School of Life Sciences, University of KwaZulu-Natal, P/Bag X01, Scottsville, 3209, South Africa.
Department of Environmental Sciences, University of Helsinki, Niemenkatu 73, FIN-15140, Lahti, Finland.
Sci Rep. 2017 Jul 26;7(1):6549. doi: 10.1038/s41598-017-06747-2.
Afrotemperate forests situated in the Drakensberg mountains of South Africa are characteristically small (1-10 s ha) and widely dispersed in a vast fire-prone grassland. Compared with lowland forests, they are typically species poor with low levels of endemism and species turnover, patterns that are to date unexplained. Here we show that the richness, composition and functional traits of tree species distributed on extremely small (10-100 s m) rocky fire-refugia situated in grassland are indistinguishable from that in forest. Afrotemperate forest tree species in the Drakensberg are widely dispersed and conform to the habitat generalist strategy. Most forest trees are bird dispersed; wind dispersal is rare and is associated only with species that resprout in response to fire. We present the 'matrix refuge hypothesis', which proposes that fire and extreme conditions associated with exposed rocky outcrops have filtered the Afrotemperate forest tree composition resulting in convergence in functional traits essential for trees to arrive, establish and persist on fire refugia in the grassland matrix. Most Afrotemperate forest tree diversity in the Drakensberg thus resides in the matrix where it may function as a recolonisation reservoir during climatic bottlenecks.
南非德拉肯斯堡山脉的亚热带森林的特点是面积小（1-10 公顷），广泛分布在极易发生火灾的草原上。与低地森林相比，它们的物种通常较少，特有种和物种更替率较低，这些模式目前还无法解释。在这里，我们表明，分布在草原上极小（10-100 平方米）的岩石火避难所的树种的丰富度、组成和功能特征与森林中的树种没有区别。德拉肯斯堡山脉的亚热带森林树种分布广泛，符合生境广适种策略。大多数森林树种通过鸟类传播；风传播很少见，仅与那些对火灾有再生能力的物种有关。我们提出了“基质避难所假说”，该假说认为，与裸露的岩石露头相关的火和极端条件已经过滤了亚热带森林的树种组成，导致在草原基质的火避难所中，对树木到达、建立和生存至关重要的功能特征趋同。因此，德拉肯斯堡山脉的大多数亚热带森林树种多样性都存在于基质中，在气候瓶颈期间，它可能作为再殖民的储备库发挥作用。
