Graduate Thesis Or Dissertation

Shrub epiphyte communities in relation to stand management in forests of western Oregon

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  • This dissertation describes the epiphyte communities on tall shrubs in forests of western Oregon, with a focus on potential effects of management practices on these communities. Shrubs and other hardwoods have recently gained recognition as hotspots of diversity for epiphytes in young conifer forests of the region. Yet little is known about how shrub epiphytes differ among stand types or in response to management. The first study presented here compares shrub epiphyte communities among unthinned young stands, thinned young stands and old growth in 17 areas within the Coast Range and Cascades. In young stands where shrub epiphytes are sparse, overstory thinning may have enhanced richness of lichens on shrubs and increased similarity of the communities with those in old stands. However, when thinning was associated with a decrease in the density of older shrub stems, bryophyte cover also decreased relative to unthinned stands. To gain perspective on shrub epiphyte diversity at the landscape level, I compared communities in our initial study sites with those in nearby putative "hotspots" of macrolichen diversity, located using stand structural features and topography (e.g. riparian areas and rocky outcrops). Hotspots had greater mean richness of both lichens and bryophytes on shrubs than other stand types, and a high number of uncommon species. Differences detected in bryophyte cover among stand types led me to develop and test transplant methods for comparing accumulation rates of mat-forming bryophytes among stands of different ages. Both Antitrichia curtipendula and Isothecium myosuroides grew as well, on average, in a young stand as in an old-growth stand, though they apparently died in a clear cut. This suggests that the distribution of these species may be limited more by dispersal or establishment than by an inherent inability to grow in young stands. I conclude that protecting a portion of the shrub stems during thinning and harvest operations should provide refugia and help minimize negative impacts of management on bryophytes and lichens associated with older shrub stems, as well as the overall epiphyte community. Local and regional diversity of shrub epiphytes may also benefit from identification and protection of landscape-level hotspots.
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