Litterfall production and chemistry of Koompassia malaccensis and Shorea uliginosa in a tropical peat swamp forest: plant nutrient regulation and climate relationships

Key message This study shows that two emergent tree species growing in a nutrient-limited tropical peat swamp forest use different mechanisms for nutrient regulation. Abstract The main aim of this study is to understand the contribution of litterfall to nutrient supply and regulation of two emergent tree species in a tropical peat swamp forest (TPSF) in Peninsular Malaysia. The questions posed by this study include: (1) Do coexisting tree species in TPSF differ in terms of litter production, physico-chemical traits and litterfall patterns? (2) How do these relate to possible nutrient regulation mechanisms of the tree species and do the strategies involved differ between a nitrogen (N) fixing legume (Koompassia malaccensis, Family Fabaceae) and a dipterocarp (Shorea uliginosa, Family Dipterocarpaceae)? (3) Is litterfall timing of the selected tree species driven by climatic variables? Litterfall was collected from litter traps placed under the selected trees in the Sungai Karang TPSF. Green leaves of the selected tree species were also collected. Both leaf litter and green leaves were assessed for their physico-chemical properties (toughness, total phenols, total tannins, proximate fibre-cellulose-lignin and a range of nutrients) and compared. Results obtained indicate that K. malaccensis relies on a combination of high litter quality (higher N coupled with lower amount of tannins, fibre and cellulose) and low annual litterfall mass (388.17 g m(-2)) for nutrient regulation while the opposite strategy is used by S. uliginosa, which was found to produce an annual litterfall mass of 918.14 g m(-2). Due to the aseasonal environment, no significant relationships were observed between climatic variables and litterfall. Therefore, litterfall characteristics in aseasonal tropical regions may depend more on species-specific physico-chemical properties than on climatic variables.