The Environment

Mediterranean climate and vegetation

Mediterreanean climate

• Each hemisphere of Earth has three wind belts: in the northern hemisphere, easterly 'Trade' winds extend to about 30°N, 'Westerly' winds to about 60°N; and polar easterlies to the pole; although this is complicated by the effects of continental land-masses, etc.
• The shores of Provence are at 42-43°N, and thus close to the boundary between the Trade wind belt and the Westerly wind belt. This boundary is a region of descending air and high pressure, and thus typically fine dry conditions.
• However, the wind belts shift seasonally, with the result that spring and summer is a hot dry season (with no wind or easterly winds) and autumn and winter are cooler and wetter (with westerly winds and depressional rain).
• A local feature of Provence is the 'Mistral', a north wind that blows in winter when there is cold high pressure air over central France and lower pressure over the Mediterranean; the wind is funnelled by the Rhône valley instead of being diverted by Coriolis.

Mediterreanean vegatation

• A biome "consists of a distinctive combination of plants and animals in a fully developed or climax community." Each biome "is characterised by a uniform life form of vegetation, such as grass or coniferous trees. It also includes the developmental stages, which may be dominated by other life forms". (Smith, R.L., 1992. Elements of Ecology' 3rd ed.)
• The Mediterranean biome is characterised by evergreen trees, which can grow during the wetter but well-illuminated winter, and which can resist dry conditions during summer. The main tree species under natural climax conditions are:
  • Quercus ilex, the (ever)green oak;
  • Pinus pinea, the parasol pine;
• Authorities differ as to which was the most important species, and this depend on local conditions. The downy-leaved, deciduous, oak Quercus pubescens might also be present and certainly would be increasingly important inland.
• Rock on Provence is mainly limestone; this is porous, and water drains away rapidly;
• However, the evergreen trees have deep roots that penetrate the rock and tap water reservoirs here during summer; the leaf-fall from the trees enriches the soil, and the shade of the trees, and the shelter they provide from wind, keep the soil moist.
• During the last few thousand years, most of the original Mediterranean woodland has been eradicated by humans, using it for timber and replacing it by agriculture;
• Grazing by domesticated animals prevented tree regeneration, and, without the shelter of trees, heavy autumn rainfall washed away much of the soil;
• fires caused deliberately or accidentally by humans burns trees and bushes and further damages the soil; it favours annuals and plants that can regenerate rapidly from underground or near-ground buds;
• During the walk at Luminy we saw two main plant communities:
  • near the coast was an open community of shrubs or bushes, mostly forming low mounds separated by bare rock; this is the garrigue, and some of the characteristic plants we saw were:
    • the kerm oak Quercus coccifera, a spiny-leaved evergreen, the characteristic shrub of this community, forming low mounds, or larger bushes in sheltered conditions;
    • rosemary Rosmarinus officinalis
    • white rock rose Cystus albida
    • the tall heather Erica arborea
    • the gorse or whin Ulex europaeus.
  • sheltered by the hill from sea winds and protected from grazing and fire during recent years, was a young wood in which the main tree was:
    • the aleppo pine, Pinus halepensis, originally from the eastern Mediterranean;
    • there were also a few Pinus pinea;
  • underneath the pine trees were many of the plants of the garrigue that had originally covered the land here but which are now gradually being shaded out as the pine trees grow;
  • there were also a few small Quercus pubescens and Q.ilex, which may, given a long period of stability, come to grow large and hence take over the wood;
  • however, the accumulation of pine needles potentiates fires, which are more damaging to the tree oaks than to the thick-barked pines;
• the garrigue and pine wood may be seen as successional stages leading back to the Mediterranean evergreen oak wood; disturbance by humans, their grazing animals, and fire, prevents this succession, and so garrigue is now the typical vegetation of poor land in much of Provence;