| The natural secondary forest of Keteleeria davidiana(CE Bertrand)Beissn.is a multi-layered forest ecosystem mixed by needles/broad-leaved species with unique species,complex structure and rich diversity.This study was based on a fixed rectangular monitoring sample plot of 100 m × 80 m in the typical natural secondary forest of K.davidiana in Guangxi Yachang Orchid National Nature Reserve and studied the basic characteristics of the community,community-distribution,community structure and connection relationships between major populations.For understanding and mastering the structural characteristics of the natural secondary community of K.davidiana,and obtaining basic information about the characteristics of the forest ecosystem,providing scientific basis for strengthening conservation and restoration,structure adjustment and sustainable development,sustainable management of K.davidiana.The main conclusions are as follows:(1)The secondary forest of K.davidiana has rich diversity with 55 species which diameter are more than 1cm including 12 species with density more than 10 plants/hm2,a total of 2 phylums,9 families,11 genuses and 12 species.The relative abundance of Quercus variabilis,Lindera glauca,and K.davidiana was much higher than the rest species.The heights of individual trees have less variation,and the distribution of DBH of each tree species is similar with the whole plot.(2)In the living standing tree layer(DBH ? 5cm),the total number of trees was 1072,and the average density was 1340 plants/hm2.The important values of K.davidianaand Quercus variabilis are much higher than the rest species,indicated that K.davidiana and Q.variabilis occupied the dominant position in the community.There are 665 trees in the grade of mall tree(5cm?DBH?14.8cm),accounting for 62.03%of the total number of living standing trees,and 407 large trees(DBH?14.80cm),accounting for 37.97%.The breast diameters of individual trees are mostly smaller than the mean value of the plot.The fitting accuracy of the correlation functions betweem DBH and height for the entire plot and each tree species were not high(R2<0.80),and only Q.variabilis and P.sibirica showed regularity in self-similar model matching.The confidence interval of Q.variabilis contains 2/3 compliance with the elasticity similarity model hypothesis,L.glauca matched two hypotheses including the pressure similarity model and the elasticity similarity model(confidence intervals included 1/2 and 2/3).(3)In the sapling layer(DBH<5cm),the total number of plants was 1459,the average density was 1824/hm2,and the community density was higher than the living standing layer.With the increase of height,the number of saplings shows the tendency to increase first and then decrease.When the height is higher than 2.5m,the differences between the number of sapling trees in every height level were not significant.and maintained at about 85/height level.(4)All community in the plots only showed random distribution in the Green index GI = 0.00,and all other indexes showed a high intensity clustering.In the distribution pattern of each tree species,in addition to the average degree of crowding degree m*<0.00 and the clustering index PAI<0.00,which shows a uniform distribution,the rest of the tree species in the dispersion index is within 1.11 to 9.07,and the aggregation index is within 0.18?25.04,the average degree of congestion was within 0?59.22,both the cluster index and the Green index were greater than 1.00,and all trees showed higher intensity aggregation.The indicators showed little difference,indicating that the aggregate distribution is the basic attribute of the community.With the increase of the size of the grading,the density of the community gradually decreased,and the aggregation intensity of each tree species gradually decreased.(5)The frequency of the binary distribution of living plant structure parameters is mostly distributed in a random distribution,indicating that most trees with different advantages and disadvantages are randomly distributed.The mixed grades of forest trees are basically balanced,and the difference in size differentiation is not significant.In the small tree layer,when the angular dimension W is 0.50,the frequency value of the size ratio is maintained within 0.0980?0.1235,which is the maximum of the frequency distribution of the same size than the number scale,indicated the small trees are distributed in the random distribution and moderate mixing.This shows that most of the small trees with different advantages and disadvantages are associated with other tree species and in a random distribution.When the W of the big tree layer is 0.50,the frequency values at different scales are between 0.1063 and 0.1438,which are the maximum values of the frequency of the same size and counts,indicating that the big tree has different advantages and disadvantages.Indicated most of the trees are in a random distribution.(6)The VR of the whole community is higher than 1.00,showed a positive correlation but not significant,indicated there is a certain association between species,but failed to form a stable allocation relationship,the community was not stable and in the stage of continuous improvement.In determination about holistic association of different levels,VR of young trees small trees and large tree were higher than 1.00 showed positive correlation without significance,the community characteristics were consistent with the entirety.In the x2 test of the community,,the logarithm of the negative,positive and non-linking species of the dominant tree species in the natural secondary forest community of K.davidiana was no significant difference,accounting between 32.00%?36.00%.The positive correlations in Pearson correlation and Spearson rank correlation analysis were 55.13%and 56.13%respectively,higher than negative correlations.There was no significant positive correlation and consisted with the whole community. |
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