Study On Spatial Structure And Growth Regularity Of Cypress Plantations With Different Site Types In Hilly Area Of Sichuan

Cypresses（Cupressus funebris）are the main afforestation tree species in the hilly area of Sichuan and occupy an important position in Sichuan’s forest resources,but the operation of Sichuan cypress plantation has problems such as unreasonable stand spatial structure,slow growth,and extensive operation and management.Near-natural management is a research hotspot of forest management,and the"target tree management operation system"is a near-natural forest management operation system carried out with a single forest as the research object,which is a way to transform the near-natural management of planted forests.Reasonable stand spatial structure is the prerequisite for realizing near-natural forest management,and the determination of target tree density and the study of growth regularity are of great significance in target tree management.In this study,the nearly mature cypress pure forest of the state-owned forest farm in Qiqushan in Zitong County was used as the research object,and the spatial structure unit of the stand was constructed based on the Voronoi diagram based on the field survey data,and the uniform angle index((2₄)),neighborhood comparison(₄)),opening degree(₄)),forest layer index(₄))and competition index(₄))Five spatial structure parameters were used to compare and analyze the spatial distribution pattern,size differentiation degree,light transmission conditions in the forest,forest layer diversity status and forest space competition of three different site types;the spatial structure parameters were divided into three levels,and the target trees were selected based on the actual forest stand and the trunk analysis was carried out to analyze the growth regularity of the target trees of the cypress plantation,which provided a theoretical basis for improving the stand structure of the inefficient cypress forest in the hilly area of Sichuan,rationally managing and cultivating excellent large-diameter cypress.The main conclusions are described below:（1）In this study,15 cypress forest standard plots were divided into three site types:I,Ⅱand III.（2）There were no significant differences in the minimum spatial structure unit,uniform angle index,dominance index and opening degree of cypress stands among the three site types（P>0.05）.The spatial structure of the three site types of cypress stands was composed of one central tree and six neighboring trees;the overall spatial distribution pattern of forest stands was uniformly distributed;the degree of differentiation of forest stand breast diameter is similar,and the growth pattern is moderate;the light transmission conditions in the forest are poor,and the growth space is insufficient.（3）There were significant differences in the forest layer index and competition index of cypress stand among the three site types（P<0.05）.The vertical stratification of cypress forest stands of site type III was the most obvious,and the vertical structure of cypress of site type I was the simplest;the competition for the space of cypress stands of site type III is the most fierce,and the space competition of cypress stands of site type I is the weakest;the larger of cypress diameter grade,the less competition is from the surrounding trees in the entire stand,and the more advantageous it occupies a favorable position in growth.（4）Regularity of breast diameter growth:the growth of chest diameter of target trees of cypress trees of the three standing types showed a trend of"slow-fast-slow"overall.The average growth and continuous growth of cypress target trees of site types I and II did not intersect in the first 50a（except the starting point）,while the joint growth of site type III appeared in 50a,and the continuous annual growth of the breast diameter before intersection was greater than the average growth.Cypress plantations have the largest growth rate in the first 20a and are the fast-growing stage of breast diameter.The final fitting optimal chest diameter growth equations for site type I～III were₁=92.538*（1-0）^{（-0.007*）})^1.511、₂=33.834*0)^-75.70*.、₃=27.615*（1-0）^{（-0.021*）})^1.633.（5）Tree height growth regularity:the target trees of the three site types showed a trend of"slow-fast-slow"in the overall high growth of cypress trees.The age of the intersection of the average growth rate and continuous growth of cypress of site type I～III was 20～30 a,30～40 a,and 40～50 a.Cypress grew the fastest in the top 10 a tree height,the growth rate was about 20%,and with age,the growth rate of cypress trees slowed down.The optimal fitting results of tree height growth equations for site type I～III were₁=28.753*（1-0）^-0.022*)1.475、₂=17.844*（1-0）^-0.041*)1.5、₃=2.697*0)-3.043*0).*.（6）Volumetric growth regularity:the volume growth of the three types of cypress target trees in the first 50a showed a trend of slow first and then fast,and there is no intersection between the annual growth and average growth of the volume（except for the starting point）,and there was no downward trend,so the volume did not reach quantitative maturity in the first 50a.The growth rate of mass gradually decreases with age.The fitting results of the optimal volumetric growth equations for site type I～III were（1₁=4.996*0）^-.534*0.*)、（1₂=6.983*0）^-10.25*0.*)、(1₃=5.58*（1-0）^{（-0.004*）})^3.415.In summary,the spatial structure of stands of cypress with different site types has significant differences in vertical stratification and spatial competition.It is feasible to select the target tree based on the spatial structure index of the forest stand and then determine the suitable density of the target tree.In addition,the trunk analysis data can be used to fit the breast diameter,tree height and volume growth process of the target cypress tree,which can effectively simulate the growth process of cypress and analyze the growth law,and the fitting results meet the accuracy requirements.