GROWTH AND VITALITY OF EPIPHYTIC LICHENS .1. RESPONSES TO MICROCLIMATE ALONG A FOREST EDGE-INTERIOR GRADIENT

We tested the hypothesis that changed microclimate at induced forest e dges causes reduced growth of epiphytic lichens. Two foliose, green al gal lichens were transplanted to the lower canopy of a mature Picea ab ies forest at six distances (2, 6.25, 12.5, 25, 50 and 100 m) from a c learcut. The biomass growth in Platismatia glauca (6.2% in 16 months) was 41% higher than in Lobaria pulmonaria (4.4%). We found no growth r eduction near the forest edge. In contrast, the highest growth in both species occurred within 12 m from the edge. Further, fluorescence and chlorophyll measurements showed that lichen vitality was unaffected b y distance from edge. The light intensity was 4.3 times higher at the edge than in the interior during the growing season, but there were on ly minor differences in air temperature and relative humidity. Monitor ing of thallus water content revealed clear differences in both number and length of wetting and drying cycles. However, the total time with water content sufficient for photosynthetic activity was only slightl y higher at the edge. The data thus indicate that our gradient in micr oclimate was too small to significantly affect lichen growth, and that lichens are largely metabolically inactive when large edge-interior c ontrasts in microclimate occur. Lichen response to forest edge microcl imate results from intricate interactions among several biotic and abi otic factors. Linking data on lichen growth, microclimate and thallus water content with physiological measurements provides a framework for future studies of the mechanisms behind abiotic edge effects.