Maintaining features from mature forest following final harvest can provide habitat refugia for forest species and facilitate colonization of regenerating stands. However, more research is needed to understand how spatial configuration of retention patches supports populations and communities of mature forest organisms, but also how habitat structure within retained patches changes during stand regeneration and growth. We examined plant structure and community dynamics among 5 retention treatments that varied by amount and spatial distribution of mature forest structures across 10 blocks in southwest WA and western OR, USA. We examined canopy cover, shrub cover, and herbaceous species cover, richness, and community composition using sample grids established in each retention patch and paired with a grid in the adjacent harvest area. Grids were sampled within one to two years after harvest, and again three years later.
Results/Conclusions
Structural characteristics of retention patches differed between the first and second sampling periods. Canopy cover increased over time or was stable in patches across all treatments. Shrub cover decreased in clumped retention patches, but maintained similar cover over time in treatments with split or dispersed retention. Herbaceous total cover remained relatively stable in treatments with clumped retention, but increased in split or dispersed retention; proportional herb cover (by growth form, origin, and seral stage) had varied results by treatment over time. In general, treatments with clumped retention (i.e., larger single patches) continued to provide refugia for mature forest understory vegetation, and smaller dispersed patches were less effective at maintaining mature forest habitat, but all retention patches showed some change with time. Even over a short time period, we detect considerable change in these retained patches, likely due to the harvest of surrounding forest and resulting edge effects in these remaining forest patches. Considering both longer-term spatial and temporal dynamics is essential to understanding the effectiveness of retention patches in managed forest ecosystems.