Carbon continuum across Eastern Himalayan forests: Elevational shifts in productivity, storage and turnover

Abstract

Nature-based solutions (NbS) that enhance carbon (C) sequestration while maintaining ecosystem resilience are central to climate-change mitigation and sustainable land management. Forests of the Eastern Himalaya, spanning steep elevational gradients, offer a unique opportunity to examine how productivity, carbon storage, and turnover together sustain these outcomes. This study quantified biomass, net primary productivity (NPP), vegetation and soil organic carbon (SOC) pools across tropical (TRF), subtropical (STRF), and temperate (TMF) forests in Mizoram, Northeast India, using intensive field-based measurements of trees, shrubs, herbs, litter, fine roots, and soils. Carbon dynamics varied significantly with elevation. The STRF exhibited the highest total biomass (286.70 Mg ha⁻¹), vegetation C (134.75 Mg C ha⁻¹), SOC pools (104.3 Mg C ha⁻¹), and C sequestration rate (10.81 Mg C ha⁻¹ yr⁻¹), reflecting an optimal balance between productivity and carbon residence time. In contrast, TRF showed rapid C turnover with lower standing stocks (107.00 Mg C ha⁻¹) but high fluxes, while TMF functioned as a long-term C reservoir with moderate biomass (254.10 Mg ha⁻¹) and slow decomposition kinetics. Distinct litter and fine-root dynamics revealed complementary C cycling strategies along the elevational gradient. Collectively, these forests constitute a functional C continuum in which tropical systems act as high-exchange zones, subtropical forests as efficient C sinks, and temperate forests as stable long-term C stores. Conserving this elevational mosaic represents a robust nature-based sustainability solution that simultaneously supports climate mitigation, ecosystem resilience, and regional C balance in the Eastern Himalayan forests.