77 Short Communication Development and Validation of Ecological Site Quality Model: An Example of Chamaecyparis formosensis in Taiwan Fong-Long Feng* 1 and Chang-Ching Wu* 2 ABSTRACT An ecological site quality model was developed to aid in predicting the suitability of new locations for growing tree species. This model uses environmental variables to evaluate potential productivity. Data was input into a geographic information system, including 3rd Forest Resources and Land Use Inventory of Taiwan by integrated data from the climate data of the Central Weather Bureau of Taiwan, the Taiwan Forest Bureau, the Council of Agriculture in Taiwan, and the United States Naval Observatory to model the distributions of elevation, slope, aspect, solar radiation, rainfall, evapotranspiration, temperature, and soil nitrogen within Taiwan. Ecological requirements of Chamaecyparis formosensis were derived from the literature and from 211 ground survey plots. Using 22,501,993 40 m × 40 m grids within Taiwan, we modeled the requirements of C. formosensis for solar radiation, temperature, evapotranspiration, soil moisture, and soil nitrogen. We tested the model by comparing predicted sites to its known distribution of C. formosensis in Taiwan. All of the known locations of C. formosensis fell within the area predicted by the model and about 63.91% of the ecological site quality (ESQ) values were above 0.6. It showed that the model is good for evaluating the site quality for the tree species. Keyword: Chamaecyparis formosensis, geographic information systems, GIS, individual response function, species distribution, site quality INTRODUCTION The Red Cedar, Chamaecyparis formosensis, is an endemic species of Taiwan. A dominant species in Taiwan’s temperate coniferous forests (Horng et al., 2000), it is found between 1,000 m–2,600 m in elevation (Wang, 1968). It can reach a height of 50 m and a diameter of 300 cm (Wang, 1968). It is a large, slow-growing tree (Kuo, 1995) with an excellent longevity beyond 2,000 years, as recorded by Wang (1968). Because of its great size and the durability of its rot resistant wood (Wang, 1968), it was in great demand. Since 1912, this tree species was harvested so intensively that it was in danger of extinction (Lee, 1962; Horng et al., 2000). Almost 57% of the estimated 102,000 ha–112,000 ha orig- inal forest of C. formosensis, and its congeneric C. obtusa var. formosana, was logged (Horng et al., 2000). Apart from the cease of C. formosensis in 1989, also there is an ongo- ing efort to plant new stands and to regenerate the forests (Horng et al., 2000). About half of this forest has since been replanted. Much of its range is now protected by national parks and nature reserves (Horng et al., 2000). Since histori- cal records are limited (Horng et al., 2000), however, there is some difculty in identifying suitable places in which to plant new stands. The site index model is useful to estimate the quality of various stands of a given species of tree (Clutter et al., 1983). Since this method relies on detailed information from the trees in the stand, it requires current or previous existence of a particular tree species within the stand (Clutter et al., 1983). This means that the site index model cannot be used to asses a site in which to grow a new tree species. Botkin (1993) developed an individual response function that combines the environmental variables (light, tempera- ture, drought, and nitrogen) of a stand with the maximum basal area of a tree species to classify the quality of the stand for the tree species. By requiring information on the basal area, the applicability of Botkin’s model is also limited for sites Corresponding author: Fong-Long Feng * 1 Department of Forestry, National Chung Hsing University, Taichung, Taiwan., 250, Kuo Kuang Rd., Taichung 40227, Taiwan, R.O.C. E-mail: ffeng@nchu.edu.tw * 2 SuperGeo Technologies Inc. 8F, NO.217, Sec.3, Nanjing E. Rd. Taipei 10410, Taiwan, R.O.C. J. For. Plann. 22: 77–83 (2018)