MEDITERRANEAN SCLEROPHYLLS

Lecture Schedule

Lecture

The similarity of form andfunctional response of the vegetation to the rigorous mediterraneanenvironment is therefore a striking example of evolutionary convergence,and has resulted in a high degree of endemism within the regionalfloras." (Archibold, 1995)

 I.  MediterraneanBiome, Climate and Location

Mediterranean regions occur between approximately 30° to 40° north and south latitude on the west sides of continents. Temperatures in these areas are from warm to hot in the high sun season with high evaporation rates and are mild in the low sun season with reduced evaporation rates. These regions have thus been called 'winter-rain and summer dry' climates.

The climate diagrams represent a range of Mediterranean climates that differ only in regards to the extent of summer drought. [see examples from Chile coast, and California coast]

The dry summer climate of mediterranean regions arises from the seasonal change in position of the semi-permanent subtropical high pressure systems which are centered over the tropical deserts roughly over the tropics of Capricorn and Cancer. The westerlies that are produced provide a constant stream of dry and warm air to the Mediterranean regions, some like Santa Ana can be quite strong with real threats of fire. As the subtropical high retreats towards equator during the winter, maritime airmasses and cyclonic storms developing along the polar front make their way into the Mediterranean region bringing coolness and moisture.

The Mediterranean biome is divided into five floristic biome subtypes, according to the various floristic realms into which each fall:

1. Mediterranean
2. Californian
3. Chilean
4. Capensic
5. Australian

The types sound like what? Types of wines! - the grape plant is well suited for the Mediterranean climate.

The largest of these groups is the Mediterranean, forming more than half of the total area of the biome worldwide. This is due to several reasons:

1. deep inland penetration of the Mediterranean climate along the margins of the Mediterranean Sea

2. Australian and South African mediterranean vegetation is limited by the termination of these continents in the south

3. Chilean and Californian vegetation is limited on the east by Andes and Sierra Nevada

 II.   MediterraneanVegetation

A. Life forms

The Mediterranean vegetation is dominated by evergreen shrubs and sclerophyllous trees adapted to the distinctive climatic regime of summer drought and cool moist winters with only sporadic frost. The most favored time for vegetative growth is spring, when the soil is moist and the temperatures are rising, or autumn, after the first rain. The winter temperatures of 10°C and lower are already too cool for growth.

As can be seen from the handout on lifeforms, life forms other than the trees and shrubs can be important in certain of the mediterranean regions:
1 .bulb or tuber bearing herbs
2. annuals

 

B. Fire ecology

Fire is a regular part of the ecosystem (tell that to a Californian!)

40 yr cycle in fynbos (southern Africa)
10-25 yrs in Mediterranean region
10-13 yrs in Australia

adaptations:

bark protection

new shoots from base roots or burls or lignotubers

serotinous cones / seed coats (eg. pines, Banksia, Acacia)

stimulate geophytes to increase and/or flower (eg. Gladiola in Cape, Crocus and Ornithogalum in Mediterranean)

 III. Floristics

A. Convergence

1.  Leaf shape and size

Leaf shape, size, and texture is strikingly similar among all the Mediterranean regions. For example, the holly (Ilex) leaf shape and leathery texture is seen in many unrelated families - many of the species have their second name as 'ilicifolia', or translated 'holly leaf', becasue of their remarkable convergence with the Mediterranean holly.

2.  California and Chile life form convergence

Vegetation transects of Chile and California from coastal scrub to interior mattoral or chapparal show similar kinds of life forms in the two transects (different genera and/or families!)

These include shrubs of two unrelated genera of Anacardiaceae, two trees - a laurel (Lauraceae) and an oak (Quercus), and two heath plants - a mint (Labiatae) and chamise (Rosaceae).

 

B.  Mediterranean flora

Most original woodland gone. These comprise two main types: maquis = dense shrub formations, and garrique = more open heathy and aromatic shrubs (lavender, thyme)

Trees and shrubs include: Quercus ilex (Holm's oak), Quercus suber (cork oak), Pinus (pines), Ilex (holly), Cedrus atlantica (Atlas cedar), Buxus sempervirens (boxwood), Arbutus (arbutus, Ericaceae), Oleaceae (olive family).

Heath layer includes: Erica (heath, Ericaceae), legumes (Cytisus, brooms; Ulex, common gorse), Cistaceae, Lamiaceae (mint family), Compositae, Ophrys (Orchidaceae)

C.  South Africa (cape or capensis) flora

'fynbos' = heathy vegetation, very few trees

'veld' = more shrubby vegetation

Protea (proteas, Proteaceae), Erica (600 species, Ericaceae), Restionaceae, Pelargonium (florist geranium), Iridaceae, Amaryllidaceae

D.  Australian flora

'mallee' = heathy vegetation on poor soil

Banksia (and other Proteaceae), Eucalyptus diversicolor [karri] and Eu. marginata [jarrah] (Myrtaceae), Casuarina (desert oak, Casuarinaceae), Xanthorrheaceae (grass trees), Epacridaceae (= Ericaceae), Orchidaceae and other herbaceous families

 

E.  Californian flora

'chaparral' = shrub/tree vegetation

Trees and shrubs include: Quercus dumosa (and other oaks), Ceanothus (Rhamnaceae), Arctostaphylos (manzanita), Adenostoma fasciculatum (chamise, Rosaceae)

Annuals or geophytes inlude: Clarkia (Onagraceae), Calochortus (Liliaceae), Brodiaea (Alliaceae), Escholtzia (California poppy)

 

F.  Chilean flora

'matorral' = shrub/tree vegetation

Woody vegetation includes: Lithraea caustica (Anacardiaceae), Quillaja saponaria (Rosaceae), Jubaea chilensis (Chilean wine palm)

Other vegetations includes: Colletia armata (Rhamnaceae), Ephedra andina, Mesembryanthemum (Aizoaceae)