Mediterranean and Alpine Mountain Vegetation

Mediterranean vegetation is the evergreen, drought-resistant scrub and woodland of regions with hot, dry summers and mild, wet winters, and alpine mountain vegetation is the series of plant zones that change with altitude, ending above the tree line in low alpine meadows and bare rock and snow. In brief: Mediterranean climates occur on the west sides of continents at about 30–40° latitude (the Mediterranean basin, California, central Chile, the Cape in South Africa and parts of southern Australia); the plants have small, tough leaves. In mountains, temperature falls by about 6 to 6.5 °C per 1,000 m, so vegetation changes from forest to meadow to rock and snow as you climb.

Both types of vegetation show how plants adapt to a limiting climate factor: summer drought in one case and cold and wind in the other. This guide explains the Mediterranean climate and its plants, the altitude zones of mountains, compares them in a table, works through temperature and rainfall calculations, outlines the history of the research and corrects common mistakes.

What is a Mediterranean climate?

The Mediterranean climate is created by the seasonal shift of global wind and pressure belts. In summer, the subtropical high-pressure zone moves poleward and brings stable, dry, sunny weather. In winter, it moves toward the equator and lets westerly winds bring rain from passing depressions. Typical summer temperatures are 25 to 30 °C or higher, winters are mild (about 5 to 12 °C), and the annual rainfall is often 400 to 900 mm, mostly in winter. Because of this, the main stress on plants is summer drought, together with frequent wildfires.

How do Mediterranean plants adapt?

The dominant plants are sclerophyllous (“hard-leaved”) evergreens, which have small, thick, waxy or hairy leaves that reduce water loss. Examples are olive, cork oak, holm oak, myrtle, rosemary and lavender. The shrub communities have local names: maquis and garrigue in the Mediterranean, chaparral in California, matorral in Chile and fynbos in South Africa. Many plants have deep roots, and aromatic oils that give the typical scent but are also flammable.

Fire is a natural part of the system. Some plants resprout from roots after burning, and others release seeds only after fire. The Cape region of South Africa has an extraordinary variety of plants, with several thousand species, a large share of them found nowhere else. Humans have changed the Mediterranean region for thousands of years by grazing, clearing and farming olives, grapes, wheat and citrus fruit, and by irrigation. Today, expanding tourism, urban growth, wildfires and water shortages put the region under pressure.

What are the vegetation zones of a mountain?

On a mountain, temperature falls and wind and exposure increase with height, so vegetation changes in bands, called altitudinal zonation. A typical sequence in a temperate mountain range such as the Alps is:

• Foothill and montane zone: farmland and broadleaved or mixed forest at lower levels, then conifer forest.
• Subalpine zone: open conifer forest and shrubs, up to the tree line, beyond which trees cannot grow because the growing season is too short and cold. In the Alps this is at around 2,000 to 2,300 m, and in the tropics it can be above 4,000 m.
• Alpine zone: meadows of grasses, sedges and low flowering plants, then cushion plants, mosses and lichens.
• Nival zone: permanent snow, ice and bare rock, with only specialized lichens and a few insects.

The slope direction (aspect) matters: south-facing slopes in the northern hemisphere receive more sun and have a higher tree line than shaded north-facing slopes.

How do alpine plants and animals adapt?

Alpine plants are generally small and hug the ground (cushions and rosettes) to avoid wind and use the warmer air near the surface. Many have hairy leaves, dark pigments that protect against strong ultraviolet light, deep roots and the ability to photosynthesize at low temperatures. They grow slowly and flower rapidly in the short summer. Animals such as the ibex, chamois, marmot and mountain goat have thick fur and strong legs for steep ground, and some, like marmots, hibernate. Animals in the high Andes and Himalaya, such as the llama and yak, have blood and lungs adapted to the thin air, with lower oxygen availability at height.

Mediterranean and alpine vegetation compared

Worked example: temperature, rain and the tree line

1. Temperature at altitude: a valley at 500 m has a mean July temperature of 20 °C. At 2,500 m the height difference is 2,000 m, so the drop is 2 × 6.5 = 13 °C, giving about 7 °C.
2. Tree line estimate: trees need a warmest-month mean of about 10 °C. Starting from 20 °C at 500 m, the temperature falls by 10 °C over 10 ÷ 6.5 × 1,000 = about 1,540 m, so the tree line is near 500 + 1,540 = 2,040 m, which is in line with the Alps.
3. Mediterranean rainfall: a city receives 600 mm per year with 75% in the six months from October to March. Winter rain is 0.75 × 600 = 450 mm, an average of 75 mm per month, while the summer rain is 150 mm, or 25 mm per month.
4. Seasonal drought: if potential evaporation in July is 180 mm and rainfall is 10 mm, the deficit is 180 − 10 = 170 mm, which plants must survive using deep roots and water-saving leaves.
5. Air pressure: at about 5,500 m, atmospheric pressure is roughly half of the sea-level value, so each breath has about half as much oxygen, a key limit for animals and humans in high mountains.

How has this vegetation been studied and used?

Alexander von Humboldt’s 1802 study of Mount Chimborazo in Ecuador is a classic early description of altitude zones, and he linked plant zones to climate. The Köppen climate system uses the pattern of dry summers and wet winters to define Mediterranean climates (Csa and Csb types). In the 20th century, ecologists studied fire in chaparral and fynbos and the role of resprouting. Mediterranean landscapes have been used for olive, grape and cereal farming since ancient times, and mountains have supported seasonal herding (transhumance) for centuries. Today, scientists track how warming raises the tree line and threatens cold-adapted alpine species that have nowhere higher to go.

Which mistakes are common?

Mistake 1: Thinking that Mediterranean means only the Mediterranean Sea

The climate and vegetation type occurs on five continents, including California, Chile, South Africa and Australia.

Mistake 2: Saying that the Mediterranean region lacks rain

The total rainfall is moderate. The key point is that it falls in winter, leaving a dry summer.

Mistake 3: Expecting the same tree line everywhere

The altitude of the tree line depends on latitude, slope direction, wind and local conditions. It is higher in the tropics than near the poles.

Mistake 4: Considering fire only harmful

Many Mediterranean plants depend on periodic fire, although very frequent fire or human-caused fire can destroy the ecosystem.