Vertical variation in mass and CO2 efflux of litter from the ground to the 40m high canopy in a Bornean tropical rainforest

Abstract

Litter usually drops to the ground, but some is retained within the canopy. Mass and CO2 efflux from retained litter may play a significant role in carbon cycling in tropical rainforests where emergent trees with complicated canopy structures are observed. This study aimed to show vertical variation in the mass and CO2 efflux (Rlitter) of the retained litter and examined its contribution to carbon cycling in a Bornean tropical rainforest. The retained litter was collected from six 40 m tall columns with a radius of 1.6 m using an 85 m tall crane at six subplots. Dry mass and Rlitter were measured in the laboratory. The mass of the retained litter from the sampling points ranged from 0.35 g to 187.0 g, and Rlitter of the retained litter (42.4 ± 43.4 mg CO2 kg−1h−1) was significantly lower than that of the soil surface litter (85.9 ± 39.2 mg CO2 kg−1h−1) because of the lower water content in the retained litter. The mean mass of the retained litter measured from the ground to the canopy was 40.6 ± 22.2 g m−2. The greatest mass was observed at a height of 0–2 m. The ratio of the retained litter mass to the soil surface litter mass ranged from 1.0 to 11.5% with a mean of 5.2%, suggesting that litter retained within the canopy can contribute to carbon storage in this forest. On the other hand, Rlitter did not differ with height, and the ratio of Rlitter to aboveground autotrophic respiration was less than 1%. This study is the first to show that the litter retained within the canopy can sporadically be a moderate hot spot for C storage, but it is not a significant source of released CO2.