Mount Lofty woodlands, Australia
The Mount Lofty woodlands ecoregion is chiefly vegetated by eucalypt woodlands, including the Mount Lofty Mountain Ranges of Australia, surrounding lowlands, and offshore Kangaroo Island. A number of unique ecosystems are found here, but land clearing has been widespread, with only fragmented vegetation remaining in much of the ecoregion. The native fauna of this region has been widely affected by loss of habitat and habitat fragmentation. Numerous local mammalian and avian extinctions have occurred in this ecoregion, and continued clearance and alien species are threats.
Location and general description
The Mount Lofty woodlands ecoregion forms a relatively narrow strip along the Mount Lofty Ranges, and their foothills and valleys. The ranges intercept the humid southwesterly winds that predominate during the winter, creating a mediterranean-type climate. The main factors that determine vegetation structure are rainfall, disturbance, and soil characteristics. Annual precipitation varies from nearly 900 millimetres (mm) in the higher peaks of the southern Mount Lofty Ranges to below 400 mm in the northern Mount Lofty Ranges. The ancient geology of the region resulted in fairly weathered soils.
The region encompasses a range of vegetation types including sclerophyll woodlands, open and grassy woodlands, and grasslands. The woodlands are dominated by different species of Eucalyptus, changing according to rainfall distribution. The understorey is rich in species from the Myrtaceae, Proteaceae, Mimosaceae (genus Acacia in particular), Fabaceae, and Epacridaceae. Orchids are also well represented. Mallee eucalypt communities are dominated by White Mallee (Eucalyptus diversifolia), commonly growing with E. rugosa on the mainland, and also found on Kangaroo Island. Open forests of Brown Stringybark (E. baxteri), Messmate Stringybark (E. obliqua), Long-leaved Box (E. goniocalyx), and/or manna gum (E. viminalis) grow in the Mount Lofty ranges. Messmate Stringybark may grow in pure stands in areas with high rainfall, reaching heights of 25 meters. Moving to lower elevations, grassy woodlands of South Australian Blue Gum (E. leucoxylon) and Manna Gum grow on heavy soils. At still lower elevations, Grey Box (E. microcarpa), Peppermint Box (E. odorata), and mallee box (E. porosa) grow. Grasslands are dominated by species of Austrostipa and Austrodanthonia (Poaceae), and Lomandra (Liliaceae).
The western half of Kangaroo Island is largely dominated by a mixture of open forest and woodlands. Vegetation communities include areas of Sugar Gum (Eucalyptus cladocalyx) and Drooping Sheoak (Allocasuarina verticillata), as well as other mixed eucalypt woodlands. Mixed eucalypt woodlands include Pink Gum (E. fasciculosa), Brown Stringybark, Messmate Stringybark, Manna Gum, and River Red Gum (E. camaldulensis). Understories are normally dense and shrubby, with Melaleuca spp., Beaked Pincushion Tree (Hakea rostrata) and Scarlet Bottlebrush (Callistemon rugulosus).
This region is characterized less by its degree of endemism than by its peculiar combination of biota. As one of the mediterranean climate environments in Australia, this region shares biological components with the western mediterranean-type ecoregions, and with the southeastern ecoregions, resulting in unique biological assemblages. Several of these components are represented by disjunct populations, most likely genetically isolated, and often in their extreme range of their distribution. Within the ecoregion Kangaroo Island stands out as the area with the highest species level endemism (36 species, some five percent of the flora). Endemic species include E. remota, Adenanthos sericeus, A. terminalis, and Petrophile multisecta.
Almost all the medium sized, e.g. Bettongs (Betongia spp.) and Quolls (Dasyurus spp.) have become extinct in the region. In South Australia, a significant proportion of extinctions have occurred in the temperate woodlands. While the Short-beaked Echidna (Tachyglossus aculeatus) is still found throughout the region, the platypus (Ornithorhynchus anatinus) is restricted to Kangaroo Island. Eight species, many of them globally threatened, are now locally extinct from the Mount Lofty Ranges portion of this ecoregion alone. Species extirpated from the Mount Lofty Ranges include the eastern quoll (Dasyurus viverrinus), red-tailed phascogale (Phascogale tapoatafa), the extinct eastern hare wallaby (Lagorchestes leporides), tammar wallaby (Macropus eugenii), the vulnerable greater bilby (Macrotis lagotis), the endangered western barred bandicoot (Perameles bougainville), the vulnerable burrowing bettong (Bettongia leseur), and brush-tailed bettong (Bettongia penicillata).
Recently, a sharp decline of passerine birds in the region has been reported. Species that have been extirpated from woodland habitats in the Mount Lofty Ranges include the endangered regent honeyeater (Xanthomyza phrygia), endangered swift parrot (Lathamus discolor), king quail (Coturnix chinensis), brown quail (C. ypsilophora), and azure kingfisher (Alcedo azurea). The glossy black cockatoo (Calyptorhynchus lathami) has been brought to the brink of local extinction by land clearance. A number of other species that have declined in woodland habitats and in the heaths and swamplands of the Mount Lofty Ranges. As a result of vegetation clearance, birds may be moving greater distances to obtain food. Banding studies of honeyeaters, lorikeets, and silvereyes showed that birds are moving over 100 km seasonally to exploit food resources. While there have been local extinctions and precipitous declines of many birds native to this region, only one species extinction has occurred in this ecoregion. The Kangaroo Island Emu (Dromaius baudinianus) became extinct in the 1820s as a result of hunting and the burning of habitat.
Reptiles have fared better than other taxa: of the 57 reptile species found in the temperate woodlands of South Australia, only one is considered nationally endangered. The Pygmy Blue-tongue (Tilqua adelaidensis) was considered extinct, but was recently discovered to occupy a small colony near Aderlaide. However, several other reptile species have declining or localized populations in this ecoregion.
The southern and central sections of this region have been strongly modified by human activities, particularly since European settlement. The woodlands of the southern Mount Lofty Ranges were extensively cleared for agriculture, and urban sprawl around Adelaide has claimed remnant vegetation more recently. Less than four percent of native vegetation remains on the Adelaide Plains. Clearance has concentrated on lowland areas with higher agricultural potential. The northern section of the ecoregion retains more integrity, in particular along the ranges.
Overall, protected areas are fairly numerous, but small, and several vegetation types are under represented. Across the ecoregion approximately ten percent of plant species are extinct, endangered, or threatened. A large proportion of these species are endemic to the region. The fauna of this region has suffered severe reductions in its diversity as a result of the destruction of habitats, hunting, and the impact of introduced predators such as foxes (Vulpes vulpes) and domestic cats (Felis catus).
Overgrazing has heavily impacted remaining native vegetation. Remnant vegetation in this area consists of small fragments, most of them representing regrowth after clearance, and heavily invaded by alien species. A large portion of remaining vegetation is privately held. The central grasslands have mostly been replaced by agriculture, but temperate grasslands are still found extensively on the top of ranges or rocky outcrops, albeit usually overgrazed and invaded by European annual grasses. In this area a number of taxa are extinct, endangered, or threatened.
Although only an estimated 35 percent of Kangaroo Island's original woodland remains, remnant vegetation has been less severely impacted than that in regions with similar clearance. The poor ironstone based soils have discouraged agriculture, and much of the central island was not cleared until after World War II as part of a returned soldiers scheme. Although extensive areas have been cleared in the past century, large areas of vegetation were set aside in protected areas from 1919 onwards. Today, even in regions with extensive clearing, native vegetation persists in a series of ridges, riparian strips, and roadside verges, providing some connectivity between larger fragments.
Types and severity of threats
While the rate of vegetation clearance has abated, the fragmented nature of most of the vegetation remnants pose grave risks for many species of plants and animals. Although fire is a natural disturbance in the original system, it can have devastating consequences on population persistence in isolated patches that are unlikely to be recolonized from nearby populations. The relatively recent introduction of the Phytophtora cinnamomi pathogen also poses a serious threat to vegetation in the higher rainfall sections of the region.
Introduced mammals are problematic on the mainland portion of this ecoregion. Cats, foxes, and rabbits (Oryctolagus cuniculus) are common throughout the Mount Lofty Ranges and portions of this ecoregion further north. Unlike mainland Australia, Kangaroo Island is not severely affected by introduced grazers. There are no rabbits on the island, and feral goats (Capra hircus) and pigs (Sus scrofa) have only caused minor problems. However, a population of koalas (Phascolarctos cinereus) that were introduced onto the island in the 1920s have caused significant damage to some woodland communities, especially to manna gum trees. Expansion of feral koala populations in the Mount Lofty Ranges could pose a significant to remaining manna gum vegetation. Elevated western grey kangaroo (Macropus fuliginosus) populations in the Mount Lofty Ranges may be affecting native vegetation composition.
Justification of ecoregion delineation
The Mount Lofty Woodlands ecoregion comprises one Interim Biogeographic Regionalisation of Australia (IBRA), 'Lofty Block'. Original vegetation consisted of eucalypt open forests and woodlands and heath. This ecoregion is part of the Southeast Australia Endemic Bird Area.
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