A Study Of Site Quality Evaluation Of Chinese Fir Plantation Based On NFI Data Of Zhejiang Province

Site quality assessment of forests refers to the judgment and prediction of site afforestation or potential productivity,which is an extremely important basic work in scientific forest management.As an important tree species planted in China,site quality evaluation of Chinese fir plantation is an important basic work for scientific and rational planting and management of Chinese fir forests.The traditional forest site quality evaluation is based on the site index or site level as an important index,that is to say,the site quality is evaluated by two direct evaluation methods: average height and stand average height of dominant trees in stand.Although these two methods have high accuracy in the quality evaluation of the same age forest,a large number of field investigations are needed,cutting and making analytical wood,resulting in high economic cost and ecological cost.This is a major challenge for forest site quality evaluation.In order to solve this problem,the research on forest site quality evaluation assisted by 3S technology has been carried out for many years,but the results are not good in efficiency,cost and practical comprehensive performance.The national forest resource inventory data(National Forest Inventory,NFI)is a kind of data with wide coverage and reliable precision,but it is rarely used in the forest site assessment research on a large scale.The related cases are mainly combined with remote sensing images to take the total biomass of the sample land as the evaluation index.However,the total biomass of the sample plot is affected by many interference factors,such as age,human activities and so on,so it is difficult to evaluate the forest site quality accurately.Based on the NFI data of Zhejiang Province from 1994 to 2009,the maximum DBH growth rate was extracted from the four NFI survey data according to the growth law of forests,and was used as the site quality evaluation index of Chinese fir plantation.The topographic factors and soil types extracted from digital elevation model(DEM)data and soil survey data are used as site factors.Based on the quantitative theory I,the site quality model of Chinese fir plantation is established.The contribution rate of different site factors to site quality is analyzed,and the accuracy of the model is evaluated by t-test of multiple and partial correlation coefficients.To verify the applicability and generalization of the model,the model is tested by the survey data of Linan area.Finally,the site of Chinese fir forest in Linan area is tested.Quality grading evaluation.The results are as follows:(1)The maximum DBH growth rate index of sample plot based on NFI data was put forward.Using NFI continuous observation data,the time series of reduction sample growth rate and its distribution in each sample land were extracted and analyzed.The evaluation index of productivity,that is,the maximum DBH growth rate index,was obtained by using the average value of three dominant trees.The site quality evaluation model is established by using the maximum DBH growth rate,which achieves high accuracy prediction.(2)Quantitative theory model I was used to establish the site quality evaluation model of Chinese fir plantation.Using the terrain and soil survey data in the DEM data as the site factors,the model is established.Through the multiple correlation coefficient and t-test,it is shown that the regression relationship between different site factors and site quality is significant,and the contribution of each factor to the regression model is greater.On this basis,the results of variance ratio of each factor show that the contribution degree of DBH growth rate from large to small is slope direction,slope position,soil type,slope,latitude and altitude.(3)The average error and root mean square error are used to test the fitting accuracy of the site quality evaluation model of Chinese fir.The results show that the fitting degree of the model is better.The model not only evaluates the productivity of Chinese fir forest,but also predicts the productivity potential of non-forest land according to the historical data of NFI.(4)Based on the model established in this study,the site factor data in Linan area are substituted into the model for prediction.The forest site quality is evaluated,and the prediction results are compared with the measured data,and the prediction results of the model are verified.The test results show that the actual verification results are in good agreement with the predicted results.According to the prediction results,the site quality grade score was carried out by using the maximum DBH growth rate.The site quality of Chinese fir forest in Linan area can be divided into four grades.The distribution of high-grade areas is more dispersed,mainly in valleys,flat land and non-slope areas,indicating that the relationship between the site quality and the slope position and direction is more obvious.