Leaf and root production, decomposition and carbon and nitrogen fluxes during stand development in tropical moist forests, north-east India

In the present study we investigated the production and decomposition of leaves, branches and roots in two moist regenerating tropical forests (5 and 15 years old; RF-5 and RF-15 respectively) and a natural forest (NF) in north-east India. Total litter input increased during vegetation succession (759, 1089 and 1284 g m–2 year–1 in RF-5, RF-15 and NF respectively), whereas the contribution of soft litter decreased sharply. Decomposition over 450 days indicated significant seasonal (P < 0.001) patterns in mass loss of litter components, with greater rates during the wet period. Soil CO2 efflux was strongly seasonal. C stock loss followed patterns similar to those of mass loss, whereas N increased initially, followed by its gradual release. Rainfall explained 74–90% of the variability in mass loss rates. Concentrations of cellulose and N were significantly positively correlated with mass loss at an early stage of decomposition (r = 0.54–0.65, P < 0.05), whereas lignin : N and C : N ratios were negatively correlated with mass loss at later stages. Regenerating forests adapted ecosystem-level strategies that induced early leaf fall to reduce soil water loss, increase organic matter return to the soil and conserve N through immobilisation during the process of decomposition to speed up vegetation succession in the regenerating forest.