There are several characteristics that define the Mediterranean biome. The Mediterranean climate is mild, with rainy winters and warm, dry summers moderated by cold ocean currents. Due to the limited extent and isolation (almost island-like) of each area of Mediterranean biome, there is frequently a high degree of endemism in the flora and fauna. Additionally, the Mediterranean regions typically exhibit high levels of biodiversity, while convergent evolution has led to similarities in the flora with evergreen shrubland dominant in each of the regions. Fire is an important natural process in most of the Mediterranean ecosystems.

Convergent Evolution
Organisms respond to environmental challenges by evolving traits that allow them to grow and reproduce under stressful conditions. This process, where organisms unrelated to each other evolve similar traits as the best solution to meeting a specific stress, is called convergent evolution, and has occurred in the five Mediterranean-climate regions. Although these five regions are geographically isolated from each other, convergent evolution has produced a very similar solution for adapting to the stresses of summer drought that these regions share. The dominant vegetation in all five regions is a dense evergreen shrubland.

Biodiversity
The five Mediterranean-climate regions comprise only about 3% of the earth’s land area but account for 16% of the world’s plant species. In particular, the Cape Region of South Africa and Southwestern Australia show remarkable levels of species richness considering their relatively small areas. Twenty-five ecological hotspots, areas of irreplaceable biodiversity whose protection is of critical global importance, have been identified worldwide. These designations are based on a large and unique diversity of organisms occurring nowhere else and on the extreme threat to these regions from human activities. While most of these hotspots lie in tropical forest regions of the world, the five Mediterranean-climate regions are included in this select group. Proportional to their area then, these five Mediterranean-climate regions have a greater significance in protecting global diversity than do the Amazon Basin and other tropical rainforests. Moreover, the five Mediterranean-climate regions face far greater immediate threats to their environments and biodiversity than rainforest areas.

Fire Ecology
Fire has shaped the Mediterranean climate regions and is a major factor controlling nutrient cycles and energy pathways and is a natural process in all the Mediterranean regions with the exception of Chile. Fire maintains the diversity, productivity, and stability of the ecosystem. The frequency of fires however varies among regions. Plants have evolved specialized adaptations to allow for regrowth after fire. Shrubs possess one or two modes of adaptations for recovery. Shrubs either resprout from underground root crowns or have pools of seeds in the soil that are stimulated to germinate with the heat of fire. Also present are specialized fire-following annuals that are often colorful and only appear the first year after fires.

For centuries, periodic fires have roared through Mediterranean-type vegetation, clearing away the old growth, making way for the new, and recycling nutrients through the ecosystem. When humans intruded into this type of vegetation, they change the fire situation, either by attempting to exclude fire completely or by overburing. In the absence of fire chaparral grows tall and dense and yearly adds more leaves and twigs to those already on the ground. During the dry season the shrubs, even though alive, will nearly explode when ignited. Once set on fire by lightning or humans, an inferno follows.

After fire the land returns either to lush green sprouts coming from buried root crowns or to grass, if a seed source is nearby. The grass and vigorous young sprouts are excellent for grazing animals. But as the sprout growth matures chaparral becomes dense, the canopy closes, the litter accumulates, and the stage is set for another fire.