| Forest site quality evaluation is a key step to achieve accurate forest quality improvement,but the traditional site quality evaluation methods such as site level for pure forests and plantation forests are no longer applicable to today’s forestry development goals that emphasize the ecological effects of forests,especially in the northeastern region with large secondary forests.For this reason,this paper takes natural secondary forests in the Maoershan region as the research object,based on the data of Category II survey of forest resources in 2016 and fixed plots.The site quality of hard and soft broad-leaved mixed forests were evaluated by indirect evaluation methods based on site factors and direct evaluation methods(site index and site form),respectively,the differences between the two direct evaluation methods in classifying site quality levels were compared and analyzed,and the evaluation results of the 2evaluation methods of indirect and site form for site quality were validated and analyzed by hard and soft broad-leaved mixed forests,The following results were obtained:(1)Four terrain factors such as slope,eight soil factors such as soil organic matter,and a total of 12 site factors were selected,and the weights of the integrated function values of each site factor were determined by using Analytic Hierarchy Process(AHP).The weighted summation was used to calculate the integrated score of site quality based on each site factor.The small classes were divided into four site quality classes:excellent(Ⅰ),good(Ⅱ),medium(Ⅲ)and poor(Ⅳ).Among them,the number of small classes with site quality gradeⅡis the largest,accounting for 39.6%of the total area;followed by small classes with gradeⅢ,accounting for 29.8%of the total area;small classes with site quality gradeⅠandⅣaccount for 16.9%and 13.7%of the total area respectively.(2)Site index evaluation:The age-mean stand height guide curve of hard and soft broad-leaved mixed forests was determined as Richard’s(Richards)equation,and the status level index table was prepared.The results of site quality evaluation showed that the number of small classes with site quality ofⅢgrade in hard and soft broad-leaved mixed forests was the largest,followed byⅡgrade,and the number of small classes with stand quality ofⅠandⅣgrade was relatively small.Site form evaluation:The optimal model was selected by comparing the coefficient of determination(R~2)and root mean square error(RMSE)of the eight selected growth equations.Korf and Richards,which had the lowest R~2 error,were selected as the guide curves for hard and soft broadleaf mixed forests,respectively,and the site quality table was prepared.The results of the site quality evaluation showed that the number of small classes with site quality of I,II and III grade in hard and soft broad-leaved mixed forests was high,and the number of small classes of grade IV was low.Comparing the two evaluation methods,the overall trend is approximately normal distribution,but the peak of the site form index shifts to the left relative to the site index;in the evaluation of natural secondary forest site quality,the error of the site index evaluation is greater than that of the site form index.(3)The indirect evaluation results based on site factors were compared with the direct evaluation results of the site form,and the results showed that the values of indirect evaluation were significantly positively correlated with the site form index(p<0.01),indicating that the two evaluation indexes had the same trend,and the consistency of the two evaluation results for small classes of soft and hard broad-leaved mixed forests with site quality class I and II was84.2%and 81.6%,respectively,reflecting that the site quality was relatively similar.The quality of the site was similar.Most of the hard and soft broad-leaved mixed forests in the upper and middle site conditions have site quality classes I and II,and the applicability of indirect evaluation of site quality based on site factors is also verified.In this study,the prediction of growth potential of any stand based on the indirect evaluation method of site factors and the evaluation of site quality of realistic stand types based on the site form index,the two evaluation results are more consistent,and the combined application of the two methods can better reflect the use of the site by tree species(groups)and the evaluation of matching tree species with site,and provide reference for the adjustment of stand density and structure. |
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