Runoff and soil erosion responses to rainfall and vegetation cover under various afforestation management regimes in subtropical montane forest

Abstract

Abstract Soil erosion and runoff generation are a major concern in forest and agricultural ecosystem management. However, the tangled coeffects of rainfall and vegetation on runoff and erosion generation are regionally dependent and remain unclear in regions with high erosivity, such as Southeast China where the large‐scale afforestation is being implemented. Here, we present the 4‐year observations of runoff and erosion responses to various storms following three afforestation (assisted natural regeneration [ANR; windrowing harvest residues on surface]; Chinese fir cultivation [YCF]; and Castanopsis carlesii cultivation [YCP] after slash‐and‐burn) since 2012. Stepwise power‐law regressions were used to identify the key variables and formulate the responses. Results show that the YCF and YCP following slash and burn have extremely high erosion rates, over 20 t ha −1 yr −1 (twofold higher than the global tolerable threshold), during the first year. In contrast, the erosion rate is only approximately 1.3 t ha −1 yr −1 in the ANR. The high erosion rates reveal the environmental vulnerability and the necessity of management in this region. Stepwise regressions suggest total rainfall rather than rainfall intensity as key variable probably because the forest canopy substantially offsets raindrop kinetics. The nonlinear runoff and erosion responses indicate that the risk of soil erosion is extremely high when vegetation cover is less than 40% and rainfall is greater than 80 mm. This study, therefore, suggests that windrowing harvest residues into strips or maintaining a vegetation cover greater than 40% is a sound management practice for mitigating land degradation in this region.