Vertical Structure Stratification And Populations Niche Characteristics In Typical Plant Communities In The Loess Plateau Hilly Region Of Northern Shaanxi

We selected different rehabilitation ages grassland and Robinia pseudoacacia plantation forests in the Loess Hilly Region of northern Shaanxi as study object.The correlation between vertical structure and population niche and environmental factors was studied.We study community structure and population niche by field investigation and laboratory analysis.Combined with soil and microenvironment factors,and the response of population niche characteristics and communities vertical structure to environmental factors were analyzed.In this way,the adaptability of vegetation in the region and the interrelation among the species are explored.The main conclusions are as follows:1.Vertical structure stratification and its responses to environmental factorsAfforestation is an effective approach to ecological rehabilitation.The management and monitoring to forest vertical structure is an important project for ecological restoration.Forest vertical structure is one of the main indicators of biodiversity and successional stage.The goal of this study is to determine the vertical structural characteristics and its relationship with environmental factors.We conducted a total of 33 sites field survey at 10-50-y stages artificial forest on the middle of loess plateau,China.We determined the forest stand by systematic clustering analysis which is based on average height of species appearing in the sampling.All undergrowth vegetation are divided into three levels:(I)field layer(<55.33 cm)(II)tall herbaceous layer(55.33 cm-125.35 cm)(III)shrub layer(125.35 cm-234.30 cm).Our analysis revealed that the proportion of field herbs decreased and the forest stratification became clear as the growth years increased.Also,the results show that community stability positively,but not significantly correlated with diversity.The evenness index(J’)have an better correlation with community than other diversity index.RDA confirmed that SMC(F=15.9,P=0.002)and TP(F=1.9,P=0.006)were the most important contributors to the the variation in diversity in community.SMC(F=7.5,P=0.002),At(F=2.2,P=0.01)were the most important contributors to the the variation in diversity in Ⅱ layer,SMC(F=9.8,P=0.002),SOC(F=23.2,P=0.01)were the most important contributors to the variation in diversity in Ⅰ layer.Our results revealed that the diversity of field herb is the most closely related to the stability of the community,and can be used as an effective indicator of community stability in artificial forest.SMC,At,SOC,TN are the key factors that affect the species diversity,and they also as the key factors drive the development and maintenance of the vertical structure of artificial forest.2.Niche characteristics and environmental interpretationFocused on different rehabilitation ages grassland in Wuqi county in loess hilly region,the present study aimed to explore niche characteristics of populations and their influence factors.The results showed that the dominant species were Artemisia sacrorum,Artemisia leucophylla,Artemisia scoparia,Lespedeza daurica and Poa sphondylodes.And the dominant species varied along with the changing of rehabilitation age.The niche breadth of dominant populations increased with increasing of rehabilitation age from 5 to 10 years,indicating an enhanced adaptability to environment.The niche breadth indices of the populations decreased from 10 to 20 years,then increased from 20 to 25 years.After 25 years,niche breadth of the grassland narrowed gradually,indicating a weakened adaptability.The niche breadth indices of most population reached the peak at 10 and 25 years,respectively.There was no linear relationship between synthetic dominance index and niche breadth in different grass communities.With the increasing of rehabilitation age,the niche overlap indices reached highest at 15 years with a single hump pattern,indicating that the interspecific competition increased to the highest at 15 years and then decreased.It was shown that attitude,soil water content(SWC)and soil organic matter content(SOM)were the main factors that affecting the niche breadth,while soil total nitrogen content(STN),attitude and SWC were the main factors that affecting the niche overlap.There was no linear relationship between niche breadth and niche overlap of tested species in different rehabilitation age,due to resource spatial heterogeneity and growth stages of grass species.These findings indicate that with the increasing of rehabilitation age,the population adaptability to the environment are generally enhanced and the resource competition among populations increase and then decrease.It is concluded that attitude,SWC and STN were the key environmental factors that affect population adaptability and their interspecific relationship in natural grassland of loess hilly region.3.Community stabilityThe community stability of the grassland increased with increasing of rehabilitation age from 5 to 20 years,and then decreased.The community stability indices of the grassland reached the peak at 25 years.The community stability of Robinia pseudoacacia plantation forests was gradually increased in the early stage,and gradually decreased in the latter stage.The stability indices of plantation forests reached the peak at 40,35 and 20 years,respectively.There was no significant positive correlation between species diversity and community stability in the communities,and the population niche was not significantly negatively correlated with community stability.In general,the higher the species diversity,the greater the stability of the community.The growth of herb layer in acacia community is helpful to improve community stability.The relationship between population niche characteristics and community stability is not clear.Proper niche overlap contributes to community stability.In conclusion,the ecological niche characteristics of Robinia pseudoacacia plantation forest and the abandoned grassland populations showed the same trend in the growth years.While they peaked at different age.The evolution of the interspecies relationship in forest is lagging behind the grassland.The species diversity of plantation forest was lower than that of grassland in the early stage of growth,but in the middle and later stage of growth,it was opposite.Community stability of the grassland was better than that of plantation forest,but it was the opposite in the middle and late stage.Vertical structure stratification and the appropriate niche overlap contribute to the improvement of community stability.Niche characteristics and species diversity can reflect plant adaptability and growth status but cannot be a direct evaluation factor for community stability.Robinia pseudoacacia plantation forest and abandoned grassland have advantages in soil and water conservation.The reutilization of cultivated land should focus on altitude and water to choose suitable vegetation.