| Summary: | 碩士 === 國立彰化師範大學 === 地理學系 === 97 === Abstract
Temperature and humidity are important factors that affect plant growth and distribution. Drought and heat stress disturbances during foehn have major impact on plant growth. Therefore, this research aims to clarify how vegetation responses to drought and heat stress of foehn in Yilan. The Lotong stream watershed was selected as the study site. 4 SPOT images that were acquired prior to and after foehns (1997/08/06, 2003/08/07) together with geographical information system to calculate Normalized Difference Vegetation Index ( NDVI) and evaluated changes in vegetation cover.
The results indicate that severity of foehn disturbance was largely determined by drought and heat of foehns. Foehn in 1997, which had higher temperature and lower relative humidity, caused 9.5% decrease in NDVI. The smaller strength of foehn in 2003 caused 3.2% decrease in NDVI. The result suggests that the strength of foehn may be a factor that affects NDVI. The changes in NDVI caused by spatial variations were closely related to geomorphology and topography at finer scale. At lower elevations and windward slope, the decreases in NDVI were higher than higher elevations and leeward. In addition to topographical effect, NDVI decrease rates associated with foehn disturbance also differed among different stands. The NDVI variation at farms and grass were significantly higher than those at forests.
Compare the NDVI decrease caused by different plants with that caused by elevations, forests which have high drought resistance even at low elevations were still decrease much. The result suggests that there is likely a threshold foehn strength above the decrease of different plants.
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