McCune, B.; Amsberry, K. A.; Camacho, F. J.; Clery, S.; Cole, C.; Emerson, C.; Felder, G.; French, P.; Greene, D.; Harris, R.; Hutten, M.; Larson, B.; Lesko, M.; Majors, S.; Markwell, T.; Parker, G. G.; Pendergrass, K.; Peterson, E. B.; Peterson, E. T.; Platt, J.; Proctor, J.; Rambo, T.; Rosso, A.; Shaw, D.; Turner, R.; Widmer, M. 1997. Vertical profile of epiphytes in a Pacific Northwest old-growth forest. Northwest Science. 71(2): 145-152.
The vertical stratification of epiphytes is a striking feature of Northwestern forests that surely influences the distribution of other organisms in the canopy. We are just now learning how and why the stratification varies from place to place. Functional groups of epiphytes were stratified with height in an old-growth Pseudotsuga-Tsuga forest in the following order, from the ground up: bryophytes, cyanolichens, and alectorioid lichens. Other macrolichens (mainly green-algal foliose) were found throughout the vertical profile, but their relative abundance peaked in the middle to upper canopy. Cyanolichens (mainly Lobaria oregana) were concentrated in the "light transition zone." The light transition zone is the range of heights in which we found abrupt transitions in the light transmittance by the canopy. This zone extends from about 13 to 37 m in height, in an overall canopy height of 50-60 m. Bryophytes were concentrated between the ground and the middle of the light transition zone. The biomass of epiphytes macrolichens was about 1.3 metric tons/ha, composed of approximately 42% cyanolichens, 28% alectorioid lichens, and 30% other lichens.
We drew the following methodological conclusions. Using quadrats as windows from a suspended gondola overestimates the relative abundance of alectorioid lichens and underestimates cyanolichens and other lichens. Using 14, 2-m radius lichen litter plots is barely adequate to represent the epiphyte macrolichens of an old-growth stand. Ground-based canopy density measurements (photographic and densiometer) are insufficient to characterize the openness of a vertical transect, because of interference from understory vegetation.