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Forest's ecosystem is changing at an alarming rate and anthropogenic alteration of forests to other land use is a major driver of carbon (C) emission and biodiversity loss. We estimated ecosystem-level C stock and factors affecting C stock in six major forest types; tropical wet evergreen forest, montane subtropical forest, temperate forest, bamboo forest, quercus forest, and jhum land of the eastern Himalayan region (India). We determined ecosystem structure, biodiversity, and plant and soil C stock by laying random plots in each forest site. The average C stock was estimated in the range of 79.0–373.4 Mg C ha−1 and found significantly different among the forest types. Partitioning ecosystem C stocks in plant (24–55%), soils (43–75%), deadwood (1–4.8%) and litter (0.20–1.25%) components varied largely. Pearson correlation analysis shows a significant positive relation of basal area with species diversity, tree density, and ecosystem C stock. Linear mixed-effect model demonstrates the high influence of species density and soil moisture content on the ecosystem C stock. We recommend the inclusion of forest structural attributes and pedological characteristics while predicting synergies between C stock and future climatic conditions. Additionally, conversion of natural forests to jhum land should be minimized because they stored lesser ecosystem C stocks thus plays a minimum role in C accumulation and cycling. The study provides estimates of C stocks in major forests that can be useful in suggesting a path forward to partially fulfill India's commitments to REDD + policy. [Display omitted] • Determining ecosystem-level carbon stock is essential for carbon sink management. • Average carbon stock ranged from 79 Mg C ha−1 to 373 Mg C ha−1 in major forest types. • Tropical wet evergreen forests are major carbon sink in the eastern Himalayas. • Carbon stock is highly influenced by the stand density and soil moisture content. • Jhum forests practices should be reduced to enhance ecosystem carbon sink capacity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Litterfall dynamics in major forests of the India Himalayan region was investigated. • Mean annual litterfall in IHR was 4.37 Mg ha−1 yr−1 and mean k-value was 1.44 yr−1. • k-value was highest in tropical forests but litter nutrients were higher in subtropical forests. • Linear mixed model revealed a significant effect of moisture and precipitation on litterfall. • Environmental factors and forest types instead of litter quality control litter decomposition. Litter production and its decomposition are major drivers of soil carbon input and nutrient cycling in forest ecosystems. The litterfall patterns and decomposition rate still need to be explored in the geographically diverse Himalayan region. The study aims to investigate the factor affecting litterfall and its decomposition patterns in tropical, subtropical, and temperate forests by synthesizing a comprehensive database for the Indian Himalayan Region (IHR). We compiled a large dataset of annual litterfall, litter decomposition rate (k), and litter quality data from 102 published research articles and explore its relationship with environmental factors using a linear mixed effect model. Mean annual litterfall in the IHR ranged between 0.26 and 13.4 Mg ha−1 yr−1 and k-values varied from 0.006 to 4.71 yr−1. The study shows greater annual litterfall (5.89 Mg ha−1 yr−1) and k-values (2.47 yr−1) in tropical forests while litter C:N ratio (48) and lignin content (20.2%) were significantly higher in subtropical forests. The data distribution indicates higher but insignificantly different litterfall (5.45 Mg ha−1 yr−1) and mean k-values (1.86 yr−1) in the 1000–2000 m altitudinal range. Both litterfall and k-values were greater at higher temperatures (20–30 °C; 4.72 Mg ha−1 yr−1, 1.81 yr−1) and moderate precipitation (1000–2000 mm; 5.57 Mg ha−1 yr−1, 1.60 yr−1). The linear mixed effect model revealed a significant effect of moisture and precipitation on annual litterfall patterns, while aridity and precipitation significantly influence litter decomposition rate. Our study concluded that tropical forests have greater annual litterfall and k-values but subtropical forests have higher litter quality. The present study suggests environmental factors and forest types instead of litter quality in the IHR mainly control litter decomposition. The outcome of the study can be used to predict the forest carbon and nutrient cycle in future climate change scenarios. [ABSTRACT FROM AUTHOR]