The South-west of Western Australia is identified as one of 25 internationally-significant biodiversity 'hotspots' where there is exceptionally rich biota and high endemism particularly for ecosystems of the Wheatbelt such as occurs in the Avon River Basin (Myers, et al., 2000). Four broad biodiversity asset classes are relevant to the Avon River Basin:

1. Native Species – all naturally occurring flora and fauna species of the region.
2. Natural Ecological Communities - groups of native species co-existing in characteristic assemblages.
3. Ecosystems – discrete sets of ecological communities and their interaction with the distinctive physical environments they inhabit.
4. Ecoscapes – the mosaic of ecosystems that span the topography from one ridge in the landscape to the next.

Whole of Basin

Estuarine ecosystem impacts are considered as the Avon River discharges to the Swan-Canning estuary however management of the estuary is included within the Swan Regional NRM Strategy. Terrestrial ecosystems are identified within IBRA regions (Interim Biogeographic Regionalisation of Australia). For the Avon River Basin, they are:

• AVON WHEATBELT 1 (AW1 – Ancient Drainage Subregion),
• AVON WHEATBELT 2 (AW2 – Rejuvenated Drainage Subregion),
• COOLGARDIE 2 (COO2 – Southern Cross Subregion),
• MALLEE 2 (MAL2 – Western Mallee Subregion), and
• JARRAH FOREST 1 (JF1 – The Darling Range).

The Australian Terrestrial Biodiversity Assessment provides a national review of terrestrial biodiversity by use of the IBRA framework (Environment Australia, 2000). The 384 IBRA subregions are grouped within 85 bioregions on the basis of common landforms, vegetation, geology and soils. The natural biota of the Avon Region includes:

• over 4000 species of vascular plants with approximately 60% being endemic to the (Keighery et al., 2001)
• 62 species of mammals
• 203 species of birds (including 55 species of water birds)
• 16 species of frogs
• 110 species of reptiles
• 10 species of fish
• An unknown number of invertebrate species (the region's wetlands are significant - over 560 invertebrates have been identified there during recent biological surveys, with 45% restricted to fresh water).

There are 99 Vegetation Associations mapped within the Avon River Basin. Most of these are inadequately represented (less than 10% of their original area) within the existing reserve system within the region. The land used for agriculture has been substantially cleared of natural vegetation and now only 1.14 million hectares (13.2%) of this area retains its original vegetation cover. There are 648 000 hectares (7.5% of the alienated area) of natural vegetation in 'reserved crown land' (reserves for conservation, recreation and other purposes) and 491,000 hectares (5.7%) on private land.

The area of remnant vegetation on private land in the South West of Western Australia is estimated to be 2.8 million hectares (13.5%). Of this area of remnant vegetation on private land, 17.5% occurs within the Avon River Basin. The area of natural vegetation in reserves and other land secured for conservation is 14.4% of all reserves in the South West of the state.