Abstract:

Coarse woody debris (CWD) in forest ecosystems provides critical habitat for many organisms, maintains a healthy forest structure, and is important in the biogeochemical cycling of carbon and nutrients. However, the characteristics and ecological functions of CWD are poorly documented and understood in the subtropical forests of southern China. In this study, the amount and characteristics of CWD in three typical forest ecosystem types in southern China were investigated at the Dinghushan Nature Reserve. These forests were selected to form a successional sequence with a Pinus massoniana forest, a mixed coniferous broad-leaved forest, and a monsoon evergreen broad-leaved forest representing early-, mid-, and advanced-successional stages, respectively. Both the Pinus massoniana and the mixed coniferous broad-leaved forests developed on artificial Pinus massoniana plantations planted in the 1930s. Nevertheless, these two forests were at different successional stages. The Pinus massoniana forest was harvested for leaf/needle litterfall, CWD, and undergrowth until 1990 whereas human interventions were excluded in the mixed coniferous broad-leaved forest. Results indicated that human disturbance dramatically altered the successional process of the Pinus massoniana forest and its ecological functions. Total aboveground biomass was just 35% of that of the mixed coniferous broad-leaved forest. The number of tree species that contributed to CWD increased along the successional sequence with 7, 18, and 29 species in the Pinus massoniana, mixed coniferous broad-leaved, and monsoon evergreen broad-leaved forest sites, respectively. There was almost no CWD (0.1 Mg C·hm^-2) in the Pinus massoniana forest, while CWD amounted to 8.7 Mg C·hm^-2 in the mixed coniferous broad-leaved forest and 13.2 Mg C·hm^-2 in the monsoon evergreen broad-leaved forest, representing 9.1% and 11.3% of the total aboveground biomass, respectively. Only about 10% of the CWD was standing in the mixed coniferous broad-leaved and the monsoon evergreen broad-leaved forests, suggesting that sudden forest canopy gaps created by falling or snapping of trees might be more important than gradual gaps formed by standing dead trees in the succession of these forests in this region. Although the decomposition rate of CWD was relatively fast, it was still comparable to that of the soil organic carbon in the region, suggesting that CWD can play an important role in the global carbon cycle. Keeping CWD on the forest floor is a critical strategy for maintaining forest productivity and implementing sustainable forest management in southern China.

Key words: Forest succession, Carbon storage, Human impact, Subtropical forest, Dinghushan Nature Reserve