Continuous and prolonged human disturbances have caused severe degradation of a large portion of lowland in South China, and how to restore such degraded ecosystems becomes an increasing concern. The process and mechanisms of spontaneous succession, which plays an important role in vegetation restoration, have not been adequately examined. To identify the pathways of early spontaneous vegetation succession, 41 plots representing plant communities abandoned over different times were established and investigated. The communities and indicator species of the vegetation were classified by analyzing the important values of plant species using multivariate analyses. The results indicated that the plant species could be classified into nine plant communities representing six succession stages. The pathway and species composition also changed in the process of succession. We also measured 13 environmental variables of microtopography, soil structure and soil nutrition in each plot to examine the driving forces of succession and the vegetation-environment relationships. Our results showed that the environmental variables changed in diverse directions, and that soil bulk density, soil water capacity and soil acidity were the most important factors.
Wen-Jun DuanHai RenSheng-Lei FuQin-Feng GuoJun Wang
Temporal variability in soil CO2 emission from an orchard was measured using a dynamic open-chamber system for measuring soil CO2 efflux in Heshan Guangdong Province, in the lower subtropical area of China. Intensive measurements were conducted for a period of 12 months. Soil CO2 emissions were also modeled by multiple regression analysis from daily air temperature, dry-bulb saturated vapor pressure, relative humidity, atmospheric pressure, soil moisture, and soil temperature. Data was analyzed based on soil moisture levels and air temperature with annual data being grouped into either hot-humid season or relatively cool season based on the precipitation patterns. This was essential in order to acquire simplified exponential models for parameter estimation. Minimum and maximum daily mean soil CO2 efflux rates were observed in November and July, with respective rates of 1.98 ± 0.66 and 11.04 ± 0.96 μmol m-2 s-1 being recorded. Annual average soil CO2 emission (FCO2) was 5.92 μmol m-2 s-1. Including all the weather variables into the model helped to explain 73.9% of temporal variability in soil CO2 emission during the measurement period. Soil CO2 efflux increased with increasing soil temperature and soil moisture. Preliminary results showed that Q10, which is defined as the difference in respiration rates over a 10 -C interval, was partly explained by fine root biomass. Soil temperature and soil moisture were the dominant factors controlling soil CO2 efflux and were regarded as the driving variables for CO2 production in the soil. Including these two variables in regression models could provide a useful tool for predicting the variation of CO2 emission in the commercial forest soils of South China .
LI Yue-LinD. OTIENOK. OWENZHANG YunJ. TENHUNENRAO Xing-QuanLIN Yong-Biao
