To survive the dry summer months, most plants go into a state of reduced activity or dormancy in the form of underground perennating structures (tubers, bulbs) or in the form of seeds. All aerial parts of the plant dies and dries up. Other plants are evergreen but have numerous adaptations to reduce water loss by transpiration and to avoid overheating during the arid period. On such mechanism is sclerophylly where the leaves have a thickened cuticle and are reduced in size to limit transpiration. Some small plants manage to avoid the summer altogether. Being annuals, these plant species concentrate their entire lives into half a year. When the autumn rains come,they sprout leaves and grow quickly. By spring they are in flower, but with the advent of summer they die after scattering seeds wrapped in water-tight skins. Similar protective mechanisms against the summer heat and drought are also taken by animals.
The Maltese landscape thus presents are variety of habitat assemblages.
(1) Garigue: This habitat form is the most characteristic natural vegetation type present on the Maltese Islands, particularly on the flat karstic limestone platforms of western Malta and the Gozitan hilltops. Garigues are characterised by low shrubs such as the Mediterranean Thyme, the Yellow Kidney Vetch, the Olive-leaved Germander, the Mediterranean Heath and the Maltese Spurge. These are accompanied by numerous geophytes and therophytes. While some garigue areas are natural, others result from the degradation of forest and maquis, when removal of the vegetation cover leads to extensive soil erosion exposing large tracts of bed rock and leaving only patches of stony soil.
(2) Steppes: Steppes are widespread and result from the degradation of the maquis and garigue mainly by grazing by goats and sheep. Some steppes develop on abandoned agricultural land. These are dominated by grasses, umbellifers, thistles and geophytes. Steppes also develop in situation where the soil cover and the general conditions do not allow for the growth of larger plants or shrubs. Thus steppes also characterise the talus clay slopes.
(3) Maquis: The Maltese maquis is an impoverished scrub community resulting from degeneration of woodland due to cutting, grazing and the resultant soil erosion. The local maquis is characterised by a number of small trees (Carob and olive) and large shrubs (Olive-leaved Buckthorn, Mediterranean Honeysuckle, etc). A semi-natural maquis survives in relatively inaccessible sites such as the sides of steep valleys (widien) and the foot of inland cliffs (rdum). An artificial maquis develops round tress, mainly olives and carobs, planted by man. Rdum are near vertical faces of rock formed either by erosion or by tectonic movements. Their bases are invariably surrounded by screes of boulders eroded from the edges. Because of the shelter they provide and their relative inaccessibility, the sides and boulder screes provide important refuges for many species of Maltese flora and fauna, promoting rupestral habitat assemblages. Widien are drainage channels formed either by stream erosion during the Pleistocene and/or by tectonic processes. Most are now dry valleys and only carry water along their watercourses during the winter months. A few drain perennial springs promoting the development of freshwater habitat assemblages.
(4) Rupestral assemblages: The south, southwest and west coasts of Malta and the south and southwest of Gozo consist of vertical cliffs, which in some places give way to a steeply sloping substratum which is terranced and partly under cltivation. A second tier of vertical cliffs (rdum) can be found further inland. Because of the relative inaccessibility of these sites, they provide an important refuge for many plant and animal species, including a large number of endemic ones.
(5) Freshwater assemblages: Freshwater assemblages in the Maltese Islands are usually very transient since the rainwater pools dry up completely during the summer months. Temporary rainwater pools house many freshwater plant and animal species which are overall rare on the Islands. Some pools receive water from sources other than rain or are of a sufficiently large size as to remain more or less permanent. These pools are the only standing water bodies of the Islands. Freshwater assemblages are generally found along the valleys (widien).
(6) Woodland: During the Pleistocene period, the Maltese Islands were apparently covered with Mediterranean Sclerophyll Forest characterised by the Holm Oak and Aleppo Pine. In the Maltese Islands, the natural forest is all but extinct, except for four forest ramnants of small copses of Holm Oak. An artificial woodland was created at Buskett in Malta. This has now become a self-regenerating semi-natural woodland. The latter represents the only woodland ecosystem in the Islands and harbours a large number of woodland trees and animals.
(7) Coastal communities: Marshlands form an interface between marine, freshwater and terrestial environments, and thus are characterised by a muddy substratum with a cover of brackish water which dries out in the summer. Because of the harsh conditions, saline marshlands support a highly specialised flora and fauna. Another important coastal community are the sand dunes found on several Maltese sandy beaches. Beach development has however degraded many of these sand dunes, and these have become amongst the rarest and most threatened of local ecosystems. Those which are still vegetated harbour typical Mediterranean dune communities such as the Sand Couch. The Southern Marram Grass has been totally extirpated from these sites.
(8) Cave assemblages: The Maltese Islands have a number of deep caves which house a variety of organisms specially adapted to live in such habitats. A number of the invertebrate species are endemic and locally restricted such as the cave-dwelling woodlouse Armadillidium aelleni found at Ghar Hasan. One cave at Ghar Harq Hamiem (Malta) is unique in that it houses a deep pool of freshwater.
ground communities: The extensive land use has resulted in large
tracts of lands which have had marked disturbance of their ecologies. These
have resulted in various subtypes of distubed ground assemblages which
may include alien plant species in localities such as used and abandoned
fields, along roadsides and disturbed seaside habitats.