| Pinus massoniana Lamb. is the most widely distributed, the largest number of major timber species in our country, and plays an important role in the composition of the forest ecosystem. But the structure of unitary of artificial forests will lead to the decomposition and accumulation of litter incompatible, thus resulting soil erosion and fertility recession, which form inefficient forest. The qualitative research of soil and water conservation function evolution in Pinus massoniana Lamb. Plantation has an important implication for forest transformation and ecological construction in the upstream of the Yangtze River. The study examined the water retention property, soil fertility status, characteristics of yellow soil aggregates, soil anti-erodibility, used "space instead of time" approach combined analysis of variance, correlation analysis and principal component analysis to explore the different aged Pinus massoniana plantation soil characteristics and anti-erodibility, established a comprehensive evaluation model in 7 different aged Pinus massoniana plantations in Gao county, Sichuan Province, China. The results as follows:(1) The maximum storage capacity and capillary water of the soil in Pinus massoniana plantations increases first, then decreases with forest age grows. Soil maximum storage capacity and capillary water in soil level of 0-40 cm was 1521.66-1627.43 t/hm2,994.97-1262.03 t/ hm2. Soil saturated water and capillary water were significantly decreased with the increase of soil level in each forest age.(2) Total porosity of the soil was 31.812%～42.309%, capillary porosity was 24.738% 36.023%. Soil bulk density changed with forest age, increased first, then decreased, while with the soil level significantly increased. The soil bulk density in middle-aged forest was the maximum, surface was 1.293 g/Kg3, while subsurface was 1.448 g/Kg3. Bulk density was significantly negatively correlated with total porosity and capillary porosity, the decreasing of bulk density was the main reason for soil pore distributing well, and the increasing in soil water storage capacity.(3) Soil organic matter, the total nitrogen contents were 14.137～28.333 g/Kg,0.390-0.807 g/Kg respectively. The soil available nutrient was 1.507～63.898 mg/Kg. Forest age has an significant impact on soil nutrients, the overall performance was soil fertility first increased and then decreased from the young forest to middle-aged forest, increased in matured stage finally. It was significantly decreased with the increase of soil level. The lowest fertility indicators at Middle-aged and 31 years mature forest plantation, which detrimental to maintaining soil nutrients.(4) Soil aggregate fractal dimension(D) was 2.826-2.981. Water-stable fractal dimension(WD) has an significant positive correlation with R0.25, organic mater, GMD, MWD, while negative with PAD. D can be used to evaluate changes in soil physical and chemical properties of plantation.(5) Erodibility K value was 0.216-0.239. Forest age has an greater impact on soil erodibility on the surface, K value in Middle-aged forest and mature forest was significantly higher than the others, except for three-aged forest, which greatly increasing the potential risk of soil erosion.(6) There were six optimal indicators to evaluate the soil anti-erodibility in Pinus massoniana Lamb. Plantation in southern Sichuan province, they were:WR0.25, WR0.5, MWD, PAD, physical clay and organic matter, soil organic mater and physical clay were the major factors to determine the anti-erodibility, all of them can be used to to measure the evolution of soil anti-erodibility.(7) The indexes to evaluate soil anti-erodibility in Pinus massoniana Lamb. Plantation in southern Sichuan complexed in four main components, a evaluation model of comprehensive index was:Z=0.487Zi+0.312Z2+0.112Z3+0.085Z4. Forest age has an significant impact on soil anti-erodibility, soil anti-erodibility composite index first increased then decreased from young forest to the middle-aged forest stage, however it gradually increased after middle-aged forest stage. Correlation analysis showed a significant negative correlation between Z and soil erodibility K value. The soil anti-erodibility evaluation model established by principal component analysis can be used to evaluate soil anti-erodibility evolution.In summary, forest age influences on soil physical and chemical properties and soil structure. Soil fertility, structure, permeability and water storage capacity of middle-aged forest decreased, the ability to resist erosion reduced, which could lead to serious soil erosion easily. Status of soil porosity, aggregate structure, infiltration capacity and water storage capacity in mature forest improved. The ability to resist soil erosion and runoff increased, conducive to water and soil conservation. |
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