Geographical settings and tree diversity influenced soil carbon storage in different forest types in Rajasthan, India

Knowledge of soil-forest relationship in degraded dry forest ecosystem of Rajasthan is essential to understand the factors responsible for soil carbon storage in different forest types and devising climate change mitigation strategies. About 15% forest blocks across forest ranges in Rajasthan were surveyed by laying 903 plots of 0.1 ha area. Trees and shrubs were enumerated and measured and litter and coarse woody debris (CWD) were quantified. Soil samples were collected from 0 to 30, 30–60 and 60–90 cm soil layers and analysed for pH, electrical conductivity (EC), bulk density (BD), gravel (G), organic (SOC) and inorganic (SIC) carbon contents. Species richness (SR), Shannon-Weiner diversity (H′) and SOC and SIC stocks were calculated. Thirty-one forest types identified that differed (p < 0.05) in trees/shrubs SR and H′, litter and CWD, and soil parameters except SIC content/stock. SR and H′ were highest in Dry Bamboo Brakes and Riverain Forest for trees and in Secondary Dry Deciduous Forest and Dry Grassland for shrubs respectively. Soil carbon stock was highest in 0–30 cm soil layer, but SOC content/stock decreased and other soil variables increased with increase in soil depth. SIC stock showed greater (41.3-fold) spatial variation than SOC stock (4.2-fold) and were associated with forest types, elevation, rainfall and soil characteristics. Tree SR and H′ favoured SOC stock, but not the SIC stock signifying the role of pedogenic process and parent materials on SIC sequestration. Conclusively, plant species richness and diversity facilitated sequestration and storage of soil carbons in forests and plantations, but carbon stock of 33.43 Mg ha⁻¹ SOC and 49.31 Mg ha⁻¹ SIC in top 100 cm soil layer in Rajasthan forests indicated the influence of many factors on total carbon pool in this dry area.