Multi-year eddy covariance measurements of net ecosystem exchange in tropical dry deciduous forest of India

Abstract

Tropical deciduous forests are unique in terms of their geographical distribution, strong seasonality and their contribution to global carbon dynamics, but yet their carbon sequestration potential is poorly sampled. In the current study, we report the carbon balance of 65-year-old tropical dry deciduous forest in central India using the multi-year eddy covariance measurements from November 2011 to May 2019. Over the study period, the forest site was observed to be a net sink of atmospheric CO2 with a mean annual net ecosystem productivity (NEP) of 524 (± 40; ±1 SD across different years) g C m−2 yr−1 with a 233 (±15) day growing season. The NEP was partitioned into gross primary productivity (GPP) of 3358 (± 167) g C m−2 yr−1 and annual carbon loss due to respiration and decomposition (Reco) of 2834 (± 157) g C m−2 yr−1. The ecosystem showed a strong seasonality as a source of carbon during the leaf-off season (March to June), and as a carbon sink during the rest of the year with significant sequestration during the winter season (October to December). The intra-annual analysis suggested that CO2 flux is primarily controlled by canopy greenness with mean Reco/GPP ratio varying from 1.90 (± 0.12) to 0.79 (± 0.04) during leaf-off to leaf-on seasons. The monthly C fluxes in the growing season are found to be strongly correlated to the environmental variables rather than in the leaf-off season, while variability in monthly ecosystem respiration was better explained by air temperature during the leaf-off season than the growing season. Further, the inter-annual variability of NEP was mainly dependent on growing season length and mean annual temperature. The variations in annual GPP and Reco were directly dependent on the increase in mean annual temperature. The eddy covariance-based NEP was complemented by close independent biometric estimates, imparting confidence in our measurements. In conclusion, this tropical dry deciduous forest site is a substantial carbon sink and would add crucial information regarding carbon budgeting of tropical forests in global carbon balance models.