| The structure of the forest affects its health and stability,the main trees species constitute most of forest trees.Therefore,studying the structural characteristics of the main tree species can clarify the stability of the stand and its structural diversity.The number of Pinus yunnanensis var.tenuifolia was decreasing and its stability was gradually reduced because of the man-made destruction and environmental effect.The secondary forest was the main composition form of the P.yunnanensis var.tenuifolia natural forest at present.In this study,P.yunnanensis var.tenuifolia natural secondary forest in the Nanpan River basin as the research object,after overall investigation,a typical permanent plot was set up with 100m×100m sizes in Guangxi Yachang Orchid National Nature Reserve.Forest spatial structure parameters and the O-ring function of the bivariate statistical of point pattern analysis were used to analyze the structure characteristics and spatial association of the six main tree species and the trees with different diameter classes,which the DBH of the standing trees ? 5cm and the important value>5%.In order to providing reference for the management,protection and sustainable development of P.yunnanensis var.tenuifolia natural forest in basin.The results showed that:(1)The tree species which DBH>5 cm in the P.yunnanensis var.tenuifolia secondary forest were 18,they belong to 15 families and 18 genera respectively.the rank of the main tree species which the important value>5%were P.yunnanensis var.tenuifolia(27.37%)>Lyonia ovalifolia(Wall.)Drude var.elliptica(20.78%)>Quercus variabilis B1.(16.84%)>Cyclobalanopsis glauca(Thunb.)Oerst.(7.54%)>Keteleeria davidiana(Bertr.)Beissn.(7.27%)>Myrica rubra(Lour.)S.et Zucc.(5.32%),and P.yunnanensis var.tenuifolia was the dominant species.The diameter of each main tree species were continuously distributed.And the diameter distribution of P.yunnanensis var.tenuifolia was normal distribution,while the diameter distribution of other main tree species were inverted "J" shape.The overall forest stand showed a typical uneven-aged forest.(2)Uniform angle index of the main tree species with different diameter class usually hold steady around 0.5,most of the trees were clumped and randomly distribution in the forest.The dominance of the trees were growing with increase of the diameter class.In addition to the mixed degree of L.ovalifolia was slight decreasing with increasing diameter class,the mixed degree of P.yunnanensis var.tenuifolia,Q.variabilis,and M.rubra increased continuously,while the mixed degree of different diameters class of C.glauca and K.davidiana were varied.From the average spatial structure parameters values of the main tree species with different diameters sizes,we can see that excepting the W of P.yunnanensis var.tenuifolia and its small trees,the big trees of C.glauca and M.rubra were between 0.475 to 0.517,they were randomly distributed in the forest.The other trees species with diameters sizes were between 0.52 to 0.61.The dominant and inferior statue of the main tree species from high to low were P.yunnanensis var.tenuifolia(U =0.22),K.davidiana(U =0.4),C.glauca(U=0.43),Q.vdriabilis U=0.52,L.ovalifolia(U =0.56),M.rubra(U =0.78),the same as the big trees.Amo,ng them,the U of big trees of P.yunnanensis var.tenuifolia,K.davidiana and C.glauca respectively were 0.05,0.06,0.15,they were in an absolute dominant status.Most of Q.variabilis and L.ovalifolia belonged to subdominant individuals,the U of them were 0.25,0.34 respectively.And the M.rubra were in a disadvantageous position which the average dominance were 0.6.The small trees of P.yunnanensis var.tenuifolia were in a status of neutral(U =0.4),the status of Q.variabilis,C.glauca and K.davidiana were slightly disadvantaged,and their U were between 0.6 to 0.69,and the average dominance of L.ovalifolia and M.rubra were 0.74 and 0.86,most of them were inferior trees.The big trees of P.yunnanensis var.tenuifolia and Q.variabilis were highly mixed,the small trees were moderately mixed by other species,and the populations with moderrate mixture or higher mixed.Regardless of the diameters sizes of the trees,L.ovalifolia were in badly mixed(M =0.36-0.37).C.glauca were in moderate mixed(M =0.52-0.56),and K.davidiana and M.rubra were in highly mixed.(3)According to the bivariate distribution of structural parameters of the main tree species,regardless of what the status or the mixed state the trees were,most of them were rand.omly distributed in the forest stand.The difference-was that P.yunnanensis var.tenuifolia and K.davidiana were highly mixed and in a dominant state at the same time.The dominance of C.glauca was slightly weaker and moderately mixed,while L.ovalifolia and Q.variabilis were in a medium status,but L.ovalifolia were in a low mixed state and Q.variabilis were moderate mixed by species.Although M.rubra had a high degree of mixing,but most of them were inferior trees.The most of trees with big or small diameter were randomly distributed too,P.yunnanensis var.tenuifolia,K.davidiana and Q.variabilis with big diameter class were highly mixed and in a dominant or subdominant status.Lots of M.rubra were highly mixed trees with moderate or inferior status,and C.glauca and L.ovalifolia were subdominant trees with moderately mixed and low mixed respectively.The small trees had low status relatively.Many P.yunnanensis var.tenuifolia were dominated by moderately mixed and dominant or medium trees.L.ovalifolia were in a disadvantageous state and usually surrounded by same tree species.Many small trees of Q.variabilis and C.glauca were in the middle or high mixed degree with moderation,inferior status or pressure state.K.davidiana with small diameter size were highly mixed,but these trees were also inferior trees,even pressed trees.The small trees of M.rubra were pressed trees with high-mixed.(4)P.yunnanensis var.tenuifolia was dominant species in the forest stand,its spatial association with C.glauca and M.rubra was negatively correlated.On small scale,it was negatively correlated with the K.davidiana,however,there was no relationship between two species on the large scale.With the increase of spatial scale,its connection with L.ovalifolia and Q.variabilis were from negative correlation to positive correlation.There were positive correlations mainly between L.ovalifolia and Q.variabilis,C.glauca,K.davidiana and M.rubra on the big scale.They were showed no correlation at most of spatial scale between Q.variabilis and C.glauca,M.rubra,K.davidiana,the same as K.davidiana and M.rubra.With increase of the scale,the association between C.glauca and M.rubra were positive correlation to no correlation,and finally the correlation was negative,while the spatial association between C.glauca and K.davidiana was negative correlatio on mainly. |
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