Revisiting the Biogeographical and Ecological Uniqueness of the Mediterranean Heathland or Herriza of the Strait of Gibraltar
Atlantic heathlands in western Europe are usually not very diverse in woody species, the heather (Calluna vulgaris) being the predominant species. They are tightly associated to acid sandy soil and, particularly, to a temperate, oceanic climate. Heathland patches do also exist in the southwestern Iberian Peninsula and northern Morocco, under Mediterranean climate. However, they have been often ignored or regarded as mere interdigitations of the European Atlantic heathland with ‘xerophytic’ Mediterranean, garrigue-like shrublands. Likewise, and no less perplexing, population genetics and biogeographical studies on Calluna vulgaris, the flag species of European heathlands, have not extended southwards beyond the northern fringe of the Iberian peninsula into the western Mediterranean region, despite this species’ range reaching as far south as the African side of the Strait of Gibraltar. The Mediterranean heathland is also one of the most common habitats in the Strait of Gibraltar region, found mostly on ridges and crests of sandstone mountains and hills. Locally known as herriza, it is tightly associated to acid soils and to a mild Mediterranean climate with a strong oceanic influence.
The main aim of this proposal is to assess the plant biodiversity and ecological uniqueness of the Mediterranean heathland or herriza of the Strait of Gibraltar region, challenging the current view of considering it as the mere result of a contact of the Mediterranean garrigue with a ‘remnant’ Atlantic heathland flora. We will also explore the likely role of the herriza of the Strait of Gibraltar as the postglacial origin of the Calluna-dominated, European Atlantic heathland. Specifically, we will
- (i) ascertain the heathland nature of the herriza of the Strait of Gibraltar
- (ii) establish whether the herriza is a biodiversity ‘hotspot’ within Mediterranean heathlands
- (iii) infer the likeliness of the Strait of Gibraltar as the origin of the European heathland through the phylogeographic analysis of Calluna vulgaris
- (iv) explore the evolutionary history and evolutionary demography of the carnivorous subshrub Drosophyllum lusitanicum, the paradigm of floristic uniqueness of the herriza.
Results will provide solid scientific ground for the conservation of this unique Mediterranean heathland-type vegetation.