西双版纳原始热带季节雨林净初级生产力

THE NET PRIMARY PRODUCTION OF THE TROPICAL SEASONAL RAIN FOREST IN XISHUANGBANNA

研究了西双版纳原始热带季节雨林生物量增量、凋落量、叶虫食量和净初级生产量。该雨林年平均净初级生产量为２５．７６４ｔ／ｈｍ２·ａ，其中各层次的净初级生产量分别为：乔木层２３．９７２ｔ／ｈｍ２·ａ（占总净初级生产量的９３．０４％）、灌木层０．７４９ｔ／ｈｍ２·ａ（占２．９１％）、木质藤本层０．４３１ｔ／ｈｍ２·ａ（占１．６７％）、草本层０．６１２ｔ／ｈｍ２·ａ（占２．３８％）。乔木层净初级生产量分配为：凋落量１１．５６６ｔ／ｈｍ２·ａ、叶虫食量０．６９４ｔ／ｈｍ２·ａ和生物量增量１１．７１２ｔ／ｈｍ２·ａ。

The tropical rainforest area has high temperature and rich rainfall, so that among the forest ecosystems of the world,the rainforest is the most complex ecosystem with the highest productivity. Xishuangbanna(21 °09'～22 °33'N, 99 °58'～101 °50'E), southwestern China, borders on Laos and Burma, located in the north edge of tropical zones. In comparison with typical tropical rainforest zones, Xishuangbanna is cooler and has lower rainfall and there is a well_defined alternation of rainy and dry season. On the research site (21°58'N, 101 °12'E)in Menglun, Xishuangbanna, the annual rainfall was 1550mm, the 83% of the rainfall occurred in the rainy season (from May to October), and 17% of it in dry season (from November to April ), but from November to February of the dry season, it was much foggy, so the air was with high humidity. The annual mean temperature was 21.5 ℃, and the monthly temperature ranged form 15.5 ℃ in June to 25.3 ℃ in May. The representative vegetation is the tropical seasonal rainforest. In the research site, the rainforest was 48m high and the density of DBH≥5 cm trees was 949/hm 2. It is important for understanding tropical rainforest productivity and its variation in the world to research the productivity in this area. In this paper, the forest net productivity model of Pn = δB+L+G were used to study net primary production( Pn ) by measuring consecutively biomass accumulation( δB ), litterfall( L ) and leaf herbivory( G )in the fixed research site in the primary tropical seasonal rainforest in Menglun, Xishuangbanna. The result showed that the annual Pn of the rainforest was 25.764 t/hm 2·a, and the Pn of different layers in the raiforest were 23.972 t/hm 2·a (account for 93.04% of the rainforest Pn ) for tree layer, 0.749 t/hm 2·a (2.91%) for shrub layer, 0.431 t/hm 2·a (1.67%) for liana; and 0.612 t/hm 2·a (2.38%) for herb layer. The tree layer, which reached upper levels, had the highest Pn . The liana layer, which reached the upper too, had lower Pn due to a few individuals. The shrub and herb that grew in very low light understorey had very low Pn . The organ allocation of the Pn of tree layer were 8.239 t/hm 2·a for stems; 7.088 t/hm 2·a for leaves; 3.988 t/hm 2·a for branches; 2.611 t/hm 2·a for roots, 1.848 t/hm 2·a for fruits. 0.198 t/hm 2·a for flowers. Among the Pn of the tree layer, the loss by litterfall and insect leaf herbivory was 11.566 t/hm 2·a and 0.694 t/hm 2·a respectively, the remaining in the forest as biomass accumulation was 11.712 t/hm 2·a . It was concluded that in Xishuangbanna, the north edge of tropics, the primary tropical seasonal rainforest has the Pn as high as that of typical tropical rainforest.