Fractal Characteristics of Soil Aggregate Structure Under Typical Forests in Jiuqu Stream Ecological Conservation Area

The fractal characteristics of soil aggregate structure under 4 typical categories of forests or plantations, i.e., secondary broadleaved forest, Pinus massoniana plantation, bamboo plantation and tea plantation in Jiuqu Stream Ecological Conservation Area in Fujian Province were studied, and the relationship between the fractal dimension and soil MWD, GMD, physical and chemical properties was analyzed. The results showed that the fractal dimension of soil aggregate structure of the 4 typical categories of vegetation under the dry and wet sieving conditions was ranged within 2.375~2.658 and 2.627~2.863, respectively. The order of fractal dimension of soil aggregate structure sampled at depth of 0~20cm, 20~40cm and 40~60cm from the 4 typical categories of vegetation was evergreen broadleaved forest < bamboo plantation < Pinus massoniana plantation < tea plantation, which was increased with the soil depth increment. The percentage of > 0.25mm soil aggregates and >5mm large soil aggregates from the 4 typical categories of vegetation under the dry and wet sieving conditions displayed the opposite change trend to that of the fractal dimension, which was in the order as evergreen broadleaved forest > bamboo plantation > Pinus massoniana plantation > tea plantation. The order of soil structure damage rate in the 0~60cm layer was in accordance with the fractal dimension of soil aggregates, i.e., evergreen broadleaved forest (21.31%) < bamboo plantation (2618%) < Pinus massoniana plantation (3198%) < tea plantation (3825%). The fractal dimension of soil aggregates was closely related to soil MWD, GMD, and other physical and chemical properties. The soil under the broadleaved forest was relatively looser in structure, with stronger water holding capacity, higher contents of soil organic matter and nutrients and more stable soil structure, followed by bamboo plantation, Pinus massoniana plantation, and tea plantation.