Studies of Mineral Cycling in a Montane Rain Forest in New Guinea: II. The Production and Disappearance of Litter

Abstract

(1) Litter production and the quantity of litter remaining on the ground were monitored for a 12-month period in undisturbed Lower Montane Rain forest at an altitude of c. 2400-2500 m in the Eastern Highlands of New Guinea. Four sites, each 20 x 10 m, were studied in contrasting situations; one site (on a ridge) was a natural gap caused by the fall of a large tree, and the other three sites (on a broad ridge, on a steep slope and in a valley bottom) were of well-developed, mature or late-building phase trees. (2) At each site litter fall was measured in sixteen traps 1 x 1 m. The average litter production for the four sites was 755 ? 27 (s.e.m.) g m-2 yr1 (non-woody material 635 ? 20 g m-2 yr1), and no significant differences were found between the sites. (3) It is estimated that about 1000 of the leaf dry weight is grazed by phytophagous insects, and a further 100% is withdrawn by the trees before the leaves are shed. Density measurements made on healthy twigs, and on twigs in the litter fall, suggest that considerable decomposition occurs before the twigs fall as litter. (4) Estimates of the annual rate parameter for litter disappearance, based on the relationship between the standing crop of litter on the ground and the annual litter production, range between 1-04 for the Ridge Site and 1-55 for the Valley Site. (5) The decomposition of leaf litter of six tree species (Dacrycarpus cinctus, Elaeocarpus ptilanthus, Litsea sp. 65, Macaranga albescens, Planchonella firma and Schizomeria sp. 203) and a widespread bamboo (Nastus productus) was studied over 325 days at the Ridge and Valley Sites by enclosing the litter in plastic mesh. There were no significant differences between the two sites. (6) Only 1500 of the original dry weight of leaves of Elaeocarpusptilanthus remained after 325 days. Leaves of other tree species disappeared more slowly (57-74% of the dry weight remained). Of the bamboo leaves 56%/ remained. (7) The average rate of disappearance for the seven species, equivalent to 47-48% in the first year, is much less than the rate calculated from the standing crop of litter and the annual litter production (100148%0 for non-woody litter); this and other evidence suggests that the time-course of disappearance is linear rather than exponential.