关键词: 凋落物, 城市森林, 持水特性, 拦蓄能力, 失水性

Abstract: Litter of urban forest plays an important role in dispersing precipitation and mitigating surface runoff to address urban waterlogging. In this study, we explored litter accumulation and hydrological effect in each decomposition layer in Nanhu Park of Changchun City through field investigation and laboratory experiments, with litter of five common tree species including Mongolian oak (Quercus mongolica), Asian white birch (Betula platyphylla), Mongolian pine (Pinus sylvestris var. mongolica), Chinese pine (Pinus tabuliformis), and Manchurian fir (Abies holophylla). The results showed that the thickness of litter layer had a positive correlation with the accumulated amount of litter. Litter thickness of Mongolian oak was significantly higher than that of the other species  in the un-decomposed layer (P<0.05), while that of Mongolian pine and Chinese pine were significantly higher than that of the other species in the semi-decomposed layer (P<0.05). Litter accumulation of the undecomposed layer ranged from 2.44 to 9.06 t·hm^-2, and that of semi-decomposed layer ranged from 3.85 to 11.79 t·hm^-2, with higher values in Chinese pine and Mongolian pine forests. With increasing soaking time, water-holding capacity of litter firstly increased, then tended to be stable and finally reached saturation. The fitting curve of water-holding capacity (both proportion and content) of the two decomposition layers of different forest stands with soaking time showed a power function relationship (Y=at^b). The maximum water-holding capacity of the undecomposed layer was 4.52 to 18.72 t·hm^-2 across different species, with Mongolian oak being significantly higher than the other four species (P<0.05), while the maximum water holding-capacity of the semi-decomposed layer was 6.00 to 27.51 t·hm^-2. The water-holding capacity of broad-leaved forests was significantly better than that of coniferous forests in un-decomposed litter layer, while the semi-decomposed litter layer of coniferous forests performed better in water-holding capacity. Stand age was one of the important factors regulating the hydrological characteristics of litter. The maximum water loss ranged from 2.58 to 8.00 t·hm^-2 in the un-decomposed layer, and from 2.39 to 13.78 t·hm^-2 in the semidecomposed layer. Chinese pine litter had significantly higher maximum water loss than other species (P<0.05). Our results suggested that Mongolian oak pure forest, or Mongolian oak, Chinese pine and Mongolian pine mixed forest could be considered in future urban park planning for urban waterlogging mitigation in Changchun and other cities with similar site conditions, since they can maximize the hydrological ecological function of urban forests, solve the problems of urban waterlogging and groundwater level decline, and help construct sponge cities in China.

Key words: litter, urban forest, water holding characteristics, storage capacity, loss of water.