Storage and distribution of soil organic carbon in Dinghushan Biosphere Reserve

Land-use change that influences soil carbon storage and release within the tropics can have large implications for global carbon cycling. Changes in soil carbon following land-use change have become an international policy concern in terms of both sustained production at a local or regional scale, and the global consequences relating to increased emissions of CO_2 from terrestrial systems. There are eight types of vegetation in Dinghushan Biosphere Reserve (DHSBR), Guangdong province, and these vegetations can been divided into two classes: natural vegetation types (Ravine Rain Forest, Monsoon Evergreen Broad-Leaved Forest, Mountain Evergreen Broad-Leaved Forest, and Mountain Shrubby Grassland) and secondary vegetation types (Pine Forest, Pine and Broad-Leaved Mixed Forest, Secondary Monsoon Evergreen Broad-Leaved Forest, and Evergreen Shrub). In this paper, the storage and distribution of soil organic carbon for these classes of vegetation was studied based on 61 soil profiles. The objectives of our study were to provide basic data for the estimation of the soil carbon pool in subtropical China, and to provide information for the evaluation of ecological benefits contributed by nature reserves. The results were as follows: (1) Soil organic carbon concentration generally decreased with depth (2.46%, 1.52%, 0.96% and 0.53% for 0～10, 0～20, 20～40 and 40cm soil depth interval, respectively, with a range of 1.03～3.92%, 0.71～2.64%, 0.43～1.89% and 0.34～0.53%) in all vegetation type. Soil organic carbon concentrations under natural vegetation were significantly higher than that under secondary vegetation (1.7, 2.2 and 2.0 times for 0～10cm, 0～20cm and 20～40cm soil depth interval), except 40cm depth interval.(2) Soil carbon density (t/hm~2) for four soil depth intervals varied from 15.64 to 29.09, 9.25 to 24.86, 10.84 to 33.69 and 4.59 to 34.09, and their mean values (t/hm~2) were 23.46, 16.94, 21.20 and 17.75, respectively. For the whole soil profile, the carbon density was 53.56～111.46 t/hm~2, with a total mean of 73.92 t/hm~2. The highest carbon density value occurred in Pine Forest, and the lowest occurred in Mountain Evergreen Broad-Leaved Forest. Except for the Mountain Shrubby Grassland, soil carbon density in natural vegetation was significantly higher than that in secondary vegetation (1.7 to 2.3 times for four soil depth intervals).(3) The average soil thickness for all types of vegetation was 36.67～73.25cm, with a total mean of 51.99cm, decreasing with altitude. (4) The total carbon storage was 72287.0 t in the area of 1028.4 hm~2, with 32.0%, 20.6%, 25.8% and 21.6% in 0～10, 10～20, 20～40 and 40cm soil depth interval, respectively. It was found that natural vegetation had slightly higher proportion of organic carbon in the top 10cm of soil than the secondary vegetation. Of total soil carbon in DHSBR, 35.0% and 14.5% was contributed by Pine and Broad-leaved Forest and Monsoon Evergreen Broad-Leaved Forest, respectively.(5) By comparisons, DHSBR had lower soil carbon densities, and had higher proportion of carbon contained in the upper 20cm of soil than other regions. These results showed that human impact was one of factors that made soil organic carbon content in secondary vegetation types lower than in natural vegetation types.