ObjectiveThis paper aims to investigate the characteristics and relationships between soil bulk density and biomass of unstable slopes in debris flows for different climate types, which is a prerequisite for ecological restoration based on local conditions and is very important for the accurate assessment of the stable development and changes of the ecosystem in this region.

MethodThe temperate humid mountain ridge region (Dadi shady slope, Xiaojianfeng sunny slope), subtropical and warm temperate subhumid region (Duozhao Gully sunny slope), subtropical dry-hot valley region (Daaozi Gully shade slope, Chajing Gully sunny slope) for the Jiangjiagou Basin were selected as a study area. Taking the stable area, the unstable area and the accumulation area of the unstable slope of each climatic region as the sample plot, and conducting vegetation community surveys, plant and stratified soil sample (0−5 cm, 5−10 cm, 10−20 cm) collection, then soil bulk density, and the biomass of the aboveground and underground parts of the plants were determined.

Result(1) The biomass of arbor in subtropical and warm temperate subhumid region was significantly higher than that in temperate humid mountain ridge region (P < 0.05). However, the biomass of litter was significantly higher in temperate humid mountain ridge region than in subtropical and warm temperate subhumid region (P < 0.05). In unstable slopes of subtropical dry-hot valley region without trees, aboveground biomass, underground biomass and total biomass showed stable area > unstable area > accumulation area (P < 0.05). (2) The relationship between aboveground biomass and underground biomass of herbaceous plants with unstable slopes in different climatic regions was in accordance with the allometric growth model of root and crown, showing a steady growth ratio. (3) In general, climatic factors and section factors and their interactions had significant effects on biomass and stratified soil bulk density (P < 0.05), however, in this study, the soil bulk density of unstable slopes in different climate regions had little spatial variability, showing weak variability. (4) With the increase of soil bulk density of 0−5 cm, the underground and aboveground biomass and total biomass all decreased, however, there was no significant change in the root shoot ratio.

ConclusionThis study elucidates the spatial distribution pattern of soil bulk density, underground biomass, aboveground biomass and root/canopy ratio along the environmental gradient in the watershed with frequent debris flow. The systematic analysis of the relationship between them will be conducive to the analysis of the regulation characteristics of environmental factors, and is of great significance for further ecological restoration research on the effects of environmental factors.