THE INFLUENCE OF EPIPHYTIC LICHENS ON THE NUTRIENT CYCLING OF AN OAK WOODLAND

We examined the importance of the epiphytic lichen, Ramalina menziesii , in a blue oak (Quercus douglasii) woodland of California, using a fa ctorial experiment in which lichens were removed from tree canopies an d the soil surface for a 3-yr period. Each blue oak contained an avera ge of 3.8 kg of lichen biomass, totaling 590 kg/ha for the entire wood land; oak leaf biomass was 958 kg/ha. Removal of lichens affected the interception of rainfall by the forest canopy and the deposition of wa ter and nutrients in throughfall collected beneath the canopy. Trees w ith lichens had higher deposition of total N, organic N, Ca, Mg, Na, a nd Cl, and a lower deposition of SO4 under their canopy; deposition of NO3, NH4, K, and total P was not affected. Accounting for the uptake of nutrients by lichens, we calculate that canopy lichens enhance the receipt of N and P from the atmosphere by 2.85 and 0.15 kg . ha(-1). y r(-1), respectively. The bulk deposition (wetfall + sedimentation) of N and P for the same period was 0.88 and 0.06 kg . ha(-1). yr(-1), res pectively. Because retranslocation of N occurred prior to leaf absciss ion, the percentage of N in leaf litter was approximately half that in lichen litter. Lichen litter significantly slowed the decomposition o f oak leaves on the forest floor, Oak leaf and lichen litter decomposi tion was slow, with low N release; whereas P release was much more rap id. The removal of lichens had no effect on leaf biomass or nutrient c ontent, acorn productivity, or tree-ring increment of the oak trees, p robably because soil pools of N and P were large relative to the magni tude of the flux changes caused by the manipulations. In fact, no diff erences in soil mineralization rates among the treatments were detecta ble. Overall, the manipulations significantly affected annual intersys tem capture of nutrients, but the magnitude of these changes was insuf ficient to affect intrasystem fluxes or forest productivity.