西双版纳片断热带雨林30多年来植物种类组成及种群结构的变化

通过对西双版纳景洪曼仰广的“龙山”片断热带雨雨林30年前后植物区系组成和样方调查资料的对比研究，探讨了30年来该“龙山”片断热带雨林植物区系组成、生活型及群落生态成分和乔木树种的种群变化规律。在植物区系组成上，已确认有种子植物7科53属55种从该片断雨林中消失。在消失的这55种植物中，属于群落顶级成分的有18种，属于耐阴的林下和层间植物有30种，喜阳种类有2种，广生态幅的随遇种有5种。初步得出该龙山热带雨林随着30多年的片断化，8．8％的科，26．8％的属和22．4％的种类消失或被后来的成分替换了。在生活型及群落生态成分变化上，群落中小高位芽及一年生植物相对增加，阳性植物明显增加，阴生（耐阴）植物明显减少，亦即雨林固有成分减少，非雨林成分增加。在乔木树种的种群变化上，过去该片断雨林的优势成份，绝大多数现在仍存在，多数仍在优势种之列，少数优势种衰退了，少数变得更优势。首先消失的种类，或为先锋树种（短命）或为种群数量很少的树种。

Over 30-Year Changes of Floristic Composition and Population Structure from an Isolated Fragment of Tropical Rain Forest in Xishuangbanna

The plant species loss, dynamics of tree population as well as speccies compostion were enumerated based on the comparative researches of floristic composition, physiognomy and plant diversity on a fragment of tropical rain forest isolated more than 30 years in a Dai's holy hill in Xishungbanna, south Yunnan. In 1958-1959, 246 native seed plant species in 196 genera of 80 families were recorded in the fragment. By this study, 55 species in 53 genera of 7 families have not been recorded in the inventory. Among these possibly lost 55 species, 18 are climax tree species of the tropical rain forest, 30 are shade-tolerant understorey species, 2 are heliophilic specis and 5 are indifferent species. After 30 year isolation, 22.4% species lost or was replaced by other species. In the percentage of species number across plant life from groups, the microphanerophytes, therophytes and heliophilic plants increased, while the shade-tolerant plants decreased by the comparison of species composition between the historical records and present inventory. In tree population dynamics, most of the former dominant tree species are still dominant, while a small portion of them has degenerated, and also a small portion of them has proliferated during the period of isolation. The pioneer species and those with a small population are easier to become extinct than other groups.