孔隙對苗栗縣海岸木麻黃林物種多樣性之影響

Abstract

本研究在苗栗縣竹南鎮海岸林設置3個30 m × 100 m的大樣區，並將大樣區分為120個5 × 5 m2的小樣區進行植群調查以及對大樣區中的孔隙進行測量，目的在於探討孔隙對植物多樣性增加之影響。植群調查結果共記錄29科45屬49種植物，菊科、禾本科與大戟科出現的植物種數最多。 研究區中共計14個孔隙，面積範圍最小為26.93 m2，最大為453.48 m2 ，以200 m2以下的孔隙面積較多。孔隙中的植群經過群團分析後可分為：苦楝─朴樹─舖地黍型、朴樹型、構樹型等3種植群型。具有不同孔隙面積比率的5 m × 5 m小樣區內之植群可分為將不同孔隙面積比率的小樣區內之植群分為4個植群型：朴樹─舖地黍型、朴樹型、苦楝─構樹型以及構樹型。 結果證實孔隙的存在促進了海岸林下層植群的建立，舖地黍常在孔隙形成初期佔領大量面積而形成明顯的優勢，此時木本植物只有朴樹開始建立，某些已存在於林下的蔓性植物也會為了爭取孔隙中的生育地而進行競爭。在孔隙形成後期，大花咸豐草逐漸取代舖地黍等優勢植物，許多陽性木本植物的種子開始發芽，構樹的幼苗因成長較為快速而成為苗木。 孔隙的分布位置是影響朴樹幼苗分布的原因之一，更新良好的朴樹在未來可能成為已衰退的木賊葉木麻黃林下之優勢植物。藉由不同孔隙面積比率的植群分析說明構樹的生長會隨著孔隙面積比率的差異而影響數量比例，在面積比率75 %以上且生育地足夠的孔隙容易形成大面積的苗木庫以填補孔隙空間。

This study established three 30 m 100 m sample plots and one hundred twenty 5 5 m2 subquadrat in each sample plot for inventorying vegetation and surveying the area of expanded gaps in the costal foreat in Junan, Miaoli. The object of this study was to analysis the effect of the expanded gaps on adding plant diversity . The results inventory of vascular plant found 29 families, 45 genera, 49 species and the family with the largest number of species was Asteraceae, Poaceae and Euphorbiaceae. There were fourteen gaps in all. Gap areas were from 26.93 m2 to 453.48 m2 and many of them were small than 200 m2. According to the results of Matrix Cluster Analysis (MCA), the types of investigated vegetation in expanded gaps can be classified into as follows: Melia azedarach - Broussonetia papyrifera - Panicum repens type, Celtis sinensis type and Broussonetia papyrifera type. And the types of investigated vegetation in 5 5 m2 subquadrat with different gap area percent is classified by Matrix Cluster Analysis (MCA) into as follows: Celtis sinensis - Panicum respens type, Celtis sinensis type, Melia azedarach - Broussonetia papyrifera type and Broussonetia papyrifera type. The results proved that the existence of gap encourage understory vegetation to establish in costal forest, for example, Panicum respens often occupied lots of area to be main plant in early gap phase. In early gap phase, only one of wood plant established, which was Celtis sinensis and some of trailing plants which had lived in understory would compete against with each other for habitat in gap. In later gap phase, Bidens pilosa L. var. radiate replaced Panicum respens little by little. Many seeds of shade-intolerant woody species began to germinate and seedling of Broussonetia papyrifera grew more quickly than others due to many sapling of Broussonetia papyrifera in expanded gaps. The distribution of gaps was one of the factors affects to the establishment of the seeding of Celtis sinensis. Celtis sinensis regenerated well and may become the dominant species in degenerating Casuarina equisetifolia forest in the future. The influence of different gap area percent explain that the number of sapling of Broussonetia papyrifera changed with that and became sapling bank to fill gaps if the gap area percent up than 75 % and habitat is enough.