Large variations in composition and spatial distribution of epiphyte biomass on large trees in a tropical montane forest of northern Thailand

Abstract

Large amounts of epiphytic matter (EM), which comprises living epiphytes and canopy humus, play important roles in tropical montane forests. However, little is known about the composition and spatial distribution of EM in tropical Asia because the tall and complex tree structures have hampered direct and precise measurements of EM. Using the three-dimensional mapping method, we examined the composition and distribution of EM on three large trees and estimated the EM mass in a tropical montane forest in northern Thailand. EM mass per unit cover area (mean dry weight ± SE) varied widely among their physiognomies from 80.0 ± 12.7 g m−2 in sparse bryophytes, to 5882 ± 1451 g m−2 in orchid mats composed mainly of vascular epiphytes and canopy humus. With the increase of tree size, the EM mass on individual trees increased from 73.4 to 480.9 kg, and the proportions of vascular epiphytes and canopy humus to the total EM mass increased, whereas that of bryophytes decreased. The proportions of bryophytes and canopy humus varied among positions within the tree crown, and the distribution pattern of EM within the tree crown was different between the trees. Although the number of sample trees was small, our study provides an evidence that large trees contribute to the accumulation of a large mass of EM attributed to developments of vascular epiphytes and canopy humus.