Ectomycorrhizae fungi (EM) play an important role in nutrient cycling and tree protection from drought and disease. Douglas-fir (Pseudotsuga menziesii), for example, a dominant tree species in coastal British Columbia (BC) is known to form such symbioses with nearly 2000 different fungi. Variable retention (VR) is a new forest practice that is replacing clearcutting in coastal BC. Previously we found clear evidence of edge effects, observing significantly lower abundance and diversity of EM fungi with increased distance from the retained forest patches. In this study, we extend our research to survey different EM fungal species, along transects from retained portions of mature forest into adjacent replanted forests of increasing ages (5, 27, 57 yrs), in order to assess their recolonization rate. We also examined how different levels of individual green tree retention affect recolonization, by studying a VR experimental site containing 4 treatments: uncut, 0% (clearcut), 5%, 10%, and 30% green tree retention. We hypothesized that edge effects would decline as the replanted forest grows and that EM diversity and abundance will increase with the increased number of retained live trees in harvested areas.
Results/Conclusions
In the VR experiment the steepness of the edge effect curve for EM richness declined with increasing retention, however the steepness of the curve for % EM colonization was not as well related to retention level though this depended upon the suite of EM species examined and if preexisting microsite differences were accounted for. Edge effects on % colonization and richness did decline with age of regrowth and were not significantly different in the 57 year stand, though some differences in community structure did occur. Implications of finding for forestry and maintenance of EM diversity suggest that retention of forest structure can enhance, at least in the short term, maintenance of EM fungal diversity and that it will recover in the regenerating forest given sufficient time. However additional monitoring will be needed to determine if all EM species are maintained in retention patches over a longer term and in a landscape, particularly on private lands, with declining rotation lengths. Future monitoring should focus on specific EM fungal species associated with older and closed forests (eg. Russula xerampalina), developing rapid techniques, such as DNA probes, to allow for survey of a greater number of samples and sites, and developing and validating habitat response curves for those species.