Variations and drivers of biomass and soil carbon stocks in planted forests across India

Plantation forestry in India is aimed to sustain forest cover, rehabilitation of degraded land and support the forestry industry inproviding timber, fuelwood and other products. However, the effect of soil and climatic factors on aboveground and belowground biomass carbon (AGB and BGB) as well as soil organic carbon (SOC) dynamics under plantation management remains poorly understood. Therefore, the objectives of the present study are to: (i) evaluate differences in root to shoot ratios, and biomass and biomass carbon stocks (ii) measure SOC stocks among different plantation types and stand age, (iii) observe variation of SOC stock, and (iv) identify key bioclimatic drivers of carbon storage. Published data on biomass, biomass carbon and soil carbon stock were collected from 53 peer-reviewed studies encompassing 205 different plantation sites across India, covering stand ages of 1 to 50 years. Bioclimatic variables were obtained from WorldClim 2.1 based on geo-locations of the plantations. Biomass carbon and SOC stocks significantly differed among soil types. The lowest mean aboveground biomass carbon stock (21.8 Mg C ha -1 ) was recorded on Fluvisols and the highest (93.8 Mg C ha -1 ) on Acrisols. Similarly, the lowest mean belowground biomass carbon stock (5 Mg C ha -1 ) was found on Fluvisols and the highest (25.8 Mg C ha -1 ) on Acrisols. The mean SOC stock was lowest (24.7 Mg C ha -1 ) on Xerosols and highest (96.5 Mg C ha -1 ) on Regosols. Ensemble machine learning models identified precipitation and temperature as key factors influencing the soil organic carbon (SOC); however, the models failed to identify the most influential predictor for AGBC and BGBC. The XGBoost model provided the best prediction for SOC stocks (R 2 = 0.85). The results show that soil type and precipitation strongly influence carbon accumulation, underscoring the need to integrate soil–climate interactions into plantation-based carbon management strategies. • The carbon storage (biomass and soil) in the different plantation types is strongly regulated by soil type and climatic conditions. • Cambisols and Regosols exhibited higher above and below-ground biomass carbon stock, while Acrisols tended to store more SOC stock. • Greater precipitation promotes higher biomass and biomass carbon stock. • XGBoost identified Bio5 (maximum temperature) as the most influential variable in predicting SOC stock.