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Soil carbon sequestration is vital to reduce the atmospheric carbon concentration, which is expected to increase within future climatic scenarios. The present study aims to investigate the effects of land use changes to different plantation systems on SOC stocks, and simulate these changes using the RothC model in Mizoram, India. With this aim, four land uses, viz., secondary forest, oil palm, orange, and arecanut plantations, established on degraded shifting cultivation lands, and a control natural forest were selected for this study. The soils were sampled 0–30 cm in the secondary forest, plantations, and the natural forest, at an interval of five years. Measured SOC stocks were the highest in the secondary forest (67.0 Mg C ha−1) and the lowest under the oil palm plantation (37.4 Mg C ha−1), 10 years after land use conversion. The climate change projections for 2021–2035 and 2036–2050 indicated that temperature and rainfall changes, projected to increase by 0.8 and 2.0 °C, and 5.9 and 5.4%, respectively, will affect SOC stocks in the future differently, depending on the land use and carbon input from vegetation. Baseline climate simulations under land use change showed the highest increase in the SOC stock under the secondary forest (116%), and the lowest in the oil palm plantation (27%). Overall, the model predicted that SOC stocks would increase, but the rate of change (0.23–1.86 Mg C ha−1 yr−1) varied with different land uses, plant species, and land management practices. The model results indicated that restoring secondary forest following the abandonment of a shifting cultivation and orange plantations are the best options to improve SOC stocks within future climate change scenarios. Conversely, arecanut and oil palm need to be reduced because the SOC storage is lower. [ABSTRACT FROM AUTHOR]

Chir pine (Pinus roxburghii, Sarg.) forests are dominant in the Indian Himalayan region and act as a huge carbon (C) sink. However, measuring the C sink in soil is complex and time‐intensive, and therefore the present study attempts to estimate the soil organic carbon (SOC) through a remote sensing (RS) approach. We estimated SOC stock of chir pine forests along an altitudinal gradient at three soil depths (0–30, 30–60 and 60–100 cm) in the Garhwal Himalaya, Uttarakhand. Fourteen forest stands at four altitudes, viz., <1000 m above sea level (m asl), 1001–1400 m asl, 1401–1800 m asl and >1801 m asl were surveyed and served for data collection. A model for predicting SOC was developed through stepwise regression analysis based on vegetation information and altitude as independent variables with the field data on SOC. For vegetation information, we used the normalized difference vegetation index (NDVI) measured through remote sensing (RS). The mean SOC stock up to 100 cm depth was increased with increasing altitude and were in the order of 69.66 ± 19.86, 85.27 ± 17.53, 95.68 ± 7.90 and 148.41 ± 71.39 million g ha−1 (million gram per hectare) for <1000, 1001–1400, 1401–1800 and >1801 m_asl, respectively. The result showed that NDVI was a good predictor for SOC estimation. The model predicted SOC stock between 57 and 152 million g ha−1 with a mean of 93 million g ha−1, which was close to the SOCs from field inventory. Therefore, RS could be used to precisely map the SOC stock in the chir pine forests of the Himalayas through NDVI and provide information to policymakers for forest management. [ABSTRACT FROM AUTHOR]

Background: Shifting cultivation (locally known as "jhum") is a major driver of deforestation and loss of ecosystem services in rainforests. For developing any effective conservation of biodiversity and carbon service program, an in-depth understanding to the recovery of vegetation and carbon after abandonment of jhum is essential. We estimated species richness, abundance and composition of trees, shrubs and herbs, carbon distribution in aboveground and belowground components along a chronosequence of jhum fallow in northeast India, and elucidated the factors affecting the recovery processes of jhum fallows. Methods: Species composition and other plant community attributes, carbon storage in different pools were studied in 5 jhum fallows (< 5, 5–10, 11–15, 16–20, 21–25 years old) and an old-growth forest. The data were subjected to linear mixed effect modeling using R-package "nlme" for identifying the important factors contributing to the recovery of vegetation and carbon. Results: Species composition varied significantly (P < 0.05) between jhum fallows and old-growth forest. Tree density varied from 28 stems ha−1 in 5 years old jhum fallow to 163 stems ha−1 in old-growth forest. Both biomass carbon in all components and soil organic carbon were significantly (P = 0.01) lower in jhum fallows than in the old-growth forest except living non-woody biomass component. The recovery of aboveground biomass carbon was faster during early successive years than the mid-successive jhum fallows. Total ecosystem carbon and soil organic carbon stock in the oldest jhum fallow was 33% and 62% of those in the old-growth forest, respectively. The fallow age was found to be the most important explanatory factor in the recovery process of vegetation and carbon stock in re-growing fallows. Conclusion: The shifting cultivation fallows gradually recovered both vegetation and carbon and are potential repository sites for biodiversity conservation, which may take much longer time to reach up to old-growth forest in northeast India. [ABSTRACT FROM AUTHOR]

Soil organic carbon plays an important role in the stability and fertility of soil and is influenced by different management practice. We quantified active and passive carbon pools from total soil organic carbon (TOC) in seven different land use systems of northeast India. TOC was highest (2.75%) in natural forest and lowest in grassland (1.31%) and it decreased with increasing depth in different pools of lability. Very Labile Carbon (VLC) fraction ranged from 36.11 to 42.74% of TOC across different land use system. Active carbon (AC) pool was highest in Wet Rice Cultivation (61.64%) and lowest (58.71%) in natural forest. Higher AC pools (VLC and less labile) in most land use systems barring natural forests suggest that the land use systems in the region are vulnerable to land use change and must adopt suitable management practice to harness carbon sequestration. [ABSTRACT FROM AUTHOR]

• Stability of SOC fractions differed among the forest types. • SOC stock was highest in a temperate forest (132.7 Mg C ha−1). • Active and passive carbon pool was highest in temperate and Quercus forests, respectively. • Conversion of natural forests to bamboo and jhum land reduced SOC stock. • Quercus forest plays a significant role in long-term carbon sequestration. Forests are among the largest terrestrial carbon pools that are most vulnerable to land use and land cover change (LULC). Therefore, it is essential to manage forest ecosystems to enhance soil organic carbon (SOC) pools and soil functionality. The present study was carried out to analyze C stability and change in SOC stock under different forest types in the eastern Himalayan region of India. Topsoil (0–15 and 15–30 cm) samples from six dominant forests i. e. tropical wet evergreen, montane subtropical, temperate, Quercus , bamboo, and shifting cultivation (Jhum) lands were collected and analyzed for selected soil properties and SOC stock. Active (very labile + labile), slow (less labile), and passive (non-labile) C fractions were also analyzed to determine the stability of the SOC pool under the LULC scenario. Results show that the percentage contribution of active C to total organic carbon in topsoil was highest in a temperate forest (74.1%) while lowest in a bamboo forest (48.1%). Unlike, slow C (18.4%) and passive C (26.6%) were highest in Quercus forest. Pearson correlation analysis shows significant positive relation of active and slow C pool with SOC and total nitrogen concentration. The estimates of SOC stock (0–30 cm) were significantly higher in temperate forests (132.7 Mg C ha−1). However, the conversion of natural forests to bamboo forest and jhum land reduced SOC stock by 29% and 68%, respectively. C lability index shows higher labile C in jhum land while recalcitrancy index was highest in a bamboo forest. Our study concluded that LULC change significantly altered the stability and stock of SOC in natural forests. Owing to a higher percentage of slow and passive C pools, Quercus forests play a major role in C sink management. [ABSTRACT FROM AUTHOR]

Abandoned cropland is a global threat to land degradation, particularly in the eastern Himalayas, where the conversion of forests into cropland is widespread, resulting in abandonment. Agroforestry systems have the potential to mitigate land degradation and carbon (C) losses. The region lacks information on comparing soil carbon inventories between abandoned cropland and agroforestry. This has impeded carbon restoration efforts in the Eastern Himalayas. This study evaluated the responses of 18-year-old abandoned croplands to changes in total soil carbon inventories in comparison to four 35-year-old tree-based agroforestry systems (AFSs), using a 55-year-old dense mixed forest as a baseline. To speed up afforestation efforts on abandoned croplands, the study also evaluated the biomass and carbon stock input of four AFSs. The cropland was under seasonal maize cultivation from April to August for 17 consecutive years before being abandoned for 18 more consecutive years. The total C concentration in forest soils was higher (p <0.001) (3.10%, weighted mean per 1.0 m depth) than in cultivated land uses (CTNL and AFSs). CTNL experienced poor regeneration of secondary vegetation even after 18 years of abandonment, leading to the presence of invasive low-growth grass species. Compared to mixed dense forest, cultivation caused a decline in total soil carbon, which was more pronounced in CTNL (−45.5%) than in the AFSs (−25.8 to −28.1%). Similarly, CTNL registered a higher decline in total organic and inorganic soil carbon (−44.4 to −49.0%) than AFSs (-25.5 to -33.3%). Compared to AFSs, CTNL caused a significant (p <0.001) decline in microbial biomass and active carbon pool in the soil.The total carbon stock estimated for soils up to 1.0 m under forest was 358.7 Mg C ha−1. Cultivation caused a decline in total carbon stocks, with CTNL experiencing a higher drop (−35.5%) than AFSs (−16.2 to −21.1%). The total soil carbon was dominated by organic carbon, which contributed 83.1–85.7%, while inorganic carbon contributed only 14.2–16.9%. The tree biomass carbon (above and below ground) in alder was 12.0–26.0% higher than the AFS-based on Som and Silver oak trees (92.7–103.2 Mg ha−1). Leaf litter biomass in AFS contributed 1.68–1.75 Mg C ha−1 to the soil. Alder-pineapple-based AFS increased the availability of microbial biomass and very labile carbon, while also providing deep soil carbon storage comparable to other AFSs. Through alder-pineapple agroforestry, it is possible to restore carbon loss in abandoned cropland in the Eastern Himalayas and other hill ecosystems. [Display omitted] • Assessed the ecosystem carbon (C) in abandoned cropland (CTNL) and agroforestry (AFS). • Conversion of forests to AFS reduces total soil C and C-pool inventories. • Decline in soil C inventories was greater in abandoned cropland than in AFS. • Alder + pineapple based AFS outperformed Som and Grevillea based AFSs. • AFS may mitigate C loss in degraded CTNL in the Himalayan ecosystem. [ABSTRACT FROM AUTHOR]