Wiser Susan K, Buxton Rowan P
Landcare Research, Lincoln 7640, New Zealand.
Ecology. 2008 Feb;89(2):380-91. doi: 10.1890/07-0196.1.
The extensive research on plant communities of natural-habitat islands has primarily focused on the "islands." The island analogy, however, potentially limits understanding of processes influencing composition on habitat islands because the nature of their matrix is overlooked. We determine how plant community structure of the surrounding matrix influences vegetation on volcanic outcrops in the modified landscape of Banks Peninsula, New Zealand. Our primary purpose is to address whether the matrix is more important for recently established exotic species than it is for well-established native species and whether such invasion by exotics has led to homogenization of the outcrop flora. To test this, we examined our data at three spatial scales: that of the entire outcrop flora, between individual outcrops and their immediate surrounding matrix, and between individual outcrop faces and the individual relevés of the immediate surrounding matrix. We found that 81% of the native flora and 90% of the exotic flora also occur in the matrix. This high level of species shared between the outcrop and matrix persists at the scale of individual outcrop faces (68% of the total flora of individual faces is shared with the matrix). We predicted that floras from different outcrops would vary in their distinctiveness from their immediate matrix. We found Bray-Curtis distance coefficient values to range from 0.26 to 0.64; these were even higher at the outcrop-face scale. Variability in outcrop distinctiveness relates primarily to the outcrop face properties of area, vegetation height, and soil depth, and matrix properties of vegetation structure and vegetation heterogeneity. The effect of the vegetation structure of the matrix is more pronounced on the exotic than on the native outcrop flora. The component of composition and structure of the matrix that was independent of outcrop properties and local environment accounts for similar levels of explainable variation in total and native composition (29-31%), but considerably more (40%) in composition of exotic species. Our results support our prediction that, as the surrounding matrix becomes more modified, invasion by exotics makes outcrop vegetation less distinct from its matrix.
对自然栖息地岛屿植物群落的广泛研究主要集中在“岛屿”本身。然而，岛屿类比可能会限制我们对影响栖息地岛屿植物组成过程的理解，因为其基质的性质被忽视了。我们研究了新西兰班克斯半岛改造景观中，周围基质的植物群落结构如何影响火山露头的植被。我们的主要目的是探讨基质对新建立的外来物种是否比对已建立的本地物种更重要，以及外来物种的这种入侵是否导致了露头植物区系的同质化。为了验证这一点，我们在三个空间尺度上分析了数据：整个露头植物区系的尺度、单个露头与其紧邻基质之间的尺度，以及单个露头面与其紧邻基质的单个样方之间的尺度。我们发现，81%的本地植物区系和90%的外来植物区系也出现在基质中。露头和基质之间这种高水平的物种共享在单个露头面的尺度上依然存在（单个露头面总植物区系的68%与基质共享）。我们预测，来自不同露头的植物区系与其紧邻基质的差异程度会有所不同。我们发现布雷 - 柯蒂斯距离系数值在0.26至0.64之间；在露头面尺度上这些值甚至更高。露头独特性的变化主要与露头面的面积、植被高度和土壤深度等属性，以及植被结构和植被异质性等基质属性有关。基质植被结构对外来露头植物区系的影响比对本地露头植物区系更为明显。基质中与露头属性和当地环境无关的组成和结构成分，在总组成和本地组成中可解释变异的水平相似（29 - 31%），但在外来物种组成中所占比例更大（40%）。我们的结果支持了我们的预测，即随着周围基质变得更加改造，外来物种的入侵使得露头植被与其基质的差异变小。
