Conversion of forest to rubber plantation has been the most important driver of land-use change over the past four decades in Xishuangbanna. Currently, a popular practice to improve soil quality in the region is to develop rubber/tea association, i.e. rubber trees which are intercropped with tea plants (Camellia sinensis). However, little is known about the effectiveness of this system for runoff and erosion control. The effect of the litter layer on practical soil conservation activities in the rubber monoculture or rubber/tea agroforestry practice is also relatively understudied.

Prof. LIU Wenjie and his team of Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences conducted a study to investigate the influence of the litter layer and undergrowth intercrops (tea plants) on surface runoff and soil erosion in rubber monoculture and rubber/tea agroforestry.

Their field experiment selected rubber monoculture and rubber/tea agroforestry system with litter removed (i.e. with bare soil or with undergrowth only), and with litter intact (i.e. with litter or with litter plus undergrowth) as the treatment and control stands.

Their study showed that over the entire rainy season, the cumulative runoff from plots with bare soil was 1.7 and 2.3 times higher than plots with a litter layer, and with litter layer plus undergrowth, respectively. Rubber/tea agroforestry with a thick, intact litter layer was more effective in runoff and erosion control than rubber monoculture.

In the early rainy season when litterfall was considerably abundant, runoff and soil erosion in both the litter plots and litter plus undergrowth plots were significantly lower compared to the bare soil plots, or plots with only undergrowth.

However, in the late rainy season when litter coverage became less than 40%, runoff and soil erosion in plots with litter layer or litter plus undergrowth were no longer significantly lower than those in the bare soil or undergrowth plots.

The results indicated that the thick, intact floor leaf litter was an important soil protection agent, and that the undergrowth plants add relatively little extra protection. Litter layer had an immediate effect in reducing both runoff and soil erosion.

The study entitled “The effect of litter layer on controlling surface runoff and erosion in rubber plantations on tropical mountain slopes, SW China” has been published in CATENA.

Rubber plantation with thick and intact litter layer (L) and Rubber plantation with litter decomposed (R) (Image by LIU Wenjie)