Weeds and soil erosion in a montane agro-ecosystem of Northern Thailand: a multidisciplinary analysis

In Mountainous South-East Asia, rapid agricultural intensification and the expansion of rubber tree plantations in the past decades led to drastic biodiversity losses and intense soil degradation. Weeds provide diverse ecosystem services, including soil protection and support for biodiversity at higher levels. However, the determinants of weed communities in mountainous areas of Southeast Asia, and the interactions of these communities with soil characteristics and erosion processes, are still largely unknown. We conducted soil characterisation and botanical inventories in Huai Lang, Northern Thailand, in 20 fields from different land uses along the transition from annual crops to mature rubber tree plantations twice a year from 2016 to 2018. Using 1m2 erosion microplots, we also measured runoff and soil erosion in different land uses, and in rubber tree plantations under different weeding practices. We show that weed communities composition was mostly determined by land use and landscape characteristics, while crop temporal variability was an important determinant of plant diversity. Rubber tree plantations had specific weed communities and had exceptionally high soil detachment rates compared to maize or young plantations, but weed cover was effective in decreasing these erosion rates. Altogether, our results suggest that soil and plant biodiversity conservation in mountainous Southeast Asia should involve both on-field adaptations (e.g. less intense weeding practices, especially under rubber tree plantations) and landscape-scale management programs, with a focus on maintaining landscape diversity.