Limestone cliffs predominate on the northern and eastern sides of the Rock. They support an interesting plant community and this is where many of Gibraltar’s special plant species grow. Iberis gibraltarica thrives on all cliffs, whereas Cerastium gibraltaricum and especially Saxifraga globulifera var. gibraltarica prefer north-facing cliffs. Other noteworthy species are Dianthus caryophyllus, Petroselinum crispum, Chaenorrhinum villosum, Campanula mollis and Helichrysum boissieri. In areas with enough soil to allow the development of woody vegetation, the typical components of the maquis grow alongside numerous Chamaerops humilis. There are also pockets of relict vegetation that include Laurus nobilis. Some invasive species are very successful on cliffs, where they cause problems for native flora. Aeonium arboreum is abundant along some of the eastern cliffs, whereas Opuntia ficus-indica thrives throughout the Rock.
This is a site that is quite different to any other in Gibraltar. The moist, shady conditions here favour trees such as Celtis australis, Ficus carica and Laurus nobilis, whereas the more shaded cliffs support large stands of Hedera helix. The area holds a number of rare species that are found nowhere else on the Rock. The east and south-facing cliffs are notable for their population of Capparis orientalis, a species found nowhere else in Gibraltar. Other species that have only been recorded around North Gorge in recent years are Asplenium sagittatum, Rosa sempervirens and Frangula alnus subsp. baetica.
This largely undisturbed sand slope, with limestone rocks and boulders of all sizes, supports a large variety of plant species generally found in open garigue habitats. Many are typical of coastal regions and are well adapted to the dry, sandy conditions, exposed to salt-laden winds and the occasional sand-slide. These include Ononis natrix subsp. ramosissima var. ramosissima, Verbascum thapsus subsp. giganteum, Malcolmia littorea, Daucus carota, Glaucium flavum and Solanum linnaeanum. The more consolidated areas of the slope include many species typical of garigue such as Elaeoselinum foetidum, Ferula tingitana, Pistacia lentiscus, Thapsia villosa, and even Petroselinum crispum. The garigue is quite stable here, as the sands prohibit the development of maquis. The invasive Nicotiana glauca is typical of areas where the terrain has recently been disturbed.
EAST SAND SLOPES
These slopes consist of prehistoric wind-blown sands, consolidated over time. At the beginning of the 20th century, most of the surface was covered with corrugated iron sheets to serve as rain-water catchments. These catchments were decommissioned and the sheets removed during the late 1990s, and the slopes returned to nature. The section originally covered is now the only area of Gibraltar that holds grassland, which is dominated by Piptatherum miliaceum, Bromus rigidus, Lolium rigidum and Avena barbata. Among the notable species that re-populated the slopes are Ononis natrix subsp. ramosissima var. ramosissima, Verbascum thapsus subsp. giganteum, Silene nicaeensis, Spartium junceum and Phillyrea angustifolia. The lower regions, never covered with iron sheets, retain the original, rich community of plants typical of coastal sand dunes, such as Cachrys libanotis, Eryngium maritimum, Pancratium maritimum, Delphinium ambiguum and Dipcadi serotinum. This area holds a number of species that are rare or absent elsewhere on the Rock, including Euphorbia baetica, Linaria pedunculata, Silene littorea, Cyperus rotundus, Allium sphaerocephalon, Dianthus broteroi, Hypochaeris salzmanniana and Herniaria lusitanica.
SOUTHWEST COAST including EUROPA FORESHORE
The coastline stretching from Rosia Bay to Europa Point consists of a combination of sea cliffs and rocky shoreline on a wave-cut platform, the foreshore at Europa Point being the last remaining example of the latter habitat on the Rock. The cliffs in this part of the Rock are not exposed to the severe effects of the easterly storms that affect those along the east coast, and so are substantially vegetated with species typical of the maquis, such as Pistacia lentiscus, Olea europaea and Ephedra fragilis, in addition to maritime species such as Pallenis maritima. These cliffs also hold significant numbers of the exotic invasives Aeonium haworthii and A. arboreum. Throughout the area, there are extensive stands of Limonium emarginatum, a species endemic to the Strait of Gibraltar. The Europa foreshore is an important part of the habitat, holding the only population of Suaeda vera on the Rock. At the same time it is the principal site of species such as Senecio leucanthemifolius and Cichorium pumilum.
The habitat that once covered the low-lying sandy isthmus that connects the Rock to the mainland has all but disappeared. Remnants are still present at Western Beach, the margins of the frontier fence, the eastern end of the runway and, especially, North Front Cemetery. The latter is by far the more important as it retains a large number of the species that would have been found throughout the isthmus. The soil here is sandy and stony in nature and water drains through it easily, but nevertheless it is an important site for a number of species such as Pancratium maritimum, Cachrys libanotis, Erodium salzmannii, Euphorbia terracina, Asphodelus fistulosus, Ornithogalum arabicum and Papaver somniferum.
The coastline along the east side is principally composed of cliffs, rocky shoreline and adjacent sandy slopes. The sandy beaches at Catalan Bay and Sandy Bay are too built up and hold no significant vegetation. The coastal cliffs are very exposed and occasionally battered by strong easterly storms that blow salt sea spray over them. Plants that are capable of surviving these storms do well here, in particular Limonium emarginatum, Crithmum maritimum, Euphorbia segetalis var. pinea, Atriplex halimus, Senecio leucanthemifolius, Mesembrianthemum nodiflorum and the very rare Mesembrianthemum crystallinum. Gorham's Cave, at the base of these cliffs, is the only location on the Rock of Samolus valerandi, where it flourishes due to the presence of water running down the cave walls. The cliffs surrounding the cave also hold significant stands of Chaenorrhinum villosum and Helichrysum boissieri. The screes along the cliff tops, formed as a result of tunnelling activity, are extensively covered by introduced invasives such as Carpobrotus edulis, Disphyma crassifolium, and hold stands of Agave americana and Aloe arborescens.
Gibraltar’s urban areas are densely developed, with few green spaces. However, plants will exploit urban planters and landscaped areas, to which for example the moisture-dependent Equisetum telmateia is restricted. Buildings, and especially old walls hold cliff-loving species such as Ficus carica, Antirrhinum majus, Campanula mollis, Trachelium caeruleum and Helichrysum boissieri, as well as the exotic Nicotiana glauca and Ageratina adenophora. Weeds growing in landscaped areas and waste ground typically include Erigeron bonariensis and E. sumatrensis, Symphyotrichum squamatum, Nothoscordum borbonicum, Cyperus rotundus and Phytolacca americana.
The man-made coastline within and around the harbour holds some interesting plants, especially where this consists of limestone boulders or areas that hold ruderal species. Plants that grow throughout the urban zone are joined by typical coastal species such Daucus carota, Crithmum maritimum, Glaucium flavum and the locally rare Medicago marina, as well as other more generalist species that are rare in Gibraltar but common in the Spanish hinterland, such as Cistus salvifolius.
MEDITERRANEAN STEPS & SOUTH SLOPES
The habitat along Mediterranean Steps and on the southern slopes of the rock is an interesting mosaic of different vegetation types. Whilst the maquis that is typical of the Upper Rock is widespread, there are also significant patches of lower and more open garigue vegetation on rocky slopes. This is some of the richest habitat in Gibraltar for flowering plants. They are characterised by low, thermophilous shrubs such as Euphorbia squamigera, Ephedra fragilis and Chamaerops humilis, the grass Stipa tenacissima and more open areas with a high diversity of annuals and bulbs. The maquis habitat here is itself interspersed with more open areas that harbour garigue and screes that are the result of tunnelling for military purposes during the early 20th Century. Cliff habitat is also dominant in this area. The combination of open habitat, rocky slopes and cliffs make the Mediterranean Steps & South Slopes a stronghold for special Gibraltar species such as Iberis gibraltarica, Cerastium gibraltaricum and, close to the top of the steps, Saxifraga globulifera var. gibraltarica. It is also one of the areas where these species are most easily accessible to the public.
UPPER ROCK MAQUIS
The maquis of the Upper Rock consists of tall and largely impenetrable Mediterranean scrub. It dominates most of the Upper Rock but is secondary in nature, dominated by fruit-bearing shrubs, the result of colonisation via birds’ droppings following the clearance of woody vegetation on the Rock that culminated in the 18th Century. The most common and widespread shrub is Olea europaea, which in the most developed patches forms large trees. Other widespread species are Osyris lanceolata and Rhamnus alaternus, with Phillyrea latifolia common only near the top of the Rock. Pistacia lentiscus and Pistacia terebinthus are also widespread but do best in lower formations of maquis. A number of climbing plants are widespread throughout the maquis, the most prominent being Smilax aspera, Dioscorea communis, Aristolochia baetica and Clematis cirrhosa. This type of maquis is also prevalent in other parts of the Rock.
UPPER ROCK FIREBREAKS
The firebreaks within the maquis provide open habitat that favours the growth of a large number of species that would otherwise not exist within the dense overgrowth of the maquis itself. The terrain is composed of rich soil interspersed with rocky limestone outcrops which, together with the plentiful sunlight afford ideal conditions for growth. However, being an artificial habitat, the profusion of plant species found there is only sustained if these open areas are cleared and maintained on a regular basis. Otherwise the maquis vegetation will begin to redevelop. Typical species found in the firebreaks are Asphodelus ramosus, Narcissus papyraceus, Gladiolus communis, Phlomis purpurea, Acanthus mollis, Oxalis pes-caprae and numerous species of the Pea family (Fabaceae).
Although much of the habitat in the suburbs of the South District consists of garden, it also includes patches of woodland and features of such woodland within the gardens themselves. Typical trees are Olea europaea, Celtis australis, Fraxinus angustifolius and Laurus nobilis in addition to the more typical components of the Gibraltar maquis. The shady understory is typically dominated by Acanthus mollis but the presence of the locally rare Rubus ulmifolius is obvious in places.
The maquis formations in the southwest of Gibraltar are similar in species composition to those of the Upper Rock. However, the rocky terrain and strong south-westerly winds keep some patches of maquis low, allowing species such as Pistacia lentiscus to dominate alongside Olea europaea. Areas close to cliffs typically hold Ficus carica.
WINDMILL HILL FLATS
The flat, open terrain on Windmill Hill Flats is exposed to strong winds from all directions. This results in the vegetation being kept low, forming a very open and colourful garigue habitat. The soil is stony and not particularly rich and water drains quickly. The area supports a rich flora, with many species not found elsewhere on the Rock, such as Salvia verbenaca, Filago pygmaea and Plantago serraria. Other species that are rare elsewhere but thrive here are Ornithogalum orthophyllum, Moraea sisyrinchium, Atractylis cancellata, Echium parviflorum, Cichorium pumilum, Minuartia geniculata and the more localised Ophrys apifera, which has largely disappeared elsewhere on the Rock. A particular feature of the more open areas is the abundance of the umbellifers Ferula tingitana and Foeniculum vulgare subsp. piperitum. Rocky outcrops and more sheltered corners hold other species found nowhere else on the Rock such as Crocus serotinus subsp. salzmannii and Thesium humile, and others which are rare elsewhere such as Romulea clusiana, Hedysarum coronarium and Lotus tetragonolobus. These more sheltered areas also hold important stands of Euphorbia squamigera that form the dominant component of a very particular, species-rich garigue habitat.
The terrain above and below the Hole-in-the-Wall Road, together with the screes that stretch south to Europa Flats, make up the south-east garigues, with low-lying vegetation and shrubs kept low by the strong winds that affect the area. The stony soil and rocky outcrops of these garigues are host to many species of plants such as Limonium emarginatum, Romulea clusiana, Jacobaea maritima, Lavatera arborea, Foeniculum vulgare subsp. piperitum, Rumex scutatus subsp. induratus, Ecballium elaterium and good stands of Iberis gibraltarica. However, the large numbers of exotic invasives such as Opuntia ficus-indica, Carpobrotus edulis, Aeonium haworthii, Aloe arborescens and Aloe maculata are a very real threat to the native species.