Niche Analysis for A. formosana

Although A. formosana is distributed widely below 1,800 m MSL in Taiwan, we still lacked niche information; therefore, we performed this study to gain an understanding of the niche. Slope and aspect were computed using Horn’s algo­rithm. The aspect values were grouped into eight principal directions (north, northeast, east, southeast, south, southwest, west, and northwest). Data of the slope and aspect helped us to measure the terrain spatial distribution of A. formosana. The relationship between environmental factors (slopes and aspects) and (LU/LC) was evaluated using two-way analysis of variance (ANOVA) and cluster analysis. Above the synthesis states, we integrated the ortho-aerial photo­graphs and DTM after considering the characteristics of A. formosana. A textural image was created with the gamma filter to help us to estimate the distribution accurately. The niche area of the species was also calculated using both methods [normal and three-dimensional (3D) methods], and we discussed the benefits of texture image enhancement and the 3D method. Then, the niche information was also obtained. Figure 18.4 is a flowchart that describes all these concepts.