FINE LITTER DYNAMICS WITHIN THE TREE CANOPY OF A TROPICAL CLOUD FOREST

Fine litter deposition and decomposition within the upper tree canopy was measured in a neotropical cloud forest to determine the potential nutrient input to epiphyte communities from intercepted tree litterfall. A comparable amount of fine litter passed through the canopy (752 g.m-2.yr-1) as arrived on the forest floor (820 g.m-2.yr-1), but < 1% of the biomass and nutrients of this ''gross litterfall'' was retained within the upper tree canopy. The standing crop of litter in the canopy (almost-equal-to 170 g/m2 of branch surface area, 8.8 g/m2 of ground area) is equivalent to only 1% of the standing crop of litter on the forest floor. Measurements of leaf litter attrition (whole leaf loss from branches due to wind and other disturbances) with marked leaves documented that 70% of leaves deposited on branches are lost in the first 2 wk and nearly all are gone in 16 wk. Certain branch characteristics (branch angle, number of epiphyte stems and clumps) appear to affect the amount of litter retained at particular microsites. Decomposition of tethered, dead leaves within the canopy over a 12-mo period was half that of leaves on the forest floor (canopy litter turnover time = 2.8 yr). Assuming that litter accumulation within the canopy is at steady state, the biomass of fine litter retained and decomposed within the canopy was calculated as only 2.0 g.m-2.yr-1 and < 0.02 g.m-2.yr-1 for all nutrients. Nutrient replenishment of epiphyte communities appears to be decoupled from the litter-fall pathway, as input from litterfall retained within the canopy is small relative to epiphyte productivity and nutrient requirements reported in other studies.