Fragmentation of remnant vegetation
The south-eastern bioregions are the most heavily fragmented in Queensland and are prone to further degradation due to the proximity of large tracts of cleared land and future development pressure. The New England Tableland, Southeast Queensland and the Brigalow Belt have the highest proportion of core remnant areas 100 hectares or less in size, indicating a very high level of fragmentation. The Central Queensland Coast, Wet Tropics and Mulga Lands also have significant levels of fragmentation.
Landscape fragmentation is the ‘breaking up’ of large areas of intact native vegetation. Fragmentation reduces ecological connectivity, the connection between ecosystems and habitats that allows wildlife to cross the landscape in search of food, shelter and suitable breeding sites—all critical to maintaining population levels. While heavily fragmented landscapes can become biodiversity-poor, the opening up of surrounding areas can further decrease species survival through predation, exposure and decreased food availability.
The statistics below are derived from a landscape fragmentation analysis of the Queensland Regional Ecosystem mapping (version 10). The analysis is similar to the Landscape Fragmentation and Connectivity (LFC) Tool developed to test for Significant Residual Impact on Connectivity Areas under the Environmental Offsets Framework.
- ‘Core’ areas represent remnant vegetation that is further than 100 metres from cleared areas, where there is less chance of weed invasion and feral animals.
- ‘Edge’ areas represent remnant vegetation within 100 metres of cleared land, where ‘edge effects’ are greater and the condition of the remnant vegetation is generally lower.
- ‘Patch’ areas represent isolated fragments of remnant vegetation less than 100 metres wide, that are most vulnerable to threatening processes and are likely to have impaired ecosystem functioning.
The size distribution of core remnant areas show that each bioregion has a unique configuration, although there is a trend from very large core areas in western bioregions through to a larger number of progressively smaller core areas in the more developed south-eastern bioregions.
In the Channel Country, Northwest Highlands, Mitchell Grass Downs, Gulf Plains, Cape York Peninsula and Mulga Lands, core areas greater than one million hectares cover more than 80% of all existing remnant vegetation. In the Brigalow Belt, by far the largest bioregion in Queensland, core areas greater than one million hectares occur in less than 40% of existing remnant vegetation.
The New England Tableland, Southeast Queensland and Brigalow Belt have the highest concentration of core remnant areas less than 10 hectares in size, with an estimated density of 102, 54 and 30 respectively, per 100 square kilometres. For comparison, the city of Toowoomba is approximately 100 square kilometres in size.
Looking at the smallest fragments of remnant vegetation remaining in the landscape, Southeast Queensland (83), New England Tablelands (41), Wet Tropics (30), Central Queensland Coast (12) and the Brigalow Belt (12) have the highest concentration of remnant patches, per 100 square kilometres.
New England Tableland also has by far the largest concentration of remnant areas subject to ‘edge effects’ at over 70 edge areas per 100 square kilometres, followed by Southeast Queensland (50).
Distribution of remnant vegetation in the 13 bioregions, expressed as a proportion of remnant core areas of various size classes, the density of remnant core areas per 100 square kilometres, and the density of remnant patch and edge areas per 100 square kilometres. Based on Regional Ecosystems mapping (version 10, 2016).