| Forest site quality evaluation is an important basic work of forest cultivation.Quantitative index method is most commonly used to evaluate site quality.It is generally necessary to know the age of trees in the application,and mainly for the even-aged forest and pure forest.With the transformation of China’s forestry from timber production to ecological benefit with consideration of timber production,near natural management will be more adopted in production and management,which is more conducive to the construction of healthy and stable forest ecosystem.More uneven-aged and mixed forest will be cultivated,but even-aged pure forests will be fewer and fewer,and the traditional site indexes and methods will not meet the needs of modern forest management.We explore an index and method which can be used flexibly in a large area without limiting the tree species structure and age structure of the stand and measuring the age of the tree.In the past decades,a large number of data of permanent sample plots and permanent sample trees have been accumulated in the National Forest Inventory.These data are generated by probability sampling,with wide coverage and reasonable distribution.The indexes and methods proposed in this paper will be established by these data.The advantages of this data are:a)the modeling data is sufficient without additional investigation;b)the model has a good application foundation after it is established.The specific methods of index construction are as follows:a)Select the remeasuring data of the adjacent two periods of sample plots and select the 5 samples trees with the largest DBH in the later period in each sample plot,and form 5 pairs of DBH data.b)Modelling a maximum density model.Based on this model,5 pairs of DBH data of two periods are transformed into 5 pairs of volume per hectare data(y1,y2)under the maximum density,that is,one DBH corresponds to one volume data.3)Modelling based on the(y1,y2)of the same tree group in all sample trees Where c0 and c1 are the parameters,and ΔA is the review interval.S is the site quality evaluation index defined in this paper,which is actually the asymptote parameter of the model.The site quality index S can be calculated with(y1,y2).The model has two characteristics:a)no age;b)the data in the two periods are independent variables and dependent variables.In this paper,a new parameter estimation method is proposed,which is called "hierarchical iterative parameter estimation method of curve cluster age implicit model",to solve the problem that the common parameter estimation is unreasonable.In this paper,the hectare volume under the maximum density is calculated based on the DBH of sample trees,and the DBH growth of sample trees is affected by tree competition.In order not to make the model too complex,the competition factor is not considered in the growth model.After obtaining the index S(5 S for each plot,1 sample tree is to calculate a S),the following equation is used to adjust the S to eliminate the influence of competition Where β is the parameter,DR is the relative DBH,that is,the ratio of the current sample DBH to the maximum DBH in a sample plot.Based on the data of year 1999-2004 in Zhejiang Province,the models are established,including Pine tree model,Chinese fir model and broad-leaved tree model.The remeasuring data of 2004-2009 and 2009-2014 are used to test.The test method is variance analysis,that is to test whether the difference between the 5 site indexes within the sample plot is significantly smaller than that between the sample plots.The test results show that the variance analysis of modeling data and test data is very significant,that is,the change of index within the sample plot is significantly less than that between the sample plots,which shows that the indicators and methods proposed and established in this paper have the ability to distinguish the site quality and have application value.The regression equation between S and environmental factors is established,it can be used for the evaluation of non-forest land and the mapping of site quality on a large scale.The main innovations are as follows:1)A new quantitative index is proposed,which does not need age,and require the even-aged and pure stand.The index is the asymptote parameter of the maximum density volume growth model.2)A new method of parameter estimation is proposed,which is called hierarchical iterative method for age-implicit curve cluster model. |
