Biodiversity And Soil Ecological Characteristics Of Pinus Tabulaeformis Forests Of Different Ages In Pisha Sandstone Area

The ecological environment of Pisha sandstone area is bad and soil erosion is very serious.The ecological restoration of plantation is an important measure to improve the ecological environment of this area.In order to explore the change rule and influencing factors of ecological characteristics(vegetation diversity,soil water holding capacity and fertilizer conservation)of Pinus tabulaeformis forest at different forest ages in Pisha sandstone area,the Pinus tabulaeformis forests and natural grasslands in the small watershed of Hetong Valley for 5a,10 a,15a and 20 a were selected as the research objects,contrasted with natural grassland by using the method of space instead of time.The effects of forest age on biodiversity,soil water and fertility retention and soil PSD characteristics were studied through field biological investigation,soil collection and laboratory experiments.And based on the fractal parameters,the distribution characteristics and correlation of soil PSD and soil water and fertility retention performance indexes were discussed,and the improvement mechanism of forest age on soil texture and fertility was revealed.Results showed that:(1)The herbaceous vegetation density,root dry weight and herbaceous ? diversity of Pinus tabuliformisforest at different forest ages in Pisha sandstone area were better than those of natural grassland.With the increase of forest age,plant density showed an upward trend on the whole.In the 5a~10a period,the growth rate of each index was the highest in all growth stages,and it was the fastest stage of vegetation restoration and succession under Pinus tabuliformis forest.The succession sequence of understory vegetation in Pinus tabuliformis forest changed obviously with the increase of forest age.The direction of vegetation succession was from the coexistence of Gramineae—Leguminosae—Chenopodiaceae plants to the coexistence of Gramineae—Leguminosae—Compositae plants,and eventually to the coexistence of Gramineae—Leguminosae communities.Its associated species experienced the succession process from Chenopodiaceae to Compositae to Leguminosae.(2)With the increase of forest age,the middle and fine sand grains in the soil of Pinus tabuliformis forests were gradually refined and transferred to the silt grains.The effects of different forest ages on soil PSD were different.The distribution,dispersion and soil fineness of Pinus tabuliformisPSD were higher than those of natural grassland,and showed an increasing trend with the increase of forest ages(?? increased in a wave-like manner with the increase of forest age).With the increase of soil depth,the change law of soil particle sizedistribution and fractal parameters of Pinus tabuliformisforests of different ages are not consistent.(3)Pinus tabuliformis forest can significantly improve soil water holding capacity and nutrient content.Except for 5a,the saturated hydraulic conductivity of Pinus tabuliformis forest is lower than that of natural grassland,the water holding capacity of other Pinus tabuliformis forests is higher than that of natural grassland.Among the indexes of water holding capacity,Pinus tabuliformis forest has the greatest effect on soil saturated hydraulic conductivity.Among the indexes of water holding capacity,Pinus tabuliformis forest has the greatest effect on soil saturated hydraulic conductivity.The water holding capacity of surface soil of Pinus tabuliformis forest in 5a and 20 a was better than that of deep soil,while that of10 a and 15 a Pinus tabuliformis forest was the opposite.Soil carbon and nitrogen content and reserves increased significantly with the increase of forests age.Soil carbon and nitrogen content and reserves of Pinus tabuliformis forest in 5a and 10 a were lower than those of natural grassland,contrary to 15 a and 20 a Pinus tabulaeformis forests The accumulation of carbon and nitrogen in surface soil of Pinus tabuliformis forest in 5a,10 a and 15 a was lower than that in bottom soil,while that in natural grassland and 20 a Pinus tabuliformis forest was the opposite.(4)Soil bulk density,field capacity,saturated hydraulic conductivity,carbon and nitrogen content and reserves all showed good correlation with the soil PSD distribution characteristics and fractal parameters.Soil organic matter and soil bulk density,field capacity and saturated hydraulic conductivity were the main factors affecting soil water holding capacity.clay and silt are fine-grained soils that determine the water-holding capacity and nutrient content of the soil in the region,while medium-fine sand is coarse-grained soil that determines the water-holding capacity and nutrient content of the soil in the region.