Estimation of Niche Area for A. formosana

Because A. formosana is a rock plant, the DTM was integrated to estimate the niche area more accurately. The raster data of slope degrees and slope areas were calculated. The slopes ranged from 0.00° to 81.82°; this means that the increases in the hypotenuse and area ranged from 1 to 8.73 fold (with trigonometric function method). The distribution of A. formosana was extracted from the original photo­graphs and enhanced image. The RS data (0.25 m x 0.25 m) have a dissimilar spatial resolution compared to that obtained by DTM (5 m x 5 m). A pixel of the DTM image was separated into 400 subpixels to overlay raster data with two different resolutions appropriate. This system could be used to estimate the target area with the 3D method more easily.

Fig. 18.5 Original ortho-aerial photograph (a) and enhanced image (b)

Fig. 18.6 Estimation results of original photographs and enhanced image. (Punctiform polygons are classification results with image tone; Slash polygons are results with image tone and texture)

Because of cloud cover, the total study area was recalculated using ArcGIS (from 1,198.45 ha to 1,138.79 ha). The niche area for A. formosana was estimated using normal and 3D methods (combined with DTM). The results, including two classifica­tion results (classification by only color and by both color and texture) and the 3D method results, are listed in Table 18.2. The texture could help us extract another 15.62 ha (1.37%) of the target. The niche areas for A. formosana were estimated to be

Fig. 18.7 Field survey data in part of the Jiou-Jiou Peaks Natural Reserve: specific terrain in study area (a) and land cover of different directions in parts of study area (b)

Table 18.1 Error matrix of land use image in Jiou-Jiou Peaks Natural Reserve Reference data

Classified data

Forest

Arundo formosana

Basin

Bare soil

Row total

Forest

57

7

0

0

64

A. formosana

7

55

0

2

64

Basin

0

0

60

4

64

Bare soil

1

2

6

55

64

Column total

65

64

66

61

256

Overall classification accuracy = 88.67 %

Table 18.2 Estimation of areas for A. formosana in Jiou-Jiou Peaks Natural Reserve

A. formosana area (ha)

A. formosana area (%)

Total area (ha)

Image tone

284.38

24.97

1,138.79

Image tone and texture

300.00

26.34

1,138.79

3D method

628.07

32.86

1,911.26a

aEstimation of three-dimensional (3D) total area with the same 3D method

26.34 % and 32.86 % of the total investigated area by using the normal and 3D methods, respectively. This species can grow in steep regions where trees cannot. The (LU/LC) percentage of the species increased if the slope was considered; this was the reason why the area extended about 6.52 % with the 3D method.