Ecological Effects In The Restoration Of Rocky Desertification Vegetation In Southeast Yunnan Karst Area

Kaiyuan city,located in the southeast of Yunnan Province,is a typical karst area.Rocky desertification area accounts for 19.41% of the total area in Kaiyuan city.The problem of rocky desertification has become a main factor to restrict the local social and economic development.In recent years,Kaiyuan city has carried out a series of vegetation restoration measures to control rocky desertification.The vegetation restoration measures mainly include closing mountains for afforestation,artificial afforestation and retiring farmland to forest.This paper studies on ecological effects of the process of rocky desertification,which provides a theoretical basis for the optimization of vegetation restoration measures to control karst rocky desertification in the future.First of all,with the method of " replacing time replacing temporal series ",four rocky desertification vegetation restoration plantations with restoration forest ages of 3a,9 a,14 a and 20 a were selected in Kaiyuan city.In order to minimize the impact of spatial heterogeneity,the four plantations are all Cupressus lusitanica Mill.forests located in Beige Town.Sample plots were set in the four woodlands for investigation,sampling and index determination,The ecological effects of plant communities and soil environment in the process of vegetation restoration in rocky desertification were studied.Secondly,the natural restoration forest and artificial forest of rocky desertification vegetation with a restoration period of 9 years are selected for comparative analysis of soil factors and vegetation diversity,and the optimization scheme of vegetation restoration measures suitable for the region is put forward.Thirdly,the correlation between the vegetation diversity index and soil factors was analyzed to study the correlation between the indicators.The main conclusions are as follows:(1)In the process of rocky desertification vegetation restoration,the vegetation species richness index and species diversity index of the artificial forest tend to increase first and then decrease.The increase of richness and diversity occurs in the growth period of the vegetation,and the decrease occurs in the mature period of the vegetation,indicating that the artificial vegetation will hinder the growth of the surrounding species due to soil nutrition occupation and shading during the mature period,and it is necessary to improve the species richness and diversity of the artificial vegetation in the mature period,Nutrients can be applied or artificial vegetation can be properly pruned.The species evenness index did not change regularly in the process of rocky desertification vegetation restoration,but the species evenness of tree layer showed an increasing trend.(2)In the process of rocky desertification vegetation restoration,soil bulk density decreases,soil total porosity,capillary porosity and non-capillary porosity increase,soil p H first increases and then decreases,soil organic carbon content continues to increase,soil total nitrogen and total phosphorus content increase and then decrease,reaching the maximum at the restoration age of 14 a and 9 a respectively,indicating that there will be a lack of nitrogen According to the situation of phosphorus,proper and timely application of nitrogen and phosphorus fertilizer can improve the effect of rocky desertification vegetation restoration.Soil invertase activity and catalase activity increased with the vegetation restoration,and in the vertical direction,with the deepening of the soil layer,the two kinds of soil enzyme activities decreased.Soil urease activity first increased and then decreased.When the restoration period was 14 years,the soil urease activity reached the maximum value,and the soil acid phosphatase activity increased first and then remained basically unchanged.It was concluded that soil fertility increased and soil biological activity increased in the process of vegetation restoration.(3)Compared with natural restoration forest,artificial forest limits the richness and diversity of vegetation community.However,artificial forest is planted at fixed spacing,so the species evenness index is greater than that of natural restoration.Soil bulk density,p H and organic carbon are natural recovery > artificial forest,soil porosity,total nitrogen and total phosphorus are natural recovery > artificial forest,soil sucrase,urease and catalase activities are natural recovery > artificial forest,and soil acid phosphatase activities are natural recovery < artificial forest,indicating that Mexican cypress has extensive ecological adaptability and rapid growth,and its growth process consumes less soil nitrogen and phosphorus,However,it is inferior to natural restoration measures in improving soil organic carbon and promoting enzyme activity.The artificial afforestation of rocky desertification in this area can simultaneously plant a variety of symbiotic species and timely supplement soil nutrients.(4)Through correlation analysis,it was found that soil invertase activity was negatively correlated with soil porosity,p H,total nitrogen and total phosphorus,and positively correlated with organic carbon;Soil urease activity was positively correlated with p H,organic carbon and total nitrogen;Acid phosphatase activity was positively correlated with total phosphorus;Catalase activity was positively correlated with organic carbon content.The correlation analysis between plant diversity and soil factors showed that total nitrogen and soil urease activity were significantly related to species richness index;Soil organic carbon,total nitrogen,soil invertase activity and soil urease activity were significantly correlated with species diversity index;Soil organic carbon and soil acid phosphatase activity were significantly correlated with species evenness index.