Changes Of Stand Structure Characteristics Of Subtropical Evergreen Deciduous Broad-leaved Mixed Forest In Mulinzi Nature Reserve At Temporal And Spatial Scales

The natural forest-subtropical evergreen deciduous broad-leaved mixed forest in Mulinzi Nature Reserve was taken as the object in this paper,and the temporal scale and spatial scale were divided based on the establishment and data survey of 9 hm~2large permanent plot.The temporal scale was 2014 and 2019,and the spatial scale was the large permanent plot was divided into five spatial scales according to the equidistant spacing of 60 m(2019 database).On this basis,the spatial structure(Uniform angle index,Dominance,Mingling)and non-spatial structure(tree species composition,diversity index,diameter class structure)of subtropical evergreen deciduous broad-leaved mixed forest in the region were analyzed under temporal and spatial scales,and the spatial and temporal scale variations of natural forest structure in the region were revealed.Hope the findlings would provide theoretical guidance for the restoration and protection of natural forest management decision.The conclusions are as follows:1.Variation characteristics of non-spatial structure indicators at temporal scale.The number of individual trees and the average DBH of the natural forest stand in Mulinzi increased,the species diversity index did not change greatly during this period,the important values of the main tree species fluctuated slightly,and the tree species composition was relatively stable.The tree species such as Carpinus fargesiana,Quercus multinervis,Quercus myrsinifolia and Sorbus folgneri dominated the stand.The diameter distribution of the stand presented as the inverted“J”shape fitting by Weibull distribution function.No fault phenomenon was found in the diameter class trees,and the community structure was stable and well renewed.2.Variation characteristics of non-spatial structural indicators at spatial scale.The main dominant tree species,Carpinus fargesiana,always kept the first place in five spatial scales.At 60 m to 240 m scale,the important values of Cornus kousa subsp.chinensis and Sorbus folgneri were ranked first,but Quercus multinervis and Quercus myrsinifolia began to occupy the dominant position in the 300 m×300 m scale.Under the influence of changeable karst landforms,Mulinzi natural forest has distinct diversity differences at different spatial scales.The Shannon-Wiener and Simpson index in the study area generally show an increasing trend with the increase of scale,while Pielou index shows a decreasing trend with the increase of scale.The diameter distribution of trees is inverted“J”in five spatial scales,and the small-diameter individuals accounted for a large proportion,and the structural characteristics of each scale were not obvious.3.Variation characteristics of spatial structure indicators at temporal scale.The dynamic change of stand spatial structure was small in 5 years,and the horizontal spatial distribution pattern of the whole stand tended to be gathered distribution after5 years of natural growth.The dominance of whole stand was about 0.5,which implicated the nature forest stand had certain advantages and development potential;The forest was mixed well in 2019,which was basically the same as five years ago,but the development trend was not significant.The forest is still in the process of succession,and has not reached the level of the natural climax community on the whole.The structure unit was being as the absolute dominance,random distribution and of four different tree species associated with trees(M=1,W=0.5,U=0)in the stand was more advantageous in the natural forest.In the process of natural forest protection and restoration,in order to improve the forest quality and make the spatial structure of the stand tend to an ideal state,the absolute inferior trees(M=0,W=1,U=1)from the same species in the stand would be preferred to be subjected to moderate human interference,so as to optimize the stand structure and improve the forest quality accurately.4.Variation characteristics of spatial structure indicators at spatial scale.The results of zero and one variate distribution of spatial structure indicators showed that the stands are slightly aggregated at different spatial scales.With the increase of scale,the Uniform angle index mean first increases and then decreases,and finally tends to random distribution pattern;The Dominance was dominant at small scale,and the ratio above 120 m×120 m was moderate.The Mingling of the stand was good,and more than 45%of the trees were in the state of extremely strong mixing.The relative frequency of binary distribution results shows that the difference at 60 m×60 m scale is significantly higher than that at other scales,and it is relatively stable above 120 m×120 m scale.Therefore,it is suggested that the minimum plot size for the study of stand spatial structure change of subtropical evergreen deciduous broad-leaved mixed forest in this region should be 120 m×120 m(1.44 hm~2).