BIOMASS AND NUTRIENT DYNAMICS OF EPIPHYTIC LITTERFALL IN A NEOTROPICAL MONTANE FOREST, COSTA-RICA

To investigate the importance of the epiphyte community to ecosystem n utrient cycling, we assessed the standing crop, input rates, and turno ver rates of litterfall derived from epiphytic material and compared t hem to litterfall derived from terrestrially rooted material in a neot ropical cloud forest in Monteverde, Costa Rica. The standing crop of f allen epiphytic material in 1988 was 0.5 t ha-1 and 0.3 t ha-1 in 1990 . Annual input of fallen epiphytic material was 0.5 t ha-1, more than two times as much as has been reported for other tropical cloud forest s. This is equivalent to 5-10 percent of total fine litter at the site (7.5 t ha-1). Nutrient input from epiphytic material was (kg ha-1 yr- 1): N, 7.5 (7% of nutrient transfer via total fine litter); P, 0.5 (8% ); Ca, 4.2 (4%); Mg, 0.8 (5%); and K, 0.1 (1%). Assuming a steady stat e condition in this old-growth forest, epiphyte-derived litter biomass had a higher annual decay rate (K(a) = 1.3) than did litter derived f rom terrestrially rooted plants (0.7). However, turnover time (1/K(a)) of all nutrients except K in fallen epiphytic material was four to si x times slower than for nutrients in terrestrially rooted material; K was tenfold faster. Over half of the fallen epiphytic material was col lected in less than 2 percent of the collections, indicating the depos ition of epiphytic material is highly sporadic in space and time and m ust be measured at the appropriate spatial scale.