Net Ecosystem Exchange of CO₂ in Deciduous Pine Forest of Lower Western Himalaya, India

Abstract

Carbon cycle studies over the climate-sensitive Himalayan regions are relatively understudied and to address this gap, systematic measurements on carbon balance components were performed over a deciduous pine forest with an understory layer. We determined annual net carbon balance, seasonality in components of carbon balance, and their environmental controls. Results indicated a strong seasonality in the behavior of carbon exchange components. Net primary productivity (NPP) of pine forest exceeded soil respiration during the growing phase. Consequently, net ecosystem exchange exhibited a net carbon uptake. In the initial phase of the growing season, daily mean uptake was −3.93 (±0.50) g C m−2 day−1, which maximizes (−8.47 ± 2.3) later during post-monsoon. However, a brief phase of carbon release was observed during peak monsoon (August) owing to an overcast condition. Nevertheless, annually the forest remained as a carbon sink. The understory is extensively distributed and it turned out to be a key component of carbon balance because of sustained NPP during the pine leafless period. Temperature and evaporative fraction exhibited a prime control over the seasonal carbon dynamics. Our observations could lend certain useful insights into the application of coupled climate-carbon cycle models for the Himalaya and ecological functions in the region.

Keywords

• net primary productivity
• soil respiration
• carbon use efficiency
• <i>Pinus roxburghii</i>
• understory
• subtropical Himalaya