Jarrah Forest
Jarrah Forest 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 and open forest in which jarrah is the dominant overstorey species.
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 comprising, and Southern Jarrah Forest comprising.
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 rainfallon the scarp than inland or to the north-east.Flora
Jarrah Forest is unique in that it shares the co-dominate Corymbia species marri. 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, and other eucalypts such as the swamp yate and the Albany blackbutt.The eastern forest is largely wandoo woodland, dominated by the canopy species wandoo, and, on breakaways, powderbark . Other eucalypts in these eastern areas include York gum. 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, bullich and blackbutt. 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, sheoak, snottygobble and woody pear. 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, Gilbert's potoroo, western quoll or chuditch, woylie, tammar wallaby, western ringtail possum, common brushtail possum, quenda or western brown bandicoot, and red-tailed phascogale. 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.
Carnaby's black cockatoo is endemic to south-west Western Australia and is listed as endangered under the EPBC of 1999. Other birds to inhabit Jarrah Forest include rare birds such as the forest red-tailed black cockatoo, Muir's corella, black-throated whipbird, western bristlebird, noisy scrub-bird and Baudin's black cockatoo.
Reptiles inhabiting Jarrah Forest include legless lizards, dragon lizards, skinks, blind snakes, pythons and venomous snakes. The western bearded dragon was found in restored forest rather than old growth forest.
Amphibians found in the northern sector of Jarrah Forest include the rare white-bellied frog, yellow-bellied frog and sunset frog. Endemic frogs inhabit the southern sector of Jarrah Forest such as the small western froglet and the western marsh frog.
Diverse invertebrate fauna communities are also present within Jarrah Forest. Many of these invertebrate species are responsible for nutrient recycling, an essential element of Western Australia's biodiversity. In particular, the insect group Apocrita, which includes wasps, bees, and ants, are a keystone group that, through predation and parasitism, keep other invertebrate populations controlled. The loss of Apocrita could be detrimental to the invertebrate community and to the jarrah forest ecosystem. Rare and endandered native bees include Leioproctus douglasiellus and Neopasiphae simplicior.
History
The first evidence of human habitation of the region was 50,000 years ago at Devil's Lair by ancestors of today's Aboriginal people.The Noongar are the Aboriginal inhabitants of the bioregion. The Noongar comprised 14 groups, which spoke distinct but mutually-intelligible languages. Aboriginal populations were generally denser on the coastal plain and along the coastal forest edge, and in the interior woodlands and shrublands, particularly near permanent streams and river estuaries. Population was sparse in the forested areas of the south.
The Aboriginal inhabitants deliberately set fires to manage the land and vegetation. Evidence from lake and estuarine sediments and firsthand accounts suggest that fire intervals in well-settled areas were frequent – from one to ten years – compared to unoccupied forests and offshore islands, where fire intervals were 30 to 100 or more years. Frequent burning reduced woody cover and encouraged the growth of low shrubs, herbs, and grasses, fostering open woodlands, shrublands, and savannas and limiting areas of dense forest and thicket.
Settlement of the region by Europeans began in the 19th century. Forests were logged for timber, and areas cleared for agriculture and pasture. The Noongar were dispossessed from much of the land, and the fire regime changed from one of deliberately-set low-intensity fires to one of general fire suppression, with accidental or lightning-set fires which are less frequent but often more intense.
Jarrah is considered one of the best general purpose hardwoods in the world. The British started logging the jarrah forest in the 1840s to produce timber for use in construction, transport and power, and to protect water supplies. Logging was largely unregulated until the release of the Forests Act of 1918. The following 50 years saw forest management expand to include water quality and yield, soil management, rehabilitation of mined forest, recreation and nature conservation. Jarrah was harvested for woodchips as well as high quality furniture and flooring until the WA government responded to decades of campaigning by placing a ban on native forest logging in 2024.
Environmental threats
Most of Jarrah Forest has been cleared for agriculture, timber and mining, leading to the consequent degradation of flora and fauna species and ecosystems. The areas managed for forest production have been logged two to three times such that this forest bears no resemblance to the original forest. This is further threatened by broad scale bauxite mining and the replacement of native vegetation with exotic grasses and weeds, introduced grazing species and predators such as the fox. Native flora also suffers from disease and exploitation of water sources for agriculture. Less anthropological threats include periodic wildfire, pathogens, variable climate and outbreaks of defoliating insects.Introduced species
The significant population loss of fauna species in Jarrah Forest is attributed to the fox and cat. Predators can influence abundances and ranges of species at all trophic levels, including primary producers, prey and other predators. Between 1933 and 1944 the terrestrial range of the quokka, the woylie, the chuditch, the brushtail possum, the western ringtail possum, the tammar wallaby and the numbat contracted quite dramatically. This was blamed on the fox. Population numbers, however, of woylies and boodies were already declining in 1911, most likely due to cats introduced by Europeans. Another introduced species that is a major threat to birds in some areas of Jarrah Forest, but for a very different reason, is the feral bee. Swarms of feral bees take over tree hollows, stealing the nesting sites of hollow-nesting birds.Habitat loss and fragmentation
Landscape fragmentation and the loss of suitable macro- and microhabitats can be detrimental to an animal's ability to live in or traverse through an area. The range of the western quoll has dramatically reduced since European settlement. With matrix permeability greatly reduced this wide-ranging carnivore is highly susceptible to being hit by vehicles as it crosses road reserves moving from one area to another. The roadkill count of fauna in general on bauxite mines fringing Jarrah Forest is high. Despite the restoration and protection of jarrah forest in areas previously used by mine sites, the lack of hollow logs and stumps on the ground is evident. Low understory cover, low plant species richness and relatively low biomass are all problems associated with protected restored jarrah forest. Suitable habitats can take decades to form and animals that rely on these for shelter, such as the chuditch and Egernia napoleonis, are left without. Similarly birds that nest in tree hollows will not do so until trees are big enough and old enough to have sufficient hollows. Jarrah is a slow growing species and 130 years can be considered the minimum age for the development of appropriate hollows in jarrah and marri.The loss of forest for agriculture and timber has resulted in diminishing population numbers of many fauna species. Nine mammal and seventeen bird species are obligate users of tree hollows. Species that use large hollows usually have a relatively small home range and depend on their hollows for breeding. These species are most likely to be negatively impacted by logging. Roost sites are critical for the persistence of insectivorous bats living in Jarrah Forest. Spending a large portion of their lives in roosts, they are used as diurnal shelters, shelter during maternity, and shelter for bachelors, migrating and hibernation sites. Facilitating complex social interactions including information transfer, roost sites also act as breeding sites, they provide protection from bad weather and predators, they minimise parasite load and promote energy conservation.