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四湖海岸木麻黃林下海檬果天然更新特性之研究

Characteristic of Natural Regeneration of Cerbera Manghas and Casuarina in Sihhu Coastal Windbreaks

摘要


本研究自1995年、1998、2002至2004年分次調查四湖海岸木麻黃林下海檬果族群之變遷,探討其族群結構變化及其與林分更新之關係。設置一個由70個4m×4m小區所組成的永久樣區。以1995年之調查結果為基準,依各小區之幼苗、幼木、成木、母樹之株數、胸徑、樹高及樹冠幅等變項,運用平均階層分析法進行群團分析,共區分為3群不同更新區塊之鑲嵌體。經10年監測結果,樣區內木麻黃株數均呈下降趨勢並衰退。至於林下海檬果成熟木(成木及母樹)之株數則呈現增加趨勢,其幼苗之成長卻呈現波動現象,顯見海檬果種子在林下萌發並無困難,但成長上卻有競爭壓力。四湖海岸木麻黃林經長年變遷,冠層主林木之木麻黃族群已有明顯改變,總株數減少61%,族群結構由原先的反J形曲線,轉變為鈴型曲線,林下無更新小苗,顯見此族群逐漸衰退並形成孔隙。而海檬果族群則呈現反J形曲線,因林下具有穩定的小苗,其比值(樹木:苗木)在2004年為1:1.49,故族群具拓展潛力。目前整體木麻黃林帶平均高度為8.3m,而海檬果成熟木平均高度為6m,與10年前之高度(6.4m)比並無增加,故未來整體林帶如被海檬果取代後是否能達到木麻黃林帶之防風機能,尚待進一步評估。

並列摘要


This study was started from 1995, and continued in 1998, 2002 and 2004, aiming at the changes and regeneration of the population of Cerbera manghas under Casuarina plantation in the Shihu coastal windbreaks areas. One permanent plot with 70 aggregated 4m×4m subplots was set up in the Sihhu coastal windbreaks. Based on the result of the investigation in 1995, the variation of individual number, Dbh, height and canopy of seedling, young tree, vigorous trees, mother trees of subplot, were analyzed with the K-mean cluster method. The result could be clustered in 3 mosaic groups. In this permanent plot, the population of Casuarina showed a serious decline. But Cerbera manghas population, showed an increasing trend and with some extent of fluctuation. Cerbera manghas seeds had no difficulty in germination under the Casuarina plantation, but the competition was getting keener in the growth of seedling. In this permanent plot, the main canopy of Casuarina had a significant change. The total individual number reduced 61%. Their population structure turned from a reverse J to bell-shaped curve, and without regeneration of seedling under the plantation. The population was obviously in decline and the canopy gaps formed and expanded. But Cerbera manghas population still showed a reverse J curve, with steady occurrence of seedling. The rate of tree: seedling was 1:1.49 in 2004, which indicated a potentially developing population. The total average height of Casuarina was 830 cm, different than 600 cm of the mother tree of Cerbera manghas, showing no increase comparing to the height (640 cm) 10 years ago. Therefore, if the total forest area is replaced by Cerbera manghas, whether the windproof mechanism of Cerbera manghas can be as good as Casuarina still needs further evaluation.

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