Leptospermum laevigatum_Neal Kramer
Photo: Neal Kramer

Leptospermum laevigatum Risk Assessment

Common names: Australian tea tree

Leptospermum laevigatum -- California

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Created by: Lynn Sweet
Created on: Tuesday, Sep 20th, 2016
Evaluation Summary
Summary: 
General Evaluation Information
Date of Evaluation: 
September 20, 2016
Evaluation Time (hrs): 
2 Hours
Evaluation Status: 
Completed
Plant Information
Plant: 
Leptospermum laevigatum
Plant Material: 
If the plant is a cultivar, and if the cultivar's behavior differs from its parent's (behavior), explain how: 
Regional Information
Region Name: 
California
Climate Matching Map
These maps were built using a toolkit created in collaboration between GreenInfo Network, PlantRight, Cal-IPC, and Agricultural Sustainability Institute at UC Davis.
Link to Climate Matching Map: 
Climate Matching Maps PDF: 
Invasive History and Climate Matching
1. Has the species (or cultivar or variety, if applicable; applies to subsequent "species" questions) become naturalized where it is not native?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
Yes. Naturalized in California and South Africa, as well as New Zealand.
Reference(s): 
2. Is the species (or cultivar or variety) noted as being naturalized in the US or world in a similar climate?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
High
Answer / Justification: 
This species has naturalized in 11 counties in California (Calflora), mostly along the coast. The areas in South Africa that have occurrences in GBIF as well as the areas described by the Invasive Species South Africa site match California's climate.
Reference(s): 
3. Is the species (or cultivar or variety) noted as being invasive in the U.S. or world?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
Medium
Answer / Justification: 
It is listed as a problematic invasive species in South Africa, and has specific regulatory legislation regarding its status. It is not reported to be present anywhere else in the US beyond California.
Reference(s): 
4. Is the species (or cultivar or variety) noted as being invasive in the US or world in a similar climate?
Yes or No: 
Yes
Points: 
3
Confidence Level: 
Medium
Answer / Justification: 
It is listed as a problematic invasive species in South Africa, and has specific regulatory legislation regarding its status. In California, DiTomaso and Healy note this species under non-native rarely naturalized species, indicating that it is an ornamental escape in disturbed coastal areas.
Reference(s): 
5. Are other species of the same genus (or closely related genera) invasive in a similar climate?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Leptospermum scoparium is considered invasive in areas that do not match California's climate. L. petersonii is considered a minor/potential environmental weed in New South Wales, but the distribution is more coastal than the climate match area. Several other Leptospermum species in Randall that have sources for "environmental weed" status (L. ericoides (=Kunzea ericoides, GISN), L. polygalifolia, L. rotundifolia, and L. scoparium), but on examination only Kunzea ericoides could be confirmed to be invasive in an area that matches California's climate, in a preserve NE of Melbourne, in Victoria, Australia (GISN).
Reference(s): 
6. Is the species (or cultivar or variety) found predominately in a climate matching the region of concern?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
The native distribution in Australia (using AVH) contains some areas that match California's climate: the western tip of Western Australia and the coast of South Australia. However, most of the areas in coastal Victoria, New South Wales and Queensland as well as the range within north and east Tasmania do not match California's climate. Within the naturalized range, the areas with GBIF occurrences in New Zealand do not match California's climate, but the areas of occurrences in South Africa in the Western and Eastern Cape, as well as the California coast do match California's climate. Because much of the native range does not match, being more coastal than the climate match areas, I am giving this a "no."
Reference(s): 
Impact on Native Plants and Animals
7. Does this plant displace native plants and dominate (overtop or smother) the plant community in areas where it has established?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Indicated to form dense stands and outcompete and replace native species in South Africa. Even within its native range in Australia, it is noted to be aggressive, spreading into natural areas and forming dense stands.
Reference(s): 
8. Is the plant noted as promoting fire and/or changing fire regimes?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Cheal conference paper notes that this species changes fire regimes in Australia (note full text of this citation is unavailable; exerpt from the PIER assessment), as well, the Burrell paper notes that this species is increasing in communities where it was not as abundant and although this species is killed by fire, prolific seeding follows, leading to a dense thicket susceptible to reburning.
Reference(s): 
9. Is the plant a health risk to humans or animals/fish? Has the species been noted as impacting grazing systems?
Yes or No: 
No
Points: 
0
Confidence Level: 
High
Answer / Justification: 
Cattle are known to graze on this species.
Reference(s): 
10. Does the plant produce impenetrable thickets, blocking or slowing movement of animals, livestock, or humans?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Noted to produce "thickets" and "impenetrable stands."
Reference(s): 
Reproductive Strategies
11. Does this species (or cultivar or variety) reproduce and spread vegetatively?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
Sources indicate reproduction by seed. PIER assessment indicates "no" to this question (but notes a source as mentioning horticultural propagation by cuttings, as is common for many many plants), and that there is no evidence that this is a natural mode of reproduction. Bennett indicates that this species is killed by fire and does not reproduce vegetatively.
Reference(s): 
12. If naturally detached fragments from this plant are capable of producing new plants, is this a common method of reproduction for the plant?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
Sources indicate reproduction by seed. Note that the PIER assessment indicates "yes" to this question, but notes the source as mentioning horticultural propagation by cuttings, and that there is no evidence that this is a natural mode of reproduction.
Reference(s): 
13. Does the species (or cultivar or variety) commonly produce viable seed?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
Yes reproduction is by seed, and experiments using seed indicate easy germination of wild-collected seed.
Reference(s): 
14. Does this plant produce copious viable seeds each year (> 1000)?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Although the species may produce seed each year, and it may be numerous, it is held serotinously on the plant until fire releases it from capsules, taking up to 5 years. It is noted therefore by Bennett that fire intervals <5 years disadvantage this species, as it takes at least that long to grow to maturity and set seed. That said, HEAR indicates "yes" to this question, citing several sources that list "prolific" seed production in the thousands. In the spirit of the question, I believe the interpretation here should be "no" as either this Q14 or Q15 needs to indicate that the plant does not set seed that can produce seedlings annually, and this species requires fire. The relevant section from Bennett is included for the benefit of the reviewer as an exerpt in the bibliographic section. Comment from Denise Knapp: I agree that Q. 14 & 15 are difficult to interpret for this species, and the answer should be yes for one of the questions and no for another. But I think this question should get a Yes, and Q. 15 should get a No. The plant is producing viable seed each year, but the fruit requires heat to open and disperse seed. The seeds also may need other germination cues (heat, smoke, etc.), but those are separate factors from viability.
Reference(s): 
15. Is there significant germination (>25%) of seeds the next growing season, with no requirement of an infrequent environmental condition for seeds to germinate (i.e. fire) or long dormancy period?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
As above in Q14, there is some limit to when seed is set, which is that it is released following fire, and requires an age of >5 years to achieve seed set at all. The questions don't align well with the life history of this serotinous species, so either Q14 or this one needs to be "no." Although the species may produce seed each year, and it may be numerous, it is held serotinously on the plant until fire releases it from capsules, taking up to 5 years. It is noted therefore by Bennett that fire intervals <5 years disadvantage this species, as it takes at least that long to grow to maturity and set seed. That said, HEAR indicates "yes" to this question, citing several sources that list "prolific" seed production in the thousands. In the spirit of the question, I believe the interpretation here would be "yes." The relevant section from Bennett is included for the benefit of the reviewer as an excerpt in the bibliographic section. Comment from Eric Wrubel: I believe the answer to this question should also be No. As stated above (Q. 14), this is a serotinous species that requires fire to disperse and germinate. Therefore it is a species that requires an infrequent environmental condition to germinate, i.e. fire. The criteria state that the objective of this question is to determine if the species can establish quickly after it has escaped by germinating large amount of seed quickly, rather than waiting for fire or etc.
Reference(s): 
16. Does this plant produce viable seed within the first three years (for an herbaceous species) to five years (for a woody species) after germination?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Bennett indicates that the species requires 5 years to produce viable seed, but other sites indicate 3 or so.
Reference(s): 
17. Does this plant continuously produce seed for >3 months each year or does seed production occur more than once a year?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
Plant requires infrequent conditions (fire or felling) to set seed. Comment from Denise Knapp: This question is about the annual duration of seed production, not dispersal or germination. I believe the answer should still be no, based on the reported bloom period of "spring", in the Jepson Manual, and the San Marcos Growers website. Since the species flowers for < 3 months, it can be inferred that annual seed production is < 3 months duration.
Reference(s): 
Dispersal
18. Are the plant’s propagules frequently dispersed long distance (>100 m) by mammals or birds or via domestic animals?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Low
Answer / Justification: 
PIER assessment indicates "no." This is not a fleshy-fruited species-- seeds are small, flat and woody. Comment from Denise Knapp: There is some evidence that possums or birds disperse other fruits in the Myrtaceae. Answer is changed to Yes with low confidence. Possum dispersal: http://www.australianwildlife.net.au/pdf/school/Native_wildlife.pdf Bird dispersal: https://birdsqueensland.org.au/downloads/bq_birds_in_gardens_part1.pdf
Reference(s): 
19. Are the plant’s propagules frequently dispersed long distance (>100 m) by wind or water?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Although there are no specific structures listed, the seeds are described as light and several sources cited in HEAR assessment list wind dispersal.
Reference(s): 
20. Are the plant’s propagules frequently dispersed via contaminated seed (agriculture or wildflower packets), equipment, vehicles, boats or clothing/shoes?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Florabase lists dispersal vectors: "wind, vehicles, soil movement, water, garden refuse." A conference paper also confirms common dispersal from these vectors.
Reference(s): 
Evaluation Notes

Calflora: http://www.calflora.org/cgi-bin/species_query.cgi?where-calrecnum=4727

HEAR assessment: http://www.hear.org/pier/wra/pacific/Leptospermum_laevigatum_CGC.pdf

ARC Factsheet: http://www.arc.agric.za/arc-ppri/Pages/Australian-myrtle-Leptospermum-la...

San Marcos Growers: http://www.smgrowers.com/products/plants/plantdisplay.asp?plant_id=964 

Jepson eFlora: http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=30642

Reviewed by Ramona Robison, Eric Wrubel and Denise Knapp.

Total PRE Score

  • < 13 : accept (low risk of invasiveness)
  • 13 - 15 : evaluate further
  • > 15 : reject (high risk of invasiveness)

PRE Score: 
18
Number of questions answered: 
20
Screener Confidence (%): 
67.0
PRE Content Access and Privacy
Organization: 
California Invasive Plant Council (Cal-IPC)
Evaluation visibility: 
Public - accessible to all site users

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