Effect Analysis Of Thinning Of Cryptomeria Fortunei Plantation In Mid-mountain Of Western Sichuan

Cryptomeria fortunei is a suitable tree species in high altitude areas,and is one of the main afforestation tree species in high altitude areas in southern China.In order to construct a suitable cultivation model for large-diameter trees of Cryptomeria fortunei and improve the ecological benefits of the ecosystem,this study relied on the central financial subsidy forest tending project,and took 8-year-old pure Cryptomeria fortunei plantation in mid-mountain of Western Sichuan as the research object.Four treatments were set according to the intensity of tending and thinning(control,(unthinning),T1:20%,T2:30%,T3:40%).The growth status of Cryptomeria fortunei forest,characteristics of understory plant community,hydrological,Soil chemical properties and enzyme activity were observed regularly.The main results of this study are as follows:(1)Tending thinning promoted the growth of Cryptomeria fortunei plantation.Under light thinning and medium thinning,the diameter order distribution of Cryptomeria fortunei stands conformed to the normal distribution curve function.The annual increment of DBH and single volume was largest in heavy thinning.There was no significant difference between the four treatments after thinning in annual increment of tree height and stand volume per unit area of Cryptomeria fortunei plantation.(2)Tending thinning increased the species and quantity of undergrowth plants and increased the diversity of vegetation of Cryptomeria fortunei plantation,among which the important values of herbs and ferns were higher in four treatments.The increase of Margalef index was proportional to thinning intensity.Pielou index,Shannon-wiener index and Simpson index of heavy thinning were the most significant.(3)Tending thinning promoted the decrease of bulk density,increase of porosity and increase of water storage capacity of topsoil(0-20cm),which was significantly different between unthinning and other treatments.The indexes of surface runoff were inversely proportional to thinning intensity,and there were significant differences between unthinning and other treatments.The soil hydrological benefit of Cryptomeria fortunei plantation is higher in light and medium thinning mode.(4)After thinning,the coefficient of variation of soil chemical indexes of Cryptomeria fortunei plantation is larger,and the coefficient of variation of total phosphorus is the largest.Soil pH value was inversely proportional to thinning intensity,which had a great influence on the surface soil(0-20cm),and there was a significant difference between unthinning and other treatments.Nursing thinning has a great influence on the chemical index of topsoil(0-20cm).Soil hydrolytic nitrogen,total nitrogen,organic carbon are proportional to thinning intensity,and the content of hydrolytic nitrogen is the largest in heavy thinning;the content of total nitrogen and organic carbon in soil is the largest in light thinning,which is significantly different from the unthinning;the difference between soil carbon and nitrogen and other treatments is significant.Thinning reduced the available and total phosphorus content in the soil of Cryptomeria fortunei plantation.Soil available phosphorus content was the largest in comparison with other treatments,total phosphorus content was the largest in light thinning,which was significantly different from other treatments,and tending thinning had little effect on available potassium,total potassium,calcium and iron in soil,but there was no significant difference among different treatments.In conclusion,the soil chemical properties measured under light and medium thinning patterns are more conducive to forest growth.(5)Tending thinning can improve soil enzyme activity of Cryptomeria fortunei plantation,catalase activity of severe thinning is the largest,which is significantly different from other treatments;sucrase activity of medium thinning is the highest,which is significantly different from that of unthinning and light thinning.Medium and heavy thinning could increase the activities of catalase and invertase in soil.(6)There was a significant negative correlation between surface runoff and vegetation diversity in Cryptomeria fortunei forest,and a significant negative correlation between erosion and Margalef index and Shannon-wiener index.The correlation of elements in 0-20 cm soil layer is large and significant.Catalase was positively correlated with total phosphorus,organic carbon and total nitrogen,while total phosphorus was the most correlated.pH was negatively correlated with catalase,and sucrase was positively correlated with total potassium and carbon-nitrogen ratio.(7)The final results of this study showed that medium thinning intensity was more conducive to the growth of Cryptomeria fortunei and the improvement of its growth environmental factors.