A climate with a dry summer
A Mediterranean climate has mild, wet winters and hot, dry summers. It is named for the lands around the Mediterranean Sea, but similar climates occur in California, central Chile, the Cape region of South Africa and parts of southern Australia. The key feature is timing: rain arrives in the cool season, when plants grow slowly, and the warm season, when growth would be fastest, is dry.
That mismatch is demanding. Trees must survive months with little or no rain, high temperatures and strong sun, and then use winter and spring moisture efficiently. The woodlands that result look quite different from the lush deciduous forests farther north.
Typical trees
Around the Mediterranean Basin, typical woodlands are dominated by evergreen oaks, such as holm oak and cork oak, and by pines, including Aleppo pine, stone pine and maritime pine. Other trees and large shrubs, including olive, carob, strawberry tree, juniper and cypress, also occur, and in some mountain areas cedars and firs replace them. Other regions have their own tree communities. In California, for example, evergreen oaks are common in similar climates, mixed with pines in some areas.
These woodlands vary from fairly dense forest to open, savanna-like stands with scattered trees over grass, as well as shrublands often called maquis or garrigue. Often the shrubland and the woodland form a mosaic, depending on soil, slope, fire history and land use.
How the trees cope with drought
Plants in this climate have several ways of dealing with summer drought:
- Tough, small, leathery leaves with a thick waxy coating, which reduce water loss. Many are evergreen, so the tree is ready to photosynthesize whenever moisture allows, including mild, wet winter days.
- Deep and wide root systems that reach water stored in cracks in rock or deeper soil layers.
- Reduced activity in the hottest period. Trees may close their leaf pores and slow growth during the driest weeks.
- Thick bark, which protects living tissue from heat, as in cork oak.
- Resprouting. Many oaks can regrow from the base after fire or cutting, drawing on energy stored in roots.
Even with these traits, severe drought can kill branches or whole trees. The general topic is covered under drought stress, and the physical limits on how water travels through trees are described in the article on water transport. Hot, dry spells can also leave trees more open to insect attack.
Fire as a regular visitor
Dry summers produce dry fuel, and fire is a natural part of many Mediterranean-climate landscapes. Some species respond to fire by resprouting, and others, notably certain pines, rely on seeds. Aleppo pine, for example, stores seed in cones that open after fire or heat, though details vary by species. These responses are part of the wider subject of fire ecology.
At the same time, fire regimes today are strongly affected by people. Where old farmland has been abandoned and fuel has built up, or where homes sit next to flammable vegetation, fires can be larger and more damaging. Forest fires in these regions are a serious safety concern, and wildfire smoke can affect air quality over large areas. Fire behavior is influenced by many factors, so these statements describe general patterns only.
A long history with people
Mediterranean landscapes are among the most long-inhabited in the world. People have cut wood, grazed animals, farmed terraces, collected fuel and burned vegetation for thousands of years. Because of that, it is hard to say what a “natural” Mediterranean woodland looks like, since much of what exists is the result of long interaction between climate, fire and human use.
Traditional uses include:
- Grazing by sheep and goats, which can keep land open and, if heavy, suppress tree regeneration. See livestock overgrazing for the general effects.
- Cutting for firewood and charcoal. Resprouting oaks suit systems like coppicing, in which stems are cut regularly and regrow from the stump.
- Cork harvesting from cork oak. The bark is stripped by hand at intervals, and the tree regrows it. Such products are among the better-known non-timber uses of woodlands.
- Acorn use for feeding pigs and other livestock in open oak pasture systems, in which trees and animals share the land. These resemble the systems described under silvopasture.
- Fruits, nuts and resins, including olives, pine nuts and pine resin.
Some of these systems, such as open oak pasture, are valued today for wildlife and as cultural landscapes. Many have declined as rural populations have moved to cities, which can lead to denser regrowth and, in some places, higher fire risk.
Pressures and change
Mediterranean-climate regions are expected to become hotter and drier in many places, though projections vary by location. Longer droughts and more intense heat can add stress to trees and increase the chance of large fires. Species ranges may shift, with some trees moving upslope or declining at their dry lower edges. Overgrazing, urban expansion, tourism development and invasive species add further pressure.
Management in these woodlands often involves thinning dense stands, reducing fuel near settlements, encouraging mixed species and sometimes using prescribed burning. Which approach fits depends on local conditions, and results are uncertain in a changing climate.
Why they matter
These woodlands hold a large number of plant species for their area, including many found nowhere else, which is why several Mediterranean-climate regions are counted among the world’s biodiversity hotspots. They also protect soil on steep slopes, where loss of cover can lead to soil erosion during heavy winter rains. Because they are dry, slow-growing and long-used, they deserve cautious management, and their survival depends on balancing human use, fire and a changing climate.