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Invasiveness Assessment - Holly leaved senecio (Senecio glastifolius) 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 Holly leaved senecio.

Victorian Weed Risk Assessment (WRA) method (PDF - 630 KB)
Victorian Weed Risk Assessment (WRA) method (DOC - 1 MB)
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Common Name: Holly leaved senecio
Scientific name: Senecio glastifolius

Question
Comments
Rating
Confidence
Establishment
Germination requirements?Sow seeds from mid-summer to autumn (van der Walt, 2002).

Pulses of germination…when temperature above 25c…relatively high temps required (Williams et al. 1999). Germinates in wetter conditions from early autumn through winter (CRC Weed Management, 2003). Fire also seems to stimulate germination (see Brown and Brooks, 2002) but is not necessary for germination. Requires natural seasonal rainfall/temperatures.
MH
MH
Establishment requirements?Establishes in full sun to light shade, either winter or all-year-round rainfall (Williams et al., 1999) in Eucalyptus woodlands and Allocasuarina open woodlands (Brown & Brooks, 2002). This suggests that S. glastifolius can establish under moderate canopy cover
MH
MH
How much disturbance is required?Invades coastal areas (Dept. cons., 2002), motorways and hillsides, river mouth, dunes, wasteland, sparingly on the coast, embankment, spreading very aggressively into Banksia woodland and coastal shrubland on deep sands, occurs naturally in pastoral areas, is abundant on old burn sites, a troublesome weed in newly planted plantations and a general ruderal [poor land or waste] and agricultural weed, strongly associated with sparsely vegetated sites, partially stabilised sand dunes, recently felled pine plantation. Often seen after fires and in disturbed areas where it is one of the first pioneers to germinate (Williams et al., 1999). The aggressive spread into Banksia woodland indicates that it has the potential to invade relatively intact natural ecosystems.
MH
H
Growth/Competitive
Life form?Asteraceae herb (Dept. cons., 2002). Perennial herb (sometimes annual) (Williams et al., 1999).
L
H
Allelopathic properties?None recorded.
L
L
Tolerates herb pressure?In NZ leaves are eaten by the larvae of the native magpie moth. Appears to be palatable to sheep. Williams et al states that “vegetative response to damage is…not a significant method of … persistence” and that a few plants were sprouting new shoots after the top parts had died off (Williams et al., 1999). Not enough evidence was found to support either herbivory suppressing reproduction (ML) or the ability to seed under moderate herbivory pressure (MH), so a medium rating was chosen between the two.
M
H
Normal growth rate?Displacing low-growing herbs and ferns and preventing establishment of native seedlings (Dept. cons., 2002). Stems 1-1.5 m tall and occasionally up to 2 m tall. Plants can be 0.5 m wide (Williams et al., 1999). Has the ability to dominate understorey vegetation in open damp areas (CRC Weed Management, 2003). All evidence points to the potential for this species to exceed the growth of most forbs.
H
MH
Stress tolerance to frost, drought, w/logg, sal. etc?Prefers wetter areas…often seen after fires (van der Walt, 2002). This is most likely from fire stimulated germination of seeds, as documented in Brown and Brooks (2002): “fire followed by good rains led to prolific germination.” Terrestrial dry and terrestrial wet substrates and…on nutrient-poor deep sandy soils , some tolerance of high soil moisture, unlikely to tolerate permanently saturated soils. Some capacity to tolerate salt as indicated by its…proximity to sea water at Motueka and Whitiau. In drought conditions it may not grow at all over summer (Williams et al., 1999). Some tolerance to salt, probably susceptible to permanent waterlogging and drought.
L
H
Reproduction
Reproductive systemSeed or cuttings (van der Walt, 2002). The main method of reproduction is sexual but can be grown from cuttings in ornamental horticulture. May occasionally form roots where stems lie horizontally, but vegetative reproduction not a significant method of spread or persistence (Williams et al, 1999). Potential may exist for self and cross pollination.
ML
H
Number of propagules produced?2–3 to several hundred flower heads x 12-22 ray florets (Williams et al., 1999) (so presume more than 12-22 disk florets) = >6,600 propagules
H
H
Propagule longevity?“Some evidence for a persistent soil seed bank” (Williams et al., 1999). But no specific information found.
M
L
Reproductive period?Not very long-lived perennial (van der Walt, 2002). No evidence for plants older than 4 years
(Williams et al., 1999).
MH
H
Time to reproductive maturity?Cultivation of S. glastifolius suggests that if plants germinate early enough and develop a bushy habit before spring, they will flower in the same year that they germinate. If they are too small, they will delay flowering until the following year (van der Walt, 2002).
H
ML
Dispersal
Number of mechanisms?Seed spread by wind and dumped in garden waste (Blood, 2001).
MH
MH
How far do they disperse?Seed spread by wind and dumped in garden waste (Blood, 2001). Seed has a pappus 7-9 mm long and “fluffy” (Williams et al, 1999). Presume that the pappus would likely carry it at least 20 m but few would reach 1 km.
ML
MH


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