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Studies on relationship between tree diversity and carbon stock has not been consistent. The present study was undertaken to quantify and compare the plant diversity and carbon stock in a subtropical broadleaved and a subtropical pine forest of Meghalaya, northeast India. Biomass-based carbon estimation was undertaken in two subtropical broadleaved forest stands viz., Mawnai (MBF) and Nongkrem (NBF) and adjacent Pinus kesiyadominated forest stands (MPF and NPF), occurring in similar topography, climatic conditions and soil type. The aboveground and belowground tree biomass was estimated using existing allometric models. Carbon was estimated as 47.4% of the total biomass. Tree species richness was greater in the subtropical broadleaved forest stands at MBF and NBF (117 and 21 species) than in the adjacent pine forests, MPF and NPF (15 and 16 species). The density values were 1294 and 1127 individuals ha−1in the broadleaved forest stands, and 894 and 1032 individuals ha−1in the adjacent pine forest stands, respectively. The broadleaved forest stands, MBF and NBF had tree biomass carbon stock of 140.4 Mg C ha−1and 133.6 Mg C ha−1, respectively, which were significantly greater (F = 26.6; P< 0.05) than the pine forest stands, MPF and NPF (74.7 Mg C ha1and 63 Mg C ha−1). The contribution of trees belonging to the higher DBH classes (> 66 cm) to the total biomass carbon was greatest in MBF, while the lower diameter trees belonging to 5–15 cm and 16–25 cm were the major contributors to the total biomass carbon in the pine dominated stands.

Litter plays a crucial role in forest ecosystem functioning as its production and decomposition govern the pools and fluxes of forest nutrient cycling. The release of nutrients through litterfall and decomposition influences forest productivity. Therefore, these two factors are considered to be important indicators of forest ecosystem health. Such processes vary across different ecosystem types because of natural as well as anthropogenic factors. Hence, studying such processes would help in better understanding and management of forest ecosystems. Litter production and decomposition rates between a broadleaved and a coniferous forest ecosystem of Meghalaya in Northeast India were compared. We selected six subtropical broadleaved forest stands in Muthlong, Ialong, Nongbah, Mukhla, Nongkrem and Mawnai, and six adjacent coniferous forest stands dominated by pine. We estimated leaf litter production, decomposition and nutrient release, and analyzed the nitrogen and phosphorus contents in the litter of both the forest types. The study revealed that litter production and decomposition rates, and the litter nitrogen and phosphorous contents were significantly higher in the broadleaved forest compared to the pine forest. The variability in the litter characteristics was greater in the broadleaved forest compared to the coniferous forest indicating that the former is functionally more dynamic than the latter. Such dynamism in the broadleaved forest could be an important factor for providing greater ecological services compared to the coniferous forest, which nevertheless requires an in-depth study.

Shifting cultivation (Jhum) has been a threat to the rich biodiversity of Northeastern India (NEI). Here, we applied an integrated spectral enhancement technique to map the shifting cultivation fallow/ current jhum area in NEI for 2014, 2016 and 2018 using Landsat-8 data. The natural vegetation in shifting cultivation fallow land was analyzed through field sampling. Manipur state occupied the highest shifting cultivation fallow area of 1528.5 km2(2014), and it was minimum in Tripura state with 178.3 km2(2018). The shifting cultivation fallow hotspot map was derived to identify the repetitive patches, in which the state of Arunachal Pradesh topped with 24.9% and Tripura with lowest 3.6%. Field sampling revealed dominance of four invasive species viz., Mikania micrantha, Ageratum houstonianum, Chromolaena odorataand Ageratina adenophora.We provided an insight into shifting cultivation fallow dynamics and vegetation composition in less than 3 year old shifting cultivation fallow lands. The study using remote sensing approach revealed that the fragile ecosystems of NEI are still facing the threat from shifting cultivation, though the trend has started declining. The generated database can be regularly updated in future using recent Sentinel-2 data with higher spatial and temporal resolution that would enhance the quality of land use management plans.