In Xishuangbanna, dramatic land-use changes have occurred due to the rapid increase in monoculture rubber plantations at the expense of tropical rainforests. Previous studies have shown that the conversion of tropical rainforests to rubber plantations has resulted in high bulk densities and compact and crusted soil. However, little is known about other soil physical properties (i.e., soil porosity and water storage capacity) and their relationships with sediment yield in this region.
Prof. LIU Wenjie and his team of Xishuangbanna Tropical Botanical Garden (XTBG) measured the effects of changes in soil physical properties and vegetation traits on runoff and sediment yield under different types of land use in Xishuangbanna.
The researchers chose the tropical rainforest, rubber monoculture and four rubber-based agroforestry systems representing different land-use types in Xishuangbanna. They compared the effects of land-use changes by employing space-for-time substitution (SFT), a tool used for estimating vegetation status and environment at separate locations.
The results showed that conversion of tropical rainforest to rubber monoculture resulted in unfavorable vegetation (i.e., low leaf area index, low canopy cover) and soil conditions (i.e. low porosity and low hydraulic conductivity) as well as less litter.
Those drawbacks reduced rain water infiltration and thereby increased surface runoff and sediment yield, which could ultimately cause land degradation.
Compared with rubber monoculture, the runoff and sediment yield in rubber-based agroforestry systems decreased, because of the partial improvement in soil physical properties (i.e., lower bulk density, higher field capacity) and increased protection provided by the multi-layered canopy or litter layer.
The researchers thus recommended that local governments and farmers should consider intercropping F. macrophylla and T. cacaotree species within rubber monoculture plantations in Xishuangbanna.