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Figure 6: Number of priority vascular plant species under each threat category in each habitat. Figure 7: Number of important vertebrate species under each threat category in each habitat. Key Species & Habitats - 45 -
Biodiversity Action Plan, Gibraltar: Planning for Nature - 46 - Figure 8: Number of priority species found in one habitat alone, for each habitat. It is evident from figs. 6, 7 and 8 that cliffs constitute the most important habitat in Gibraltar for species with an unfavourable international conservation status. This is true for both vascular plants and vertebrates. This is not surprising. Gibraltar holds an extensive network of cliffs and steep, rocky slopes, making the Rock ideal for species that favour cliff habitats. Many of the internationally threatened or vulnerable vertebrates found in Gibraltar rely on cliffs as breeding sites. The Peregrine Falco peregrinus, the Eagle Owl Bubo bubo and the European Free-tailed Bat Tadarida teniotis are examples. The importance of cliffs to plant species derives from two main factors in addition to their extent. The Rock is composed of Jurassic limestone, unlike the Spanish countryside to the north. This means that limestone-loving plant species will favour Gibraltar but not nearby Spain. The second factor is that Gibraltar lies close to North Africa, and is composed of a similar limestone to that found in the closest parts of Morocco. This means that some North African species are found only in Gibraltar, and nowhere else in Europe. These North African species, as well as the species and other taxa that are restricted to the Rock, are all cliff specialists. These examples illustrate the importance of conserving cliff habitats in Gibraltar. These habitats are currently under threat in Gibraltar. Chapter 4 discusses their importance more fully, as well as the factors threatening these and steps that should be taken to conserve them. Figures 6 and 7 suggest that, although the Upper Rock harbours more priority species than other sites, it is actually the habitats that cover a proportionally small area that are most important for these species. The maquis, which covers the majority of the Upper Rock’s surface area, is actually fairly poor in priority plant species, and not as rich in priority vertebrate species as some other habitats. The maquis is also fairly poor in invertebrate species richness and density (pers. obs.). The importance of cliff habitats, a large proportion of which are found within the Nature Reserve, has already been discussed. Garigue habitats, which cover only a small proportion of the Upper Rock’s surface area, and which are decreasing in size and threatened by the encroaching maquis, hold the highest number of both priority vascular plant and vertebrate species. In addition, this habitat type is extremely rich in invertebrates and supports important populations of the endemic beetle Buprestis sanguinea calpetana (pers. obs.). The importance of garigue habitats when compared to the dense maquis, as well as their threatened status, would suggest that habitat management is necessary both to maintain current areas of garigue and to clear some areas of maquis to make way for garigue. Although large areas of the maquis should be conserved, due largely to the unique composition of this habitat on the Rock, some areas should be cleared partially and enriched with tree species that were found on the Rock before its Mediterranean woodland was cleared, as recommended by Perez & Bensusan (2005). These actions would enhance the Nature Reserve’s biodiversity considerably.
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7. References & Glossary
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References • Adendorff, R., and R
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• Menez, A. in prep. Land Mollusc
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