Every 2 years Biosecurity Queensland produces a comprehensive series of pest distribution maps that show where over 100 weeds and pest animal species occur in Queensland.
Where the data comes from
The data for the maps comes from the pest distribution survey. Information for each pest is gathered through regional workshops, where participants include local government, Biosecurity Queensland officers and others with knowledge of local pest locations.
At these workshops a grid framework is laid over a map of Queensland, and the distribution and density of each pest is collectively rated by survey participants on a cell-by-cell basis. Each cell of the grid framework equates to 16.67km x 16.67km square for all species.
Species included in the survey
Species included in the survey are a wide range of restricted invasive plants and animals as listed under the Biosecurity Act 2014 and emergent species. See the APDS species list (PDF, 158.1KB).
During the survey workshops species are assessed using three criteria, each of which has a different level of accuracy:
- species occurrence - if the species is present within the cell, (present, absent or unknown)
- distribution - how much of the cell contains infestations of the species (localised or widespread)
- density - how thick or sparse the infestations are (occasional, common or abundant)
Species occurrence - present/absent/unknown
It is essential to know if a pest is present or absent in each cell. If the survey participants cannot say with a very high degree of accuracy whether the pest is present or absent, the cell is flagged as unknown. This criterion has the highest level of accuracy.
Distribution - localised/widespread
Once it has been established that a pest is present within a cell, it is necessary to indicate how much of the cell contains infestations of the species.
Infestations that occur across more than half the cell in any density are considered widespread, while those that cover less than half the cell are considered localised.
While distribution gives us a useful indication of the size of pest infestations within grid cells, its accuracy should not be relied on too heavily. Reasons for this include:
- Survey participants may have differing perceptions of distribution measures.
- Survey participants may lack knowledge of particular species.
- It is difficult to accurately assess large areas of remote and impenetrable land.
This criterion has a lower level of accuracy than 'occurrence', and should only be used as a guide when making statewide comparisons.
Density - occasional/common/abundant
Density refers to how thick or sparse pest infestations are. The following three descriptors are used:
- Occasional: single plants/animals spaced apart at wide intervals
- Common: a middle measure between occasional and abundant
- Abundant: infestations that have reached their full potential and provide little opportunity for additional plants/animals to survive in that area.
Density is a particularly difficult criterion to apply due to factors such as:
- Different species have different density measures, e.g. grasses spaced at 1 m apart may be considered occasional, whereas trees spaced at 1 m apart may be considered abundant.
- The size of the species will directly influence the perception of density, e.g. many small seedlings may receive the same density rating as a few mature trees.
- Some areas may be able to support higher densities of a species than other areas, due to environmental conditions.
This criterion has a lower level of accuracy than 'distribution'. Density can be considered more accurate at the shire level than at the state level and should only be used as a guide when making statewide comparisons.