The Maltese Islands are relatively young in age and are composed mainly of sedimentary rocks of marine origin. Soils, which are quite similar to the parent rock, are also young and soil horizon development is largely inhibited by climate. Soil cover over parts of the islands is quite sparse, especially where limestone rock forms karstland with only small pockets of soil where vegetation must grow in harsh conditions. The climate of the islands is typically Mediterranean with two main seasons: a hot dry summer and a mild wet winter. The annual distribution of precipitation is considered to be more of a determining factor for vegetation development than the actual quantity of water.
Three main types of soil are known on the Maltese Islands:
Terra Rossa Soil: a red clayey soil derived from both types of coralline limestone (mainly upper coralline limestone) when the climate favoured leaching. It is reddish due to the high iron oxide content and has a calcium carbonate content of 2-15%. It has a low humus content, but is however higher than in other soils.
Xerorendzinas: a whitish to red marly soil with a calcium carbonate content of 58-80% and derived from Globigerina limestone.
Carbonate Raw Soil: a grey soil with a calcium carbonate content of 80-90% derived from fragmented Globigerina limestone and Blue Clay, sometimes mixed with detritus from the yellow Greensand. It is a young soil containing little humus, and is formed as a result of dry conditions.
Maltese soils tend to have a suitable physical structure due to its texture and also the calcium carbonate content which decreases the risk of soil erosion but simultaneously increases the water-holding capacity and allows good drainage after a heavy rainfall. Even though organic matter is low nutrients are kept quite well due to the fact that the clay content varies between 20-50%. Soil formation under the Maltese climate and geological conditions is a very slow process and hence the amount of soil in Malta is rather low. The soils tend to have a direct affect on the habitat since the depth of the soil and nutrient availability promote or inhibit growth of particular species and characterize particular habitats.
The topography of the islands is also a factor which contributes to the formation of various habitats: low lying shores with gentle slopes are characterised either by sandy bays and inlets (which may form sand dunes or wetlands further inland), or rocky coasts and shore platforms (with coastal karstland). Specialised habitats are also found on cliffs, clay slopes, valleys, permanent springs and temporary watercourses.
As with other Mediterranean islands and coastal areas, human impact and interference is one of the major influential factors which have shaped the Maltese Islands since old times. This has led to a general deterioration of natural habitats and their associated ecosystems.
The distribution of flora in various habitats can be vaguely classified as follows – 40% of the total flora grows on disturbed or arable land, 40% grows on rocky ground (including valleys, scarp edges, coralline plateaux and the remaining 20% is found in particular habitats such as sandy beaches, coralline cliffs, salt marshes, etc.
Vegetational assemblages can be generally categorised as falling into one of three types, often with an overlap between them:
1. Vegetation which forms part of a community pertaining to the natural successional series, i.e. woodland, maquis, garigue and steppe
2. vegetation communities of specialised habitats:
- rupestral areas
- coastal communities, e.g. sand dunes, rocky shores, saline marshlands and transitional coastal wetland
3. vegetation communities of disturbed ground
Woodland, or more appropriately Mediterranean Sclerophyll Forest, is the most typical habitat of the entire Mediterranean region and is characterized by hard leaved evergreen trees and shrubs. It is the climax of the successional vegetation series (steppe –> garigue –> maquis –> woodland).
In Malta this habitat was almost totally exterminated following the arrival of humans on the islands and, today, only few remnants are left. These few patches of woodland are usually dominated by the Evergreen Oak (Balluta, Quercus ilex) and are considered as being living fossils of ancient forests. The largest area is the Ballut tal-Wardija which has trees thought to be 500-900 years old.
Buskett, the major part of which was planted by man, has now acquired the character of a semi-natural woodland, where the trees regenerate naturally. The dominant trees in this area are the Aleppo Pine (Żnuber, Pinus halepensis), Evergreen Oak (Balluta, Quercus ilex), Olive (Żebbuġ, Olea europea) and Carob (Ħarrub, Ceratonia siliqua).
The next habitat in the successional series is the maquis, characterized by small trees and large shrubs. This habitat in the Maltese Islands is relatively widespread and of secondary origin whilst artificial maquis may develop into man-made groves. Maquis communities tend to grow along valley sides or at the bottom of deeper ones, on rocky slopes or beneath inland cliffs. Maquis species include the Lentisk (Deru, Pistacia lentiscus), Bay Laurel (Rand, Laurus nobilis) and the introduced Carob (Ħarrub, Ceratonia siliqua) and Olive (Żebbuġ, Olea europea). Possible remnants of ancient woodlands are a group of Sandarac Gum Trees (Għargħar, Tetraclinis articulata) which grow in a maquis type community.
The garigue is an ecosystem which develops on large expanses of limestone bearing numerous depressions and fissures. It is characterised by dense, low-growing, aromatic hardy shrubs such as the Mediterranean Thyme (Sagħtar, Thymbra capitata) and the Mediterranean Heath (Erika, Erica multiflora). Natural garigue communities form on karstic landscapes while others are formed as a result of degraded maquis communities. Other species of Garigue plants include Rosemary (Klin, Rosmarinus officinalis), the endemic Maltese Spurge (Tengħud tax-Xagħri, Euphorbia melitensis), and various orchids such as the Maltese Pyramidal Orchid (Orkida Piramidali ta’ Malta, Anacamptis urvilleana).
Steppe communities, which are rather common throughout the islands, usually occur either due to maquis or garigue which degraded due to a number of causes including overgrazing or fire or as natural steppic communities which are found, for instance, on clay slopes. In the latter case a natural steppe will not progress into a garigue type community as it will have reached its climax as allowed by environmental factors. Clay slope communities are often dominated by Esparto Grass (Ħalfa, Lygeum spartum). Steppic species include herbaceous plants, in particular grasses (Poaceae), umbellifers (Apiaceae), legumes (Fabaceae) and tuberous or bulbous species such as the Branched Asphodel (Berwieq, Asphodelus aestivus) and the Seaside Squill (Għansar, Urginea maritima).
Rupestral vegetation, which is the term given to those species of plants living on cliff faces, is one of the most important habitats for local vegetation since it provides the last refuge from human interference. By lying on the southern and western sides of the islands cliffs are also home to many endemic species and particularly those with a North African affinity. On cliff faces, plants adapt to living in very exposed and saline areas and on very steep cliff faces exploiting minute pockets of soil and sediment which is trapped in crevices or ledges. Plants growing in cliff areas amongst boulder screes utilise the shelter provided by some of the large rocks and crevices. Some endemic species growing on cliff faces include the monotypic Maltese Rock-centaury (Widnet il-Baħar, Palaeocyanus crassifolius) and the Maltese Cliff-orache (Bjanka ta’ l-Irdum, Cremnophyton lanfrancoi) together with the Maltese Salt-tree (Xebb, Darniella melitensis), the Maltese Sea-lavender (Limonju ta’ Malta, Limonium melitensis), the Maltese Fleabane (Tulliera ta’ Malta, Chiliadenus bocconei) and the Maltese Everlasting (Sempreviva t’Għawdex, Helichrysum melitense). Species not endemic to the Maltese Islands include species with a restricted Mediterranean distribution such as the Egyptian St. John’s Wort (Fexfiex ta’ l-Irdum, Triadenia aegyptica), the Rock Crosswort (Kruċanella, Crucianella rupestris), Wolfbane (Siġra tal-Ħarir, Periploca angustifolia) and the Sicilian Snapdragon (Papoċċa Bajda, Antirrhinum siculum).
The Maltese Islands, being surrounded by sea on all sides are rich in coastal habitats and hence are characterized by halophytes, i.e. plants capable of utilising small amounts of saline soil. Species include endemic ones restricted to this type of environment, such as Zerafa’s Sea-lavender (Limonju ta’ Zerafa, Limonium zeraphae) and the Maltese Sea Camomile (Bebuna tal-Baħar, Anthemis urvilleana). Other plants include the African Tamarisk (Siġra tal-Bruk, Tamarix africana), Shrubby Glasswort (Almeridja tal-Blat, Arthrocnemum macrostachyum) Golden Samphire (Xorbett, Inula crithmoides) and the Smooth-leaved Saltwort (Ħaxixa ta’ l-Irmied, Salsola soda).
In several coastal localities, one may also find a number of shallow areas which fill up with water during the winter. The resultant mixture of water rich in salt, with mud is brackish water and forms saline marshlands. Evaporation of water in summer leads to a large increase in salinity and may even dry up the marshland completely, leaving behind a pool rich in mud and salt. However, in spite of these harsh and adverse conditions certain species of plants and animals are restricted to these habitats. One such habitat in Malta is the saline marshland at Marsaxlokk, declared a nature reserve in 1993. This habitat acts as an “interface between the marine, freshwater and terrestrial environments” and is colonized by halophilic plants such as the Seaside Sea Lavender (Limonju tal-Baħar, Limonium virgatum) and the three Juncus species – Sharp Rush (Simar Niggież, J. acututs), Hollow Leaved Rush (Simar ta’ l-Ilma, J. subulatus) and the Sea Rush (Simar tal-Baħar, J. maritimus).
A short distance inland from the few sandy beaches we have, the last remaining sand dune systems struggle to survive against human interference. The present sand dunes have been much degraded and disturbed and have now become threatened habitats which contain some very rare plants. Some have already become extinct as exemplified by the Marram Grass (Ammophila littoralis). Today, these habitats are dominated by the dune grasses Sand Couch (Elytrigia juncea) and Dropseed Grass (Sporobolus arenarius). The climax can be said to be the African Tamarisk (Tamarix africana) which grows further inshore. Other species include the Sea Rocket (Cakile maritima), the Sea Holly (Eryngium maritimum) and the Sea Daffodil (Pancratium maritimum).
Freshwater habitats are very scarce in Malta and Gozo, particularly during the summer months. In winter, water collects in small rock pools and freshwater species live here for a short period of time. A few freshwater pools and springs are also found in certain valleys and these are enriched by a number of species, considered rare owing to the scarcity of these habitats. The majority of Maltese plants and animals that live in freshwater habitats tend to live in valley beds when these are filled with water during the wet season. Apart from freshwater species, watercourses also support a rich fauna of terrestrial organisms that are associated with the vegetation that grows along them. One plant associated with the presence of water is the Great Reed (Qasba Kbira, Arundo donax).
In spite of being made up almost exclusively of limestone, the Maltese Islands have surprisingly few deep caves. The few examples illustrate that the caves are inhabited by organisms which are only adapted to live in such habitats and hence are very restricted in their distribution. The best known cavedwellers are bats but there are many other species, particularly invertebrates. Moreover, a number of these species are endemic to the Maltese Islands and therefore of great scientific interest. They are also highly vulnerable, both because of the limited habitat available and because of their poor dispersive ability.
Owing to the fact that the Maltese Islands are characterized by a very high human population density and its considerable land use, this community type has a large coverage. The habitats mentioned above have all been affected to some extent by anthropogenic factors and hence no part of the islands can be said to be in a truly natural state. In this context, however, disturbed ground refers to land which has been highly degraded as result of direct human impact. Resistant species which can survive under poor conditions are found growing here and alien species have been particularly successful in colonising such areas, using them as springboards to spread further thus becoming invasive ‘pests’. The wet months of the year in particular reveal the vast array of plants that have exploited such disturbed habitats. With a large portion of land occupied by disturbed ground and rubble, wild plants and ‘weeds’ often act as the only relief to an extensive eyesore. Given time, such habitats may even progress into holding some woody species and grow back into a semi-natural state.
Alien species growing in disturbed areas, such as roadsides or abandoned fields, include the Cape Sorrel (Ħaxixa Ingliża, Oxalis pes-caprae), the Castor Oil Tree (Siġra tar-Riċnu, Ricinus communis), the Narrow-Leaved Aster (Settembrina Salvaġġa, Aster squamatus), the Crown Daisy (Lellux, Chrysanthemum coronarium), the Perennial Wall-Rocket (Ġarġir Isfar, Diplotaxis tenuifolia) and the Prickly Pear (Bajtar tax-Xewk, Opuntia ficus-indica), together with the Acacia and Eucalyptus species. Other species found in disturbed habitats are the Vervain (Buqexrem, Verbena officinalis), the Borage (Fidloqqom, Borago officinalis), the Milk Thistle (Xewk tal-Madonna, Silybum marianum), the Mallow Bindweed (Leblieb tax-Xagħri, Convolvulus althaeoides) and the Common Poppy (Pepprin, Papaver rhoeas).
Old man-made structures such as bastions and ditches often act as refuges for local flora which could not survive otherwise. High walls are usually inaccessible (unless they are cleaned up) and allow for some vegetation growth (which may or may not be dangerous to the stone itself). Some particular species such as the Maltese Toadflax (Papoċċi ta’ Malta, Linaria pseudolaxiflora), the Maltese Star-Thistle (Xewk Malti, Centaurea melitensis) and the Maltese Salt-tree (Xebb, Darniella melitensis) are all found on bastions dating from the time of the Knights of St. John.
Past afforestation programmes have created small woods such as those found at, Miżieb, L-Aħrax tal-Mellieħa, Pietà, Fort Chambray (Mġarr) and Kennedy Grove (Salini). None of these woods, however, can be termed as natural and in some cases the choice of trees and the methods used were inadequate. Afforestation on a smaller scale has also been taking place at the Wied Għollieqa Nature Reserve.
The Maltese Islands have been settled since Neolithic times, from about 5000BC and at present, the islands’ total population is 404,962 (2005 census) and the overall population density is at 1281 people per km2 (2005 census). The growth rate is 0.7% per year (2005 statistics) but the resident population is augmented by substantial tourist arrivals which have tended to increase over the years and have even topped the 1 million mark. Thus, it is no surprise that human influence is a key feature of the islands’ ecology.
The first settlers on the islands cleared the land for agriculture and also introduced sheep and goats which prevented the trees from regenerating through their grazing activities. This process of deforestation has continued to the present day and has resulted in the almost total destruction of the native forests and most indigenous trees. Much of the land area of the islands is given over either to agriculture or to buildings and roads.
Globigerina Limestone is quarried for use as a building stone while Coralline Limestone is quarried for use as spalls. Many of the old quarries have been worked out and abandoned, often without any form of reclamation. New quarries are being established but in some cases in ecologically sensitive areas, such as in valleys and close to cliffs.
Another problem with the development of our islands is the disposal of domestic, building and industrial waste, which is currently deposited in a number of official land-fill sites. However, many unofficial, and hence illegal, dumps also exist in all parts of the countryside.
Much agricultural land is now abandoned on sloping ground which is terraced with retaining walls made of limestone rubble. Rubble walls have fallen into disrepair with a concurrent increase of soil erosion. Also, most of the agricultural land is not irrigated, which leaves the soil bare of vegetation during the dry period of the year, leading to accelerated erosion. During the transition from the dry to the wet season, short but very heavy rainstorms are common leading to an increased runoff and hence its subsequent erosion.
Loss of soil through runoff is also accentuated due to the large number of roads which provide an unimpeded channel to the sea for storm water. One positive aspect in Malta is that there is very little contamination of water sources by industrial pollutants, however there are problems with high levels of chlorides (from overpumping) and nitrates (from fertilizers).
The intense human pressure on the natural environment over the years has resulted in the loss of habitats and in a number of indigenous species of wildlife becoming extinct while others are threatened in various ways.