Estimating gross primary productivity of a tropical forest ecosystem over north-east India using LAI and meteorological variables

Abstract

Tropical forests act as a major sink of atmospheric carbon dioxide, and store large amounts of carbon in biomass. India is a tropical country with regions of dense vegetation and high biodiversity. However due to the paucity of observations, the carbon sequestration potential of these forests could not be assessed in detail so far. To address this gap, several flux towers were erected over different ecosystems in India by Indian Institute of Tropical Meteorology as part of the MetFlux India project funded by MoES (Ministry of Earth Sciences, Government of India). A 50 m tall tower was set up over a semi-evergreen moist deciduous forest named Kaziranga National Park in northeastern part of India which houses a significant stretch of local forest cover. Climatically this region is identified to be humid subtropical. Here we report first generation of the in situ meteorological observations and leaf area index (LAI) measurements from this site. LAI obtained from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) is compared with the in situ measured LAI. We use these in situ measurements to calculate the total gross photosynthesis (or gross primary productivity, GPP) of the forest using a calibrated model. LAI and GPP show prominent seasonal variation. LAI ranges between 0.75 in winter to 3.25 in summer. Annual GPP is estimated to be 2.11 kg C m −2 year −1 .

The effect of Indian summer monsoon on the seasonal variation of carbon sequestration by a forest ecosystem over North-East India

“…This is in line with the studies reporting the cloudy conditions to have negative impacts on the GPP globally [2,47]. At KNP, such a decrease in GPP dd results in a diminishing trend in the LAI [20]. As the plant growth is restricted, the growth respiration of plants also goes down reflecting in a decreasing trend in TER dd (Fig.…”

“…This photosynthetic uptake of carbon by the ecosystem results in a sharp increase of GPP dd in this season (Fig. 4), also supported by the increasing LAI in this season [20]. However, such high growth of plants also results in the increased plant growth respiration.…”

“…4). Further this inhibition of plant growth is also supported by a decreasing LAI during this period [20]. The NEE continues to be negative from pre-monsoon, but its strength gradually reduces, i.e.…”

“…4. This hindrance of photosynthetic uptake is also reflected in the low LAI values in this season [20]. This situation changes in the pre-monsoon when the T a [19] precip mm ( Fig.…”

“…Hence, it would be important to study the effect of ISM on an Indian ecosystem in this context. Several flux towers have been erected over multiple ecosystems in India for continuous monitoring of the ecosystem-atmosphere fluxes under the aegis of the MetFlux India project initiated by the Ministry of Earth Sciences (MoES), Government of India, and implemented by the Indian Institute of Tropical Meteorology (IITM) [14,20,34]. We take this opportunity in the present study to use the observations from one of the forest sites of this project to address the issues mentioned above.…”