西双版纳热带森林动态监测样地——树种组成与空间分布格局

 西双版纳热带雨林是中国生物多样性最丰富的生态系统之一，西双版纳也被公认为国际上重要的生物多样性保护的热点地区之一。2007年，在中国科学院生物多样性委员会、加拿大Alberta大学和中国台湾东海大学等相关单位的支持下，由中国科学院西双版纳热带植物园和西双版纳州自然保护区管理局在西双版纳州勐腊县补蚌村的望天树(Shorea wantianshuea)林中建立了一块面积为 20 hm²的热带森林动态监测样地，该样地是中国森林生物多样性动态监测网络建设的重要组成部分之一，其建设技术是按照美国史密森热带研究所的热带森林研究中心(Center for Tropical Forest Science, CTFS) 1980年在巴拿马Barro Colorado Island建立50 hm²样地的技术规范进行的。我们逐一测量并记录了样地中所有树干胸径大于1 cm树木的胸围，并对其挂牌标记、鉴定种名和确定坐标位置。并应用Ripley’s L-Function分析了样地内4种上层优势种和12个稀有种的空间分布格局。研究结果表明：样地内共含有胸径 ≥ 1 cm的乔木95 834株，其中已经鉴定的有95 498株，占总个体数的99.65％；有乔木种类468种 ，隶属于213个属和70个科；另外有336个个体没有鉴定出来，仅占总个体数的0.35％。上层乔木中的望天树重要值排名第2，但具有最大的胸高断面积；中、下层的假海桐(Pittospo ropsiskerrii)个体数最多，占样地内已鉴定乔木个体总数的21.90％。样地内4个上层优势种的小径阶个体数量较多， 而大径阶个体数量较少，径阶分布呈倒“J”型，因此这4个种群可以维持自我更新。在分布格局上，样地内的4个上层优势树种的幼树和中龄树以聚集分布为主，而成年树则以随机分布为主。另外，大多数稀有物种也表现出聚集分布的格局。

ESTABLISHMENT OF XISHUANGBANNA TROPICAL FOREST DYNAMICS PLOT:SPECIES COMPOSITIONS AND SPATIAL DISTRIBUTION PATTERNS

Aims Tropical seasonal rain forest in Xishuangbanna is one of the most species-rich forest ecosystems in China. This area is also one of the biodiversity hotspots for conservation priorities of the world. For the purpose of monitoring long-term dynamics of tree populations, a 20-hm² plot was established in a dipterocarp forest in Mengla Nature Reserve in 2007 by Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences and Xishuangbanna Administration of Nature Reserves, in collaboration with Alberta University, Canada and Tunghai University (Taiwan, China). 
Methods The construction technology and field protocol followed those applied in the establishment of the 50 hm² plot in the tropical forest of Barro Colorado Island in Panama, developed by Center for Tropical Forest Science, Smithsonian Tropical Research Institute in 1980. All free-standing trees with diameter at breast height (DBH) ≥ 1 cm were tagged, mapped, measured (girth) and identified to species in the plot. Spatial distribution patterns of four dominant canopy tree species  (among different tree size classes) and 12 rare species were analyzed by using a point pattern analysis Ripley’s L-function.
Important findings A total of 95 834 free-standing individuals with DBH ≥ 1 cm were recorded in the 20 hm² plot. Of which, 95 498 individuals were identified to species level. This plot included 468 species belonging to 213 genera and 70 families, except for another 336 individuals that could not be identified yet. The flora of plot was mainly composed of species in tropical families. Shorea wantianshuea that dominates the forest canopy was ranked the second in terms of importance value, although it had the largest basal area. Pittosporopsis kerrii, an understory tree species showed the highest abundance (20 918 individuals). The four canopy species had a large number of juveniles and exhibited size structures with reverse-J shape associated with continuously regenerating populations. Young trees (saplings and poles) revealed a clumped spatial distribution, but adults tended to have a random distribution. Most of the 12 rare tree species in the plot also showed aggregated distribution pattern.