Research directed by C. Daehler (UH Botany) with funding from the Kaulunani Urban Forestry Program and US Forest Service

Information on Risk Assessments
Original risk assessment

Grevillea robusta (silky oak)

Answer

1.01

Is the species highly domesticated?

y=-3, n=0

n

1.02

Has the species become naturalized where grown?

y=-1, n=-1

y

1.03

Does the species have weedy races?

y=-1, n=-1

n

2.01

Species suited to tropical or subtropical climate(s) (0-low; 1-intermediate; 2-high) – If island is primarily wet habitat, then substitute “wet tropical” for “tropical or subtropical”

See Append 2

2

2.02

Quality of climate match data (0-low; 1-intermediate; 2-high) see appendix 2

2

2.03

Broad climate suitability (environmental versatility)

y=1, n=0

y

2.04

Native or naturalized in regions with tropical or subtropical climates

y=1, n=0

y

2.05

Does the species have a history of repeated introductions outside its natural range? y=-2

?=-1, n=0

y

3.01

Naturalized beyond native range y = 1*multiplier (see Append 2), n= question 2.05

y

3.02

Garden/amenity/disturbance weed y = 1*multiplier (see Append 2)

n=0

3.03

Agricultural/forestry/horticultural weed y = 2*multiplier (see Append 2)

n=0

n

3.04

Environmental weed y = 2*multiplier (see Append 2)

n=0

y

3.05

Congeneric weed y = 1*multiplier (see Append 2)

n=0

y

4.01

Produces spines, thorns or burrs

y=1, n=0

n

4.02

Allelopathic

y=1, n=0

4.03

Parasitic

y=1, n=0

n

4.04

Unpalatable to grazing animals

y=1, n=-1

n

4.05

Toxic to animals

y=1, n=0

n

4.06

Host for recognized pests and pathogens

y=1, n=0

n

4.07

Causes allergies or is otherwise toxic to humans

y=1, n=0

n

4.08

Creates a fire hazard in natural ecosystems

y=1, n=0

n

4.09

Is a shade tolerant plant at some stage of its life cycle

y=1, n=0

n

4.1

Tolerates a wide range of soil conditions (or limestone conditions if not a volcanic island)

y=1, n=0

y

4.11

Climbing or smothering growth habit

y=1, n=0

n

4.12

Forms dense thickets

y=1, n=0

n

5.01

Aquatic

y=5, n=0

n

5.02

Grass

y=1, n=0

n

5.03

Nitrogen fixing woody plant

y=1, n=0

n

5.04

Geophyte (herbaceous with underground storage organs -- bulbs, corms, or tubers)

y=1, n=0

n

6.01

Evidence of substantial reproductive failure in native habitat

y=1, n=0

n

6.02

Produces viable seed.

y=1, n=-1

y

6.03

Hybridizes naturally

y=1, n=-1

n

6.04

Self-compatible or apomictic

y=1, n=-1

n

6.05

Requires specialist pollinators

y=-1, n=0

6.06

Reproduction by vegetative fragmentation

y=1, n=-1

n

6.07

Minimum generative time (years) 1 year = 1, 2 or 3 years = 0, 4+ years = -1

See left

3

7.01

Propagules likely to be dispersed unintentionally (plants growing in heavily trafficked areas)

y=1, n=-1

n

7.02

Propagules dispersed intentionally by people

y=1, n=-1

y

7.03

Propagules likely to disperse as a produce contaminant

y=1, n=-1

n

7.04

Propagules adapted to wind dispersal

y=1, n=-1

y

7.05

Propagules water dispersed

y=1, n=-1

y

7.06

Propagules bird dispersed

y=1, n=-1

n

7.07

Propagules dispersed by other animals (externally)

y=1, n=-1

n

7.08

Propagules survive passage through the gut

y=1, n=-1

n

8.01

Prolific seed production (>1000/m2)

y=1, n=-1

n

8.02

Evidence that a persistent propagule bank is formed (>1 yr)

y=1, n=-1

8.03

Well controlled by herbicides

y=-1, n=1

y

8.04

Tolerates, or benefits from, mutilation, cultivation, or fire

y=1, n=-1

y

8.05

Effective natural enemies present locally (e.g. introduced biocontrol agents)

y=-1, n=1

Total score:

5

Source

Notes

1.01

No evidence

1.02

"This tree is sometimes used in forestry plantings. It is naturalized in Hawai'i.; "Naturalized and starting to spread on the island of Rurutu (Austral archipelago, French Polynesia)."

http://www.hear.org/pier/grrob.htm

1.03

No evidence

2.01

Grevillea robusta has gained widespread popularity in warm temperate, subtropical and tropical highland regions of many countries …'

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

2.02

Grevillea robusta has been introduced to warm temperate, subtropical and tropical highland regions around the world commencing in the mid to late 19th century and is widely planted in India, Sri Lanka, Central and South America and many countries in Africa

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

2.03

(1) ' It is found across a wide range of altitudes from sea level to mountaintop occurrences at 1120 m in the Bunya Mountains.' 'Altitude range: 0 - 2500 m'
(2)USDA hardiness zones 9B to 11 (3) GROWS ON THE COAST AND DRIER WESTERN SLOPES. (4)High resistance to frosts. (5)Rainforest and depauperate rainforest of coastal districts [suggests narrower range]

(1)CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International. (2)Sothern Trees. CDROM database. (3)http://www.wyeenursery.com.au/html/trees6.html (4)http://www.forests.qld.gov.au/qts/treetext.html (5)Stanley and Ross. 1983. Flora of South-eastern Queensland Vol. 1. Queensland Dept of Prmary Industries, Brisbane

2.04

The natural habitat of G. robusta is in northern New South Wales and southern Queensland, Australia, where it occurs from the east coast to as far west as the Bunya Mountains, Queensland, some 160 km inland.

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

2.05

Introduced to several countries.

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

3.01

"It is naturalized in Hawai'i.; "Naturalized and starting to spread on the island of Rurutu (Austral archipelago, French Polynesia)."

http://www.hear.org/pier/grrob.htm

3.02

No evidence that it is a weed of gardens -- left black for disturbance weed because of positive answer to 3.04

3.03

No evidence

3.04

(1)Grevillea robusta (silky oak) invasive throughout Sydney area, a known weed in the lower Blue Mountains . (2)Listed as a "Garden Thug" in New South Wales, with designation "X" weed of unknown importance (3)Listed as an invasive species in Jamaica, defined as "those alien species which threaten ecosystems, habitats or species." but the section on "Impacts" is left blank (4)Locally common at middle elevations in the more exposed parts of the eastern mountains 900-4200 ft [documents abundance in natural areas of Jamaica] (5)Category 3 invader in South Africa [the lowest category, prohibited within 30 meters of the 1:50 year flood line of a river, stream, spring, natural channel in which water flows regularly or intermittently, lake, dam or wetland]

(1)http://www.bluemountains.org.au/conservation/DLEP2002/bmcssi2.shtml (2)Randall, R. 2001. Garden thugs, a national list of invasive and potentially invasive garden plants. Plant Protection Quarterly 16:138-171. (3)http://www.jamaicachm.org.jm/aliens_i_pl.htm (4)Adams, C.D. 1970. Flowering plants of Jamaica. University of the West Indies Press, Mona (5)http://www.weedwarriors.co.za/Pests1.html

3.05

(1)This noxious, medium-sized, evergreen tree is similar to silky oak in most features. There is a major infestation in the Ka'u District, Hawai'i, and north-east Kaua'i. [G. banksii]
(2)Infests pastures and natural areas in mesic areas [G. banksii was considered an environmental weed, and was on the noxious weed list of Hawaii]

(1)http://www.botany.hawaii.edu/faculty/cw_smith/gre_ban.htm (2)http://www.hear.org/pier/grban.htm

4.01

No evidence

4.02

The leaves produce an allelopathic substance that inhibits the establishment of all species, including itself apparently. [There is some controvery about this; See Harper, J. 1977. Plan Population Biology.]

http://www.hear.org/pier/grrob.htm

4.03

No evidence

4.04

(1)"Physical control: Goats will control silver oak (An Peischel)." (Motooka, P., L. Castro, D. Nelson, G. Nagai and L. Ching . 2002. Weeds of pastures and natural areas of Hawaii and their management. In press.)" (2)Used as fodder

(1)http://www.hear.org/pier/grrob.htm (2)http://www.easternarc.org/html/gumstudies.html

4.05

No evidence

4.06

Pests recorded
Insect pests:
Asterolecanium pustulans [1]
Fungus diseases:
Amphichaeta grevilleae [2]
Botryosphaeria dothidea [3]
Cercospora
Corticium salmonicolor [4]
Phyllosticta
Footnotes:
1. A scale insect - a serious pest of G. robusta in the Caribbean.
2. Causes leaf-spot and defoliation.
3. Has caused severe cankers in G. robusta in Guatemala.
4. Rust fungus, causes cankers (commonly known as Pink Disease).
None of the above pests were found to be recognized pests. [Botryosphaeria dothidea is the casual agent of a variety of diseases to economically important woody plants, i.e. shoot blight of pistachio, grape vine, peach, avocado etc.BROAD HOST RANGE]

4.07

(1) AB: A 73-year-old Australian man presented with an 8-year history of a dermatitis affecting his face, dorsum of hands, and forearms. He was patch tested and found to be positive to colophony and sawdust samples from four different timbers: Silky Oak (Grevillea robusta ), Queensland Hoop Pine (Araucaria cunninghamii ), Radiata Pine (Pinus radiata ) and Australian red cedar (Toona australis [Toona ciliata] ).
(2) AB: "Pollen of 12 ornamental trees of potential importance as causes of seasonal allergies was examined using light and scanning electron microscopy, in the district of Santa Cruz-La Laguna in Tenerife, Canary Islands. The 12 species were: Cupressus macrocarpa, Schinus molle, Casuarina cunninghamiana, Quercus suber, Acacia cyanophylla [A. saligna], Eucalyptus globulus, Ligustrum ovalifolium, Platanus hybrida [P. acerifolia], Tilia tomentosa, Jacaranda ovalifolia, Spathodea campanulata and Grevillea robusta . " [Occasional allergic reactions only in sensitized people]

4.08

(1) Probably not- 'G. robusta is vulnerable to fire and hence is excluded from the fire-prone Eucalyptus forests and grasslands that occupy much of its natural range.'
(2)It is an evergreen tree, single-trunked tree.

(1)CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International. (2)http://www.cuyamaca.net/oh170/Characteristic%20Pages/Grevillea%20robusta.asp

4.09

(1) 'Silk Oak is a light-demanding species and a pioneering colonizer of disturbed sites, growing rapidly for the first years, then slowing as competition from surrounding vegetation increases.' (2)Exposure: full sun.

(1)http://216.239.39.100/search?q=cache:DAXgUC191wwC:www.echonet.org
/tropicalag/plantinfo/Grevillearobusta.pdf+Grevillea+robusta&hl=en&ie=UTF-8 (2)http://www.cuyamaca.net/oh170/Characteristic%20Pages/Grevillea%20robusta.asp

4.1

(1)The pH range for good growth is around 4.5 to 7.5. Best growth is obtained on sandy loam, loam and clay loam textures. (2)Fast growing tree on well-drained sandy soils [no information provided for growth rate on other soils]

(1)CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International. (2)Little et al. 1974. Trees of Puerto Rico and the Virgin Islands Volume 2. USDA, Washington DC.

4.11

No evidence

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

4.12

No evidence

5.01

An erect, single-stemmed tree typically reaching an adult size of 20-30 m in height and 80 cm in diameter

5.02

Protaceae

5.03

Protaceae

5.04

No evidence

6.01

'Flowering commences in October in lowland occurrences in the natural range, and seed is mature by the end of December.'

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

6.02

'The species seeds heavily and regenerates strongly after site disturbance in rainforests and along river banks, so younger-aged individuals are common in most natural occurrences.'

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

6.03

'It does not appear to be closely related to other species in the genus Grevillea and natural hybrids with other species have not been detected.'

Harwood, C.E., Moran G.F., and Bell, J.C. 1997. Genetic differentiation in natural populations of Grevillea robusta. Australian Journal of Botany. 45(4): 669 -678.

6.04

'Inflorescences bagged to exclude birds set no fruits, and unmanipulated flowers and flowers bagged with self-pollen set no fruits, indicating a self-incompatibility mechanism. ' 'The species showed both protandry and a self-incompatibility mechanism.'

Kalinganire-A {a}; Harwood-C-E; Slee-M-U; Simons-A-J. 2001.Pollination and fruit-set of Grevillea robusta in western Kenya. Austral-Ecology. 26 (6): 637-648.

6.05

(1)'The flowers are visited mainly by birds and insects. The likely pollinators of G. robusta are sunbirds (Nectarine amethystina, N. cyanolaema, N. olivacea, N. superba and N. venusta) and white-eyes (Zosterops kikuyuensis and Z. senegalensis).' 'Seed production stands for G. robusta should be established where flowering is prolific and bird pollinators are abundant.'
(2)Pollinating agents could also probably be flying foxes which have been observed to frequent the flowers of G. robusta. [Insect might be pollinators as cited in Reference 1]

(1)Kalinganire-A {a}; Harwood-C-E; Slee-M-U; Simons-A-J. 2001.Pollination and fruit-set of Grevillea robusta in western Kenya. Austral-Ecology. 26 (6): 637-648. (2)Harwood, C.E., Moran G.F., and Bell, J.C. 1997. Genetic differentiation in natural populations of Grevillea robusta. Australian Journal of Botany. 45(4): 669 -678.

6.06

Propagation is usually from seed.

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

6.07

(1)fast growing tree (2)Quick-growing [minimum estimate for a fast growing large tree]

(1)http://www.aoi.com.au/atcros/A1231P2.htm (2)http://edis.ifas.ufl.edu/ST285

7.01

Probably not - no evidence that the propagules have any means of attachment.

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

7.02

Probably yes -'With its fern-like pinnate leaves and prominent attractive, orange flowers, it is also popular as an ornamental.'

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

7.03

Probably not -seeds relatively big. 'Seeds are winged, 13-19 mm long x 8-10 mm wide and 0.8-0.9 mm thick, with a papery wing around the brown, ovate central seed body.'

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

7.04

Seeds are winged, 13-19 mm long x 8-10 mm wide and 0.8-0.9 mm thick, with a papery wing around the brown, ovate central seed body.

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

7.05

'The seed are light and winged and might be carried long distances by water flow, seed could be washed downslope to watercourses and then downstream before being deposited and germinating on flood banks (young individuals of Grevillea have been observed growing on flood banks distant from adult stands). Long distance wind dispersal might also be affected by violent summer storms...'

Harwood, C.E., Moran G.F., and Bell, J.C. 1997. Genetic differentiation in natural populations of Grevillea robusta. Australian Journal of Botany. 45(4): 669 -678.

7.06

7.07

7.08

No evidence that fruit is consumed (dry fruit)

8.01

(1). 'Seeds are winged, 13-19 mm long x 8-10 mm wide and 0.8-0.9 mm thick, with a papery wing around the brown, ovate central seed body.' (2)The species is a prolific seeder...The number of seed per kilo is 70,000 to120,000.' [Probably not -seeds relatively big]

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

8.02

Seed will retain viability for at least five years if dried to below 8% moisture content and stored in a dry, cool (20°C or lower) environment [stored in air-tight laminated plastic bags] (2)For best results, extract seed from mature, unopened follicles and plant immediately. (3)Seeds of G. robusta can lose viability fairly rapidly if not stored correctly: at or below 2-5°C

(1)CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International. (2)http://edis.ifas.ufl.edu/ST285

8.03

Chemical: “Sensitive to triclopyr ester (2.5% product in diesel oil) applied to frill cuts (66). HAVO staff reported control with triclopyr ester at 5% product in diesel oil applied to basal bark (Zimmer, HAVO). Susceptible to cut-surface and continuous frill applications of picloram and glyphosate and tolerant of 2,4-D and dicamba (45). Applications of glyphosate and triclopyr to drilled holes in unreplicated demonstrations were very effective.” (Motooka et al., 2002)

http://www.hear.org/pier/grrob.htm

8.04

'...it tolerates heavy pruning of its roots and branches.'

CAB International, 2000. Forestry Compendium Global Module. Wallingford, UK: CAB International.

8.05

No longer recommended for planting becaused the rees are heavily attacked by scale insects

Little et al. 1974. Trees of Puerto Rico and the Virgin Islands Volume 2. USDA, Washington DC.