Study On Stand Structure And Its Influence On Understory Vegetation Biomass Of Quercus Secondary Forest In Hunan

Stand structure has a significant impact on the biomass of understory vegetation.For natural forest,how the complex stand structure affects the biomass of understory vegetation is still a hot topic in the study of forest ecological management.In this paper,Quercus secondary forest in Hunan Province is taken as the research object.K-means cluster analysis is used to classify forest types,and the characteristics of forest structure and understory vegetation biomass under different forest types are compared.Pearson correlation analysis and multiple stepwise regression analysis are used to study the influence of stamd structure on understory vegetation biomass under different forest types,and the prediction model of undergrowth vegetation biomass based on stand structure was established to provide theoretical basis for forest scientific management.The results are as follows:(1)K-means cluster analysis divides the stand into five types,which are Castanopsis eyri-Rhododendron latoucheae mixed forest(CR),Fagus lucida-Fargesia spathacea mixed forest(FF),Lithocarpus glaber-Damnacanthus indicus+Camellia japonica mixed forest(LDC),Castanopsis eyri+ Quercus serrata-Rhododendron latoucheae mixed forest(CQR),Cyclobalanopsis glauca-Camellia oleifera+Rhododendron latoucheae mix forest(CCR).(2)There is a certain adjustment space in the spatial structure of Quercus secondary forest in Hunan Province.There were significant differences(P<0.05)in every Quercus secondary forest except for stand angle scale,aggregation index and Competition index.Among them,the forest canopy degree is basically above 0.7,and all kinds of stands are basically closedThe number density of each stand type was the highest in LDC stand type,,which was twice as high as that of other plot types.Among the five forest types,the high,medium and low density stands all exist,but the overall stand density is relatively largeThe mean DBH of five stand types is "3 segments",among which the mean DBH of CR stand types and FF stand types is 18cm,the mean DBH of CQR stand types and CCR stand types is 15cm and LDC stand types is less than 10cm.According to the distribution of DBH,except that the DBH of LDC stand types is partial normal distribution,the other four kinds of forest plots are all inverted "J" distribution.At the same time,it can be clearly seen that the DBH of each forest type is concentrated in the middle and small steps(10-20cm,5-10cm),and the average DBH of Quercus secondary forest in Hunan is low.The average height of the four stand types was about 15m except FF stand type,which was 18m.In general,the average height of each stand type was not different.From the perspective of tree height,the tree height of five forest types are all partial normal distribution.At the same time,among the forest classification types,the tree height distribution in the 8-12m range accounts for the largest proportion.From the perspective of tree height,it is generally seen.From the perspective of comprehensive average DBH,the single tree growth of FF forest type is the best.The age of stand is between 20-80 years.Among them,CR stand types,FF stand types and CQR stand types stand types are multi middle age forest,with a certain amount of near mature forest and young forest;LDC stand types is all young forest,CCR stand types are only a small part of middle age forest,others are all young forest.Except for LDC stand types,the age of each stand type has some changesThe horizontal distribution pattern of the stand is basically aggregation distribution.From the uniform Angle Index,only one sample plot of CR stand types forest classification type is random distribution,and from the aggregation index direction,only seven sample plots are aggregation distribution.So on the whole,the horizontal distribution of Quercus secondary forest in Hunan is too centralized,and there is a large adjustment space.From the distribution of individual trees,the distribution probability of the Competition index of each stand type is similar in five cases(absolute advantage,advantage,mean,disadvantage and absolute disadvantage),while from the whole stand type,the average Competition index of five stand types is about 0.5,the differentiation of stand size is moderate,and the competition among individual trees in the sample plot tends to be stable.The mixed degree of stand varies greatly,and all kinds of mixed intensity exist.Among them,CR and FF stand types of intensity mixed plots and extremely strong mixed plots account for a large proportion,and the mixed degree of stands is high,while LDC stand type and CQR stand types of moderate mixed and intensity mixed occupies a large proportion,and the mixed degree is moderate.The main type of CCR stand type is low mixed and medium mixed,but the mixed degree is poor.As a whole,the mixed stand of Quercus secondary forest in Hunan is better.The change of stand openness is small,which is basically below 0.3.The light condition of LDC stand type is the worst and seriously insufficient,while the light condition of CQR stand type is better than the other four stand types,but on the whole,the light of the stand type is insufficient,and the vegetation in the forest gets less light resources.(3)The level of the biomass of Quercus secondary forest in Hunan is low,and the biomass of the understory is below 2.3 t · hm-2,among which,the biomass of CR forest is below 1.5 T·hm-2,while that of the other four stand types:FF,LDC,CQR,CCR is about 2.0 T · hm-2.In addition,in FF,LDC,CQR and CCR stand types,the biomass ratio of shrub layer and herbaceous layer is similar,but the herbaceous layer is slightly dominant.At the same time,the herbaceous biomass of CR stand type was significantly lower than that of other four stand types,which was the main reason that the biomass of undergrowth vegetation was significantly lower than that of other four stand type.(4)Pearson correlation analysis showed that there was no significant correlation between the mean DBH,mean height,stand age,Competition index and the biomass of undergrowth vegetation.Among them,canopy density has a significant impact on the biomass of herb layer of CR stand type and shrub layer of FF stand type;plant density has a significant impact on the plant density of CQR stand type;angle scale has a significant impact on the herb layer of CR stand type;mixing degree has a significant impact on the biomass of herb layer,total undergrowth and undergrowth of CQR stand type;aggregation index has a significant impact on the biomass of shrub layer of LDC stand type;open The total biomass of CR stand type was significantly affected by the exposure.However,the results of stepwise retrospective analysis are similar to Pearson correlation analysis.Only in FF stand type,the regression equation of undergrowth vegetation biomass in shrub layer further chooses the angle scale as the significant influence factor.(5)The best prediction model of undergrowth shrub biomass is WS=0.4791+0.0873Hs+0.0104Gs,and(R2)is 0.5381.When the aggregation index of the stand is added as a fixed effect,the accuracy of the prediction model of undergrowth shrub biomass increases the most,(R2)increases to 0.71,32.6%,plant density increases to 0.6997,30.03%;the smallest is canopy density,(R2)only increases up 5.7%.The best prediction model of understory herbage biomass is Wh=0.7054+0.4708Dh+0.9062Hh,with R2 of 0.3307.When the aggregation index of the stand is added as a fixed effect,the accuracy of prediction model of understory herbage biomass increases the most,(R2)increases to 0.5591,69.1%,followed by canopy closure,0.5507,66.5%;and the least is openness,R2 only increases.20.8%.In order to adjust the biomass of Quercus secondary forest in Hunan Province,we should adjust the horizontal distribution pattern of the stand and consider the covering degree and tree species structure.