Response of Hydro-Ecological Functions of Natural Secondary Forest Litter Layer to Different Stand Densities in Mountainous Area of Northern Hebei Province

In order to study the hydrological and ecological functions of the natural secondary forest litter layer in different density areas in the Mountain area of northern Hebei Province, the hydro-ecological effects of litter layers of five dense natural secondary forests were quantitatively measured by indoor immersion method. The results showed that:(1)the litter thickness ranged from 45.34 mm to 60.70 mm, and the accumulations ranged from 11.56 t/hm2 to 19.64 t/hm2. The litter thickness decreased in the order: 930 trees/hm2>1 190 trees/hm2>780 trees/hm2>520 trees/hm2>280 trees/hm2;(2)the maximum water holding capacity of litter layer ranged from 23.26 t/hm2 to 44.67 t/hm2, 21.15 t/hm2 to 39.56 t/hm2 and 17.66 t/hm2 to 32.86 t/hm2, respectively; the maximum water holding capacity decreased in the order: 930 trees/hm2>1 190 trees/hm2>780 trees/hm2>520 trees/hm2>280 trees/hm2;(3)there was a logarithmic function relationship between litter water holding capacity and soaking time(R2>0.93), and a power function relationship between litter water holding rate and soaking time(R2>0.99);(4)the comprehensive water holding capacity and retention capacity of litter layer showed that the ecological and hydrological effect of 930 trees/hm2 stands was the strongest, while the hydrological and ecological function of other densities was relatively poor. Therefore, effective tending measures for the natural secondary forests with too high or too low density in this area can be conducive to increasing the water conservation capacity of the stands.