The true mediterranean–climate zone of Chile can be divided phy siographically into four regions: the Cordillera de Los Andes in the east with numerous peaks over 5000 metres; the Cordillera de la Costa in the west with peaks that seldom rise over 1000 metres; between these two ranges lie a series of graben known as the ‘Depresion Intermedia’ or Central Valley. The fourth region is the littoral fringe, a narrow coastal strip of step–like marine terraces, sea cliffs, stacks, headlands, dunes and beaches bordering the Pacific Ocean.

The natural vegetation of the arid and semi-arid zones of central Chile comprises perennials of mostly evergreen sclerophyllous shrubs and succulents, and annuals which appear after the onset of winter rains and complete their life cycles during the short wet season.

The matorral vegetation is centred in the summer-dry region of central Chile extending from 32° to 30° S latitude (di Castri, 1981) and along an altitudinal gradient from the coast to 2000 metres. The coastal scrub, occupying ocean bluffs and ocean-facing lower slopes up to 300 metres altitude, is formed mostly by chamaephytes such as Baccharis concava, B. macraei, Haplopappus foliosus, Schinuspolygamus and Senna candolleana. Among the phanerophytes the dominant species are Pouteria splendens, Peumus boldus, Schinus latifolius, Lithrea caustica and Flourensia thurifera (Montenegro et al., 1981). The dune vegetation is characterised by the presence of Puya chilensis, Eryngiumpaniculatum, Bahia ambrosioides, Chenopodium paniculatum, Centaurea chilensis, Scirpus nodosus, Poa lanuginosa, Festuca tunicata and several species of Oenothera (V.Poblete, personal communication).