Abstract: Quantitative analysis on the soil aggregates under dark coniferous forest,coniferous and broad-leaved mixed forest,fargesia under the gap of dark coniferous forest,and sclerophyllous oaks (Quercus semicarpifolia) at Wolong Natural Reserve in the upper reach of Minjiang River showed that wet-sieving soil aggregates were of logarithmic-normal distribution,and the geometric mean diameters were negatively correlated to geometric standard deviation.The aggregates under coniferous and broad-leaved mixed forest and sclerophyllous oaks had larger sizes than those under other vegetations.The range of fractal dimension of soil aggregates was 2.402.78,along with more aggregates less than 0.25 mm in size.The fractal dimension of soil aggregates under dark coniferous forest and fargesia were larger than that under other vegetations.The soil aggregates with 31 mm and 10.5 mm in size had a higher stability,while those with >10 mm and 0.50.25 mm in size were in adverse.The aggregate stability index of soil under coniferous and broad-leaved mixed forest was the highest,followed by that under sclerophyllous oaks,fargesia under the gap of dark coniferous forest,and dark coniferous forest,which meant that coniferous and broadleaf mixed forest and sclerophyllous oaks were favorable for soil aggregate stability.Significant correlations were found among the three quantitative characteristics,which could be used to indicate the stability of soil aggregates.

Key words: Vegetation, Soil aggregate, Logarithmic normal distribution, Fractal dimension, Soil aggregate stability index