Edaphic properties enable facilitative and competitive interactions resulting in fairy circle formation

Millions of generally regularly spaced, roughly circular barren patches called fairy circles occur in a narrow band ca. 100 km inland of the south-west African coast. These generally have conspicuously taller peripheral grasses in a shorter grass matrix. The origins of these fairy circles are controversial, but one possibility is that they are self-organizing emergent vegetation patterns that are the consequence of interplay between positive (facilitative) and negative (competitive) interactions between grasses. We hypothesized that the coarse textured sand on which fairy circles occur creates a hydraulically and nutritionally connected landscape, in which neighbouring fairy circles competitively influence each other over several metres, while providing opportunity for focusing of resources around the peripheral grasses. To test our hypotheses we conducted three main groups of analyses: 1) We measured grass biomass to assess facilitative and competitive effects of the component grasses;...在非洲西南海岸内陆约100公里的狭长地带中，分布着数以百万计的、大致呈规则排列的近似圆形贫瘠斑块，这类斑块被称为仙女圈（fairy circles）。此类斑块的外围通常生长着明显更高的草本植物，周围则是较为低矮的草本群落。这些仙女圈的成因尚存争议，其中一种假说认为它们属于自组织涌现的植被格局，由草本植物间正（促进）与负（竞争）相互作用共同塑造。本研究提出假说：仙女圈所依托的粗粒沙质基质形成了水力与营养连通的景观，使得相邻仙女圈可在数米范围内产生竞争性相互影响，同时为外围草本植物的资源汇聚提供了条件。为验证上述假说，本研究开展了三大类分析：1）通过测定草本生物量，以评估组成群落的草本植物的促进与竞争效应；...