Abstract: Preferential flow, a critical component of soil infiltration, affects water conservation capability of forest plantations, and threatens groundwater quality by facilitating the rapid downward migration of soil pollutants generated by forestry practices. Therefore, understanding the developmental characteristics of preferential flow during the rotation period of plantations can provide a scientific basis for their sustainable management. We investigated preferential flow characteristics during the rotation period of Chinese fir plantations in the Beijiang River Forest Farm in Rongshui, Guangxi, using methylene blue dye tracing. A multi-index evaluation method was employed to assess the relative development degree of preferential flow in Chinese fir plantations of different ages. The results showed that soil dyeing in Chinese fir plantations decreased with increasing soil depth, with the main infiltration area being 0-20 cm. The lateral preferential flow was the dominant infiltration mode of the soil infiltration process, which occurred at the beginning of infiltration. The preferential flow indicators for different aged Chinese fir plantations were in the order of 5-year-old (0.64) > 8-year-old (0.59) > 11-year-old (0.47) > 15-year-old (0.39). Our results indicated that lateral preferential flow predominates in the infiltration process of Chinese fir plantations, and that the degree of preferential flow development decreases with increasing forest age. The findings can provide a theoretical basis for the formulation of scientific forest management measures in Chinese fir plantations, and thereby can promote the sustainable management of plantations.

Key words: forest plantation, preferential flow, dye tracing, multi-index evaluation