In recent decades, carbon (C) management is an important point on the agenda to identify the best viable mitigation strategies for its reduction. The study was conducted at Jaldapara National Park located in the Eastern Himalayan region of India. The study quantified litter production, decomposition, periodic nutrient release, soil fertility status, and soil organic carbon (SOC) of five major forest stands i.e., Tectona grandis (TGDS), Shorea robusta (SRDS), Michelia champaca (MCDS), Lagerstroemia parviflora (LPDS) and miscellaneous stand (MS). A stratified random nested quadrate method was adopted for sample collection. Results reveal that the greatest amount of litter production and decomposition was under MCDS followed by MS, LPDS, SRDS, and the smallest under TGDS. The material annual turnover through litter decomposition in all the stands varies between 96.46% and 99.34%. The content and amount of the available nutrients in litter varied significantly among the stands. Moreover, release of these nutrients was nearly equal to the amount available in the initial litter mass. In general, the magnitude of the total nutrient return was in the same order as the total litter fall and the nutrient availability was more closely related to litter nutrient content and soil organic carbon. The range of pH (4.86–5.16), EC (0.34–0.50), soil moisture (27.01–31.03) and available primary nutrients (N: (0.21–0.26 Mg/ha), P: (0.09–0.12 Mg/ha), K: (0.13–0.14 Mg/ha)) also varied significantly among the stands. Significant positive correlations were observed between SOC, N and K. Both the fertility indices exhibited no definite pattern in the stands but a significant correlation between the two indicates the healthy soil fertility status of the stands. SOC varies significantly under different forest stands, but the greatest content was found under MS. The estimated SOC ranges between 75.9 and 107.7 Mg ha⁻¹ up to 60 cm and is reported to be below the Indian average of 182.94 Mg ha⁻¹. The present study strongly recommends that Tectona grandis, Shorea robusta, Michelia champaca, and Lagerstroemia parviflora should be the important commercial timbers of the Eastern Himalayan region because they may help further to increase the C sink in agricultural and degraded landscapes.

In the modern era, Gmelina arborea plantations are a hotspot of future research because of their high carbon sequestration potential. The present work was conducted during 2018 to 2020 on a young unmanaged Gmelina farm to understand the ecosystem’s carbon and its dynamics. The study area was categorized into three age classes: ≤5, 5–10, and 10–15 years. In a plantation, Gmelina trees (10%) were randomly selected while other trees (90%) were also taken into the consideration for ecosystem carbon. A stratified random nested quadrate sampling method was adopted for analyzing other vegetation forms under study. Overall, 51 individual species in the studied Gmelina farm were found which includes 23 tree species, 7 shrub species, 16 herbs, 2 climbers, and 3 species of ferns. The estimated quantitative vegetation parameters and diversity indices indicate that the plant assemblages were heterogeneous with native diverse species evenly distributed with fairly higher densities, frequencies, and abundance. Herbs were the most important species followed by shrubs and trees. Consequently, with the increasing age of plantation, the richness of plant species increased. Soil properties were significantly influenced by the age of the plantation but exhibited no discreet trend. Total biomass density and total carbon density increased with increasing plantation age while no drastic variation was found in available soil organic carbon (SOC) because of insignificant variability in litter production. Total carbon, available SOC (up to 60 cm depth) and ecosystem carbon in the three age class plantations fell in the ranges of 54.51–59.91, 48.18–55.73, and 104.81–110.77 Mg ha⁻¹, respectively. The carbon sequestration potential of Gmelina arborea is higher compared to other reported species and highly supportive of converting unutilized agricultural landscapes to reduce the atmospheric carbon dioxide in future.