Evaluating Tree Ring Proxies For Ecosystem Productivity In India Through Observations And Model Products

Abstract

Terrestrial ecosystems are one of the major sinks of atmospheric CO2 and play a key role in climate change mitigation. They also modulate the local climate by exchanging scalar, energy and momentum with the atmosphere. On the other hand, the ecosystem-atmosphere interactions are also modulated by climate variability. For example, depending on the environmental parameters, plant carbon synthesis and the allocation of assimilated carbon into its different biomass pools, such as roots, trunks, leaves, etc. Several studies have focused on understanding the carbon sequestration processes in terrestrial ecosystems and their response to climate change. Most of these studies have used the Eddy Covariance (EC) technique to measure the ecosystem-atmosphere carbon, water and energy fluxes. However, very few of them address the linkage of tree-ring growth with the ecosystem-atmosphere carbon exchange. EC has been a fairly advanced technique, and these studies span the last few decades at the most. Particularly for India, the EC flux records do not extend beyond the last decade. However, the tree-ring records typically extend up to a few centuries and may capture long-term climate variability's effects on carbon sequestration in forest ecosystems. We study the Coupled Climate Carbon Cycle Model Intercomparison Project (C4MIP) model outputs (a project under CMIP6) for its 165-year-long simulated records of mainly mean monthly gross primary productivity (GPP) and net primary productivity (NPP) and compare them with the tree-ring growth indices over the northwestern Himalayan region. Through their correlations with other climate variables and their statistical correlation measures, we establish confidence in tree-ring growth indices as proxies for reconstructing aboveground woody biomass and estimating ecosystem productivity.