关键词: 叶寿命, 比叶面积, 叶氮含量, 适应策略, 常绿植被, 落叶植被, 生态系统

Abstract: Over the past two decades, society has become increasingly aware of problems of forest degradation. The effects of forest degradation transcend individual countries and now impact global processes. Research on the restoration of degraded forests has become a key issue in global ecology. Of particular concern are the effects of human activities on forest productivity and site fertility, especially as the demands for fuel and timber from tropical forests increase. Removal and burning of biomass causes nutrient losses and changes to the soil’s physical and chemical characteristics. The amount of nutrient loss depends on the intensity of the activities, local environmental factors, and the type and successional state of the forest. If nutrient losses cannot be recovered during regrowth, forests often become degraded through time. Thus, it is important that the nutrient dynamics of human-impacted forests are well understood in order to develop plans for restoration of degraded forests and for sustainable forest management. Most of the primary tropical forests in southern China have been degraded by human activities during the past several hundred years. Factors leading to their degradation include: timber harvesting, unsustainable agriculture, overgrazing by domestic animals, and intensive harvesting for fuel. In extreme cases, the land has become completely denuded. Attempts to reverse this process of land degradation have been initiated in this region of southern China. Over the last few decades, large areas have been reforested with a native pine species, Pinus massoniana, to prevent further degradation to the landscape. Cutting of trees is now prohibited, but harvesting of the understory and collection of litter is still allowed to satisfy local fuel needs. Compared with whole-tree harvests, this practice removes less biomass from the forests; however, as the understory and litter are relatively nutrient-rich, this practice may slow or prevent the recovery of soil fertility and productivity of these forest ecosystems. The objective of this study was to determine the effects of harvesting understory plant species and litter on nutrient accumulation dynamics in a Pinus massoniana forest of subtropical China. The results are used to address the following questions: 1) How are nutrients distributed in plants of this pine forest; 2) What quantity of nutrients are removed annually from the ecosystem by the practice; 3) Is this harvesting practice sustainable or not; 4) What alternative management options are available for continued use to meet fuel needs while at the same time improving site fertility, productivity and regeneration processes; and, 5) How do stressed ecosystems respond when the stressors are removed, that is, how would the forest respond if the harvesting practice was stopped. In order to achieve the objectives above, an experiment was established in a MAB reserve of subtropical China in May 1990. The experiment was a paired-plot design with 20 replicates. Each pair consisted of a treatment (continued harvest) and control (no harvest) plot, 10 m×10 m in size and surrounded by a 10 m wide buffer strip. In the treatment plots, local people continued to harvest litter and understory plants according to local practice (about 2－3 times a year) from the beginning of the experiment in May 1990. The harvesting according to local practice occurred during the period of 1990 to 1995 and was stopped after this time. Control plots were protected from any harvesting. Each set of paired plots was similar in soil, slope, aspect, and elevation. In this paper we report only the results of nutrient dynamics and its responses to human impacts over a ten-year period from 1990 to 2000.

Key words: Human impacts, Harvesting practices Forest degradation, Forest restoration, Nutrient dynamics, Pinus massoniana, Dinghushan, Subtropics