Effect of vegetation types on chemical and biological properties of soils of karst ecosystems

Inappropriate human activities have caused widespread reductions of forests and have produced degradation in karst regions of China. In the past two decades, numerous attempts have been made to promote recovery of the degraded soil using afforestation and natural regeneration approaches. A better understanding of the effects of vegetation types on the chemical and biological properties of the soil is very important for both reforestation approaches. Five vegetation types, namely, natural old-growth forest (>80 years old), grassland (15-25 years old), natural regeneration (20-25 years old), bamboo plantation (23 years old) and pine plantation (22 years old), were investigated in the Maolan karst area of Guizhou Province. The soil quality index (SQI) was evaluated with a cluster analysis and a principal components analysis to compare soil quality classes among the vegetation types. The results indicated that soil organic matter, the MBC/TOC ratio and soil basal respiration were the most important factors reflecting the general chemical and biological properties of the soil. Based on the SQI values, the soil quality under the selected vegetation types could be divided into three groups: low soil quality (pine plantation with SQI = 0.26 and grassland with SQI = 0.29), intermediate soil quality (bamboo plantation with SQI = 0.41 and natural regeneration forest with SQI = 0.46) and high soil quality (natural old-growth forest with SQI = 0.63). The results of this study suggested that the pure plantation of Pinus massoniana had a negative impact on soil quality and that natural restoration may represent a more effective approach to the improvement of soil quality in degraded karst areas. These results also showed a strong interaction between soil quality, nutrient dynamics and vegetation types.