Characteristics of Suspended Solid Responses to Forest Thinning in Steep Small Headwater Catchments in Coniferous Forest.

We examined the responses of suspended solids to forest thinning in steep small headwater catchments, P_T (0.8 ha) and P_R (0.7 ha), that drain a Korean pine (Pinus koraiensis) plantation forest. Based on a paired-catchment design, the relationship between total suspended solids (TSS) and the time differential of water runoff (dQ/dt) indicated a difference in the characteristics of TSS in the rising and falling stages within the initial two years after forest thinning. The relatively high initial TSS responded to the concentration-based first flush criterion in the early stage of the rainfall event concentrated in this initial period after the thinning. The rate of TSS event loads in the P_T catchment was 4.3-fold greater than that in the P_R catchment within the initial two years after forest thinning. This was induced by the low disturbance of soil surface by forest workers using chainsaws and non-heavy machinery. Three years later, the TSS event loads in the P_T catchment appeared to decrease due to trapping and settling by protective vegetation. Therefore, mitigating accelerated TSS events during forest thinning requires appropriate site-specific land preparation, particularly for improving stream water quality in forested catchments. [ABSTRACT FROM AUTHOR]