Effects of understory vegetation on infiltration capacity in Japanese cypress plantation

Abstract

To examine the effects of understory vegetation on infiltration capacity, a series of field infiltration test was conducted by using an oscillating nozzle rainfall simulator at 14 sites in steep Japanese cypress plantation. The simple regression analysis among the maximum final infiltration rate (FIR max), percentage vegetation cover and dry weight of surface cover materials such as understory vegetation were also conducted. The FIR max for the 14 sites ranged from 5 to 322 mm h-1, and significant correlations were found between the FIRmax and the dry weight, percentage cover of understory vegetation. The lower FIRmax was observed at the site where the percentage vegetation cover was less than 50%, suggesting that Hortonian overland flow may occurs under natural rainfall. This indicated that the cover abundance of 3 or less based on the Braun-Blanquet's method may result in the significant reduction in infiltration rate. The results indicate that densely vegetated surface can maintain high infiltration capacity on forested steep hillslopes, and cover abundance of the Braun-Blanquet's method were useful to estimate infiltration capacity in Japanese cypress plantation. This study suggested that the measurement of understory vegetation cover can be used to assess the degradation of unmanaged Japanese cypress plantation, and to establish soil and water conservation practice based on the management of infiltration capacity.