Impact of monsoon season rainfall spells on the ecosystem carbon exchanges of Himalayan Chir‑Pine and Banj‑Oak‑dominated forests: a comparative assessment

Abstract

The Chir-Pine (Pinus roxburghii) and Banj-Oak (Quercus leucotrichophora)-dominated ecosystems of central Himalaya provide signifcant green services. However, responses of these ecosystems, with respect to ecosystem carbon fux variability, to changing microclimate are not yet studied. Since quantifcation of ecosystem responses to fuctuation in the microclimate, particularly rainfall, is expected to be benefcial for management of these ecosystems, this study aims (i) to quantify and compare amplitude of rainfall-induced change in the carbon fuxes of Chir-Pine and Banj-Oak-dominated ecosystems using wavelet methods, and (ii) to quantify and compare dissimilarities in the ecosystem exchanges due to varying rainfall spell and amount. Eddy covariance–based continuous daily micrometeorological and fux data, during the 2016– 2017 monsoon seasons (total 244 days, 122 days of June–September), from two sites in Uttarakhand, India, are used for this purpose. We fnd that both Chir-Pine and Banj-Oak-dominated ecosystems are the sinks of carbon, and Chir-Pine-dominated ecosystem sequesters around 1.8 times higher carbon than the Banj-Oak. A systematic enhancement in the carbon assimilation of the Chir-Pine-dominated ecosystem is noted with increasing rainfall spell following a statistically signifcant power-law relationship. We have also identifed a rainfall amount threshold for Chir-Pine and Banj-Oak-dominated ecosystems (10±0.7 and 17±1.2 mm, respectively) that resulted in highest ecosystem carbon assimilation in monsoon. The general inference of this study accentuates that Banj-Oak-dominated ecosystem is more sensitive to maximum rain within a spell whereas the Chir-Pinedominated ecosystem is more responsive to increasing rainfall spell duration.