The Mediterranean Biome

The Mediterranean biome is also called as sclerophyll ecosystem or biome because of the development of special feature and characteristic in the dominant trees and shrubs to adapt to the typical environmental conditions of the Mediterranean climates (dry summer and wet winter).

Location

The Mediterranean biome has developed between 30°-40° (some time upto 45°) latitudes in both the hemispheres in the western parts of the continents.
This biome includes the European lands bordering the Mediterranean Sea, central and southern California of the U.S.A., central Chile of South America, north-western coastal lands of Africa bordering the Mediterranean Sea and the far southwestern part of South Africa and the coastal zones of western and southern Australia and the Asiatic coastal lands bordering the Mediterranean Sea (western Turkey, Syria, western Israel and Lebanon).

Climate

The Mediterranean climate has three typical characteristic features which give sclerophyll characteristics to the vegetation of this biome :
- Winters are cool but wet whereas summers are dry, most of the annual rainfall is received during wet winter months
- Summer season is warm and dry whereas winters are moderately cool
- There is sufficient sunlight throughout the year but summer is more sunny.
These characteristic climatic features of the Mediterranean climate have developed because of the seasonal shifting of the pressure and wind belts due to northward and southward migration of the sun.
The average temperature during cool winter season ranges between 5°C and 10°C whereas mean summer temperature varies from 20°C to 27°C and thus the annual range of temperature becomes 15°C to 17°C or even more.
Mean annual rainfall ranges between 370mm and 650mm, the most portions of which is received during winter season.
The winter rainfall is received through the cyclonic storms associated with the westerlies.
The summer season is almost dry.
This seasonal regime of rainfall causes fluctuations in the soil-water and soil-moisture regime during winter and summer seasons.
The amount of soil-water increases during winter season because of winter and spring rainfall which is responsible for maximum growth in the vegetation but the dry summer season causes deficiency in the soil-water content because of loss of water and moisture due to increased evaporation and evapotranspiration because of substantial increase in temperature and of course due to general lack of precipitation during summer season.
Thus, the deficiency in soil- water content during dry summer season prevents vegetation growth.

Natural Vegetation

Though the Mediterranean regions are widely scattered over different continents, there is more or less broad generalization in the overall structure and composition of the vegetation community of all the regions of the Mediterranean biome.
The structure of the Mediterranean vegetations is such that they can withstand the aridity of the summer season.
Consequently, the leaves have developed sclerophyllous characteristics wherein they are stiff and hard and the stems have thick barks.
The Mediterranean vegetation community consists of a variety of sclerophyll plant formation classes which range from Mediterranean mixed evergreen forests (in the coastal lands immediately bordering the seas and the oceans) to woodland, dwarf forest and scrubs.
The vegetation community is dominated by trees and shrubs.
The shrubs are differently named in the various parts of the Mediterranean biome on the basis of local names e.g., maquis or garrigue in southern Europe, chaparral in California, fymbos or fymbosch in south Africa and mallee scrub in Australia.
The plants of the Mediterranean biome have developed several morphological characteristics to withstand dry conditions.
Such structure is called xeromorphic structure such as thickened suticles, gradual hairs, sunken stomata etc.
The sclerophyllous structure of the plant leaves enables them to regulate the gaseous exchange according to the availability or scarcity of water during different seasons of the year.
A few species of trees such as mastic trees, have the mechanism of adjusting themselves to the changing weather conditions during the year.
For example, the mastic trees are able to close their stomata during dry summer season or even during winter drought so that they can reduce transpiration from their leaves to minimum and hence can conserve moisture.
Some trees have developed smaller leaves (such as chamise) so that they allow minimum loss of moisture through transpiration.
Some trees have thorny leaves (such as succulent cactus family).
The plants of the Mediterranean biome have also developed special types of root systems in accordance with the regional environmental conditions mainly the availability of moisture.
For example, some plants have extensive root systems with strong tap root which extends even into the consolidated parent rocks (such as the roots of almond); some plants have such root systems which develop above the ground as well as quite deep inside the ground (such as the root of chamise); some plants have bulbous or tuber roots (such as the geophyte plants, e.g. different types of flowers like dahlia) etc.

There are some regional variations in the species composition and vertical structure of the vegetation community in the various parts of the Mediterranean biomes as given below:

European Mediterranean Biome:

European Mediterranean Biome is characterized by multi-layered structural pattern of the vegetation community wherein three distinct layers (strata) have developed.
The topmost first layer or the canopy layer is dominated by oak tree which is of two types e.g.: Evergreen oak, and Deciduous oak.
There are several species of oak in the European Mediterranean biome.
The sequence of trees changes with the increasing altitude e.g., the evergreen oaks are found at the lower height and with the increasing height the sequence of trees is formed by deciduous oaks, beech, fir and pine.
The second or the middle layer is formed of shrubs which include the species like Arbutus, Pistacia, Rhammus, Ceratonia etc. These shrubs attain the height of 2m or even more which are clearly differentiated from the topmost layer of the dominant oak trees of 3 to 4m in height. These shrubs provide valuable forages to the animals and valuable products to human beings like gums, resins, tannins, dyes etc.
The continuous grazing, natural and anthropogenic frequent fires and felling of trees have largely transformed the shrub community called as maquis into garrigue.
The garrigue shrubs have also been modified by continued human activities and transformed into hatha (dwarf shrubs).
The third or the ground layer consists of numerous herbaceous plants.

North American or Californian Mediterranean Biome:

North American or Californian Mediterranean Biome is dominated by different species of oak trees and chaparral shrubs.
The first or the topmost layer is formed by the canopy of oak trees reaching the height between 6m and 23m.
The oak has short but thick stem and flattened crown.
The second or middle layer is dominated by various shrubs locally called as chaparrals.
The ground layer is dominated by herbaceous plants and grasses.
Chaparrals generally become gregarious in the areas of less fertile and light soils
The chaparrals of California are the counterpart of the European maquis.
The dwarf shrubs (like hatha of the European mediterranean biome) locally called as sage scrub have developed in many parts of the Californian Mediterranean biome.
The Mediterranean biome of Chile of South America has also developed vegetation quite similar to that of the Californian Mediterranean biome.
The Californian chaparrals are called mattoral in Chile.

South African Mediterranean Biome

South African Mediterranean Biome is characterized by the dominance of small but attractive flowering plants of numerous varieties.
These plants have been extensively migrated by deliberate actions of man to various gardens of numerous countries of the world.
These garden flower plants include Erica, Ereesia, Lobellia, Kniphofia species etc.
The shrubs belong to sclerophyllous categories as these are characterized by hard, stiff and thick leaves.
These sclerophyllous shrubs are locally called as fymbos.
It may be pointed out that this region was originally covered by temperate forests before the arrival of Europeans in this area.
The Europeans largely removed the original forests for the purpose of agriculture and thus there developed the secondary succession of vegetation which now has taken the form of present-day fymbos.
The large-scale transformation of original habitats through forest clearance and mass hunting of animals by the Europeans resulted into the obliteration of several species of animals front the South African Mediterranean biome.
For example, quagga, a species of zebra, has now become totally extinct.
Only a few species of antelope like duiker and steenbuck are found only in the dense cover of fymbos. Hyraxes, baboons, and leopard and found in small number only in the mountainous areas.

Australian Mediterranean Biome:

Australian Mediterranean Biome is dominated by the species of eucalyptus. Thus, the topmost layer or the canopy layer is formed by about 100 species of evergreen eucalyptus trees with the height of 70m or even more.
The tallest species of eucalyptus is karri. It may be pointed out that the forms of vegetations change inland from the coastal areas and thus several zones of vegetations are found from north to south.
The southernmost coastal land having maximum amount of annual rainfall is characterized by the dominance of eucalyptus forest which is replaced by jarrah forest in the north.
Further northward the forest cover becomes thin and is finally replaced by grasslands. Malle scrubs have developed to the north and east of grasslands.
There are numerous animals in the malle scrubs.
The average net primary productivity (NPP) of the Mediterranean biome is about 700 dry gram per square metre per year whereas the total net primary production of all parts of the Mediterranean biome is 6xl0⁹tons per year.
The NPP of 700 dry gram per square metre per year generates a biomass of 6000 grams per square metre.

Animal Life

Like vegetation, there is also regional variation in the animal communities of the various parts of the Mediterranean biomes of the world.
The Mediterranean biomes of California and Chile are characterized by more or less similar animal species
There are numerous animals in these two regions because of abundant supply of food from the good cover of various types of shrubs.
There are about 201 species of vertebrate animals in south California, of which about 75 percent are bird species.
The large mammals of Californian and Chilean regions include mule deer (in California) and Chilean guanaco but the latter is no more a browsing animal rather it has changed its feeding habit and it has been transformed to grazing animals.
The mammals are now dominated by ground squirrels, wood rats and mule deers.
Many of the predator species like wolf and mountain lion, diversivores like grizzly bear have now become rare species because of increasing pressure of man on the Mediterranean vegetation.
The other important animals include several species of rodents such as rabbits, the rabbits predators such as cyote, similar to Chilean fox, other predators such as lizards, snakes, and several types of raptorial birds like kites, falcons, hawks etc.
Most of the original native animals of the South African Mediterranean biome have now become either extinct or rare due to the destruction of their natural habitats through extensive forest clearance by the European settlers.
For example, quagga, a type of zebra, which was an important species, now has become totally extinct whereas bontebok, a type of antelope, has now become a rare species and has been pushed to remote areas.
Some animal species, which were very important before the arrival of Europeans in this area, have now occupied remote areas to escape from the hunters.
These animals include some species of antelopes (which now live in the dense shrubs of high ground) like duiker and steenbuck; rodent like browsing small animals like hyraxes (which have now been pushed to mountainous areas); baboons and leopards (which also live, though in very small number, in the remote hilly and mountainous areas).
The Australian Mediterranean biome is characterized by numerous types of birds and animals. The marsupials include kangaroos mainly western grey kangaroo. There are numerous varieties of wallaby and mice. The typical birds of the shrub habitats and grasslands are honeyeaters, whistlers, wrens, robins, quail-thrushes etc.