Evergreen broad-leaved forest (EBLF), covering a lot of area in China, is the zonal vegetation type in subtropical area. However, under long-term human disturbances, this forest is shifting to include much more degraded area dominated by secondary forests, shrub and grassland. Unfortunately, forest nutrients dynamics remain poorly qualified, despite the growing view that these processes might be extremely important in helping us understand changes of biogeochemical cycle in the context of the global change (particular in the change of land use), and shedding light on the conservation and restoration of EBLF.
To understand the impacts of the degradation of EBLF on soil carbon and nutrient pools, we chose mature EBLF as the reference climax forest, and secondary and young evergreen broad-leaved forest, secondary conifer and evergreen broad-leaved mixed forest, secondary coniferous forest, shrubs and grassland to represent different degradation stages in Tiantong National Forest Park. After examining soil nutrients and carbon pools, we obtained the following results and conclusions: (1) Soil total N stocks displayed the following order: mature evergreen broad-leaved forest > secondary and young broad-leaved forest > shrub > secondary coniferous forest > grassland > secondary conifer and broad-leaved mixed forest; (2) soil total P is in the order: mature evergreen broad forest > secondary coniferous forest > secondary conifer and broad-leaved mixed forest > secondary and young broad-leaved forest > grassland > shrub; (3) soil organic carbon is in the pattern of mature evergreen broad forest > secondary coniferous forest > secondary and young broad-leaved forest > shrub > grassland > secondary conifer and broad-leaved mixed forest; (4) stock of soil NH₄⁺-N displayed an “U” shape in the series of EBLF degradation; and (5) stock of soil NO3^- was highest in the grassland than other degraded types, in which significant differences were not found. These results suggested that soil carbon and nutrients pools decreased gradually during degradation of EBLF. The mature EBLF can be considered as a major carbon sink and a huge nutrient pools in this region.