Soil amelioration through afforestation and self-repair in a degraded valley-type savanna

• Tree species control soil amelioration processes in a degraded valley-type savanna.
• Soil physical constrains are difficult to ameliorate, compared with biochemical constrains.
• Leucaena leucocephala and Acacia auriculiformis are recommended for soil amelioration.
• Self-repair of degraded savanna is also recommended for soil amelioration.

Land degradation and soil deterioration are key environmental problems in the savanna of southwestern China. Restoration programs require scientific information about tree species that represent the best options for rehabilitating degraded lands and about the responses of key edaphic constraints to these tree species. Five plantations (Leucaena leucocephala, Albizia kalkora, Acacia auriculiformis, Azadirachta indica and Eucalyptus camaldulensis) and one self-repair treatment were established to restore a degraded savanna, and soil properties associated with these treatments were investigated four times during 22 years of vegetation restoration.The results showed that treatment and sampling time have significant effects on the soil properties of the degraded savanna following vegetation restoration. Soil physical properties improved slowly relative to its microbial and chemical properties. After 22 years of vegetation restoration, soil amelioration via self-repair mechanisms was more successful than via the planting of A.kalkora, A.indica and E.camaldulensis but was inferior to or close to the planting of L.leucocephala and A.auriculiformis.The tree species control the soil amelioration process in the degraded savanna. The manual restoration of vegetation (i.e., afforestation) could not always accelerate soil amelioration relative to natural restoration (i.e., self-repair) in the savanna. L.leucocephala and A.auriculiformis are recommended as pioneer trees for soil amelioration of the degraded savanna. The cost-free self-repair of the degraded savanna is also a recommended approach to soil amelioration.