Abstract: A short-term laboratory incubation was conducted to study the variations of soil organic carbon and mineralizable organic carbon concentrations in four forest stands (Cunninghamia lanceolata plantation, Pinus massoniana + Lithocarpus glaber mixed forest, Choerospondias axillaries deciduous broadleaved forest, and L. glaber + Cyclobalanopsis glauca evergreen broadleaved forest) in a hilly region of central Hunan Province. In the four forest stands, the concentrations of soil organic carbon and mineralizable organic carbon and the proportion of soil mineralizable organic carbon to soil total organic carbon decreased with soil depth. In the same soil layers, the concentration of soil organic carbon ranked in the order of L. glaber + C. glauca evergreen broadleaved forest > P. massoniana + L. glaber mixed forest > C. axillaries deciduous broadleaved forest > C. lanceolata plantation. In 0-30 cm soil layer, the organic carbon concentration in the secondary forests was 20.8%-31.9% higher than that in C. lanceolata plantation. The concentration and the proportion of soil mineralizable organic carbon were in the order of L. glaber + C. glauca evergreen broadleaved forest > C. axillaries deciduous broadleaved forest > P. massoniana + L. glaber mixed forest > C. lanceolata plantation. The soil mineralizable organic carbon concentration in L. glaber + C. glauca evergreen broadleaved forest, C. axillaries deciduous broadleaved forest, and P. massoniana + L. glaber mixed forest was 51.6%, 45.2%, and 41.0% higher than that in C. lanceolata plantation, and the proportion of mineralizable organic carbon in 0-30 cm soil layer in the former three secondary forests was 35.8%, 29.3%, and 20.0% higher than that in C. lanceolata plantation, respectively. In the four forest stands, soil mineralizable organic carbon had significant correlations with soil total organic carbon, microbial biomass carbon, total nitrogen, and the ratio of total organic carbon to total nitrogen.

Key words: Pb isotope, priority areas, NDVI, distance analysis, coastal wetlands.