The Effect Of Vegetation Recovery On The Diversity Of Undergrowth Vegetation And The Physical And Chemical Properties Of Soil In The Loess Plateau Of Western Shanxi Province

The Loess Plateau is one of the most serious areas of soil erosion in China,witch has complex and diverse geomorphic conditions and poor ecological environment.It is of great significance to reduce soil erosion,improve ecological environment and increase species diversity to carry out the project of returning farmland to forest and grass.The species diversity and soil physical and chemical properties are the hot topic in ecological and environmental sciences.The study of response of vegetation recovery to species diversity and soil physical and chemical properties is one of the important contents of forestry and soil and water conservation science.We choosed 42 sample plots including the various age of Robinia pseudoacacia,Pinus tabulaeformis and Platycladus orientalis plantations（10 a,15 a,20 a,25 a）to study two aspects.One was the change of the richness index（R M）,the diversity index（H’、D）and the evenness index（Jsw）in herbaceous layer with increasing vegetation restoration years.Another was the change of soil physical and chemical properties including soil bulk density,total porosity,capillary porosity,non-capillary porosity,organic matter,pH,total nitrogen,total phosphorus,ammonia nitrogen,nitrate nitrogen,available phosphorus and available potassium in various soil layers（0～10 cm,10～20cm,20～30 cm,30～40 cm,40～50 cm,50～60 cm）with increasing vegetation restoration years.We used mathematical method to establish the evaluation model of coupling relationship between soil and vegetation,so that to determine coupling coordinative degree in different woodlands.The purpose was to provide theoretical basis for vegetation restoration and reforestation in the loess area of Western Shanxi Province and to provide reference for the protection and management of the biodiversity under the artificial forest.The results were3 as follows.（1）A total of 20 understory species belonging to 10 families and 16 genera were recorded.The diversity of herbaceous plants in different woodlands had its particularity.The highest frequency of occurrence in the area were Artemisia gmelini and Carex spp.With the growth of vegetation recover,the diversity index（Margalef and Patrick index）,the richness index（Simpson and Shannon index）and the evenness index（Pielou index）of herbaceous layer decreased in the Pinus tabulaeformis plantations.The diversity index in Robinia pseudoacacia plantations increased as the vegetation recover increased.However,the index in the Platycladus orientalis plantations increased firstly and then decreased.The size of the index were about shown as Robinia pseudoacacia plantations>Platycladus orientalis plantations>Pinus tabulaeformis plantations.That revealed the Pinus tabulaeformis plantations were not more suitable for the growth of herbs than the Robinia pseudoacacia and Platycladus orientalis plantations.（2）The biomass of herbaceous layer in the Pinus tabulaeformis plantations was the smallest,which the range of change was 5.4-7.4 g·m^-2.And the biomass in Robinia pseudoacacia plantation was the largest(24.93-57.67 g·m^-2).As the vegetation recover increased,the biomass in the Robinia pseudoacacia and Platycladus orientalis plantations increased firstly and then decreased,and the Pinus tabulaeformis plantations diminished.The litter volume of Pinus tabulaeformis plantations was the largest,which the range of change was 15.68-27.31 t·hm^-2and that of Platycladus orientalis plantations was the smallest(8.36-12.38 t·hm^-2).The litter volume of Robinia pseudoacacia plantations increased gradually with the increase of vegetation recovery,while the Pinus tabulaeformis and Platycladus orientalis plantations were irregularly variable.（3）The soil bulk density decreased with the increase of vegetation recover in different plantations.The change trend of soil total porosity and capillary porosity were opposite to that of bulk density.With the increase of soil depth,soil bulk density tended to increase,while the total porosity and capillary porosity tended to decrease.When the vegetation recovery was about 25 years,the average values of soil bulk density of 0～60 cm in different plantations were the Pinus tabulaeformis plantations(1.16g·cm^-3),Platycladus orientalis plantations(1.18 g·cm^-3),Robinia pseudoacacia plantations(1.18g·cm^-3),respectively.The bulk density of 0～20cm soil layer of forest land had the biggest change in10-15 years,and it was basically stable at 1.16g·cm^-3after 23 years.As for total porosity,the periods of greatest change was 5-10 years old The value of it had been stable in 55.61%after 25 years old.The capillary porosity of forest land was basically stable in 0～20cm topsoil after 15 years,and its value was stable at about 54%.（4）The change trend of soil chemical properties of 0～60 cm in different woodlands was not the same,as the vegetation recovery increased.The content of soil organic matter,pH,and available phosphorus was Platycladus orientalis plantations>Robinia pseudoacacia plantations>Pinus tabulaeformis plantations.The content of nitrate nitrogen and available potassium were Robinia pseudoacacia plantations>Platycladus orientalis plantations>Pinus tabulaeformis plantations.The content of ammoniacal nitrogen was Pinus tabulaeformis plantations>Platycladus orientalis plantations>Robinia pseudoacacia plantations.The content of total nitrogen was Platycladus orientalis plantations>Pinus tabulaeformis plantations>Robinia pseudoacacia plantations.The content of total phosphorus was Robinia pseudoacacia plantations>Pinus tabulaeformis plantations>Platycladus orientalis plantations.The content of total nitrogen,organic matter,available potassium,nitrate nitrogen and ammonium nitrogen decreased,as soil depth increased and there were obvious effects of the surface.With the increase of vegetation recovery,soil nutrients had enrichment process;soil fertility improved and soil nutrients increased gradually.（5）Coupling coordination index between soil and herbaceous vegetation ranged 0.49-0.52.The size was Platycladus orientalis plantations（0.5111）>Robinia pseudoacacia plantations（0.5069）>Pinus tabulaeformis plantations（0.4932）.Pinus tabulaeformis plantations belonged to near offset-vegetation profit and loss type;Robinia pseudoacacia and Platycladus orientalis plantations belonged to fundamental coordination-vegetation lag type.The coordination of herb and soil physical and chemical properties in Platycladus orientalis and Robinia pseudoacacia plantations was better than that in Pinus tabulaeformis plantations.The results show that the Robinia pseudoacacia and Platycladus orientalis plantations should be given priority in vegetation restoration.（6）Regression analysis indicated that,the diversity of herbaceous vegetation was mainly affected by total phosphorus,pH and total nitrogen.The diversity index（H’）.Richness index（M）,and evenness index(J_SW)all had a good linear relationship with total phosphorus（TP）.Biomass（W-P）was linearly correlated with available phosphorus（AP）,total nitrogen（TN）and pH.There was also a good linear relationship between litter volume（W-L）and soil bulk density（BD）,total soil porosity（STP）and pH.