| Ancient trees are important products and cultural resources of a country.They also witness climate,ecology,biology,geography and so on.Because of their strong adaptability and resistance to stress of environment,they have passed natural selection,thus they can continue to continue.Therefore,ancient trees often become important reference objects when choosing native tree species or suitable tree species in gardens.Therefore,it is of great social significance for the widely exploitation and utilization of ancient tree resources to carry out the investigation of ancient trees.The age of the ancient tree is the basis for classifying the ancient tree,and it can be used to protect and strike resale behavior for ancient tree.In the actual investigation,the growth indexes such as DBH,height and crown width of the ancient tree can be read directly by the relevant instruments,and the determination of the age of the ancient tree is a very difficult technical problem.At present,the ancient tree age determination methods mainly include the traditional age-dating method,the science and technology age-dating method and the regression model age-dating method,in which the traditional age-dating method mainly includes the count tree rotation method,the consulting literature method,the interview method,and so on.The traditional age-dating method has the advantage of low cost,but the precision is not enough.The science and technology age-dating method mainly includes CT scanning method,X-ray method,14C method and so on.Compared with the traditional method,science and technology age-dating method has high accuracy,but it needs to rely on the excellent measuring equipment,so the cost is high.The regression model age-dating method is equivalent to a compromise method,which is more accurate than the traditional age-dating method,and has the advantage of low cost compared with the scientific and technological age-dating method.After investigating the ancient and famous trees in Changsha County,this study takes tree age as dependent variable,DBH,tree height and crown width as independent variables,set to x1,x2,x3,and establishes single-factor model,double-factor model and three-factor model according to the number of independent variables.Seven common tree growth models were used for fitting,and the correlation coefficient R was used to judge whether there was phase between the independent variable and the tree age,correlation,when p<0.05 indicates that there is correlation between them,and the optimal model of tree age prediction is selected according to the determining coefficient R2,when the value of R2 is closer to 1,the fitting effect of the model is better.The main findings are as follows:(1)There are 331 ancient Cinnamomum camphora in Changsha county,includes 5 first class ancient Cinnamomum camphora,with an average age of 756.00 years,an average height of 13.60 m,an average DBH of 230.60 cm,an average crown width of 17.20 m;and 14 second class ancient camphor trees,with an average age of 362.12 years.The average tree height is 15.10m,the average DBH is 147.30cm,the average crown width is 18.10m;and 312 third class ancient camphor trees.the average tree age is 150.09 years,the average height is 15.58m,the average DBH is 80.46cm,and the average crown width is 13.88m.From the point of view of the distribution area,there were 313(94.60%)ancient camphor trees in the rural area and only 18(5.40%)in the city.According to the analysis of ownership,285(86.10%)were state-owned,32 were collective-owned and 14 were individual-owned.Most of the ancient Cinnamomum camphora grow near the rural streets and the environment is good.(2)By observing the relationship between tree age with DBH,tree height and crown width,we can preliminarily judge that DBH has a significant positive correlation with tree age,that is,DBH continues to increase with the increase of tree age,However,there was no significant correlation or even negative correlation between tree height or crown width with tree age.(3)The eancient Cinnamomum camphora age model is classified according to the number of independent variables.It can be divided into single-factor model,double-factor model and three-factor model.When the model is a single factor model,the best model for predicting the age of ancient Cinnamomum camphora is age-DBH model,the expression is Y = 1.71×1.02;When the model is a two-factor model,the optimal model for tree age prediction is age-DBH model and height model,and its expression is Y=2.08x1-1.22x2+5.54;When the model is a three-factor model,the tree age prediction model is still is Y=2.08x1-1.22x2+5.54.Owing to the R2 value of single-factor age-DBH model is greater than that of double-factor age-DBH and tree height model and three-factor age-DBH,tree height and crown width model.Therefore,the optimal model for predicting the age of ancient Cinnamomum camphora in Changsha County is Y =1.71x1.02.(4)Checking the model reveals that:when the DBH is about 20cm,the model Y =1.71x102 is used to predict the age of Cinnamomum camphora,which is often larger than the measured ones,so the relative error is about 95%.Therefore,this model is not suitable for predicting the age of Cinnamomum camphora with smaller DBH.When the DBH is about 40cm,the relative error is about 13%,and the relative error between the predicted value of tree age and the measured value is reduced greatly.When the DBH is getting larger and larger,that is,when the tree age is hundreds of years old,the relative error between the predicted value and the measured value of the tree age is only 5%.Therefore,it can be inferred that the relative error becomes smaller and smaller when the DBH is increasing,so this model is suitable for predicting the age of Cinnamomum camphora with larger DBH,that is,the model Y=1.71x1.02 is suitable for the prediction of the age of ancient Cinnamomum camphora.(5)The growth of trees is often affected by their site conditions.When the site conditions are good,the trees tend to grow faster,so the time required to reach a certain amount of growth is shorter.When the site conditions are poor,trees tend to grow slowly and take longer to reach a certain amount of growth,so that the same tree species in the process of reaching the same growth amount,The time required for site conditions is often shorter than that for poor site conditions.According to the results of this study,when the site conditions are good,the ancient Cinnamomum camphora age prediction model is Y = 0.9*1.71x1.02,when the site conditions are general,the ancient Cinnamomum camphora age prediction model is Y = 1.71x1.02,and when the site conditions are poor,the old camphor tree age prediction model is Y = 1.71x1.02.The age prediction model of ancient Cinnamomum camphora is Y = v＝1.1*1.71x1.02. |
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