Impact Assessment - Desert ash (Fraxinus angustifolia) in Victoria
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Assessment of plant invasiveness is done by evaluating biological and ecological characteristics such as germination requirements, growth rate, competitive ability, reproduction methods and dispersal mechanisms. Assessment of plant impacts, however, is determined by the extent to which a plant affects a land manager’s environmental, economic and social resources.
The relative importance of these resources varies depending upon the value people place on them and, as such, the assessment process is subjective. For example, a farmer is likely to place a higher emphasis on the impact of a plant on production (economic resource) than its impact on areas of natural vegetation occurring on the farm. Conversely, a Landcare or Friends group would value environmental or social resources more than economic resources.
Recognising that the value of resources vary between different land tenures, plant impact assessments allow a prioritisation of resources by land managers. Assessments can apply at a local, regional or state level, and the relative values of each resource identified may differ at each level.
The impact assessment method used in the Victorian Pest Plant Prioritisation Process uses three broad resource categories: social, environmental and agricultural, each with a number of related attributes. For example, social resources include such attributes as how the plant affects human access for recreation, or if it creates a health risk due to toxicity or by producing allergens.
| Each resource attribute, or criterion, is assessed relative to a list of intensity ratings. Depending upon information found in relation to each criterion, a rating of Low, Medium Low, Medium High or High is assigned. Descriptions of the impact criteria and intensity ratings used in this process can be viewed here. |
The following table provides information on the impact of Desert ash.
A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:
Victorian Weed Risk Assessment (WRA) method (PDF - 630 KB)
Victorian Weed Risk Assessment (WRA) method (DOC - 1 MB)
To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).
Common Name: Desert ash
Scientific name: Fraxinus angustifolia
| Question | Comments | Rating | Confidence |
| Recreation | |||
| 1. Restrict human access? | The species is very fast growing, invades riparian vegetation and is reported to be able to form dense stands (Blood 2001; Carus & Çiçek 2007). As the species is reported by Fustec et al (2001) to be able to re-shoot from the stump when cut down, to create and maintain access to an invaded waterway, significant works may be required as the species would need to be controlled to prevent reinvasion. | H | MH |
| 2. Reduce tourism? | Ornamental deciduous tree species would be obvious and may have some aesthetic impact. | ML | L |
| 3. Injurious to people? | There is no evidence of this. | L | M |
| 4. Damage to cultural sites? | Ornamental deciduous tree species would be obvious and may have some aesthetic impact. | ML | L |
| Abiotic | |||
| 5. Impact flow? | The species is reported to tolerate periodic inundation and is invading riparian vegetation (Muyt 2001, Richardson, Richardson & Shepherd 2006). The species is not reported to impact water flow however little information is available on this species impact on water in areas where it is an invading species. | M | L |
| 6. Impact water quality? | Occurring in riparian vegetation the species is deciduous and in addition to this it’s litter has a fast decomposition rate (Pérez-Corona, Pérez Hernández & de Castro 2006). Therefore the species may have similar impacts upon water quality as Salix species altering shading patterns and therefore temperature and changing the time, quantity and possibly the quality of litter inputs which could then impact upon dissolved oxygen. The extent this species can have on water quality has not however been reported on. | M | L |
| 7. Increase soil erosion? | Unknown. | M | L |
| 8. Reduce biomass? | There is conflicting evidence on this; the species is a fast growing tree with recorded biomass increases of 15 m3ha-1 per annum (Carus & Çiçek 2007). The species however can form monocultures shading out other tree and shrub species (Muyt 2001). Therefore the only biomass accumulation would be by this species and if the shrub layer is removed this could result in a net decrease however this is not known. | M | L |
| 9. Change fire regime? | Unknown. | M | L |
| Community Habitat | |||
| 10. Impact on composition (a) high value EVC | EVC= Creekline Herb-rich Woodland (V); CMA= Corangamite; Bioreg= Central Victorian Uplands; VH CLIMATE potential. The species is reported to be able to form monocultures and prevent the regeneration of other species over time (Muyt 2001). | H | MH |
| (b) medium value EVC | EVC= Sedgy Riparian Woodland (D); CMA= Corangamite; Bioreg= Otway Plain; VH CLIMATE potential. The species is reported to be able to form monocultures and prevent the regeneration of other species over time (Muyt 2001). | H | MH |
| (c) low value EVC | EVC= Riparian Forest (LC); CMA= Corangamite; Bioreg= Otway Ranges; VH CLIMATE potential. The species is reported to be able to form monocultures and prevent the regeneration of other species over time (Muyt 2001). | H | MH |
| 11. Impact on structure? | The species is reported to be able to form monocultures and prevent the regeneration of other species over time (Muyt 2001). This would be a have a major impact on all layers. | H | MH |
| 12. Effect on threatened flora? | Unknown | MH | L |
| Fauna | |||
| 13. Effect on threatened fauna? | Unknown | MH | L |
| 14. Effect on non-threatened fauna? | The species is reported to be able to form monocultures and prevent the regeneration of other species over time (Muyt 2001). This level of change to vegetation is likely to impact upon species in terms of food sources and availability of appropriate shelter. The species impact upon native fauna however has not been reported. | M | L |
| 15. Benefits fauna? | Is used a nesting sites by birds in Europe (Polo & Veiga 2006; Suárez, Balbontin & Ferrer 2000). Therefore the species may provide some support in terms of shelter. | MH | H |
| 16. Injurious to fauna? | There is no evidence of this. | L | M |
| Pest Animal | |||
| 17. Food source to pests? | Possible but not thought to be significant. | L | M |
| 18. Provides harbor? | Is used a nesting sites by birds in Europe including starling species (Polo & Veiga 2006). Therefore the species may provide some shelter to low priority best species. | ML | MH |
| Agriculture | |||
| 19. Impact yield? | The species can be used as plantation timber (Carus & Çiçek 2007). It is considered an environmental weed and is only recorded to significantly invade orchards that have been abandoned (Debussche, Lepart & Devieux 1999). | L | M |
| 20. Impact quality? | Considered an environmental weed. | L | M |
| 21. Affect land value? | Considered an environmental weed. | L | M |
| 22. Change land use? | Considered an environmental weed. | L | M |
| 23. Increase harvest costs? | Considered an environmental weed. | L | M |
| 24. Disease host/vector? | There is no evidence of this. | L | M |
This table can also be viewed as a PDF document (printer friendly).
Impact Assessment Record - Desert ash (PDF - 82KB)
Impact Assessment Record - Desert ash (DOC - 56KB)
To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).
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