Abstract:

Amomum villosum is a perennial herb that occurs in the understory of tropical and subtropical forests and is an important medicinal plant. A. villosum, native to Guangdong Province, was introduced intentionally to Xishuangbanna, Yunnan in 1963 and was planted under tropical rainforests. Farmers often thin out some of the canopy trees (5%-85%) when they grow this plant for commercial purposes in these primary forests, resulting in a loss of biodiversity in these forests. A. villosum fruit yield is low and varies greatly among fields and years due to the crude cultivation method. The area of primary rainforest is much smaller than secondary forests in Xishuangbanna. The influence of A. villosum cultivation on rainforest biodiversity, biomass, and net productivity was significant, but the influence on secondary forests was negligible. To improve A. villosum yield and to protect rainforest biodiversity, we explored the possibility of cultivating A. villosum in secondary forests. Plant density, biomass, biomass allocation, and fruit yield were measured in A. villosum cultivated in tropical wet seasonal rainforests and secondary forests in Xishuangbanna. The density and biomass of vigorous plants were 72.60% and 85.29% of the total plants in the secondary forest and 71.27% and 86.69% in the rainforest and was significantly higher than those of other plant types. The density of shoots, seedlings, and senescent plants were not significantly different within the same forest types, but the biomass of senescent plants was significantly higher than that of shoots and seedlings. The sum of shoots and seedlings in secondary forest and rainforest were 1.45 and 2.18 times of senescent plants, respectively, indicating that A. villosum populations could be maintained. In the rainforest, many A. villosum seedlings were old and most of them grew poorly and could not develop into normal, healthy and vigorous plants. It is worthwhile to note that the A. villosum yield was very low, stem biomass ratio was very high (above 0.58), and fruit biomass ratio was extremely low (about 0.01). This suggests that increasing the yield potential of A. villosum could be achieved by improving biomass partitioning between the fruit and stem. In one of the experimental plots in the secondary forest, soil water conditions were improved by a rivulet, and fruit yield production was 211.149 0 kg•hm-2, much higher than that of other fields. Apparently, A. villosum cannot tolerate dry conditions and moderate dry periods might influence A. villosum yield. These yields were related to its low root biomass ratio and shallow root system. Leaf area index, biomass of both vigorous plants and other plants were significantly and positively correlated with fruit yield in A. villosum. Fruit yield and leaf area index were 105.034 5 kg•hm-2 and 2.908 2 in the secondary forest, and 60.931 9 kg•hm-2 and 2.560 0 in the rainforest, respectively. The density and biomass of the same plant types were not significantly different between the secondary forest and the rainforest. These results suggest that A. villosum can be cultivated in secondary forests.