Ecological changes along the transition from annual crops to rubber plantations in Northern Thailand

In the past decades, mountainous areas of North-East Asia have been subject to severe environmental degradations due to population growth and land-use changes. In particular, the transition from annual to perrenial crops such as rubber (Hevea brasiliensis) plantations could have important consequences on biodiversity and erosion control, which might be alleviated by enhanced management of non-cultivated biodiversity. In this study, we investigate the relations between soil physical properties (bulk density, humidity), weed communities (composition, abundance) and management practices (use of herbicides, fire) in two small catchments of Huai Lang, Thailand. A nested sampling protocol was set and we sampled 20 plots from 4 main land-use types along the transition (upland rice, maize, young rubber plantations, mature rubber plantations). We found distinct plant communities (“clusters”) for A. rice fields, B. maize and young rubber plantations and C. rubber plantations, with rice fields having the richest and most abundant communities. Herbicide practices appeared to have unconsistent effects on communities' composition and abundance. Regarding soil characteristics, soil humidity was higher in cluster C, where it decreased with plant densities; it increased with plant densities in cluster A. Surprisingly, soil bulk density was low in cluster C and globally decreased with plant abundance. Altogether, we found that weed communities, management practices, soil characteristics and landscape are closely intertwined. Further research is needed to investigate precise mechanisms underlying these interactions, in particular regarding adaptation of weeds' rooting systems