The Characteristics And Environmental Interpretation Of The Species Composition Of Secondary Forest In The Southern Taihang Mountains

The forest cover rate of Taihang Mountains had dropped from 20-40%(8000 B.C.)to<5%(A.D.1950).Compared to the forest higher up on the mountain,the forest on hilly land of Taihang Mt.has been seriously destroyed.It is important to understand the effects of environmental factors on secondary forest assembly for effective afforestation and vegetation restoration.We investigated 104 quadrats(20x20 m)in JiYuan,which covers typical secondary forests types of southern Taihang Mt.We used a principal components analysis(PCA)to analyze environmental data and Hellinger pre-transformed species data,and used the Kaiser-Guttman criterion to decide how many axes are worth representing and displaying on the basis of the amount of variance explained.Two-way indicator hydrocarbon analysis,canonical correspondence analysis(CCA)and parsimonious CCA(PCCA)were used to analyse the relationship between community vegetation and environmental factors.The biplots of PCA,CCA and PCCA were produced in scaling 1(optimal display of quadrats)and scaling 2(optimal display of variables).The main results of this research are as follow:(1)Soil bulk density,soil total porosity,and pH had low CV values(<15%),while soil gravel content and organic C had high CV values(>60%).All 13 variables were sorted by their contributions to habitat variety:elevation>electric conductivity>soil pH>bulk density>pore space>total N>organic C>topography>moisture content>aspect>slope>soil depth>gravel volume percent.Ward's minimum variance clustering results showed that vegetation types varied along elevation and soil nutrient gradients.(2)Gleditsia microphylla,Quercus baronii,Cotinus coggygria,Quercus variabilis,and Koelreuteria paniculata were 5 species with the largest contributions among all 42 tree species to community variety.This result agrees with reality as these 5 species were dominant species in 17 quadrats.The species composition has been largely affected by the topographical gradient,and has been less affected by the nutrient gradient.(3)The CCA showed that 13 terrain and soil variables shared 56.95%of the total variance.The principal environmental variables in the most parsimonious CCA model,based on the result of forward selection,were(in order)elevation,soil total N,soil gravel content,slope,soil electrical conductivity,and pH.The vegetation-environment relationship in the southern region was different than the middle of the Taihang Mt.,and vegetation restoration was at an early stage.The terrain of the southern region,especially elevation and slope,should be considered for vegetation restoration and conservation.(4)Samples were clustered into four forest types,with forest diversity affected by elevation,nutrients,and water gradients.Topographical variables affected forest assembly more than soil variables.(5)According to the environmental and assembly characteristics and the relationship between vegetation and environment,the natural community was simulated,and 4 kinds of near-natural restoration modes were constructed.