Threatened ecosystems of Mediterranean sclerophyll woodland

Mediterranean shrublands and woodlands occur in only five parts of the world, yet host more than one-fifth of all known plant species on Earth. Increased fire frequency is threatening the historic shrub lands and converting them to annual grasslands. The threats to these habitats include those from grazing, agriculture, timber harvest and urbanisation.

The Mediterranean chaparral vegetation types are fire-induced and have a high capability to withstand frequent burning. These vegetation types may have evolved features that make them more flammable: resinous oils, high surface-to-volume ratios, and a majority of stems less than 1 cm in diameter. The climate produces a long period of summer drought, which translates as low plant moisture and, as a result, high flammability. The combination of wet winters and dry summers produces a distinctive natural vegetation of hard-leaved evergreen trees and shrubs. Sclerophyll forest develops forming a dense tree layer that changes the availability of nutrients. As a result, sclerophyll forest and heathlands are usually different expressions of the one ecological continuum.

In California, USA, land use patterns have changed. From the 1920's through to the early 1970's, fire was used to eliminate shrub land. This management practice was used because it was thought to increase water yields, resulting in increased grassland production. Urban residents' use of forested areas for recreational purposes and careless agricultural burning, also cause many fires.