Abstract: [Objective] In order to explore the ecological consequences caused by secondary earthquake disasters and to provide scientific evidences for disaster-affected soil restoration, the physical and chemical properties of forest soil in Li County, Sichuan Province, were investigated comparatively. [Method] Wenchuan earthquake happened on May 12^th, 2008, and the investigation and sampling in Cupressus chenginana plantation of disaster-affected area was conducted in November, 2013. Three earthquake-affected stands and one stand as control (no obvious damage caused by secondary earthquake disasters) were chosen in Xionger Mountain (mountain cinnamon soil), and two earthquake-affected stands and one control stand were chosen in Puxi Gully (mountain brown soil). Soil physical properties such as soil density, total porosity and particle composition in 0-20 cm soil layer were measured. Meanwhile, soil nutrient indices such as soil pH value, total nitrogen (TN), alkali-hydrolysable nitrogen (AN), available phosphorus (AP), available potassium (AK), soil organic matter(SOM)content and cation exchange capacity (CEC) in three soil layers (0-20, 20-40, and 40-60 cm) were also analyzed. [Results] Soil density in 0-20 cm soil layer was significantly increased in the earthquake-affected sites, the average value of earthquake-effected soils was 1.28 g·cm^-3. In comparison with the controls, average values of soil density were increased by 6.1% and 18.6% in Xionger Mountain and Puxi Gully, respectively. The increased soil density caused the reduction of total soil porosity (a significant negative relationship between them, r=-0.998^**), which brought in a reduction of soil water permeability and an increase of surface runoff and soil & water erosion. Affected by secondary earthquake disasters, the average soil organic matter contents were decreased by 56.1% and 52.2% in Xionger Mountain and Puxi Gully, respectively. Meanwhile, clay contents in surface soil (0-20 cm) decreased by 54.8% and 57.1% on average, respectively. But soil sand and silt contents increased significantly. The soil pH values were significantly increased at different soil depths (0-20, 20-40, and 40-60 cm) in both of the two study sites, and the average pH value was increased by 11.5%. The variability of pH value showed no significant relationship with the soil type and soil depth. The decrease of soil organic matter content and loss of soil clay content may be the main causes for the increase of pH value. Affected by secondary earthquake disasters, soil TN, AN, AP and AK contents were decreased significantly. The AP and AK contents were decreased by 67.1% and 72.2% in Xionger Mountain, meanwhile, decreased by 80.3% and 78.0% in Puxi Gully, respectively. Content of SOM was positively correlated with contents of TN, AN, AP, AK and CEC, respectively. The CEC values in earthquake-affected soils from both investigated areas were significantly decreased by 79.7%-90.3%. The soils showed a very low capacity in maintaining soil water and nutrient. The changes of soil C/N ratio indicated that the C loss was higher than the N loss in earthquake-affected soils. [Conclusion] Affected by secondary earthquake disasters, the soils of Cupressus chenginana plantation in this study showed severe soil degradation: Increase of soil density, decrease of soil porosity, increase of soil pH value, loss of soil clay and nutrients and reduction of soil CEC. It is recommended that the soil remediation measures in the studied forest soils should be focused on the following aspects: increasing soil organic matter, improving soil water and nutrient retention, and reducing loss of soil clay.

Key words: Forest soil, physical and chemical properties, nutrients, Wenchuan earthquake, ecological restoration, Cupressus chenginana plantation, secondary earthquake disasters, Li County