Effects of land use changes on soil properties in Wolong Nature Reserve
卧龙自然保护区土地利用变化对土壤性质的影响

Natural secondary succession, forest planting and agricultural practices after deforestation or human disturbance affect soil properties in many aspects. Characterizing soil nutrients in relation to land use/land cover types and history is important for understanding how ecosystems work and assess the effects of future land use change. A study was initiated in Wolong Nature Reserve, Sichuan province, China to elucidate the complex relationships in the humid mountainous region. Six typical ecosystems (natural forestland, grassland, shrubby land, secondary forestland, cultivated land and reforested land) were compared.Significant differences among land use were found for soil bulk density (BD), total nitrogen (TN). Cultivated land had the lowest levels for most soil nutrients compared to other ecosystems and shrubby land had a higher soil organic carbon (SOC), total nitrogen (TN) and available nitrogen (AN). There was no much difference in 0-40 cm soil carbon mass between different land use practices. Soil carbon storage (TC) of different land use indicated that land use had a greater effect on SOC greater than on BD. The comprehensive soil deterioration index (DI) showed that the cultivated land, grassland and reforested land had the lower and negative values, while the shrubby land and secondary forestland had positive values, 12% and 1% respectively. The results gave a hint that in areas where the climate is fit for secondary succession "leave the nature as it is" is a better choice for the policy of "returning farmland to forest land" in China especially for the mountainous region lack of labor and finance support. Five reforestation periods were arranged from 0-10, 11-20, 21-30, 31-40 and 41-50 years. The results showed that reforestation could greatly change soil properties. The BD, SOC and TN were significantly different between the reforested periods, but the pH, TK, AN, AP and AK showed no significant trends.Further studies on the relationship of reforestation and the soil properties gave the results that the TC and TN had a good linear relationship with the reforested years and the DI index increased since reforestation.