A Preliminary Study on the Net Primary Production of the Secondary Tropical Forest in Xishuangbanna

Abstract

Vast areas of secondary tropical forest occur in Xishuangbanna owing to slash and burn cultivation and the destruction of tropical forest, which is a huge carbon and nutrient element bank. In order to know the dynamics of growth and bio_productivity of secondary tropical forests in different stages, “size class standard and “the dimension analysis methods were used to estimate the net primary productivity of four secondary tropical forests in different stand ages in Xishuangbanna. The results showed that the net primary productivity of four stands increases with stand age, which was 1 154.3 g·m -2·a -1 in 5_year_stand, 1 348.5 g·m -2·a -1 in 10_year_stand, 2 212.1 g·m -2·a -1 in 14_year_stand, and 2 660.1 g·m -2·a -1 in 22_year_stand respectively. The allocation of net primary productivity in four stands showed that annual net growth had the highest net productivity, which was 93.82%, 92.83%, 91.72% and 92.09% in four stands respectively, leaf grazed ranked the second and represented 4.97%, 3.92%, 5.23% and 3.96% respectively, and reproductive parts contributed 1.20%, 3.25%, 3.05% and 3.95% respectively. In the allocation of net primary productivity among different parts of plants in four stands, the net primary productivity of stem ranked the first, which occupied 35.79% of the total in 5_year_stand, 38.96% in 10_year_stand, 38.82% in 14_year_stand and 35.94% in 22_year_stand, and that of root was the second which made 23.03%, 21.38% and 23.18% of the total in 5_year_stand, 10_year_stand and 14_year_stand respectively except that of 19.26% of the total in 22_year_stand. Branch productivity increased with the stand age from 15.54% of the total in 5_year_stand to 23% of the total in 22_year_stand, while leaf contributed 23.53%, 17.81%, 18.50% and 18.49% of the total in four stands respectively which gradually decreased with the stand age. Although reproductive parts contributed only a little, it also increased from 1.20% of the total in 5_year_stand to 3.95% of the total in 22_year_stand. Concerning the allocation of net primary productivity in different layers of four stands, the net primary productivity of the tree layer increased with the stand age which was 69.07%, 74.52%, 66.07% and 93.74% of the total in four stands respectively, and net primary productivity of shrub layer did not increase until 14_year_stand, and then sharply dropped, which was 22.05% of the total in 5_year_stand, 19.49% in 10_year_stand and 32.24% in 14_year_stand, but only 2.96% in 22_year_stand, while the net primary productivity of the herb layer decreased from 8.01% in 5_year_stand to 4.41% in 10_year_stand, and that of liana plants increased with the stand age from 0.87% in 5_year_stand to 3.30% in 22_year_stand. The index of leaf area (LAI) in four stands increased with the stand age from 2.70 in 5_year_stand to 7.41 in 22_year_stand, which was lower than that of other forests. The optimum regression models of the organic growth of the dominant plants and the sample trees in arborous layer for four stands were built. These models can be used to estimate net primary productivity of the same secondary tropical forests in Xishuangbanna. Compared with other tropical forests, net primary productivity of 22_year_stand was higher than that of tropical seasonal rainforest (2 576.4 g·m -2·a -1) in Xishuangbanna, and net primary productivity of aboveground parts in 22_year_stand was also higher than that of a 20_year_stand of secondary tropical forest in Northeastern India. From the results, we can conclude that secondary tropical forest which regenerated from tropical rain forest after slash and burn cultivation in Xishuangbanna can grow fast under protection. So taking protective measures for vast secondary tropical forest is an effective way to speed recovery.