Quality assessment at subcompartment level of forests used for timber production based on factor analysis: a case study in Jiangle national forest farm, Fujian Province.

To study the quality of forests used for timber production at the Jiangle national forest farm of Jiangle County, Fujian Province, we analyzed and categorized its forest management inventory data and used factor analysis to find correlations among several forest quality indices. We then established an index system of timber forest quality at the subcompartment level. Four assessment aspects were covered, i.e.,a timber factor, understory vegetation, soil conditions and terrain conditions. After that we used the inventory data to calculate the weights of the four indices with factor analysis. formula for a quality index (SQI) at the subcompartment level is proposed based on this index system and quality indices for each of the 325 subcompartments of the Mingtoushan and Yufang regions were calculated and the number of species and density of trees in the various management subcompartments with optimal SQIs listed. The study results are as follows: (1) the SQI in stands at the sapling stage was low, it increased gradually in immature and near-mature forests and reached its maximum level in mature and overmature forests where the index remained stable. (2) The quality of the subcompartment in the Mingtoushan region was higher than that in the Yufang region at every age group. (3) From a quality point of view, there was no excellent-level subcompartment in either region. Even when there were only a few good-level subcompartments, most subcompartments were of the average and below average level. There is therefore ample room for improvement in the quality of the forests in the Jiangle national forest farm. The source of data was conveniently accessible, the weights were objective and the results comparable, to the use of our index system of forest quality at the subcompartment level, as in our case. The SQI calculated from our index system reflects the comprehensive benefits of forest management and provide references for making forest management plans in the future.