Lobaria oregana is a nitrogen-fixing cyanolichen that is spectacularly abundant in old-growth forests of the Pacific Northwest. This species provides a major source of nitrogen for older forests, but the ecological factors that determine its distribution are not well understood. In this study, we used the Wind River Canopy Crane Research Facility (http://depts.washington.edu/wrccrf/) to study the physiological activities and growth of transplanted pendants of L. oregana at 3 positions in the canopy: Top (62 m above the ground), Middle (39 m), and Bottom (2 m). There was a complex pattern of seasonal and spatial variation, but in general nitrogen fixation was greatest at the Middle position and photosynthesis at the Top position. Greatest growth was found at the Middle position where there was a 16.4 % increase in dry weight over the 10-month study period. Lichens at the Bottom position died after transplanting. Activities were strongly correlated with hydration except that very high hydration (>200%) inhibited photosynthesis. Laboratory experiments showed that photosynthesis increased at PPFD's of up to 1000 mmol m-2 sec-1. This study represents the first attempt to describe how the physiological activities of L. oregana respond both spatially and temporally to the extremely variable environment within the canopy.

Key words: Lobaria oregana, nitrogen fixation, old-growth forest canopy, photosynthesis