Impact Assessment - Bent grass (Agrostis capillaris / Agrostis castellana) 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 Bent grass

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 - 1026 KB)
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: Bent grass
Scientific name: Agrostis capillaris / Agrostis castellana

* Refer to ‘Note’ at end of document acknowledging confusing species identification and nomenclature.

Question	Comments	Rating	Confidence
Recreation
1. Restrict human access?	Perennial grass of height 20-80 cm (Tutin et al 1980). There is no information to suggest that A. castellana would restrict human access.	L	MH
2. Reduce tourism?	There is no information to indicate it would reduce tourism, and as a grass species (Edgar & Forde 1991) it is not likely to be obvious as a weed to the ‘average’ visitor.	L	M
3. Injurious to people?	Nothing was found in the literature to indicate that A. castellana possesses any injurious properties.	L	M
4. Damage to cultural sites?	Perennial grass of height 20-80 cm (Tutin et al 1980). No information found to suggest it would cause damage to cultural sites.	L	M
Abiotic
5. Impact flow?	As a terrestrial species it is unlikely to impact on water flow.	L	M
6. Impact water quality?	As a terrestrial species it is unlikely to impact on water flow.	L	M
7. Increase soil erosion?	It produces rhizomes (Batson 1998) so may decrease the probability of erosion in some situations.	L	MH
8. Reduce biomass?	When displacing native vegetation (DECC 2004), there is potential for direct replacement of biomass, as it would most likely replace other grass species.	ML	M
9. Change fire regime?	Produces thick dry mats of coarse grass that are very sensitive to fire (Bernaldez 1991). Potential to increase fire frequency in some of the less fire prone ecosystems it invades, with a likely varying level of impact.	M	MH
Community Habitat
10. Impact on composition (a) high value EVC	EVC= Plains Grassland (BCS= E); CMA= West Gippsland; Bioreg= Gippsland Plain; CLIMATE potential=VH. Described as a ‘very serious threat’ to several vegetation formations in Victoria (Carr et al 1992), and as displacing native vegetation (DECC 2004). Thick dry mats suppress annual herbs in pasture (Bernaldez 1991) and a similar affect is likely in natural systems, as it is documented dominating large areas of permanent grassland (Hubbard 1968). Potential for major displacement of some dominant species within the ground layer.	MH	MH
(b) medium value EVC	EVC= Grassy Dry Forest (BCS= D); CMA= Corangamite; Bioreg= Central Victorian Uplands; CLIMATE potential=VH. Described as a ‘very serious threat’ to several vegetation formations in Victoria (Carr et al 1992) and as displacing native vegetation (DECC 2004). Thick dry mats suppress annual herbs in pasture (Bernaldez 1991) and a similar affect is likely in natural systems, as it is documented dominating large areas of permanent grassland (Hubbard 1968). Potential for major displacement of some dominant species within the ground layer.	MH	MH
(c) low value EVC	EVC= Coastal Tussock Grassland (BCS= LC); CMA= West Gippsland; Bioreg= Gippsland Plain; CLIMATE potential=VH. Described as a ‘very serious threat’ to several vegetation formations in Victoria (Carr et al 1992) and as displacing native vegetation (DECC 2004). Thick dry mats suppress annual herbs in pasture (Bernaldez 1991) and a similar affect is likely in natural systems, as it is documented dominating large areas of permanent grassland (Hubbard 1968). Potential for major displacement of some dominant species within the ground layer.	MH	MH
11. Impact on structure?	Displaces native vegetation (DECC 2004). Thick dry mats suppress annual herbs in pasture (Bernaldez 1991) and a similar affect is likely in natural systems, as it is documented dominating large areas of permanent grassland (Hubbard 1968). Potential for major effect on <60% of the floral strata.	MH	MH
12. Effect on threatened flora?	Described as a ‘very serious threat to one or more vegetation formations in Victoria’ (Carr et al 1992) and as displacing native vegetation (DECC 2004). Its affect specific to threatened flora was not described.	MH	L
Fauna
13. Effect on threatened fauna?	Described as a ‘very serious threat to one or more vegetation formations in Victoria’ (Carr et al 1992) and as displacing native vegetation (DECC 2004). Its affect on native flora is likely to lead to reduced habitat availability, however the possible impact on native fauna was not documented.	MH	L
14. Effect on non-threatened fauna?	Described as a ‘very serious threat to one or more vegetation formations in Victoria’ (Carr et al 1992) and as displacing native vegetation (DECC 2004). Its affect on native flora is likely to lead to reduced habitat availability, however the possible impact on native fauna was not documented.	MH	L
15. Benefits fauna?	Though described as having relatively low agricultural value (Hubbard 1968) and only nutritious to stock for part of the year (Hill et al 1996) it is likely to provide some food source to native grazing animals such as macropods.	MH	M
16. Injurious to fauna?	No information to suggest it would be injurious to fauna.	L	M
Pest Animal
17. Food source to pests?	Grazed by rabbits (Gillham 1955 in HDRA 2006). Supplies food to one serious pest.	MH	MH
18. Provides harbor?	Not described providing harbour to pests, and unlikely to being a relatively low growing grass (Tutin et al 1980).	L	M
Agriculture
19. Impact yield?	‘…bent grass has become one of the worst pasture weeds of the high rainfall zone of Victoria. It was estimated to dominate over 1 million hectares (Siefert 1971) and, after rapid spread recently the authors consider that it now restricts production on a further 1 million hectares (Hill et al. 1996)’. ‘It is not unusual for a perennial ryegrass and phalaris pasture dominated by bent grass to have its capacity to produce meat, milk or wool reduced by one third (Lamp et al …). Potential to decrease yield by >20%	H	MH
20. Impact quality?	No information found to suggest it would impact on the quality of agricultural yield.	L	M
21. Affect land value?	Described as one of the worst pasture weeds of the high rainfall zone of Victoria (Hill et al 1996), it could affect the land value of grazing properties due to its capacity to restrict production, however, no specific reference was found in the literature.	M	L
22. Change land use?	As a serious pasture weed (Hill et al 1996), and with significant effort and outlay required to renovate infested pastures (Batson 1998b), some pastures would be utilised less than others and there is potential for a downgrade of their priority land use to occur to one with less agricultural return.	M	M
23. Increase harvest costs?	It is recommended that heavily infested pasture >40%), undergo full renovation consisting of cutting, spraying, cultivating, re-sowing and fertilising (Batson 1998b), resulting in considerable time and cost outlay. In addition because stocking capacity is significantly reduced (Hill et al 1996), increased time allocation for stock movement would also be required. Potential for major increase in production costs.	H	MH
24. Disease host/vector?	Not found, described as a host of agricultural disease or vector.	L	M

Note: Literature relevant to both A. castellana Boiss. & Reuter and A. capillaris has been used to complete this assessment. This is due to the considerable debate about the identity of the most common bent grass species that exists in Victoria. There is debate about the presence or otherwise of A. castellana in Victoria (not listed in the current ‘Census of the Vascular Plants of Victoria (Walsh & Stajsic 2007)’). Some authors consider it to be present (Batson 1998, Hill et al 1996), others acknowledge A. capillaris and/or two varieties of this species (Walsh & Entwisle 1994). It is also recognised that introgression and hydridisation readily occur between A. capillaris and A. castellana (Pers. Com. N. Walsh & A. Brown). In addition, the two species are documented as being similar (Hafliger & Scholz 1982).

This table can also be viewed as a PDF document (printer friendly).

Impact Assessment Record - Bent grass (PDF - 120 KB)
Impact Assessment Record - Bent grass (DOC - 63 KB)
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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