Energy flow in arboreal epiphytic communities : An empirical model of net primary productivity in the alga Pleurococcus on larch trees.

Energy enters the arboreal epiphytic ecosystem by a number of different pathways. Primary producers such as algae and lichens, together with fungal and bark materials derived in the main from the tree substrate, form the major food components for populations of epiphytic grazing herbivores, notably psocids and collembolans.This paper describes a series of experiments to determine empirically the combined influence of three climatic variables, temperature, light and relative humidity, on the uptake of 14CO2 by the main epiphytic alga, Pleurococcus. A model is produced which indicates that relative humidity is the most important of the variables, followed by light. Temperature appears to be relatively unimportant.The model is discussed with respect to its realism, its predictive powers and its relationship to published data on forest productivity and grazing pressure by psocids.