Water conservation capacity of litter layer and soil layer in typical forest stands in the North China rocky mountain area

The North China mountainous region is a vital water conservation area for the Beijing-Tianjin-Hebei region． However, the forest ecosystems struggle to effectively meet regional water security demands due to issues such as monotonous stand structures and degraded water conservation functions in planted forests． In this study water conservation capacities of litter layers and soil layers across five typical forest stands (chestnut, locust, populus, pinustabulaeformis, Thujaorientalis) were compared to enhance ecosystem stability, to promote ecological restoration, and to establish water conservation forests． Samples were collected in field surveys, hydrological effects of litter and soil layers were measured and analyzed (by weighing, laboratory soaking, ring-cutting, and regression analysis)． Water conservation capacity was evaluated in entropy weight analysis． Among litter layers, chestnut exhibited significantly higher total thickness (5.41 cm) and maximum water-holding capacity (15.35 t·hm²) than other stands (P<0.05), with undecomposed layer accounting for over 60% of water retention． Poplar litter total thickness (4.96 cm) equaled that of locust tree, significantly exceeding oil pine (4.04 cm) and Chinese juniper (4.55 cm) (P<0.05). Maximum water holding capacity (14.7 t·hm²) ranked only below chestnut． The water-holding capacity of litter in all five forest stands exhibited logarithmic growth with immersion time (R² > 0.9), and natural moisture content showed a strong negative correlation with effective storage capacity (r = −0.753, P < 0.01). In the soil layer, chestnut exhibited the highest total porosity (30.3%) and saturated water storage capacity (3188t·hm²), while black locust had the highest soil bulk density (1.43 g·cm³), significantly inhibiting water-holding capacity (P<0.05)． The effective water storage capacity of Chinese juniper and Chinese pine was only 60%–70% that of chestnut． Comprehensive evaluation indicated that the water conservation capacity followed the rank of: chestnut (0.23) > poplar (0.22) > locust (0.2) > pine (0.18) > cypress (0.17)． Chestnut and poplar should therefore be prioritized as core tree species for promotion in shallow mountain watersheds and slope farmland restoration areas, leveraging their synergistic water retention advantages through litter and soil layers． Arborvitae and pine can serve as native companion species for mixed planting in rocky mountainous areas, to balance ecological adaptability with water conservation functions．