The Vegetation of the Maltese Islands

In this paper the results of a phytosociological investigations concerning the Maltese Archipelago, represented by some islands localized South of Sicily in the central Mediterranean, are provided. The vegetation of these islands is currently markedly altered by anthropic activities, because this territory was colonized since the Neolithic period (about 7000 years ago) by many peoples, who in the time have degraded its natural landscape. Despite this, these islands show still a relevant environmental interest, especially for the occurrence of a very interesting flora rich in endemisms and rare or relict species, that characterize many relevant plant communities, nowadays many of which are often reduced to small patches. The first our field research dates back to about 45 years ago, when mass tourism in these islands had not yet begun and continued until today. During this period, substantial changes in the landscape have been witnessed, with the increase in urban, industrial and tourist areas, as well as the modification of agricultural lands. From the biogeographical point of view, the Maltese Islands belonging to Holarctic Kingdom, Mediterranean Region, Western Mediterranean Subregion, Italo-Tyrrhenian Province, Sicilian Domain, Pelagian Sector, Maltese District (Brullo et al. 1995). As a whole, the territory has a total extension of 315.6 km², with 140 km coastline and is inhabited by a population with a density that exceeds 1500 people per km² on the larger island. Besides, most of its surface is used for agricultural activities (51%) or is urbanized (15%), while only 18% is currently covered by natural vegetation (Lanfranco et al. 2013). The topography of the islands is the result of geological, climatic, paleogeographic events that during the last 5–10 million years, since the archipelago emerged from the sea, have affected its surface (Fig. 1.1). The tectonic movements of the continental plates, as well as the repeated exposure of the Islands to erosion and meteoric infiltrations, have considerably altered the surface and the subsoil of these islands, with the formation of well-diversified environments, as incised river valleys, caves, plateaux, karstland, marshs, cliffs, budlands, rocky coasts, islets, dunes, temporary rocky pools, etc. (Figs. 1.2 and 1.3).

According to literature data (Haslam 1969; Schembri 1993) the Maltese Islands consist in a small archipelago aligned along an axis with NW-SE trend, situated in the Central Mediterranean about 96 km to the South of Sicily and about 284 km to Tunisia (Fig. 2.1). The main islands are Malta (245.7 km², coord. 35° 55′ 4″ N and 14° 24′ 35″ E), which is the largest and southern, Gozo (67.1 km², coord. 36° 2′ 39″ N and 14° 15′ 4″ E), which is the northernmost, and Comino (3.5 km², coord. 36° 00′ 45″ N and 14° 19′ 37″ E), which is located between these two islands. They are currently inhabited by about 445,000 people, most of which reside in Malta. Nearby these island there are numerous rocky islets, all uninhabited, among them the most extensive are Cominotto, Filfla, Islands of St. Paul, Fungus Rock, Gallis Roch, Delimara island, Xrobb I-Ghagin Rock, etc. Along the coast bays and inlets, often very deep, which are excellent harbors, are frequent some of which are characterized by sandy beaches. The eastern slopes of the islands are generally represented by low reefs and beaches, while the southern ones are mostly constituted by vertical cliffs, often exceeding 100 m from sea level. In the more depressed coastal stretches, separated from the sea by sandy or silty-clay deposits, are frequent salt marshes, periodically flooded by sea and meteoric waters. Along the low calcareous rocky shoreline often occur chequerboards of rock-cut saltpans, which are used by the local people for salt production as result of the seawater evaporation. It’s believed that these saltpans existed since Roman times. The current landscape of the Maltese Islands is characterized by low hills, alternating with terraced plateaux, which are generally furrowed by more or less shallow valleys, locally called “Wied”, which were formed prevalently by river erosion in periods characterized by very wet climatic regimes, as during the Pleistocene (Fig. 2.2). This is nothing but the result of tectonic movements and subsequent processes of surface erosion and karsism, which starts on the land immediately after its emersion from the sea. The islands do not reach high altitudes, the highest point in Malta is Ta′ Dmejrek near Dingli at 253 m, while in Gozo the highest point is Ta′ Dbiegi, reaching 195 m. As concerns the rivers, there are only few small watercourses that flow on the bottom of some valleys mainly during the wet season, which are dry for the rest of the year. In fact, usually no permanent rivers and lakes occur in the Maltese Islands, except of few streams fed by small springs of fresh water, such as those ones at Ras ir-Raħeb near Baħrija and at l-Imtaħleb. Most of the Maltese territory is today under cultivation with crops localized especially in land characterized by terracing with walls that surround them, preventing the soil erosion. Usually, the terrace walls follow the contours of the slopes radiating from the hill top and probably their realization dates back to ancient times and was continued until the nineteenth century. The terrace farming and in general the cultivated areas are more widespread on the freshest and humid slopes of hills and valleys or on flat surfaces where is possible the irrigation. The surfaces constituted by barren rocks very washed out and eroded, however without soil, are covered by a scattered and wild vegetation, represented by small shrubs and grasses. Only in few undisturbed and rocky stands it is still possible to find patches of natural woody vegetation, as maquis, garigues and shrublands. Besides, examples of natural woodlands, such as those with Quercus ilex, today are very rare and can be considered as relicts of the forestal vegetation that originally covered part of these islands. It should be noted that the present landscape of the Maltese Islands is nothing but the result of the anthropic impact that has acted on this territory in the last 7000 years. According to literature (Renfrew 1972; Cutajar 1982), the first human colonization goes back to about 5200 BC and this prehistoric period ended in 750 BC. In particular, the earliest human civilization that reached these islands coming from Sicily dates back to Neolithic period (5200–4400 BC), with people having a hunter-gatherer culture, who probably did not have a strong impact on the natural environment. Towards the end of this period (4500–4100 BC) the population began to practice a primitive agriculture. During the Chalcolithic Age (4200–2500 BC), due to the arrival of other people from Sicily there was a marked improvement in agriculture that became more efficient and intensive, with a spread of pastoral activities. The Chalcolithic civilization of Malta, which is associated to the buildings of megalithic temples, due to intense sheep-grazing caused a depletion of natural resources with the degradation of vegetation cover and consequent denudation of the surfaces for soil loss. This was probably the main cause of the disappearance of this civilization towards 2500 BC, since it triggered off famines and diseases in the population of these islands, as hypothesized by the archaeologists. After 2500 BC, Malta remained unpopulated for several decades, until the arrival of a new migratory flow of people, called builders of Dolmen, who started the Maltese Bronze Age. This new civilization lasted about 1000 years, until 1450 BC, its end coincides with the eruption of Santorini which caused upheaval throughout the Mediterranean. After up to 750 BC, other peoples arrived in Malta, mainly farmers, who then became fully integrated with the culturally far superior Phoenician civilization, whose population colonized the islands later this date. After this prehistoric period, during which Malta suffered a first devastation of the original vegetal cover, the islands from 218 BC fell under Roman rule, becoming a prosperous colony (Ballou 1893; Cassar 2000). Malta remained part of the Roman Empire until the early sixth century AD. After a brief occupation of Vandals and Ostrogoths, Malta in 535 AD was conquered by the Byzantines, becoming a colony. The successive invasion was that of Muslims that began in 870 AD. The native population was massacred, remaining the island uninhabited for about 150 years. After, the islands were colonized by a Muslim community that, although short-lived, introduced, apart of the language, also many innovative crops and new irrigation techniques, that are still used by farmers. Around 1100, with the expulsion of the Muslims, the Maltese islands returned under Christian rule with the Normans, remaining part of the Kingdom of Sicily for about 440 years. From 1530 to 1798 it was ruled by the Knights of Malta who embellished and fortified the islands, protecting it from the Ottoman invasions. After a brief Napoleonic period, Malta since 1800 became a protectorate of the British Empire which lasted until 1965, when the state of Malta was created.

The flora of the Maltese islands was investigated by numerous authors, who since the seventeenth century have contributed to provide information on the indigenous and cultivated plants occurring in this Central Mediterranean territory. The earliest records date back to some prelinnaean authors (Abela 1647; Boccone 1674, 1697), who cited from Malta only few species or reported lists of species (Bonamicus 1670; Cavallini 1689). Later, some plants from Malta were mentioned by Linnaeus (1753), Forskåll (1775), Dumont D’Urville (1822), Giacinto (1811), Bertoloni (1829), Brenner (1838), etc., while the first checklists on Maltese flora were published by Zerapha (1827–1831), who recorded 644 indigenous and cultivated species, but with numerous incorrect identifications, Nyman (1844) listing 73 species, Grech Delicata (1853) published a list of 716 phanerogams, lastly Duthie (1872, 1874–1875) and Gulia (more works, see Sommier and Caruana Gatto 1915) increased the lists of previously published Maltese floras of several species not yet reported from the islands. During the twentieth century, several floras regarding the Maltese Islands were published, among these one of the most important is “Flora Melitensis nova” by Sommier & Caruana Gatto (1915), which is the most comprehensive flora of the period, where all the species occurring in the Maltese territory are listed with a detailed indication of the growth locality and of the authors who had quoted them, often with taxonomic comments. These authors report 902 species of phanerogams and 1085 species of cryptogams (fungi, algae, lichens, mosses, liverworts and ferns). Other Maltese floras were published by Borg (1927), in which almost all the species reported by Sommier and Caruana Gatto (1915) are examined, and successively by Lanfranco (1969a, b), Haslam et al. (1977), Weber and Kenzior (2006), Casha (2015), Lanfranco and Bonnett (2015) and by numerous other authors, who have published various floristic contributions, among the more recent can be quoted: Lanfranco (1970, 1971, 1972, 1973, 1975, 1989), Silverwood (1971), Kramer et al. (1972), Briffa (1986), Stevens and Lanfranco (1995), Bartolo et al. (2001), Buttigieg and Lanfranco (2001), Mifsud (2007, 2008, 2009, 2010, 2011, 2012), Stevens (2003), Tabone (2007, 2008), Casha (2009), Sciberras and Sciberras (2010), Sciberras et al. (2012), Casha and Mifsud (2013), Mifsud et al. (2016a, 2016b). Based on these floras, the autochthonous and allochthonous ferns and spermatophytes amount to about 1100 taxa (species and subspecies enclose), even if some of them have not been found anymore or are thought to have become extinct. Besides, there are numerous taxonomic contributions regarding the Maltese flora, where critical species and groups were investigated with the description of a lot of new taxa, many of which endemic, all based on specimens collected in these islands. Among these papers are to be mentioned: (a) Bertoloni (1829) proposing for the Centaurea spathulata Zerapha nom. inval. the new name C. crassifolia (Fig. 3.1a), an endemic species currently included in the genus Cheirolophus by Susanna et al. (1999); (b) Sommier (1907), who described Melitella pusilla new genus and species considered initially endemic to Malta, but later found in various other countries of the Mediterranean and also in Australia, which was attributed by Merxmüller (1968) to the genus Crepis (Fig. 3.4a); (c) Béguinot (1907) described Romulea melitensis (Fig. 3.4b) as new species endemic of the Maltese Islands, providing successively a larger observations (Béguinot 1908), which more recently has been recorded from southern Sicily by Brullo et al. (2009a, b, c), while Mifsud (2015) believes that R. melitensis is an uncertain name replacing it with R. variicolor, which must be considered an superfluous name; (d) Sommier and Caruana Gatto (1915) described from Malta Anacaptis urvilleana (Fig. 3.1d), a neglected species of Orchidaceae, later revalued by Del Prete et al. (1984), proposing also as distinct species Anthemis urvilleana by Candolle de (1838) considered as var. urvilleana of A. secundiramea Biv. (Fig. 3.1b); (e) Ciferri and Giacomini (1950) considered a distinct species Allium melitense (Fig. 3.3b), taxon proposed by Borg (1927) as A. ampeloprasum L. var. melitense Sommier & Caruana nom. prov.; (f) Botschantzev (1976) basing on a herbarium specimen identified a new shrub species of Salsoleae from Malta, describing it as Salsola melitensis, by Brullo 1984a, b transferred to the genus Darniella Maire (Fig. 3.2c), which is noticeably distinct from Salsola L. for several significant morphologic features; (g) Brullo (1979) described Chiliadenus bocconei (Fig. 3.1b), endemic of North African origin first reported by Boccone (1674) and later recorded with different names, all illegitimate or invalid; (h) Brullo (1980a, b), proposed to consider the sea-lavender previously attributed to Statice reticulata auct.fl.melit. not L. (1753), by Del Guacchio et al. (2018) more recently proposed as a reject nomen, to a new species named Limonium zeraphae (Fig. 3.2d), which is endemic to the Maltese islands; (i) Brullo et al. (1982) described a new Maltese species of Allium, indicated as A. lojaconoi (Fig. 3.1e), which in the past was attributed to A. parciflorum Viv., which is exclusive of Sardinia and Cosica; (j) Brullo and Pavone (1985) attributed the populations of Desmazeria sicula, previously quoted from Maltese Islands and Southern Sicily, to a new species named D. pignattii (Fig. 3.4c), which must be considered a geographic vicariant of D. sicula; (k) Brullo et al. (1988a, b), in a contribution on Mediterranean Limonium, pointed out that the Maltese populations previously referred to Statice cosyrensis Guss. must be attributed to a new species named Limonium melitense, morphologically well differentiated from L. zeraphae; (l) Brullo and Pavone (1987) attributed an archaic shrubby species of Chenopodiaceae, discovered in the Maltese island, to a new species Cremophyton lanfrancoi (Fig. 3.1c), including it within a monophytic genus, that, although morphologically and karyologically very differentiated from the other genera of the tribe Atripliceae, has been attributed by Kadereit et al. (2010) to the genus Atriplex, but from the phylogenetic tree published by these authors Cremonophyton lanfrancoi, constitutes together with Atriplex cana, both representing an old lineage of Atriplex, a sister isolated clade well separated from all other investigated Atriplex, for which these two species must be clearly to attribute to two different genera distinct from Atriplex; (m) Brullo et al. (1988a, b) published a taxonomic note on the Maltese flora, where they examined some endemic or rare species from Malta, such as Helichrysum melitense (Pignatti) Brullo et al. (Fig. 3.2f), belonging to the group of H. panormitanum Tineo ex Guss., Matthiola incana (L.) M.T. Aiton subsp. melitensis Brullo et al. (Fig. 3.3d), Elatine gussonei (Sommier) Brullo et al. (Fig. 3.4a); (n) Brullo and Pavone (1988) in their review on the genus Hyoseris described from Gozo a new suffruticose species named H. frutescens (Fig. 3.1f), more recently recorded also from Malta (Sciberras and Sciberras 2010); (o) Raffaelli and Ricceri (1988) recognized the specific rank of Euphorbia melitensis (Fig. 3.3a), critical species described by Parlatore (1869) from the Maltese islands, differentiating morphologically it from the related E. bivonae Steud. and E. papillaris (Boiss.) Raffaelli & Ricceri both occurring in Sicily; (p) Devillers and Devillers-Terschuren (1994) considered a distinct species (Ophrys melitensis) the orchid described from Malta by Salkowski (1992) as O. sphegodes Mill. subsp. melitensis; (q) Brullo et al. (2001a, b, c) referred the Maltese populations of Zannichellia palustris s.l. to a new endemic species named Z. melitensis (Fig. 3.3e), which represents a taxonomically very isolated species; (r) Brullo and Giusso (2006) attributed the Maltese population of Anthyllis hermanniae L. to a distinct endemic subspecies, named subsp. melitensis (Fig. 3.2a); (s) Peroni et al. (2013) referred the populations from Gozo of a rare Polypodium to P. vulgare subsp. melitense; (t) Mifsud et al. (2015) treated the Sedum album from Malta as an endemic subspecies, named subsp. rupi-melitense; (u) Brullo et al. (2017a, b) within taxonomic researches on the Silene colorata group, described from the Maltese Islands a new endemic species, represented by Silene melitensis (Fig. 3.3c), which is closely related to Silene crassiuscula from Sicily; (v) Brullo et al. (2018) emphasize that the Maltese populations of Ferula communisis must be treated as a morphologically well distinct species proposed as F. melitensis (Fig. 3.2e). Several others endemic species occurring apart from Malta also in some localities of Sicily and surrounding islands are: Senecio pygmaeus DC. (Maltese Islands, Lampedusa and southern Sicily) (Fig. 3.4d), Linaria pseudolaxiflora Lojac. (Maltese Islands and Linosa) (Fig. 3.3f), Filago cossyrensis Lojac. (Maltese Islands and Lampedusa), Daucus rupestris Guss. (Maltese Islands and Lampedusa) (Fig. 3.4f), Daucus lopadusanus Tineo (Maltese Islands and Lampedusa), Iris sicula Tod. (Maltese Islands and Sicily) (Fig. 3.4e), Oncostema sicula (Tineo ex Guss.) Speta (Maltese Islands and Sicily), Ophrys caesiella P. Delforge (Maltese Islands and southern Sicily), Hymenolobus revelierei (Jord.) Brullo subsp. sommierianum (Pamp.) Brullo (Maltese Islands, Lampedusa and Egadi Islands) (Fig. 3.4c), Plantago afra L. subsp. zwierleinii (Nicotra) Brullo (Maltese Islands and Sicily) and Euphorbia sommeriana C. Brullo & Brullo (Maltese Islands and Sicily) (Fig. 3.4b). Besides, some rare species having mainly a North African distribution are recorded from Malta, such as Pteranthus dichotomus Forssk. (Fig. 3.4h), Plantago crypsoides Boiss. (Figure 3.4f), Fagonia cretica L., Enarthrocarpus pterocarpus (Pers.) DC., Crucianella rupestris Guss. (Sicily, Lampedusa, Malta, Lybia and Egypt) (Fig. 3.4e), while other have a East Mediterranean distribution, such as Hypericum aegypticum L. subsp. webbii (Spach) N. Robson (Sicily, Lampedusa, Sardinia, Malta and Greece) (Fig. 3.4d) and Convolvulus oleifolius Desr. (Malta and East Mediterranean) (Fig. 3.4g).

Currently, in the Maltese Islands the forest vegetation are very rare and localized, due to mainly for the millenarian anthropization of this territory. In fact, the woodland in the past were probably widespread especially in the inland and in the wadis, where they were mainly represented by Quercus ilex woods and perhaps also by pinewood of Pinus halepensis. As concern the first vegetation only few relict spots occur now in Malta, which are referable to Pistacio lentisci-Quercetum ilicis, while of the second one there is no trace of natural pine forests in this archipelago, since this gimnosperm is today exclusively cultivated in gardens or street edges, as well as it is used for reforestation. Conversely, the shrubby plant communities as maquis, garrigues and shrubbery are more frequent in these islands. In particular, it is possible to survey woody vegetation characterized by Tetraclinis articulata, belonging to Asparago aphylli-Tetraclinetum articulatae, thermophylous maquis with Euphorbia dendroides, represented by Periploco angustifoliae-Euphorbietum dendroidis, garrigues of Cisto-Micromerietea and halo-nitrophilous shrub vegetation of Pegano harmalae-Salsoletea vermiculatae.

In the Maltese Islands the rupestrian communities linked to the crevices of the calcareous rocky walls, represented by the very high cliffs facing the sea and the wadis, are very widespread. In these stands reside several relict endemic species, often having an old Tertiary origin, which are member of very peculiar chasmophilous vegetation of the Asplenietea trichomanis. Another very specialized rock habitat is that interested by percolating or splashed waters, as shady and damp walls, colonized by bryo-pteridophytic communities of Adiantetea:

The rocky shorelines directly affected by sea agents are colonized by perennial halophylous communities dominated by various species of Limonium, usually associated to Crithmum maritimum, Cichorium spinosum and Crucianella rupestris. This vegetation, clearly belonging to Crithmo maritimi-Limonietea, is widespread along the coast of all the islands, where it forms a more or less developed band in the stands closest to the seashore (see Brullo et al. 2017a, b). In the coastal places more distant from the sea, these communities are replaced by a pulvinate vegetation dominated by small shrubs showing a denser coverage. The latter, always included into Crithmo maritimi-Limonietea, can be considered a subhalophilous communities affected mainly by sea aerosol.

Along the coasts of the Maltese Islands the sandy beaches are not very spread. Currently, some examples can be observed only in bays or small coves, where the sandy deposits tend to form small dunes. These surfaces usually are colonized by a paucispecific psammophilous vegetation, represented by perennial communities of the Ammophilion australis. Sometimes, also annual halo-nitrophilous communities, belonging to the Cakiletea maritimae, occur in stands near the shore. Unfortunately, many of these dune environments for a long time have been destroyed by urbanization and tourist activities, remaining only a few sites, some of which are luckily designated as natural protected areas.

The coastal lagoons, usually localized in the inner part of sandy belt, are colonized by hygro-halophilous plant communities, characterized by succulent chamaephytes and nanophanerophytes, as well as by perennial helophytes and therophytes. They are splitted in several associations well distinct from floristic and physiognomic point of view, which are linked to well-defined edaphic conditions. The shrubby communities belong to Sarcocornietea fruticosae, the helophytic ones to Juncetea maritimi, while that one prevalently dominated by annual species are referable to Thero Salicornietea. The salt marshes are characterized also by submerged communities differentiated by algae and Ruppia species.

In the Maltese Archipelago although it is represented by small islands with almost absent water basins and very limited watercourses, the freshwater plant communities are quite frequent and well diversified. Within the hygrophilous vegetation it is possible to distinguish perennial and annual associations linked to stagnant or slowly flowing waters, as well as to running waters. They are mostly differentiated by helophytes, pleustophytes and submerged hydrophytes, which belong to various phytosociological classes, such as Magnocarici elatae-Phragmitetea australis, Molinio-Arrhenatheretea, Potametea and Lemnetea.

The coasts around the Maltese Islands are characterized by seagrass meadows, linked mainly to more or less sandy bottoms. These communities are mainly represented by monophytic populations of Posidonia oceanica, Cymodocea nodosa or Halophila stipulacea, which occur prevalently in the infralittoral zone from the seashore up to 30–40 m deep. For this vegetation the authors not carried out original releves, due to their localization in deep marine habitats.

The Maltese Islands are characterized by large limestone outcrops, where are very frequent rocky pools usually submerged during winter-spring period. These habitats have a relevant phytosociological role, since a specialized flora of small hydrophytes, is here localized. It is represented by several submerged and amphibious species, some of them endemic, which differentiate various peculiar plant communities. They belong mainly to the Isoeto-Nanojuncetea class, which are included in one of the most important priority habitat (Cod. 3170, Mediterranean temporary ponds). Community of Charetea and Potametea are also frequent in these habitats.

The riparian woodland in the Maltese Islands are very rare and represented by scattered and isolated patches, which are very depauperated and degraded due to intense anthropic activities. Besides, it is to be noted that in this territory the watercourses are short with a limited flow and usually dried in summertime. Currently, this type of vegetation is represented just by two associations, one more thermophilous belonging to Nerio oleandri-Tamaricetea and another more mesic of the Alno glutinosae-Populetea albae.

The marked environmental aridity featuring the Maltese Island has clearly a confirmation in the occurrence and spread mainly in rocky habitats of annual plant communities, linked to the edaphic xericity. Most of them show a pioneer character fitting well to shallow soils in contact with the rock, as well as to sands and clays. From the floristical viewpoint, they are differentiated by small therophytes and geophytes, showing a short biological life cycle, with their optimum in springtime. These communities must be referred to Stipo capensis-Trachynietea distachyae, while that ones linked to sandy soil belong to Vulpietalia, order of Tuberarietea guttatae.

The perennial herbaceous communities characterized by a marked edaphic xericity are widespread in all Maltese Islands. Physiognomically, these grasslands are differentiated by big hemicryptophytes showing a caespitose or stoloniferous habit, as Lygeum spartum, Hyparrhenia hirta, Brachypodium retusum, Andropogon distachyos, Oryzopsis miliacea, etc. Usually, they represent edaphophilous associations or can be considered as secondary aspects due to woodland degradation processes. These grasslands are included in Lygeo sparti-Stipetea tenacissimae, class with Circum-Mediterranean distribution.

During the winter-spring period in stands characterized by more or less salt soils, such as in the rocky reefs, a microphytic vegetation differentiated by rare precocious endemic species occurs. Other communities are localized also in the salt marshes, mainly in the clearings mixed to perennial vegetation of Sarcocornietea fruticosae. From the phytosociological point of view, they belong to Frankenietalia pulverulentae, order of Saginetea maritimae.

The Maltese islands, as well as all the other Mediterranean insular environments, due to the anthropic disturbance dating back to some millennia ago, show a rich nitrophilous flora, which is spread in many secondary habitats. Several and diversified plant communities are frequent in these ruderal stands, represented by footpaths, roadsides, ruble accumulations, organic matter deposits, etc. They are mainly represented by annual or more rarely perennial associations having a winter-spring or sometimes an autumnal vegetative cycle. The phytosociological class involved in these types of vegetation are Polygono arenastri-Poetea annuae, Artemisietea vulgaris, Chenopodietea, Epilobietea angustifolii and Nicotiano glaucae-Ricinetea communis.

Another type of nitrophilous vegetation regards the cultural habitats, where it is localized a very specialized and selected commensal flora. In the Maltese Islands there are many cultivated lands, represented by cereal, leguminous and horticultural crops, orchads and vineyards, which are characterized by different weedy communities. They are linked to agronomic activities carried out in these cultural environments, as fertilization, plowing, irrigation, weeding, etc. The cereal crops are characterized by a segetal weedy vegetation, belonging to Papaveretea rhoeadis, while in the other types of crops the commensal vegetation is referable to Chenopodietea. Besides, within this weedy communities can be distinguished associations having a winter-spring cycle and also a summer-autumnal cycle, which often occur in the same places, but in different period.

Another type of synantrophic vegetation frequent in the Maltese Islands is that one localized in the uncultivated lands or abandoned fields (Fig. 20.1), previously used for herbaceous crops. In these communities numerous therophytes well adapted to more or less nitrified soils are frequent and often dominant. Floristically, this vegetation is characterized by species belonging to Echio plantaginei-Galactition tomentosae, alliance of Chenopodietea widespread in the Mediterranean area.

In the last decades within the geobotanical investigations, regarding the ecological correlations between vegetation and environment, phytosociological studies have been carried out where the dynamic relationships of serial or catenal kind are taken into consideration. This methodological approach is part of the synphytosociology, which was developed initially by Rivas-Martinez (1976) and later revisited by Tüxen (1977, 1979), Gèhu (1979, 1991) and Rivas-Martinez (1983, 1985). According to Rivas-Martinez (2005), Rivas-Martinez and coaut. (2011), Pedrotti (2013) and Loidi (2017), these science is based on the concept of vegetation complexes, whose basic units are mainly represented by the sigmetum (= series), and geosigmetum (= geoseries), to which permasigmetum (= permaseries) and geopermasigmetum (= geopermaseries) are added too. In particular, it is called sigmetum the basic geobotanical unit of a local assemblage of all the communities that have the potential to develop toward a well definite single climax (see Pedrotti 2013). On the whole, it expresses the set of plant communities that can develop within an ecologically homogeneous space or tesela, including a single dynamic series of replacement and a single head series. Besides, it must be emphasized that into a sigmetum can be distinguished climatophilous and edaphophilous series, that in the latter are of two kinds (edaphoxerophilous or edaphohygrophilous). As concerns the climatophilous series, it is linked to the mesoclimate and only to rain water, with its head series usually represented by a forest as mature stage, since the highest expression of an evolved soil, while the edaphophilous series regard those ones in which the natural edaphic evolution is blocked by various environmental factors, determining more or less xerophytic soils (edaphoxerophilous series), as well as more or less wet soils (edaphohygrophilous series). In both cases the most mature stage usually coincides with a permanent woody vegetation, which is informative in defining the ecologic and phytogeographic role of the series. Instead, the geosigmetum is synonym with geoseries, which is the basic unit of the landscape phytosociology. It can be defined as a system of contiguous sigmeta replacing each other along an edaphic gradient inside of a bioclimatic belt of a given territory. Among these sigmeta, dynamic-catenal relations are established, distributing themselves according to the geological and edaphic features of the surveyed area. Another kind of series is the permaseries o permasigmetum, regarding in particular a perennial and stable plant communities occurring within a microtesela characterized by extremely specialized environmental conditions, such as coastal reefs, dunes, cliffs, rochy walls, salt marshes, etc. It is represented by a permanent and mature stage (edaphoclimax), usually mono-layered and pauci-specific, poor in perennial seral communities. It is a special kind of vegetation series from extreme environments, where a perennial climactic stage is present, without substitution perennial stages. Finally, the geopermaseries or geopermasigmetum is used in terms of catenal approach to the description of the adiacent sets of permasigmeta, clearly linked to different micro-topographic and edaphic conditions. In particular, the various permasigmeta belonging to a given geopermasigmetum are affected by a gradient of a well definited ecological situations, which are determinant in the realization of the catenal relationships. An azonal geopermaseries, like those localized in coastal habitat, can be recognized only within a bioclimatic belt and in quite uniform stands populated by permanent and perennial plant communities.

According to MEPA (2010) and ERA (2017), in the Maltese Islands within a management plan for the preservation of areas deemed deserving of protection, 34 terrestrial “Natura 2000” sites have been recognized, of which 27 are Special Areas of Conservation (SAC) and 7 are Species Protection Areas (SPAs). Inside of these protected areas there are species and habitats of Community Interest, as required by Habitat Directive of EU. On the base of our phytosociological researches and of the literature data, the habitats currently occurring in the Maltese territory are the following: