terms of accuracy and implementation efficiency and
determined the optimum for predicting the habitat of a rare
plant. The predictive outcome from SDM would be used to
prioritize field-survey areas for collecting fine resolution
microclimatic, edaphic or biotic data for refining predictions of
potential habitat in the later rounds of SDM or search areas for
new population discovery.
2. STUDY AREA
The study area consists of two parts, one part is Huisun
Experimental Forest Station (HEFS), and the other is
Tong-Mao Mountain, as shown in Figure 1. HEFS is in
central Taiwan, and situated within 242°-24°5" N latitude and
1213-121 7' E longitude. This station is the property of
Chung-Hsing University, and has a total area of 7, 477 ha.
This station ranges in elevation from 454 m to 3, 419 m, and its
climate is temperate and humid. Hence, this area has
nourished about 1,100 plant species and is a representative
forest in central Taiwan. This study took the samples from
Sihwufongshan (Pine-breeze Mountain), Duhchuanling
(Cuckoo Ridge) and Kuandaushan (Big-knife Mountain) trail in
Huisun, Sihwufongshan elevation from 680 m to 840 m, the
highest elevation of Duhchuanling approximately 810 m, and
Kuandaushan elevation approximately 760 m. According to
the climate record of this study area, the annual mean
temperature is 21.0°C ; the monthly mean temperature highest is
30.6C in July, lowest is 20.5'Cin January; mean annual
precipitation 2453.5 mm, the average relative humidity is 85%.
Tong-Mao Mountain is situated at geographic coordinate
24°11'N latitude and 120°57' E longitude, near the Ta-chia
River and Tong-Mao River, 10 km farther north from Huisun
area. The elevation of Tong-Mao Mountain rises to 1690 m
above sea level. According to the climate record of forest
district office website, the annual mean temperature is 22.6°C ;
mean temperature highest is 29°C in July, lowest is 15°C in
January; mean annual precipitation 2580 mm. The mountain
has rich ecological resources cycad-fern (CF), Blechnaceae
family, is only found in mountains in central Taiwan, such as
Huisun and Tong-Mao Mountain areas, and Huisun is the main
habitat. Because of its limited ecological range, cycad-fern
has been categorized as one of the rare, endangered species (Lu
et al, 1986).
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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
Figure 1 Location map of the study area.
3. MATERIALS AND METHODS
3.1 Data Collection
We collected digital elevation model (DEM) with grid size 5 x
5 m, orthophoto base maps (1:10,000), and nine-date SPOT
images (SPOT Image Copyright 2004 and 2005, CNES). In
situ data (cycad-fern samples) were also acquired by using a
GPS linked with an expandable antenna rod of 5m in length
and a laser range finder, the error was usually below one meter
after post-processing differential correction. Two-date SPOT
images (07/10/2004 and 11/11/2005) were chosen because they
have the best quality with the least amount of clouds among the
nine-date SPOT images.
3.2 Data Processing
Slope and aspect data layers were generated from 5 x 5 m
DEM. The ridges and valleys in the study area were used
together with DEM to generate terrain position layer. The
main ridges and valleys were directly interpreted from the
contour lines shown on the orthophoto base maps; these lines
were then digitized to establish the data layer by using
ARC/INFO software for later use. The relative position (Pj)
of the test cell in the terrain is expressed as follows:
Pj PV/ (PV * PR) (1)
PV = Euclidean distance from P to the nearest valley line.
PR = Euclidean distance from P to the nearest ridge line.
P; = 0.0, terrain position is assigned to be "valley".
P; = 1.0 , terrain position is assigned to be "ridge".
The data layer in a vector format was converted into a new data
layer in a raster format by ERDAS Imagine software, and then
combined with DEM to generate terrain position layer
(Skidmore, 1990). Vegetation indices were derived from the
two-date SPOT-5 images, one in autumn, the other in summer,
by using Spatial Modeler of ERDAS Imagine. CF samples
obtained by GPS were converted into ArcView shapefile format
for later use.
There were 221 CF samples collected from Sihwufongshan,
Duhchuanling and Kuandaushan-trail in Huisun forest station
and one site at Tong-Mao Mountain by GPS in this study, but a
part of these samples remained after data integration because
some cycad-ferns fall within the same pixels with others,
respectively. Five sampling schemes (SS), from SS-1 to SS-5,
were created with different combinations of cycad-fern samples
collected from the four sites. (A) SS-1, use two-thirds (2/3) of
Sihwufongshan and Duhchuanling dataset for base model
construction and the remaining (1/3) for model validation
(evaluation). (B) SS-2, use the same base model built in SS-1
and only use independent samples taken from
Kuandaushan-trail for base model evaluation. (C) SS-3,
merge the samples from three sites in Huisun and then separate
the dataset into two subsets, subset-1 containing two-thirds of
the dataset for first data-merged model construction and
subset-2 containing the remaining (1/3) for model evaluation.
(D) SS-4, use the first data-merged model built in SS-3 and
only use independent samples from Tong-Mao Mountain for
model evaluation. (E) SS-5, merge aforementioned four-site
samples and separate the dataset into two subsets, the first
subset containing two-thirds of the dataset for the second
