Epiphyte Succession on Quercus garryana Branches in the Willamette Valley of Western Oregon

Abstract

Static demographic samples of the epiphyte community on oak branches in the Wil- lamette Valley of western Oregon were examined to understand mechanisms of succession of the species. Branches up to 20 years old supported 28 macrolichens, five mosses, and four liverworts. One group of species colonized new growth immediately; other species, including cyanophilic lichens and pleurocarpous mosses, arrived over a longer period of time and increased in numbers and biomass with branch section age. Parmelia sulcata and Melanelia subaurifera responded positively to release from interspecific competition, Usnea spp. and Evernia prunastri were unaffected. The primary succession of epiphytes on oak branches is most influenced by the allogenic factors of microclimate change brought on by outward canopy growth. However, within the framework of allogenic factors, autogenic factors of competition and facilitation similar to those which cause secondary succession, do influence succession. Epiphyte communities present a unique oppor- tunity for the study of succession. New twigs are added to the tree canopy each year, dependably pro- viding new substrate for colonization. Most terres- trial plant succession occurs on a substrate that is opened to colonization following a disturbance that removes previous occupants from the substrate. This is autogenic succession, in which independent en- vironmental factors remain stable but microenvi- ronment and other dependent variables can be