An NFI-based site quality evaluation of Chinese fir plantation

Forest site quality assessment refers to the judgment and prediction of the appropriate forestry or potential productivity of the site. It is an extremely important basic work in the forest management. Taking Zhejiang province as a research area, based on the four consecutive National Forest Inventory (NFI) data from 1994 to 2009, the maximum DBH growth rate as a site quality evaluation indicator on Chinese fir plantation is proposed. The quantification theory model I was used to establish a regression model of the relationship between the maximum growth rate of the DBH and the site factors. The results show that the model's multiple correlation coefficient is 0.3167, and the F test reaches a significant level at the F0.01 (7,190). The model's RMSE and RRMSE are 3.4160, 30.3165%, respectively. The RMSE and RRMSE of the test data are, respectively, 3.249% and 29.1397% and the fitting accuracy is acceptable. The impact of the site quality factor on DBH growth rate of Chinese fir plantation in descending order is followed by aspect, soil, topography, slope, slope position, altitude, latitude. As an indicator on-site quality evaluation, maximum DBH growth rate is easy to be extracted from NFI data, and forest age as the traditional key dependence will no longer be essential. The method with effective use of NFI historical data is applicable to the even-aged forest and uneven-aged forest. Constructing a site quality evaluation model with the maximum growth rate of the DBH can effectively evaluate the site quality of the study area and is of great significance in forestry production.