Study On The Complexity Of Community Structure And The Change Of Soil Nutrient In The Continuous Planting Eucalypt Plantations

With the rapidly development of eucalyptus plantation,a lot of economic benefits have been brought to the social.However,a lot of ecological problems have been emerged because of irrationally management practices,which cause more and more vehement dispute in the academe.The focuses of the argument are:(1)The problem of biodiversity of the understory plants in eucalyptus plantation;and(2)The problem of decline of soil fertility.In this paper,the study site is situated on the first planting Eucalyptus plantation site(1^strotation)and the second planting Eucalyptus plantation site(2^ndrotation)planted at the same stand site,three sampling plots(each 30m×20m)were randomly selected in each site,each plot set three repetitions.We researched on the change of community structure and soilnutrient through wild investigations and indoor analysis,in order to elucidate the influence of continuous planting on complexity of community structure and soil fertility in eucalypt plantations.The results of study on community compositions showed as follows:(1) Compare SR(the second generation forest)with FR(the first generation forest)forest, the species of understory plants decreased by 38.30%,the species of shrub layer decreased by 45.31%,the species of herb layer decreased by 23.33%;(2)Continuous planting accelerated the degradation of the shrub layer plants,but it was advantaged for the growth of the herb layer plants;(3)Continuous planting brought the decrease of Phanerophytes and the increase of Therophytes;(4)The results of study on diversity index and species richness showed that the species diversity of understory has decreased;(5)The dominant species of shrub layer plants Litsea glutinosa,Rhus chinensis Mill,Mallotus repandus and Clerodendron cyrtophyllus were replaced by Rhus chinensis Mill,Clerodendron cyrtophyllus,Litsea glutinosa and Mallotus barbatus;the dominant species of herb layer plants Miscanthus floxidulus, Eupatorium odoratum,Arthraxon hispidus and Neyraudia reyraudiana were replaced by Miscanthus floxidulus,Neyraudia reyraudiana,Eupatorium odoratum,Sorghum nitidum and Pteridium aquilinum var.latiusculum;(6)Compare to the SR forest,Leaf Area Index and Mean Leaf Angle are smaller in the FR ferest,but its Exitinction coellicent.Trans.Coef.for defuse penetration and Transm.coef.for radiation penetrtion are bigger.The results of the study on the biomass and productivity showed as follows: (1)Continuous planting had no significant influence on the biomass and productivity in the tree layer,but it had a decrease trend;(2)The biomass and productivity of the understory plants decreased markedly,which decreased by 54.60%in average.The results of the study on soil nutrient showed as follows:(1)At 0～20cm soil layer,pH,available K and Ex-Ca²⁺showed a decrese trend at diffierent degree, respectively,so did the 20～40cm soil layer;(2)At 0～20cm soil layer,the content of organic matter,available N and total K decreased markedly,which decreased by 31.17 %,22.42%and 31.80%,respectively.At 20～40cm soil layer,it had no significant change,but showed a decrese trend;(3)The content of total N significantly decreased at 20～40cm soil layer,and showed a decrease trend at 0～20cm soil layer,but no significance;(4)The content of the total P and the available P showed a increase trend both at 0～20cm and 20～40cm soil layer;Moreover,the content of total P increased markedly at 0～20cm soil layer;(5)The content of Ex-Mg²⁺markedly decreased both at 0～20cm and 20～40cm soil layer,which decreased by 30.17%and 56.00% respectively.