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Geology
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Application of RS and GIS in natural disaster survey: a case study
of mountainous landslide caused by the herb typhoon
Relations between the New Bareland and Land Use in Forest Area
There are six types of vegetation in the national forest area of this study site. The area of each
vegetative type is tree 63004.11 ha, grass 984.41 ha, tea field 79.34 ha, areca field 722.05 ha,
farm 606.33 ha, and orchard 182.95 ha in 1988, while bareland occupied some area in the
summer of 1996. Analyzed results (Figure 4) showed that the largest and smallest percentage
occupied by bareland in each vegetative type is tree (2 %) and grass (18%). After Herb typhoon
event, newly-happened bareland percentage (NP) in tree area was 6%, which was also the
smallest one in the six vegetative types. It revealed that NP in grass, farm, orchard, and tea or
areca field was 6.5 to 10.5 times larger than NP in tree area. Results also showed a spatial
dependence existed in NP distribution because there was 77 percent of NP closed to the
preexistent bareland patches.
Figure 4. Bareland Occupied and Vegetation Exist Percentage of Six Vegetation Type in Forest
Area.
Relations between the New Bareland and Terrain Slope
In view of terrain slope, NP was mainly distributed in the positions under 35 degrees of slope.
Figure 5 shows the area percentage of bareland of each class of slopes. The codes A, B, and C in
legend denote the total area of the site, bareland in T1, and NP in T2. The tendencies of
preexisted bareland in T1 (blue curve),
NP in T2 (red curve), and total
bareland in T2 (green curve) are very
similar. All curves presented a
parabolic form, and bending at the 4 th
slope class, i.e. 26~35 degree, in
which a higher bareland percentage
existed far from that point was
revealed. The natural disaster or
illegal farming in slopeland might
cause this phenomenon.
Figure 5. Variations of the Area Percentage of
Bareland in Six Classes of the Slopeland.
Conclusion
Spatial pattern of newly happened bareland patches revealed that the importance and necessity
of conservation for the land nearby the riverbank and road. Although the bareland area in tree
area is larger than the other five vegetative types, but in view of bareland occupied percentage,
the disaster resistance of tree is better than grass, orchard, farm, tea and areca field. There is a
spatial dependence in related to existing bareland. It could be a reference for forest manager in
management planning. For sustainable management, manager should pay intention to sites with
a lower slope to prevent an illegal farming.
References
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Liou, J.C., Lin, C. and G.Y. Chen, 1998. The research on bare area of six districts in Chiayi slope
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