[Dynamics of soil properties under secondary succession forest communities in Mt. Jinyun]

Mt. Jinyun is located in the north suburb of Chongqing, 30 km away from the city center. It is rich in forest plants, an epitome of forests in north tropical areas of China. Under anthropocentric disturbance, there still exist large numbers of succession communities, and the process of successive development follows the way of shrub-grassland (X1)-->coniferous forest (X2)-->coniferous-broad leaved mixed forest (X3)-->evergreen broad-leaved forest (X4). By now, soil and water conservation is very important in the Three Gorges area of Yangtze River, and the investigation on the secondary succession of the forests could help to realize the changes of the forests and soils under anthropocentric disturbance, and supply information on the protection of natural forests and the artificial reforestation of this area. In this paper, some typical and representative plant communities in different succession stages were selected to study the plant composition and type and the soil properties, with species diversity indices and canopy density investigated in many standard squares and soil physical and chemical characteristics analyzed. The results showed that there were obvious variations of soil properties with time. As the plant community developed from primary stage to climax, the contents of soil organic matter, total N, and available N and K increased in order of X1 < X2 < X3 < X4, soil pH changed from 5.23 (X1) to 4.06 (X4), soil base saturation varied from 58.3% (X1) to 37.7% (X4), and soil CEC increased with the succession. It was suggested that an intense soil acid leaching was occurred in Mt. Jinyun. The contents of soil organic matter and total N in different layers showed a trend of A>B>C, e. g., soil total nitrogen in evergreen broad leaved forest was 2.31(A), 0.66(B) and 0.12(C)g x kg(-1). Gray analysis was used to study the relationships of soil properties between the climax community and other three succession communities. The relation coefficient was 0.461 0 (X3), 0.586 2(X2) and 0.6821 (X1), respectively, indicating that soil nutrients were accumulated as the forest succession community progressed. The plant arbor species followed the sequence of 0 (X1) < 7.5 (X2) < 9.0 (X3) < 12.8 (X4), and the canopy density ranked as the same way. Plant community could affect soil nutrient reserves significantly. Multivariate variance analysis showed that soil properties varied significantly among different seasons, but this variation had no impact on the community replacement and soil development during the chronosequence of community succession. The variation of soil properties adapted well to each successive community.