Jarrah Forest, also known as the Southwest Australia woodlands, is an interim Australian bioregion and ecoregion located in the south west of Western Australia. The name of the bioregion refers to the region's dominant plant community, jarrah forest – a tall, open forest in which the dominant overstory tree is jarrah (Eucalyptus marginata).
Jarrah Forest is recognised globally as a significant hotspot of plant biodiversity and endemism, and is also managed for land uses such as water, timber and mineral production, recreation, and conservation.
Location and description
The bioregion stands on the Yilgarn block inland plateau and includes wooded valleys such as those of Western Australia's Murray River and the Helena River. The Darling Scarp forms the western edge of the plateau, and the Swan Coastal Plain lies between the scarp and the coast. The scarp generally forms the western boundary of the bioregion, although it extends to the west coast at Cape Naturaliste. At the southern end of the plateau is the Whicher Range and inland is the lower Blackwood Plateau. The south eastern interior of the region includes the peaks of the Stirling Range, now preserved within Stirling Range National Park.
Soils in the jarrah forest are infertile, especially for phosphorus, and are often salt-laden.
The bioregion covers an area of . It is divided into two sub-regions, Northern Jarrah Forest () and Southern Jarrah Forest ().
The Swan Coastal Plain bioregion lies to the west below the scarp. The Warren bioregion, also known as the Jarrah-Karri forest and shrublands, is to the south. The Avon Wheatbelt bioregion, part of the Southwest Australia savanna ecoregion, is to the east.
Climate
The area has a warm Mediterranean climate, with more annual rainfall () on the scarp than inland or to the north-east ().
Flora
Jarrah Forest is unique in that it shares the co-dominate Corymbia species Marri (Corymbia calophylla). Marri, formerly formally known as Eucalyptus calophylla, is a prevalent canopy species and the jarrah forest is commonly called jarrah-marri forest. Other eucalypts are present but in much less abundance. The Southern Jarrah Forest contains extensive areas of wetland vegetation in the south–east, dominated by paperbarks including the swamp paperbark (Melaleuca rhaphiophylla), and other eucalypts such as the swamp yate (Eucalyptus occidentalis) and the Albany blackbutt (Eucalyptus staeri).
The eastern forest is largely wandoo woodland, dominated by the canopy species wandoo (Eucalyptus wandoo), and, on breakaways, powderbark (also known as powderbark wandoo) (Eucalyptus accedens). Other eucalypts in these eastern areas include York gum (Eucalyptus loxophleba). The upland areas are particularly rich in plant life, while the drier inland plateau is less so. The wetter valleys with fertile soils contain flooded gum (Eucalyptus rudis), bullich (Eucalyptus megacarpa) and blackbutt (Eucalyptus patens). Heath is a common understorey of the jarrah forest in the north and east.
The smaller trees commonly found in Jarrah Forest include bull banksia (Banksia grandis), sheoak (Allocasuarina fraseriana), snottygobble (Persoonia longifolia) and woody pear (Xylomelum occidentale). Rare plants within Jarrah Forest include orchid species Drakaea confluens and Caladenia bryceana, and Baumea reed beds are unique to the forest and adjacent areas.
Fauna
Jarrah Forest supports 29 mammal, 150 bird, and 45 reptile species. Mammals include the numbat (Myrmecobius fasciatus), Gilbert's potoroo (Potorous gilbertii), western quoll or chuditch (Dasyurus geoffroii), woylie (Bettongia penicillata), tammar wallaby (Notamacropus eugenii), western ringtail possum (Pseudocheirus occidentalis), common brushtail possum (Trichosurus vulpecula), quenda or western brown bandicoot (Isoodon fusciventer), and red-tailed phascogale (Phascogale calura). Most of these were once widespread vertebrate species but are now limited to the fragmented portions of Jarrah Forest.
The chuditch, before the introduction of large mammalian pest species, was the largest carnivorous marsupial in south-west Western Australia, distributed across 70% of mainland Australia. It now inhabits only 2% and is listed as 'Vulnerable' under the Environmental Protection and Biodiversity Conservation Act of 1999. For species such as the brushtail possum, population decline has not been extensive as they will colonise older restored minesites.