Pine Creek
Bioregional Description
The Pine Creek bioregion comprises foothill environments below and to the west of the western Arnhem Land sandstone massif. Its main defining feature is the highly mineraliferous Pine Creek Geosyncline, comprising Archaean granite and gneiss overlain by Palaeoprotozoic sediments. The major vegetation types are eucalypt tall open forests, typically dominated by Darwin woollybutt (Eucalyptus miniata) and Darwin stringybark (E. tetrodonta), and woodlands (dominated by a range of species including E. grandifolia, E. latifolia, E. tintinnans, E. confertiflora and E. tectifica), with smaller areas of monsoon rainforest patches, Melaleuca woodlands, riparian vegetation and tussock grasslands. Characteristic species include the granivorous birds Gouldian finch Erythrura gouldiae, hooded parrot Psephotus dissimilis and partridge pigeon Geophaps smithii. This relatively small bioregion has not been divided into subregions.
Special values
The bioregion includes relatively large populations of some threatened species, most notably the gouldian finch, and one of the largest known colonies of ghost bat. However its biodiversity is not especially distinctive, and it lacks the outstanding natural features which distinguish Darwin Coastal bioregion to the immediate north (extensive floodplain environments) and Arnhem Plateau to the immediate east (massive sandstone escarpments and gorges).
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Summary of overall condition and trend
The bioregion is generally in moderately good condition. There has been some generally relatively localised modification associated with mining, horticultural developments and improved pasture. Feral animals (pigs, cattle, horses and buffalo) and weeds (especially mission grass and gamba grass) are widespread. The current fire regime includes a high frequency (generally >5 fires per decade over much of the area) of relatively destructive extensive late dry season fires. Pastoralism has probably been accompanied with some broad-scale changes in plant species composition, which in turn has affected a range of animal species, but particularly granivorous birds. The bioregion is rated as continental stress class 4. -
Summary of priority management/conservation priorities
The bioregion is relatively well reserved, though with a bias away from the more fertile lowland areas. There is some scope for enhancing the reserve system to make it more comprehensive, but this may be expensive and difficult to achieve. -
Wetlands
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Nationally important wetlands
The bioregion includes parts of two nationally significant wetland systems: Kakadu NP (NT 017: wetland types A1, A2, A5, A6, A7, A8, A9, B1, B2, B3, B9, B10, B14, B17 and C1) and Katherine River Gorge (NT018: wetland type B1). It is also immediately upstream of three other nationally significant wetlands: the Adelaide River floodplain system (NT020), Mary floodplain system (NT026) and Port Darwin (NT029). In this bioregion, the wetlands are generally in moderately good condition, albeit subject to some level of degradation from feral animals (principally pigs) and weeds.
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Other wetlands of subregional significance
The bioregion also includes a range of other perennial river systems of at least regional significance.
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Nationally important wetlands
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Riparian zones
The bioregion includes significant stretches of many river systems, including the South Alligator, Wildman, West Alligator, Mary, Adelaide, Darwin and Daly Rivers, the latter including the tributary Katherine, Fergusson, Edith, Cullen and Douglas Rivers. the condition of most riparian zones is moderate to good, although many are subject to localised impacts of livestock, pollution associated generally with abandoned or current mining ventures, or some change in hydrology associated with horticulture. There are also more broad-ranging impacts from the almost pervasive occurrence of weeds and feral animals -
Ecosystems at risk
No ecosystems in this bioregion have been assessed formally for risk category. However, most rainforest patches in this bioregion have been substantially modified or affected by feral animals, weeds, livestock or fire. Riparian areas and wetlands are probably similarly at risk. The far more extensive eucalypt open forests are at risk of some change in species composition because of the rapid expansion to understorey dominance of exotic pasture grasses, with concomitant increased severity of fire impacts. -
Species at risk
23 species occurring in this bioregion are listed as threatened at national or NT level. Note that there is a major disparity in the status assigned to many plant species, due to a very recent revision of the status of all NT plant species. As all of the plant species listed are NT endemics, this revised assessment is likely to be applied also at the national scale.
A high proportion of the threatened plants and animals are marginal to this bioregion (including Oenpelli python, white-throated grass-wren and at least 5 plant species), with most of their distribution associated with the sandstone massif of the adjacent Arnhem Plateau bioregion, and entering Pine Creek bioregion only in small border areas.
However, the bioregion is important for some threatened species, most notably the gouldian finch, partridge pigeon and ghost bat.
Number of taxa in the Pine Creek bioregion listed as threatened at national and/or NT level (nb this table includes only species definitely recorded from the bioregion (rather than putative occurrences based on modelling) and presumed to be still extant in the bioregion).
| taxa | National | Northern Territory | ||
|---|---|---|---|---|
| endangered | vulnerable | endangered | vulnerable | |
| plants | 0 | 1 | 3 | 8 |
| reptiles | 0 | 0 | 0 | 1 |
| birds | 2 | 4 | 2 | 3 |
| mammals | 0 | 1 | 0 | 3 |
There is also some evidence that there is broad scale decline affecting at least some groups of mammals and birds in this bioregion, in addition to those species currently listed as threatened.
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Other flora values for eucalypts and acacias
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Endemism
There are no endemic eucalypts and one endemic acacia species known from this bioregion: Acacia malloclada.
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Richness
The bioregion has moderately high tallies of Acacia (70 species) and Eucalyptus (57 species).
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Endemism
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Birds
There were no substantial changes in the status of bird species in this bioregion over the period between the two bird Atlases. -
Mammals
The mammal fauna of Pine Creek bioregion has been relatively resilient. Of 56 species recorded from the bioregion, 2 have declined severely, 2 have declined and 52 are stable.
Management Responses
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Reserve consolidation
The bioregion includes large areas of several major reserves, most notably including Kakadu, Nitmiluk, Litchfield, and Mary River NPs. Combined, this reserve system is unusually extensive and comprehensive, however there is some bias away from the more fertile lowland areas. There is also some case for more formal protection for at least some of the many small isolated rainforest patches scattered widely across the bioregion.
All main reserves in the bioregion have established plans of management, and are generally relatively well resourced. There are extensive programs established in most conservation reserves in the region, to monitor the response of vegetation to fire, and to map the occurrence of fires. -
Off park conservation for species and ecosystem recovery
There are some cases of exclosure fencing on pastoral lands, to provide for some recovery of rainforest patches and riparian areas. Such protection could be provided more extensively. Some off-reserve protection is afforded to the major colony of ghost bats present near Pine Creek.
The bioregion includes a major military training area, at Mount Bundey station adjacent to Kakadu, which has an environmental management plan in place.
This bioregion includes a large portion of Litchfield Shire, which has a 50% limit on clearing for any property, and has recently developed a Land for Wildlife scheme for off-reserve management of vegetation.
There has been a major research and management project on the gouldian finch in the Yinberrie Hills, within this bioregion, and the management of this endangered species at this site and beyond is described within an established Recovery Plan. -
Integrated NRM
As with other bioregions in northern Australia, the major NRM priority is for enhanced delivery of integrated (cross-tenure) control of weeds, feral animals and fire. To some extent, the Integrated Catchment Plan for the Mary River system provides a good example of such integration, with participation of most landholders and relevant government NRM agencies.
A conservation plan has recently been completed for the Mary River catchment, and another is in preparation for the Litchfield Shire.
Further Information and Gaps
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Major data gaps and research priorities for bioregion
Large sections of this bioregion (notably Litchfield Shire, the Mary River system and Kakadu NP) have been subject to unusually intensive wildlife inventory and conservation assessment, however there are some geographic gaps in this coverage.
Management would also benefit from more detailed environmental mapping, in particular vegetation mapping at the scale of 1:100,000 or better.
Currently in this bioregion, there is no substantial monitoring program which includes as a major goal the assessment of trends in biodiversity conservation. Such a program should be a management priority. - Other information