Terrestrial habitats are based mainly on vegetation types; these are grouped into three main categories:
- Mediterranean communities: Part of the succession sequence towards climax communities;
- Human-linked communities: Owe their existence to anthropogenic activities;
- Other communities: Either specialised to occupy particular habitats, or occupy habitats that are rare in the Islands, or are relics from a previous ecological regime.
The process of succession
Ecosystems are formed by the interactions between a community of living organisms and the physical environment that surrounds them. These ecosystems undergo ecological succession in response to changes in environmental conditions; this is a natural process of change over time that is brought about by progressive replacement of one plant or animal community with another. This process starts with what is called as the “pioneer community”, and eventually leads to the development of a stable and mature community, referred to as the “climax community”. The process of succession can halt at a pre-climax stage when some factor is limiting; such as when the organism needed to bring about the necessary changes that lead to the creation of the following community is absent. Apart from biotic factors (living), limiting factors may also be abiotic (non-living), such as lack of water.
Succession can be of two types:
a) Primary succession: Begins when pioneer species, like mosses and lichens, colonise barren substrate, such as rock, sand or soil, which has never before supported any vegetation.
b) Secondary succession: Occurs in areas where natural vegetation has been disturbed or destroyed. The latter type is generally less species rich.
Natural habitats in the Maltese Islands appear in different stages of ecological succession. In certain localities, it is easy to differentiate between these stages, though in most cases, the habitats occur as a mosaic of the different stages of ecological succession. There are six principal stages of ecological succession in the Maltese Islands; these are relative to Mediterranean type vegetation.
Habitats that form part of the process of succession:
1. Steppe (l-isteppa)
2. Garrigue (ix-xagħri)
3. Phrygana (il-frigana)
4. Pre-desert scrub (il-ġmiem)
5. Maquis (il-makkja)
6. Woodland (il-masġar)
Examples of specialised habitat types:
7. Saline marshlands (bwar salmastri)
8. Freshwater rockpools (l-għadajjar tal-ilma ħelu)
9. Sand dunes (l-għaram tar-ramel)
10. Valley watercourses (il-widien)
11. Caves (l-għerien)
12. Cliffs and boulder shores (l-irdumijiet u l-komunitajiet rupestrali)
1. Steppe (l-isteppa)
Steppe is considered as the first stage in the ecological succession process. It is derived from maquis and garrigue as a result of some form of degradation, such as that caused by fire or animal grazing. It is widespread, and is characterised by herbaceous plants, especially grasses, such as:
(i) Umbellifers such as the fennel (MT: il-bużbież; SN: Foeniculum vulgare), the Maltese ferule (MT: il-ferla; SN: Ferula melitensis) and the wild carrot (MT: iz-zunnarija salvaġġa; SN: Daucus carota);
(ii) Legumes such as the common vetch (MT: il-ġilbiena sewda; SN: Vicia sativa subsp. nigra), and;
(iii) Tuberous or bulbous species such as the southern star of Bethlehem (MT: ħalib it-tajr żgħir; SN: Ornithogalum narbonense).
This habitat is generally devoid of shrubs, and is mainly comprised of annuals, that is, plants that live up to one year. During the dry season, this habitat type appears dry and impoverished because most plant species will, at the time, exist in the form of seeds. In contrast, the wet season brings about a change in this habitat type, which results in steppe being entirely covered by a large variety of herbaceous plants.
One also finds other types of steppe locally, including some natural ones. These are formed through climatic factors, and include the rocky steppe and the clay slope steppe.
Steppes may also be characterised by the common awn-grass (MT: in-nixxief tal-isteppa; SN: Stipa capensis) and thistles; such as the clustered carline thistle (MT: is-sajtun; SN: Carlina involucrata) and the Mediterranean thistle (MT: ix-xewk abjad; SN: Galactites tomentosa). Geophytes, such as the asphodel (MT: il-berwieq; SN: Asphdelus aestivus ) and the seaside squill (MT: l-għansar; SN: Drimia pancration), are also encountered. Other forms of steppic communities may develop on abandoned agricultural land.
2. Garrigue (ix-xagħri)
The second stage in ecological succession is garrigue. It is characterised by limestone rocky ground with a rugged surface, known as karst, and is heavily exposed to the brute force of the elements. Garrigue is typified by low-lying, usually aromatic and spiny woody shrubs that are resistant to drought and exposure. This type of habitat appears desolate, and is often referred to as wasteland. Nevertheless, it is probably the most species-diverse habitat in the Maltese Islands, and is of great importance not only to biodiversity, but also to ecosystem services.
Various types of garrigue occur; such as the thermo-Mediterranean scrub habitats, characterised by the tree spurge (MT: it-tengħud tas-siġra; SN: Euphorbia dendroides) and African wolfsbane (MT: is-siġra tal-ħarir; SN: Periploca angustifolia). The thermo-Mediterranean scrub communities are sometimes referred to as high garrigues since they usually include shrubs that exceed 0.5m, growing up to 2m in height. Additionally, some garrigue types are very rare, such as those based on species of sage (MT: is-salvja; SN: Phlomis fruticosa) and rockroses (MT: iċ-ċistu; SN: Fumana spp.), and rosemary (MT: il-klin; SN: Rosmarinus officinalis).
On the other hand, the most frequent garrigue species is the Mediterranean thyme (MT: is-sagħtar; SN: Thymbra capitata). It is known from most types of garrigue, and is an important food source for many species, including the Maltese honey bee (MT: in-naħla ta’ Malta; SN: Apis mellifera ruttneri).
In addition to the above, numerous endemic, threatened, rare and protected species thrive in garrigue habitats, such as the:
- Maltese spider orchid (MT: il-brimba sewda; SN: Ophrys melitensis);
- Sicilian squill (MT: l-għansal ikħal; SN: Scilla sicula);
- Southern dwarf iris (MT: il-bellus; SN: Iris pseudopumila);
- Maltese pyramidal orchid (MT: l-orkida piramidali ta’ Malta; SN: Anacamptis urvilleana), and;
- two endemic door-snail species (id-dussies tal-irdum; id-dussies ta’ Malta; SN: Lampedusa imitatrix and L. melitensis).
3. Maquis (il-makkja)
Maquis is the stage following that of the pre-desert scrub in the ecological succession. It is usually characterised by small trees and large shrubs, consisting mostly of an evergreen shrub community, reaching a height of up to 5m, often more. It occurs along the sides of valleys, along slopes and other areas, which are inaccessible to man, and relatively sheltered from the wind. Various types of maquis occur, such as those based upon the Myrtle (MT: ir-riħan; SN: Myrtus communis ), and the national tree of Malta, the sandarac gum tree (MT: is-siġra tal-għargħar; SN: Tetraclinis articulata), both of which are very rare and threatened.
Typical trees that populate such habitat include the:
- Carob Tree (MT: il-ħarruba; SN: Ceratonia siliqua);
- Olive tree (MT: iż-żebbuġa; SN: Olea europaea);
- Lentisk (MT: id-deru; SN: Pistacia lentiscus);
- Fig tree (MT: is-siġra tat-tin; SN: Ficus carica);
- Almond tree (MT: is-siġra tal-lewż; SN: Prunus dulcis), as well as;
- Bay Laurel (MT: ir-randa; SN: Laurus nobilis).
As one would perhaps expect, for this habitat to develop and support such trees, it requires enough water and sufficient soil depth.
This habitat type is also rich in plants, namely climbers, including the:
- Common ivy (MT: il-liedna; SN: Hedera helix);
- Common smilax (MT: il-pajżana; SN: Smilax aspera);
- Spiny asparagus (MT: l-ispraġġ xewwieki; SN: Asparagus aphyllus);
- Wild madder (MT: ir-robbja salvaġġa; SN: Rubia peregrina).
The maquis habitat type supports also large herbaceous species, like the:
- Black bryony (MT: il-brijonja sewda; SN: Tamus communis);
- Bear’s breeches (MT: il-ħannewija; SN: Acanthus mollis ), and;
- Italian lords-and-ladies (MT: il-garni; SN: Arisarum vulgare).
4. Mediterranean woodland (il-bosk)
Mediterranean woodlands are characterised by sclerophyllous (hard-leaved, evergreen) trees with an undergrowth of smaller shrubs. This is the highest type of vegetation that can develop in the Mediterranean climatic regime, in other words, the climax of the ecological succession. This habitat type develops from maquis, in the absence of disturbance caused by man.
In Malta, this habitat was virtually exterminated, following colonisation by man and through the grazing effects of introduced sheep and goats. Nowadays, only a few remnants are found in a handful of areas, with small copses of the holm oak (MT: il-balluta; SN: Quercus ilex) at Il-Ballut tal-Wardija, Il-Ballut tal-Imġiebaħ, Ta’ Baldu/Wied Ħażrun, and Il-Bosk near Buskett. Remnants are dominated by the holm oak and the Aleppo pine (MT: iż-żnuber; SN: Pinus halepensis). Some of the holm oaks are estimated to be 500 to 900 years old.
Il-Buskett, which is located on the western-south-western coast of Malta, is a semi-natural woodland where trees, namely the Aleppo Pine, together with the holm oak, the olive tree and the carob tree (il-ħarruba) regenerate naturally. This area is also important for many wood-associated species, including invertebrates, mycoflora, and birds.
Apart from the above mentioned habitats that form part of the process of succession, there are other specialised habitat types, each supporting species that are mostly confined to specific areas.
5. Saline marshlands (bwar salmastri)
Saline marshlands are transitional areas that form at the interface between the marine, freshwater and terrestrial environments. Saline marshlands are dynamic systems and undergo annual cycles of changes in salinity. The salt content changes depending on rainfall, whereas in winter the saline content is low due to a diluting effect of the rain, in summer, the salt content is more concentrated as water levels drop. Salinity in the salt marsh also depends on how close this is to sea and the influx of seawater into the system.
During winter, the Maltese coastal marshes are characterised by a muddy substratum on which a pool of brackish water is collected. Plants found in this habitat type must withstand changes in salinity and therefore have adapted to such conditions, by adopting special structural and physiological features. For instance, certain plants, such as the golden samphire (MT: ix-xorbett; SN: Limbarda crithmoides), have fleshy leaves that can store freshwater. Others, such as the shrubby glasswort (MT: l-almeridja tal-blat; SN: Arthrocnemum macrostachyum) and the twiggy glasswort (MT: l-almeridja; SN: Salicornia ramosissima), have very small, fleshy leaves that envelop the stem, in order to prevent water loss. Such plants appear to be made up of segments. Tamarisk species, on the other hand, are able to concentrate salt in their leaves, to eliminate the salt when the leaves are shed.
Vegetation patterns are observed in saline marshlands that reflect differences in chemical and physical conditions. Areas that remain dry or moist harbour those plants that are not aquatic, such as the smooth-leaved saltwort (MT: il-ħaxixa tal-irmied; SN: Salsola soda). Shallow parts of the salt marsh that hold a small volume of water for several days, are colonised by plants, which although not aquatic, are still able to withstand short periods of inundation until the water dries up or evaporates. Deeper areas, which remain filled with water for longer periods, only support aquatic and semi-aquatic plants. Plants characteristic of saline marshlands are the:
- Sharp rush (MT: is-simar niggież; SN: Juncus acutus);
- Sea rush (MT: is-simar tal-baħar; SN: Juncus maritimus), and;
- Common reed (MT: qasbet ir-riħ; SN: Phragmites australis).
Some coastal wetlands appear to be transitional between freshwater wetlands and saline marshlands, in the sense that, the biotic assemblages they support consist of species typical of both freshwater and saline habitats. Such wetlands have been termed ‘transitional coastal wetlands’, such as when wetlands arise when rainwater collects in depressions close to the sea, such as at l-Għadira s-Safra.
6. Rainwater rock pools (l-għadajjar tal-ilma ħelu)
The movement or flow of acidified water derived from precipitation and runoff, leads to the gradual erosion of limestone substratum and the eventual formation of hollows or kamenitzas (singular kamenitza). The latter collect rainwater in winter, forming shallow freshwater rock pools, which provide a suitable habitat for a number of rare species. Freshwater rock pools are ephemeral, that is, last for only a short period, because in summer these dry up completely and may become colonised by terrestrial vegetation. Therefore, the ecological cycle of this habitat spans over a year and is divided into two stages, the:
a) wet stage occurs in winter when the kamenitzas become filled with rainwater, and;
b) dry stage occurs in summer, when the kamenitzas remain dry.
Species that are specialised to this habitat type remain dormant in the soil during the dry stage, and emerge during the wet stage. Other species move out of the rock pool, when this is in the dry state, and return when conditions become favourable. Plants and algae that inhabit freshwater rock pools include the Maltese waterwort (MT: l-elatine; SN: Elatine gussonei) and the Maltese horned-pondweed (MT: il-ħarira tal-ilma; SN: Zanichellia melitensis).
The duration of how long the rock pool remains with water determines the species richness of that particular rock pool. Several aquatic insects are also found in this habitat type and namely include microcrustaceans, such as the common copepod (MT: il-kopepodu tal-għadajjar; SN: Cyclops vulgaris), freshwater shrimps such as the fairy shrimp (MT: il-gamblu tal-għadajjar; SN: Branchipus schaefferi) and the water flea (MT: iż-żagħrun tal-ġwiebi; SN: Daphnia pulicaria). Certain microorganisms that occur in this habitat are extremely rare, such as the tadpole shrimp (MT: il-gamblu tal-elmu; SN: Triops cancriformis).
7. Sand dunes (l-għaram tar-ramel)
Sand dunes are dynamic systems that form by a slow process of accretion, that is, the build-up of sand because of natural wave action. Sandy beaches are backed by dune systems, which provide an essential role in the stability, as well as in the defence of coastal communities. The formation of sand dunes depends on the sand that is carried inland by wind from the beach. Subsequently, sand is deposited and trapped upon encountering clumps of vegetation or some other form of obstacle.
Dune vegetation is adapted to the harsh conditions present in this type of habitat. Such conditions include high temperatures, dryness, occasional inundation by seawater and accumulation of sand. Plant adaptations include extensive root systems that provide efficient anchorage in the porous and mobile substrate and other distinctive morphological features, such as fleshy leaves to limit water loss, and the presence of short white hairs to help in temperature regulation.
Vegetation type changes across the dune system with distance from the beach, forming a typical zonation pattern. Maltese dunes, in the present day and age, may be described according to the zonation pattern.
a) Embryo dune
The most seaward zone of the dune is called the embryo dune. Perennial plants such as the sea rocket (MT: kromb il-baħar; SN: Cakile maritima) are first encountered; these are pioneers of the dune which enable the establishment of other plants. The sea rocket is also encountered on the drift line of the beach, that is, the highest extreme that waves reach leaving a line of organic debris. Other plants found colonising the embryo dune are the sand dropwort (MT: in-niġem tar-ramel; SN: Sporobolus pungens) and the prickly saltwort (MT: il-ħaxixa tal-irmied xewwikija; SN: Salsola kali).
b) Mobile dune
Behind the embryo dune lies the mobile dune, which is characterised by a low dune that is sparsely vegetated by plants such as the sand couch grass (MT: is-sikrana tar-ramel; SN: Elytrigia juncea) and the sea holly (MT: xewk ir-ramel; SN: Eryngium maritimum).
c) Semi-consolidated dune
The mobile dune is followed by the semi-consolidated dune, which is characterised by the carnation spurge (MT: tengħud tax-xatt; SN: Euphorbia terracina), the sea daffodil (MT: il-pankrazju tal-baħar; SN: Pancratium maritimum) and the sea fennel (MT: bużbież il-baħar; SN: Echinophora spinosa).
d) Fixed dune
Following the semi-consolidated dune, one comes across the fixed dune. This zone is vegetated with a dense thicket of salt-tolerant shrubs, such as the grey birdsfoot trefoil (MT: għantux tal-blat; SN: Lotus cytisoides) and the southern scabious (MT: il-kuxxinetti; SN: Scabiosa maritima).
Maltese sand dunes also have characteristic invertebrate fauna, namely nematodes (roundworms), annelids (segmented worms), several insects, amphipods (shrimp-like crustaceans) and isopods (sessile eyes crustaceans).
Over the years, many sand dunes have been lost and nowadays, this habitat is extremely restricted in the Maltese Islands. Presently, there are only few dunes that persist, and this habitat type is amongst the rarest and most threatened of local ecosystems.
8. Valley watercourses & riparian communities (il-widien)
Valley watercourses are one of the most species-rich habitats on a national scale. Yet, they are considered as one of the most endangered habitats in the Maltese Islands. The biotic (living) communities of valleys can be divided into two groups:
i. those growing on valley sides, and;
ii. those growing along the watercourse.
In gently sloping valleys, the watercourse community is similar to that of the valley sides, whereas in steep-sided valleys there is a clear distinction between communities along the watercourse and those vegetating valley-sides. Where the terrain permits, the valley sides are terraced and cultivated. The construction of man-made dams in certain valley systems has intentionally retarded the water flow for irrigation purposes. Such dams have created new freshwater habitats where varieties of aquatic and semi-aquatic species thrive.
The watercourse community is by nature dynamic, and its integrity depends on the amount and frequency of rainfall as well as other abiotic factors, such as the rate of siltation. Valleys are dry for some months of the year and water only flows during the wet season. However, some local valleys drain springs originating from the perched aquifers and retain some surface water even during the dry season.
In general, the greater part of local plant and animal species reliant of water during some part of their life cycle are found in valley watercourses. Various annual and perennial plants colonise the watercourse, some of which are rare on a national scale because of the restricted distribution of their habitat. An example is the very rare perennial willow-leaved knotgrass (MT: il-persikarja tal-Baħrija; SN: Persicaria salicifolia).
Plants that grow in watercourses include herbaceous perennials, such as the water plantain (MT: il-biżbula tal-ilma; SN: Alisma plantago-aquatica) and the water speedwell (MT: il-veronika tal-ilma; SN: Veronica anagallis-aquatica). Perennials, unlike annual plants, are able to withstand periods of dryness. Watercourse plants require a good underground system of roots or rhizomes for anchorage to the unstable waterlogged substrate of watercourses. Watercourse vegetation mainly comprises grasses, sedges and rushes, while algae thrive in ‘open water’, like species of Spirogyra and Zygnema. One of the most common plants to colonise valleys is the giant reed (MT: il-qasba l-kbira; SN: Arundo donax). Encroachment by this reed results in reduction of water current; however, when the water passes through the rhizomes of this plant, the water is filtered from nutrients. The giant reed is often replaced by the common reed (MT: qasbet ir-riħ; SN: Phragmites australis) at the mouth of valley watercourses where freshwater feeds into the sea.
Remnants of riparian woodlands, located on the bank of a watercourse, still exist along a few watercourses where water flow is abundant. Examples of trees growing along watercourses include the rare white poplar (MT: is-siġra tal-luq; SN: Populus alba), the Mediterranean willow (MT: iż-żafżafa ż-żgħira; SN: Salix pedicellata) and the grey-leaved elm (MT: is-siġra tan-nemus; SN: Ulmus canescens). Different subtypes occur in different localities.
In areas close to the sea the southern Mediterranean riparian thickets occur. The main native species are the African Tamarisk (MT: il-bruka SN: Tamarisk africana) and the Chaste Tree (MT: is-siġra tal-virgi; SN: Vitex agnus-castus), with the Oleander (MT: id-difla; SN: Nerium oleander) being very rare in the wild.
Watercourses provide habitat and food to various animals, the most well-known being the protected, only amphibian found in Malta, the painted frog (MT: iż-żrinġ; SN: Discoglossus pictus pictus), and the legally protected, endemic Maltese freshwater crab (MT: il-qabru; SN: Potamon fluviatile lanfrancoi). A huge variety of insect and other invertebrate fauna also thrive in local valleys, such as dragonflies and damselflies, semi-aquatic grasshoppers, mayflies, aquatic and semi-aquatic beetles, such as the large predacious diving beetle (MT: il-wirdiena tal-ilma; SN: Dysticus circumflexus), water-associating flies, bees and wasps, small crustaceans and many others. Some of these are only found in these habitats and some are only known from one or a few localities in the Maltese Islands.
9. Caves (l-għerien)
In spite of the calcareous nature of Malta’s rocks, deep caves are not frequent in the Maltese Islands. Since local caves are inhabited by organisms which are adapted to live in such habitats, they have a very restricted distribution. The best-known cave dwellers are bats but there are many other species, particularly invertebrates. Moreover, a number of these species are endemic to the Maltese Islands and so, are of great scientific interest.
10. Cliffs & boulder screes (l-irdumijiet u l-komunitajiet rupestrali)
Locally, cliffs and screes are found mainly along southern and western shores of Malta, Gozo and Comino. They represent an important natural habitat because they harbour many interesting species of flora and fauna, including endemic forms.
Rupestral plant communities consist mainly of halophytic shrubs, comprising, amongst others, of endemic species that are restricted only to this habitat type, such as the Maltese cliff-orache (SN: MT: il-bjanka tal-irdum; SN: Atriplex lanfrancoi [=Cremnophyton lanfrancoi]) and the national plant of Malta, the Maltese rock-centaury (MT: widnet il-baħar; SN: Palaeocyanus crassifolius [=Cheirolophus crassifolius]), both belonging to monospecific genera. The cliffs in Gozo support rupestral species that are not present in Malta, namely the Maltese hyoseris (MT: iż-żigland ta’ Għawdex; SN: Hyoseris frutescens) and the Maltese everlasting (MT: is-sempreviva ta’ Għawdex; SN: Helichrysum melitense). Plants found on cliffs need to be resilient to harsh abiotic conditions, such as lack of water, strong winds, sea spray and little soil. Nonetheless, the inaccessibility of cliffs resulted in relatively little interference by man.
Cliffs provide shelter and an ideal breeding habitat for many bird species, such as the:
- Scopoli’s shearwater (MT: iċ-ċiefa ; SN: Calonectris diomedea);
- Yelkouan shearwater (MT: il-garnija; SN: Puffinus yelkouan), and;
- The Maltese National bird, the blue rock-thrush (MT: il-merill; SN: Monticola solitarius).
The south-western cliffs of mainland Malta provide a vital habitat to one of the rarest animals in the Maltese Islands, the Maltese door-snail (MT: id-dussies tal-irdum; SN: Lampedusa melitensis). Other rare endemic snails also have their distribution restricted to only a few cliff-side localities, such as the Filfola door-snail (MT: id-dussies ta’ Filfla; SN: Lampedusa imitatrix gattoi) and the Għar Lapsi top-snail (MT: iż-żugraga tal-irdum; SN: Trochoidea ghar lapsi).