Effect of Stand Density on Characteristics of Soil Aggregates in Pinus tabuliformis Plantation in Badaling Area, Beijing

To identify the effect of stand density on soil structure, fractal dimension, soil aggregate saving probability and aggregate stability index were analyzed based on field survey and sampling in three Pinus tabuliformis plantation with stand density of 500-800trees/ hm2 (Low density, LD), 1000 -1200 trees/ hm2 (Middle density, MD) and 1400-1600 trees/hm2 (High density, HD) respectively in Badaling area of Beijing. The results showed that stand density had a significant influence on fractal dimension of soil aggregate (dry sieving), it was ranged from 262 to 276 with the largest in the HD Pinus tabuliformis plantations and the smallest in the LD plantations. The fractal dimension of water stable aggregate (wet sieving) was between 264 and 279 and positively correlated with stand density. The smallest fractal dimension was found at the 0-10cm layer in LD plantation and the largest one was found at the 20-30cm depth in HD plantation. All the aggregate saving probability of the forest soil was >05, the soil aggregate of 05-025 mm had the highest stability for the largest saving probability and soil aggregate of 1-05 mm was the most unstable as it was the smallest saving probability. The aggregate stability index ranged from 362 to 455, and decreased with the increasing of stand density. In general, Soil aggregate in the LD Pinus tabuliformis plantation was the most stable and was good for soil and water conservation. Therefore, we suggested stand density of 500-800 trees/hm2 of the Pinus tabuliformis plantation in the research area for improving soil aggregate structure.