The World Wildlife Fund defines an ecoregion as a large unit of land or water containing a geographically distinct assemblage of species, natural communities, and environmental conditions. Australia broadly represents seven of the 14 recognised global terrestrial ecoregions, which have guided A2O site selection at a landscape scale.
View A2O sites by ecoregion

Deserts and xeric shrublands are characterised by evaporation exceeding rainfall, and high temperature variability. Many of the habitats found in this ecoregion are ephemeral due to a lack of, or highly seasonal precipitation. Although this ecoregion is defined by extreme climatic conditions, biodiversity is high in many cases. Deserts and xeric shrublands are a dominant ecoregion of the Australian landmass.

Mediterranean ecoregions are defined by hot, dry summers, and cool, moist winters. This ecoregion is fire-adapted and has high levels of floristic endemism. Australian Mediterranean forests, woodlands and scrubs are found in the southern extent of the continent, particularly in south-west Western Australia, South Australia, and Victoria.

Montane grasslands and shrublands
Montane grasslands and shrublands are highly restricted in Australia and are only found in areas of south-eastern Australia above 1300 m. This ecoregion is found in the Australian Capital Territory, Victoria, New South Wales, and Tasmania.

Temperate broadleaf and mixed forests
Australian temperate broadleaf and mixed forests are dominated by Eucalyptus and Acacia species, and experience widely variable rainfall and temperatures. These forests range from southern Queensland to Tasmania and are characterised by distinct canopy, subcanopy, shrub and ground layers. Temperate broadleaf and mixed forests are highly diverse in plant and animal species, and exhibit high degrees of endemism.

Temperate grasslands, savannas and shrublands
Temperate grasslands, savannas and shrublands are dominated by grass species, with few or no trees, except for riparian or gallery forests associated with watercourses. Temperate grasslands, savannas and shrublands are cooler and experience more variable temperatures than tropical grasslands. This ecoregion has been heavily cleared and modified by human activity in Australia.

Tropical and subtropical grasslands, savannas and shrublands
Globally, tropical and subtropical grasslands, savannas and shrublands are characterised by rainfall levels of 900 to 1500 mm per year, and are dominated by grass species. Australian tropical grasslands are found across the northern extent of the continent, and cover a large proportion of the landmass. Savannas are more restricted in Australia and are found in moister areas along the northern coast. Dry rainforest may also be found in this ecoregion. Tropical and subtropical grasslands, savannas and shrublands are shaped by distinct wet and dry seasons, and frequent fires.

Tropical and subtropical moist broadleaf forests
Worldwide, tropical and subtropical moist broadleaf forests grow in large, discontinuous patches along the equator and between the Tropics of Cancer and Capricorn. This ecoregion is defined by high levels of annual rainfall greater than 2000 mm, and low temperature variability. Semi-evergreen and evergreen deciduous tree species dominate. Australian examples of this ecoregion are generally confined to far north Queensland, and exhibit high levels of floristic and faunal endemism.