes in 287 young- and old-growth stands in the CWH and ICH zones. Two major variables strongly influence the patterning of bryophyte diversity in these zones: stand age and habitat heterogeneity. Canonical correspondence analyses (CCA) identified these as the most important variables explaining stand–environment interactions. Alpha diversity is much greater in old-growth forests and beta diversity is high between young and old forests. Old-growth cedar–hemlock forests have between 60 (ICH) and 100% (CWH) more species than younger forests disturbed by wildfire in the ICH zones or logging in the CWH zones. Furthermore, a stand classification built on species composition partitioned species into stands of different ages and mesohabitat heterogeneity. Beta diversity was also partitioned between stands of different ages and habitat heterogeneity. This indicates that both young and old forests have a unique assemblage of species. Indicator analysis was used to choose a partial lists of species that are indicators of "old growthness". These old forests support a rich flora of hepatics and rare western North American endemics. High environmental continuity is associated with the most humid watersheds and cedar–hemlock forests within these watersheds have the highest bryophyte diversity. The establishment of rich communities of bryophytes in the moist cedar–hemlock forest has been occurring over the last 2000–7000 years, with the coastal rainforest much older than the inland rainforest. Large-scale disturbance, such as forestry, threatens the existence of these highly diverse communities. A better understanding of the patterning of bryophyte diversity will provide an opportunity to minimize the impact of forest operations on biodiversity. Bryophyte diversity in British Columbia cedar–hemlock forests will be sustained through ecosystem management of old-growth legacies (i.e., landscapes, stands, and their components) and preservation of areas of high diversity. Temporal and habitat variables are influential in the patterning of bryophyte diversity. Management plans that consider these variables will be better equipped to manage cedar–hemlock forests for maintaining biodiversity. Key words: biodiversity, bryophytes, cedar–hemlock, CWH, disturbance, ecosystem management, floristic habitat sampling, forest conservation, ICH, old growth, patterning of diversity, rare species, species richness.