Screening Of Competition Index For Pinus Tabulaeformis Plantations And The Impact Of Factors On The Diversity Of Understory Species

Pinus tabulaeformis is the main afforestation tree species in north China.P.tabulaeformis plantation has a large area and wide distribution,which is an important part of Chinese forest ecosystem.The management of P.tabulaeformis plantation is unreasonable,which leads to poor stand quality,biodiversity and stability.Most of the studies on forest competition of P.tabulaeformis plantation at home and abroad focus on the structure of competition model,the analysis of intraspecific and interspecific competition relations,stand structure and biodiversity,but few on the suitability evaluation and test of different types of competition model for P.tabulaeformis plantation.However,studies on the undergrowth species diversity of P.tabulaeformis plantation are mostly about the effects of soil nutrients,topography and biological factors on the species diversity of P.tabulaeformis community,shrub layer and herb layer.However,the response of species diversity to soil physical properties and liana species diversity to the gradient change of habitat factors is less.In order to screen the optimal competition index model of pinus tabulaeus plantation and explore the impact of habitat factors on undergrowth species diversity,and obtain the basis and theoretical support for scientific management of P.tabulaeformis plantation,the following studies were carried out:A total of 1054 P.tabulaeformis objective trees and 4216 competitive trees in a typical P.tabulaeformis plantation of Jiulong Mountain were studied,and the biomass was regression analysis with the competition indexes of Hegyi,CIO_iand the angle-based(d???CI_i),respectively.The optimum competitive index of P.tabulaeformis plantation was selected by regression analysis and k-fold cross-validation,and the competition intensity of P.tabulaeformis plantation was analyzed.The species diversity and habitat factors of shrub layer,herb layer and liana in 12 type of stand of P.tabulaeformis plantation in Zhongtiao Mountain were investigated.Multiple comparison method and correlation method were used to analyze the variation law of species diversity at different levels under different habitat factors,and principal component analysis and CCA sequencing were used to analyze the environmental interpretation of distribution of understory species.The result showed that:(1)The biomass of P.tabulaeformis obeys the power function relation with d???CI_iand Hegyi competition index,and obeys the exponential function relation with CIO_i.The coefficient of determination R~2(R~2=0.7705)and 10 times of 10-fold cross-validation R~2(Validation R~2=0.7695)values of d???CI_iwere the highest,and the loss of R~2(R~2=0.0010)was the smallest.Therefore,the quantization effect of d???CI_iwas the best,followed by Hegyi competition index,and CIO_iwas the worst.This indicates that d???CI_ican better quantify the competition intensity of typical P.tabulaeformis plantations in Beijing.(2)Forest competition is influenced by quantity,size and species.With the increase of DBH of P.tabulaeformis,the competition index gradually decreases,and the proportion of the over shading of the competition index also gradually decreases or not even.When DBH of P.tabulaeformis is not less than 20cm(about 1/4 of the total),the change of its competition index is not significant with the increase of the class.Therefore,according to the spatial distribution of competition index of P.tabulaeformis,reasonable thinning of individuals with the DBH less than 20 cm can improve the structure of P.tabulaeformis.The competition of P.tabulaeformis mainly comes from intraspecific,accounting for 93.64%of total competition intensity.The quantity and competition intensity of intraspecific competition trees increase first and then decrease with the diameter class.However,on the whole,the number and competition intensity of interspecific competition trees decrease first and then increase with the diameter class.It shows that the intraspecific competition is greater than the interspecific competition and vertical spatial segregation within and between species are important conditions for species coexistence.(3)The species number of different layers of P.tabulaeformis plantation is arranged from more to less as herb layer,shrub layer and liana.Among the habitat factors,biological factors are the main influencing factors of understory species composition.Forest density,soil noncapillary porosity and slope had the greatest influence on the species composition of shrub layer,soil noncapillary porosity and slope had the greatest influence on the species composition of herb layer,and the liana species composition was mainly affected by elevation.(4)The species diversity of undergrowth shrub layer in P.tabulaeformis plantation was higher in shady slope than in sunny slope.On the whole,species diversity of shrub layer was positively correlated with degree of intermingling,forest age,density,canopy density and slope,and negatively correlated with elevation and biomass of P.tabulaeformis.Affected by the life history strategy of species,overall,species diversity of undergrowth shrub layer and herb layer of P.tabulaeformis plantation showed an opposite trend with the change of habitat factors.(5)When controlling the structure of P.tabulaeformis plantation,it is very important to keep the balance between forest competition intensity and conservation of understory species diversity for the improvement of stand biomass,regeneration ability of P.tabulaeformis and undergrowth species diversity.