Monitoring of Carbon Dioxide and Water Vapour Exchange over a Young Mixed forest Plantation Using Eddy Covariance Technique

Studies on CO₂ and water vapour exchange in natural and man-made vegetation are necessary for quantifying their role in landscape-level carbon budget. The present study investigated variations in carbon and water vapour fluxes and monthly net ecosystem exchange (NEE) over a 9-year-old mixed forest plantation (Holoptelea integrifolia, Dalbergia sissoo, Acacia catechu and Albizia procera) in Terai Central Forest Division of Nainital district, Uttarakhand using January to September 2013 eddy covariance data. During leafless period (i.e. January), the plantation acted as a net carbon source (i.e. positive NEE) with daily mean release of 0.35 g C m^-2 day^-1, while from leaf onset to growing period (i.e. April to September), it acted as a sink (i.e. negative NEE) due to carbon uptake by an increasing number of leaves. The monthly mean daily NEE was noticed to be increasingly more negative in each subsequent month until September. The diurnal trend in NEE closely followed the variations in the intensity of photosynthetically active radiation. The diurnal NEE in all months was related to vapour pressure deficit with time-lag. Maximum daytime uptake (-29.5 μmol m^-2 day^-1) and night-time release of CO2 (8.2 μmol m^-2 day^-1) was observed in July. Monthly mean of daily NEE over plantation continuously increased from February and was highest (-5.74 g C m^-2 day^-1) in September. Rectangular hyperbolic function provided reasonably good fit between NEE and PAR. Ecosystem parameters (μ and P_max) of the light response curve also followed the canopy development trend.