Invasiveness Assessment - Pampas grass (Cortaderia selloana) in Victoria

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Plant invasiveness is determined by evaluating a plant’s biological and ecological characteristics against criteria that encompass establishment requirements, growth rate and competitive ability, methods of reproduction, and dispersal mechanisms.

Each characteristic, or criterion, is assessed against a list of intensity ratings. Depending upon information found, a rating of Low, Medium Low, Medium High or High is assigned to that criterion. Where no data is available to answer a criterion, a rating of medium (M) is applied. A description of the invasiveness criteria and intensity ratings used in this process can be viewed here.

The following table provides information on the invasiveness of Pampas 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 - 1 MB)
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Common Name: Pampas grass
Scientific name: Cortaderia selloana

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	Germination occurs in spring (Parsons & Cuthbertson 2001).	MH	MH
Establishment requirements?	In shaded areas seedling survival is reported to be low (Bossard, Randell & Hoshovsky 2000). Therefore seedlings are capable of establishing in moderate shade if only to a minor extent.	MH	MH
How much disturbance is required?	Reported to be able to invade heathland (Carr, Yugovic & Robinson 1992).	H	MH
Growth/Competitive
Life form?	A grass species, forms large dense tussocks (Parsons & Cuthbertson 2001).	MH	MH
Allelopathic properties?	There is evidence to suggest Cortaderia selloana contains phytotoxic substances which can inhibit germination; however of the species examined Cortaderia contained the least (Chou & Young 1975). Unknown to what extent these substances will impact on other species.	M	H
Tolerates herb pressure?	Under intensive grazing, small plants are reported to be able to persist (Muyt 2001). Historically used as a fodder source; tolerant of grazing (Blood 2001). Unknown however if plants are able to flower under moderate grazing.	M	MH
Normal growth rate?	Able to exclude most other ground flora (Muyt 2001). Reported to have more vigorous growth than C. jubata under both optimal and sub-optimal conditions (Stanton & DiTomaso 2004). Faster growth is reported for a plant in its second season than its first (Parsons & Cuthbertson 2001). Bassett et al (1990) shows that early seedling growth of pampas can be suppressed by other grass species, however no mortality was observed, therefore the pampas seedling will persist and eventually out-compete the other grass species.	H	MH
Stress tolerance to frost, drought, w/logg, sal. etc?	Tolerates frost (Blood 2001). Tolerates drought (Blood 2001). Tolerates fire, flowering may even be stimulated in older plants after being burnt (Blood 2001). Tolerates salinity (Blood 2001). Tolerates waterlogging; occurring in seasonal wetlands (Blood 2001).	H	MH
Reproduction
Reproductive system	Reproduces both sexually and asexually, producing seed, rhizomes and tillers (Parsons & Cuthbertson 2001).	H	MH
Number of propagules produced?	Female plants are able to produce 1,000,000 seeds per panicle while hermaphrodites are able to produce 100,000 (Domènech et al 2005).	H	H
Propagule longevity?	Seeds remain viable for two years maximum (Blood 2001).	L	MH
Reproductive period?	Plants are reported to be capable of surviving for 15 years (Bossard, Randell & Hoshovsky 2000).	H	MH
Time to reproductive maturity?	Flowering is reported to be possible during the plants first season, but more likely to occur after two or three years (Parsons & Cuthbertson 2001).	H	MH
Dispersal
Number of mechanisms?	Seeds are dispersed by wind (Duckett 1989). Seeds can be dispersed by wind and water and rhizomes can be dispersed accidentally by people (Muyt 2001).	H	H
How far do they disperse?	Seeds have the potential to be dispersed distances of 25 km (Duckett 1989).	H	H

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