Invasiveness Assessment - Mesquite (Prosopis spp.) in Victoria (Nox)

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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 Mesquite.

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: Mesquite
Scientific name: Prosopis spp.

Question	Comments	Reference	Rating
Establishment
Germination requirements?	“Seeds germinate in summer after periods of very warm temperatures and rain.” Requires natural seasonal disturbance.	Parsons & Cuthbertson (2001)	MH
Establishment requirements?	Requires a period of very warm temperatures. “Temperature appears to be more important than available water.” Optimal germination temperature is 29°C. “Honey mesquite seeds must be covered with a small amount of soil or dung for seedlings to establish. Seeds that germinate on the soil surface usually die.” Requires specific conditions to germinate.	Parsons & Cuthbertson (2001) Steinberg (2001)	ML
How much disturbance is required?	Commonly found in intermittently flowing streambeds from where they spread into adjacent areas depending upon favourable rainfall. “…often found along roadsides near areas of habitation.” Occur mostly in highly disturbed areas (riverbeds, watercourses) in open areas. “In Australia, all forms of mesquite tend to grow on heavier soils which support open woodland or grassland.”	Parsons & Cuthbertson (2001)	MH
Growth/Competitive
Life form?	Shrubs to small trees, nominally deciduous. Part of the Fabaceae family, mesquites are leguminous.	Parsons & Cuthbertson (2001)	MH
Allelopathic properties?	Extracts from the ground litter (mesquite pods and leaves) have an allelopathic effect on germinating seeds of other plant species.	Parsons & Cuthbertson (2001)	MH
Tolerates herb pressure?	Grazing animals eats pods, but spines may discourage animals from browsing on the leaves and stems. “Livestock do not consume the foliage to any great extent. Foliage consumption is high only during drought years.” Grazing does not affect the survival or reproductive ability of the tree.	Parsons & Cuthbertson (2001) Steinberg (2001)	MH
Normal growth rate?	Shoot growth is slow (compared to root growth). Maximum growth rate may be less than other species of similar life form.	Parsons & Cuthbertson (2001)	ML
Stress tolerance to frost, drought, w/logg, sal. etc?	In the U.S., mesquite is found in areas where average minimum temperature is –5°C and the frost-free growing season is longer than 200 days. The deep root system (15 to 20 metres) would ensure most trees survive periods of drought. “Fire mortality is usually low in honey mesquite. Following most range fires, honey mesquite is top-killed and then re-sprouts.” Survives fire. Information on tolerance to salt or waterlogging is not available.	Steinberg (2001) Parsons & Cuthbertson (2001)	ML
Reproduction
Reproductive system	“Deciduous shrubs or small trees, reproducing by seed and suckers.” Reproduces sexually and vegetatively.	Parsons & Cuthbertson (2001)	H
Number of propagules produced?	“…honey mesquite produces pods in… abundance.” Trees produce more than 100 pods per season, and in a Californian study, each pod contained an average of 12 seeds. Produces between 1,000 and 2,000 seeds.	Steinberg (2001)	MH
Propagule longevity?	“Little is known about honey mesquite seed banks [or] seed longevity in the field.” “Mesquite seeds have a relatively short seed longevity when the pods are kept on the soil surface. Within 12 months, less than 20% of the seeds are still viable in good seed production years while <0.1% remain viable in some years.” Seeds survive less than 5 years.	Owens et al (nd)	L
Reproductive period?	“Maximum ages that plants attain is unclear. Near Amarillo, Texas, the maximum age of plants within a stand of multi-stemmed honey mesquites ranged from 40 to 110 years. On the Rio Grande Plains of Texas, Archer found that 89% to 93% of honey mesquite plants were less than 100 years old, and the maximum age of plants sampled was 172 to 217 years.” Plants are very long-lived (more than 10 years).	Steinberg (2001)	H
Time to reproductive maturity?	“Young plants do not flower until they are 2 to 3 years old and from 1 to 1.5 metres high.”	Parsons & Cuthbertson (2001)	ML
Dispersal
Number of mechanisms?	Prosopis spp. spread is mostly by seed. Both livestock and native animals consume the seed pods, and many of the seeds pass through the digestive system intact. The pods and seeds float, so they may be dispersed long distances in floodwater. Propagules spread by water and animals.	Parsons & Cuthbertson (2001)	MH
How far do they disperse?	Floodwaters are likely to spread seed much greater than one kilometre, animals to a lesser extent.	Parsons & Cuthbertson (2001)	H

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