Objective To study the impacts of forest age on hydrological functions of humus.

Method Four Larix principis-rupprechtii plantations (mature, near mature, middle age and young) at Xiangshuihe Watershed in Liupanshan were selected in June 2017. The hydrological functions of litter of these L. principis-rupprechtii plantations were surveyed by investigating the stand structure and measuring the amount, thickness and water holding capacity of litter accumulation.

Result (1) The thickness of litter ranged from 4.5 to 6.0 cm, the total accumulation was 29.0833.21 t·hm^-2, and the storage of semi-decomposed layer were higher than that of the undecomposed layer. The thickness and accumulation of litter in these plantations were found in the order of mature forest > near mature forest > middle age forest > young forest. (2) The litter of mature forest had the maximum water holding capacity which was between 79.47 and 110.05 t·hm^-2. The middle aged forest had the highest change rate of water holding capacity, which varied from 273.32% to 341.27%. (3) Dynamic relationship between water holding capacity and soaking time of litter of all these plantations was similar. The water absorption rate of the litter was the highest within 0.5 hour, and the variation of water absorption rate tended to be gentle after 4 hours. The water content of the litter was basically saturated after 10 hours, the relationship between water holding capacity and soaking time followed a significant logarithmic relationship (R²>0.92). (4) The valid water-interception capacity of litter was between 43.64 and 70.52 t·hm^-2, the mature forest had the strongest intercepting capacity.

Conclusion The hydrological function of litter reaches their maximums in mature forest. The results of this study can be used as a reference for the research on hydrological process of the litter layer of L. principis-rupprechtii plantation.