A study on the relationship between the geomorphology and vegetation distribution of coastal dunes in the western Chianshuiwan, Sanjhih of Taipei County
Date Issued
2007
Date
2007
Author(s)
Chen, Yen-Hua
DOI
zh-TW
Abstract
Coastal dunes are very dynamic landforms where wind, geomorphology and vegetation interact within the system. Geomorphology affects exposure to wind, waves, salt spray, and resource available for vegetation. The aims of this study were to explore the geomorphology characteristics that affect coastal dune vegetation distribution in the western Chianshuiwan, Sanjhih of Taipei County. The field surveys included collecting geomorphology and vegetation data. The geomorphological characteristics were identified by establishing DEMs before and after the northeastern monsoon, and short-term changes were obtained by a subtraction between two DEMs. The six environmental variables were elevation, slope, aspect, distance from shoreline, sand movement and grain size. Classification of the vegetation was based on TWINSPAN, while CCA was used to identify environmental gradients linked to community distribution, and statistical analysis were used to compare geomorphological parameters between different vegetation types.
After a survey of contour maps, four geomorphological units were distinguished: frontal hummocks, dune platforms, longitudinal dune ridges, and dune slopes. Where elevation change most were frontal hummocks, erosion scarps and the foot of slope. In spite of abundant sand supply, wave and wind erosion happened frequently in frontal dunes, then irritated the formation of blowouts. On the margin of windward slopes, airflow was compressed both laterally and vertically, and the deflation became concentrated toward the crest.
Fifty three species in twenty nine familes were recorded from 193 quadrats located within the study area. Asteraceae, Poaceae and Convolvulaceae were the most frequent families, and Imperata cylindrica var. major, Artemisia fukudo were dominant species. The samples were classified into six vegetation types including Cynodon dactylon - Oenothera laciniata, Spinifex littoreus - Wedelia prostrate var. prostrate, Imperata cylindrica var. major - Artemisia fukudo, Bidens pilosa var. radiata- Vigna marina, Ipomoea cairica- Paederia foetida, and Pandanus odoratissimus- Pittosporum tobira. The main gradients, identified by CCA, were elevation and distance from shoreline. The vegetation zones were not only parallel to shoreline, but also varied with landform characteristics. The effect of other variables on vegetation distribution was different.
The discontinuous plant growth irritated sand accretion to form frontal hummocks, dominated by Spinifex littoreus and Vitex rotundifolia. Plants encouraged sand deposition over a wide range, leading to the development of sand platforms. Imperata cylindrica var. major - Artemisia fukudo extensively established on sand platforms and longitudinal dune ridges. The frontal dunes where Spinifex littoreus - Wedelia prostrate var. prostrate dominated were scarped by wind and waves. Because Spinifex littoreus - Wedelia prostrate var. prostrate was adapted to frequent disturbances and high sand movement, and could stabilize the foot of slopes. Once the vegetation were destroyed by disturbances, and this would led to the formation of blowouts. Then the airflow moving through gaps into the dunes made blowouts larger and deeper, until closer to the water table. The blowouts and slacks which were wetter and more sheltered could supply Pandanus odoratissimus- Pittosporum tobira shrubs with more water and nutrients. While airflow continued to erosion, the blowouts were elongated to form parabolic dunes. The largest amount of sand movement was found on southern slopes where the rake-like parabolic dunes were formed, and only Imperata cylindrica var. major - Artemisia fukudo grew on the ridges. The northern slopes were steepest in the study area, and Ipomoea cairica- Paederia foetida vines with flexile stems usually climbed upward on the steep and windward slopes. Bidens pilosa var. radiata- Vigna marina was dominant in the farthest upland platforms and closer to inland.
In conclusion, the geomorphological characteristics led some difference in coastal dune vegetation construction, composition, function and species diversity, and had different dominant communities. Coastal dune systems were too complex to understand, and needed more factors to interpret processes and vegetation distribution.
Subjects
海岸沙丘
植群圖
植物地形學
雙向列表比較法
典型對應分析
coastal dunes
vegetation map
digital elevation model (DEM)
phytogeomorphology
two-way indicator species analysis (TWINPAN)
canonical correspondence analysis (CCA)
Type
thesis
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