Effects Of Different Reform Modes On Soil Quality Of Low-efficiency Forests In Low Mountain And Hilly Areas Of Sichuan Province

As an important storage province of the National Reserve Forest Project,Sichuan Province has designated a total of 90 million mu of reserve forests in 2014.Among them,the area of masson pine,Chinese fir and cypress wood plantation is 622,000 mu,accounting for 69.1%.However,the plantation forests have pure forestation,intensification,and multi-generation continuous planting,and their ecosystem problems have become increasingly prominent.Target tree reconstruction and forest window reconstruction are important ways to transform natural forests,which is in line with the goal of human transformation of forests.It is conducive to the production of high-quality wood,achieving good economic returns,and is conducive to improving the structure of the forest,taking into account environmental requirements and balancing various ecological functions.In this study,three typical low-efficiency forests in the hilly area of Sichuan Province were studied to study the physical and chemical properties,aggregates and soil erosion resistance characteristics.This study has explored the effects of three different inefficient forest transformation models on soil and water conservation and soil improvement,and sought the optimal transformation mode of soil and water conservation.In October 2015,we selected three artificial forests(Cypress,Pinus massoniana,and Chinese fir forest)in the low hilly areas of the Sichuan Basin(Suining City,Guang'an City,and Yibin City)to operate the target trees.In 2017,we tested soil samples from different forest species in three tree species.The main contents of the study are as follows:The soil bulk density and porosity of Pinus massoniana Plantation and Cupressus plantation were improved after the target tree was retained and transformed.The sand content of Pinus massoniana and Cupressus plantation increased,and the powder particle size ratio decreased.The nutrient concentration of the three tree species in 0-10 cm soil sample increased significantly,but with the increase of soil depth,the transformation effect became weaker.Pinus massoniana Plantation and cypress plantation have the largest amount of air-dried macroaggregates after target tree preservation and management.Target trees of Pinus massoniana Plantation have the most stable water-stable aggregates,while the large aggregates of cypress plantation have the most stable water-stable aggregates.The improvement measures of air-dried aggregates MWD and GMD target trees retaining target trees in cypress plantation were significantly improved,while the improvement measures of water-stable aggregates MWD and GWD window were the most significant.The results of PAD and ELT stability evaluation were the best.Cupressus plantation has higher soil erosion resistance index and water stability index after window modification.The shear strength of three kinds of plantations was improved after target tree preservation and target tree transformation.Among them,target tree preservation and target tree transformation of cypress plantation had the best effect,followed by window transformation.The results show that,the three forests differ in tree species and habitats,resulting in differences in their soil geomorphology.But,the target tree management of the three forests has improved the soil erosion resistance to a certain extent,improved soil fertility,and played a significant positive effect on preventing the decline of low-efficiency forest soil fertility.Among them,the target tree retained 6 strains had the best effect on soil quality performance improvement of Pinus massoniana plantation,and the effect of forest window modification on soil quality performance improvement of Cypress wood plantation was generally better.The target tree of Chinese fir plantation retains 6 strains of shear and mechanical composition sand,and the target tree retains 12 nutrients.