The Stability And Distribution Characteristics Of Dominant Trees Of Robinia Pseudoacacia Plantations In Broken Gully Regin Of The Loess Plateau

The stability of plantation is an important characteristic that decides whether plantation has sustainable existence and development.Robinia pseudoacacia plantation plays an important role in soil and water conservation of the Loess Plateau.And it’s stability is very important.In this paper,Robinia pseudoacacia plantations in the residual gully area of the Loess Plateau were selected as the research object.The stability of Robinia pseudoacacia plantations was quantitatively evaluated by using the fuzzy membership function method and the principal component analysis method from the five aspects which can reflect the structure and function of plantation.The five aspects contain seventeen index,which include species diversity,productivity of forest land,renewal potential,site quality of community and soil fertility.The factors affecting the stability of Robinia pseudoacacia plantation were studied and analyzed.To explore the correlation between the proportion,distribution characteristics of dominant trees and stand stability.In order to provide scientific basis for the stability evaluation of Robinia pseudoacacia plantation.The main research results are as follows:1.The result of principal component analysis for factors affecting the stability of Robinia pseudoacacia plantation showed: The variance contribution rates of the first principal component,the second principal component,the third principal component,the fourth principal component and the fifth principal component were respectively: 33.26%、23.77%、16.46%、11.43%、6.16%.The cumulative variance contribution rate of the five principal components was 91.09%,more than 85%,which reflected most of the information of the stability index.The indicators with larger absolute value of load coefficients in the first and second principal component,species diversity(richness,diversity index,evenness index),stand structure(average tree height,DBH,stand density),forest land productivity(tree stock,shrub biomass,herb biomass,litter biomass),total phosphorus content and total potassium content in soil,had the greatest impact on the stability of Robinia pseudoacacia plantation.2.The result of comprehensive evaluation for the stability of Robinia pseudoacacia plantation by adopting membership function method and principal component analysis method showed that the plot 1(Robinia pseudoacacia and poplar mixed forest)with higher stability had abundant species,good habitat conditions and great regeneration potential.The stand productivity,site quality,species diversity and soil fertility were all higher in the plot 5(Robinia pseudoacacia over-mature forest),plot 9(Robinia pseudoacacia mature forest)and plot 10(Robinia pseudoacacia mature forest)with high stability.The most index values were smaller in the plot 2(Robinia pseudoacacia mature forest),plot 3(Robinia pseudoacacia near-mature forest),plot 4(Robinia pseudoacacia mature forest),plot 6(Robinia pseudoacacia middle-aged forest),plot 7(Robinia pseudoacacia mature forest),plot 8(Robinia pseudoacacia over-mature forest)and plot 11(Robinia pseudoacacia middle-aged forest)with poor stability.3.The study which research and analyze correlation between the stability of Robinia pseudoacacia plantation and the proportion and distribution of dominant trees in the stand showed that the proportions of dominant trees in plots 1,5,9 and 10 with higher stability were 32.6%,40.0%,48.3%,46.4% respectively and the distribution patterns were uniform distribution,random distribution,random distribution and random distribution respectively.The proportions of dominant trees in plots 2,3,4,6,7,8 and 11 with poor stability were51.3%,46.8%,58.1%,44.8%,47.8%,36.8% and 50.2% respectively and the distribution patterns were clustered distribution,random distribution,uniform distribution and clustered distribution,random distribution,random distribution and random distribution respectively.It was dominant tree in cluster distribution that only occured in the low-stability forest land.Whether the conclusion that the forest lands with dominant wood in cluster distribution have low stability can be drawn remains to be further studied.In summary,the membership function method agree basically with principal component analysis method in the comprehensive evaluation results of the stability of Robinia pseudoacacia plantation.The evaluation index system of stability of plantation community based on five indicators,which contain a total of 17 factors,including species diversity,population renewal potential,productivity of forest land,site quality of community and soil fertility of forest land can be used to evaluate stability of Robinia pseudoacacia plantation.The mixed forest of Robinia pseudoacacia and Populus davidiana have higher indices,and its stability is better than that of pure forest.