南亚热带典型森林演替类型粗死木质残体贮量及其对碳循环的潜在影响

COARSE WOODY DEBRIS BIOMASS AND ITS POTENTIAL CONTRI-BUTION TO THE CARBON CYCLE IN SUCCESSIONAL SUBTROPICAL FORESTS OF SOUTHERN CHINA

森林生态系统中的粗死木质残体(Coarse woody debris, CWD)不仅能够为其它生物提供生境,维持森林结构,而且对生物地球化学循环起着不可忽视的作用,CWD作为森林生态系统中重要的结构和功能元素,已经引起广泛关注。然而,华南地区典型亚热带森林生态系统中CWD的结构和功能方面的研究很少。该文报道了鼎湖山自然保护区内典型南亚热带森林生态系统中CWD的贮量及其特征,所选择的森林包括马尾松(Pinus massoniana)林、针阔叶混交林和季风常绿阔叶林,它们分别代表该气候区域内处于森林演替早期、中期和后期3 个阶段的森林类型。其中马尾松林和针阔叶混交林都起源于20世纪30年代人工种植的马尾松纯林,由于长期受到包括收割松针、CWD和林下层植物等在内的人为活动的干扰,到2003年调查时马尾松林仍属于针叶林;而混交林样地自种植之后就未受到人为活动的干扰,自然过渡为针阔叶混交林类型。人为干扰对马尾松人工林的结构和功能产生了巨大的影响,马尾松林的生物量仅为针阔叶混交林生物量的35%。组成马尾松林、针阔叶混交林和季风常绿阔叶林CWD的树种数量分别为7、18和29;马尾松林中几乎没有CWD存在(贮量仅为0.1 Mg C·hm-2),针阔叶混交林CWD的贮量为8.7 Mg C·hm-2,季风常绿阔叶林CWD的贮量为13.2 Mg C·hm-2,分别占地上部分生物量的9.1%和11.3%;针阔叶混交林和季风常绿阔叶林中只有将近10%的CWD以枯立的方式存在。该区域内CWD的分解速率较快,在区域碳循环中将扮演重要角色,保留林地中的CWD是维持本区域森林生产力和森林可持续管理的重要举措。

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.