西双版纳不同斑块望天树种群的密度、结构和生物量

DENSITY,STRUCTURE AND BIOMASS OF PARASHOREA CHINENSIS POPULATIONS IN DIFFERENT PATCHES IN XISHUANGBANNA,SW CHINA

根据5个不同斑块的野外调查数据,分析了残存分布在西双版纳的国家一级保护稀有树种望天树(Parashorea chinensis)的种群密度与数量、年龄结构与生物量动态,组建了不同生长发育阶段的望天树个体生长与年龄的回归模型、个体生物量模型及种群年龄结构模型,编制了不同斑块的望天树种群及整个种群的静态生命表、存活曲线和年龄结构图。结果表明,不同斑块的望天树种群因种群年龄及所受到的干扰方式的不同,其种群密度和年龄结构差异很大,不同年龄阶段的死亡率也不同。面积最小的斑块缺乏成熟个体,并出现龄级结构缺省的现象。不同斑块局部种群的生物量随林龄的变化近似于Logistic增长,但各斑块局部种群的最大生物量以及生物量随时间的动态变化有所不同。整个种群的年龄结构为稳定增长型种群,1～60龄的种群个体的死亡率随林龄的增加而下降,60～150龄的个体死亡率随林龄的增加而上升,180龄后种群呈现生理衰退,个体出现死亡高峰。种群的生物量在180龄前呈Logistic增长,此后,生物量下降。部分斑块受到严重的人为干扰,已严重威胁其局部种群的生存。

Aims Parashorea chinensis, an endangered plant listed as the first class protected in China, now survives in local fragmented forests in Mengla, Hekou in Yunnan and Bama, Tianyang, Longzhou, Napo in Guangxi. We developed regression models for individual growth, age structure and biomass and analyzed population density, age structure, biomass dynamics and survivorship curves for local populations and the entire population in Mengla, Xishuangbanna, Yunnan Province, SW China. Our objective was to understand the population dynamics to aid protection of this endangered plant. Methods We established different numbers and sizes of plots （50 m × 20 m or 100 m × 20 m ） in five local patches according to patch size, and each plot was divided into 10 m × 10 m subplots to measure the height, diameter at breast height （DBH） or basal diameter and crown of each individual 〉 0.5 m height. We also measured height, basal diameter and crown of each individual 〈 0.5 m height in 2 m × 2 m quadrats in each subplot. Important fitulings There were large differences in population density and age structure as well as mortality rate for different age stages of local populations in different patches. The local population density of the patch in which some trees were cut was 3 - 4 times as much as the patch which was protected and 16 - 18 times as much as the patch which was planted with Amomum villosum. Moreover, the local population of the smallest patch had no mature individuals and lacked individuals in some age stages. Although the biomass of local populations showed logistic increase with stand age, maximum biomass and biomass dynamics with time were different for local populations. The survivorship curve of the entire population was approximately a straight line, indicating that the age structure of entire population was stable and increasing. The mortality of 1 - 60 year-old individuals declined, mortality of 60- 150 year-old individuals increased with age, and peak mortality occurred after 180 years. The biomass of the entire population was consistent with logistic growth before 180 years and was at a maximum at about 180 years. However, some patches had been so badly disturbed that the local populations were on the edge of extinction. Effective steps must be taken to protect this endangered plant population.