Tree species composition, biomass and carbon stocks in two tropical forest of Assam

Tropical forests store higher above ground biomass (AGB) and AGB carbon (AGBC) than any other forest ecosystems. In the present study the tree composition, diversity, dominance and carbon stocks in the AGB and soil of tropical forests viz., the Gibbon wildlife sanctuary (GWS) and the Kholahat reserve forest (KRF) of Assam, India were assessed. Soil sampling, tree survey, girth above 1.3 m height of plants >10 cm girth of plants were assessed in 1000 m2 quadrate. Allometric model for moist forest stands was used to determine AGB and AGBC. A total of 71 and 108 different tree species belong to 32 and 42 families were found in the GWS and KRF, respectively. In the GWF, the Shannon diversity index (1.22) and the Simpson index (0.085) were significant, while for the KRF these indices were insignificant. The basal area, AGB and AGBC in the GWS and KRF were 62.49-90.29 m2 ha−1, 135.30-146.42 Mg ha−1, and 67.64-73.21 Mg ha−1, respectively. The average soil carbon stock (SOC) in the upper, middle and lower layers was 57.74-78.44 kg m−2, 39.22-64.93 kg m−2 and 30.32-42.86 kg m−2, respectively, in the GWS and KRF. However, compared to GWS, a higher AGB and AGBC were found in KRF. This finding reveals that the higher AGB, AGBC and SOC in the KRF were due to old growth matured forest with big and diverse tree species.