The Pilbara geographic region covers most of the ecoregion, and extends east into the Great Sandy desert.
The Hamersley Range, a region of mountain ranges and plateaus dissected by gorges, lies in the southern portion of the ecoregion. The Fortescue Plains extend east and west to the north of the Hamersley Range, forming the upper basin of the Fortescue River. The Chichester Plateau lies north of the Fortescue Plains. The Roebourne subregion encompasses the coastal plain along the Indian Ocean, including the Dampier Archipelago.[7][8]
The ecoregion lies on the Pilbara craton, a block of ancient Archean rock. The Chichester region is characterized by exposed granite and greenstone basement rocks. The Hamersley region includes iron-rich carbonate sedimentary carbonate rocks over a volcanic substrate (the Fortescue formation) which rest on the older craton. The Fortescue basin and coastal plain are alluvial.
Climate
The climate is tropical semi-desert. Rainfall averages 300 mm annually, typically from summer cyclonic storms and thunderstorms.[8]
The Fortescue Plains include the northernmost mulga woodlands, along with short grasslands. Year-round watercourses and springs support stands of red river gum, (Eucalyptus camaldulensis refulgens), Melaleuca, and the palm Livistona alfredii. Sheltered gorges along the edge of the Chichester Plateau provide water and protection from fire, and support relict communities of Terminalia, Erythrina, and Ficus.[9]
"Fairy circles" (known as "linyji" in the Manyjilyjarra language and "mingkirri" in the Warlpiri language) which are circular patches of land barren of plants, varying between 22 and 12 metres (7 and 39 ft) in diameter and often encircled by a ring of grass, are found in the western part of the Great Sandy Desert. It has not yet been proven what causes these formations, but one theory suggests that they have been built and inhabited by Australian harvester termites since the Pleistocene.[10][11]
^Eric Dinerstein, David Olson, et al. (2017). An Ecoregion-Based Approach to Protecting Half the Terrestrial Realm, BioScience, Volume 67, Issue 6, June 2017, Pages 534–545; Supplemental material 2 table S1b. [1]
^ abHeterick, B.E., B. Durrant, and N.R. Gunawardene (2010). "The ant fauna of the Pilbara Bioregion, Western Australia". Records of the Western Australian Museum, Supplement 78: 157–167 (2010).
^ abcKendrick, Peter (2001). "Pilbara 3 (PIL3 – Hamersley subregion)". in A Biodiversity Audit of Western Australia’s 53 Biogeographical Subregions in 2002, Department of Conservation and Land Management, Western Australia Government, October 2001.
^Kendrick, Peter (2001). "Pilbara 2 (PIL2 – Fortescue Plains subregion)". in A Biodiversity Audit of Western Australia’s 53 Biogeographical Subregions in 2002, Department of Conservation and Land Management, Western Australia Government, October 2001.
