Grevillea robusta (silky oak)
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PicturesTop of page
|Caption||Young open-grown individual at Tyalgum, New South Wales, Australia.|
|Copyright||David Lea/CSIRO Forestry and Forest Products|
|Young tree||Young open-grown individual at Tyalgum, New South Wales, Australia.||David Lea/CSIRO Forestry and Forest Products|
|Caption||Tea plantation, Sri Lanka.|
|Copyright||Stephen Midgley/CSIRO Forestry and Forest Products|
|Shade tree||Tea plantation, Sri Lanka.||Stephen Midgley/CSIRO Forestry and Forest Products|
|Caption||Shade trees planted along the edge of a field of maize in Embu, Kenya. Trees have been pruned to reduce competition with the crop.|
|Shade trees||Shade trees planted along the edge of a field of maize in Embu, Kenya. Trees have been pruned to reduce competition with the crop.||Chris Harwood|
|Title||Field boundary trees|
|Caption||Row of trees along the edge of a farmer's field, near Meru, Kenya. The trees have been pruned and pollarded repeatedly to produce firewood and poles, and will eventually be harvested as saw logs.|
|Field boundary trees||Row of trees along the edge of a farmer's field, near Meru, Kenya. The trees have been pruned and pollarded repeatedly to produce firewood and poles, and will eventually be harvested as saw logs.||Chris Harwood|
4. young flower (stigma retained in bud)
5. tepal with anthers directly attached
6. mature flower (extended style + stigma)
8. winged seed|
|Line artwork||1. habit
4. young flower (stigma retained in bud)
5. tepal with anthers directly attached
6. mature flower (extended style + stigma)
8. winged seed||PROSEA Foundation|
IdentityTop of page
Preferred Scientific Name
- Grevillea robusta A. Cunn. ex R. Br.
Preferred Common Name
Other Scientific Names
- Grevillea robusta var. compacta auct.
- Grevillea robusta var. forsteri L.H.Bailey
- Grevillea umbratica A.Cunn. ex Meisn
- Grevillea venusta A.Cunn. ex Meisn.
International Common Names
- English: Australian silky-oak; she-oak; silver oak; southern silky-oak
- Spanish: grevillea; pino rojo; roble australiano; roble de pelota; roble sedoso
- French: grevillaire; grévilléa robuste
Local Common Names
- Australia: river oak; silk oak
- Brazil: carvalho-sedoso; grevílea-gigante; grevilha-robusta
- Cuba: roble plateado
- Dominican Republic: helecho
- Germany: Silberstrauch, Australischer
- Hawaii: haiku-keokeo; oka-kilika
- Honduras: gravilea
- India: silver oak
- Italy: grevillea
- Java: salamandar
- Puerto Rico: roble de seda
- Tanzania: mgrivea
- USA: lacewood
- GRERO (Grevillea robusta)
Summary of InvasivenessTop of page
G. robusta is a tree which is an effective colonizer and has demonstrated invasive behaviour in Australia (New South Wales), New Zealand, French Polynesia, Jamaica, Zimbabwe, and notably in South Africa and the United States (i.e., Hawaii). Contributing to its behaviour is likely to be its early and prolific seed producing habit, and the production of potentially allelopathic compounds. In South Africa, G. robusta has been declared a category 3 invader (Henderson, 2001). It is also invasive in Hawaii (Holm et al., 1979; Cronk and Fuller, 1995; Space and Flynn, 2001), a common weed in Micronesia (Space and Falanruw, 1999) and cultivated in Niue (Space and Flynn, 2000). It seeds heavily and regenerates strongly after disturbance in rainforests and along riverbanks. Several years ago, Binggeli (1999) classified G. robusta as a moderately invasive species: currently, it is listed as invasive and potentially invasive in many countries in South America, Africa, Asia, and on many islands in the West Indies and the Indian and Pacific Oceans (Harwood, 1997; Kairo et al., 2003; Oviedo Prieto et al., 2012; PIER, 2015; PROTA, 2015).
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Proteales
- Family: Proteaceae
- Genus: Grevillea
- Species: Grevillea robusta
Notes on Taxonomy and NomenclatureTop of page
The family Proteaceae includes 80 genera and 1600 species of shrubs and trees distributed principally in the southern hemisphere, especially across Australia and South Africa. There are about 515 species in the genus Grevillea (family Proteaceae), most of which are endemic to Australia (Stevens, 2012). Grevillea robusta was described by Alan Cunningham, and the name was published in 1830 in the Supplementum Primum to Robert Brown's Prodromus Florae Novae Hollandiae. The specific epithet is derived from the Latin robustus - hard, strong, robust, in reference to the large size of this species in a genus where many species are shrubs. It has no recognized subspecies or varieties, and no hybrids with other species have been recorded (McGillivray and Makinson, 1993).
DescriptionTop of page
G. robosta is an erect, single-stemmed tree typically reaching 20-30 m tall and 80 cm in stem diameter. The crown is conical and symmetrical with major branches spaced at intervals of about 1 m and projecting upwards at an angle of 45°. Bark on the trunk is dark grey and furrowed into a lace-like pattern. G. robusta is described and illustrated by McGillivray and Makinson (1993), Boland et al. (1984), and Harwood (1997). Proteoid roots (sections of the secondary roots which develop as dense cylindrical clusters of rootlets) develop in conditions of low phosphorus availability, and are thought to increase the plant's ability to take up nutrients (Skene et al., 1996). Young branchlets are angular and ridged, subsericeous to tomentose but glabrous on older growth. The fern-like foliage of this species is very distinctive. Leaves are 10-34 cm long, 9-15 cm wide, variably pinnate to bipinnate, with a glabrous green upper surface and subsericeous silvery under-surface. Petioles are 1.5-6.5 cm long. The species is semi-deciduous in its natural range, being almost leafless shortly before flowering. The flowers are grouped into compound racemose inflorescences (conflorescences, after Johnson and Briggs (1975)), which themselves are grouped into panicles of one to six conflorescences, borne on older wood. The bright orange flowers, about 2 cm long, are borne in numerous pairs along the flower spikes, on pedicels 1.5 cm long. The perianth consists of 4 narrow tepals, 0.6-1 cm long, with the concave summit of each tepal holding a small anther 0.1 cm long. The ovary surmounts a gynophore 0.2-0.3 cm long. Fruits are two-seeded follicles 2 cm in length, with a slender persistent style. Seeds are winged, 13-19 mm long, 8-10 mm wide, 0.8-0.9 mm thick, with a papery wing around the brown, ovate central seed body.
Plant TypeTop of page
DistributionTop of page
G. robusta is native to 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. The north-south range of the species is some 470 km, from the Guy Fawkes and Orara Rivers (tributaries of the Clarence River in New South Wales, 30°10'S) to just north of Gympie, Queensland (25°50'S). It is found across a wide range of altitudes from sea level to mountaintop occurrences at 1120 m in the Bunya Mountains (Harwood, 1992a). Outside its native distribution range, this species can be found naturalized in tropical Asia, Africa, America and the West Indies (see distribution table for details; Harwood, 1997; Acevedo-Rodriguez and Strong, 2012; PIER, 2015; PROTA, 2015).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Country||Distribution||Last Reported||Origin||First Reported||Invasive||References||Notes|
|China||Present||Introduced||World Agroforestry Centre, 2002|
|-Hong Kong||Present||Introduced||Wu, 2001||Cultivated|
|Christmas Island (Indian Ocean)||Present||Introduced||PIER, 2002|
|India||Present||Introduced||Mayne , 1947; World Agroforestry Centre, 2002|
|Indonesia||Present||Introduced||World Agroforestry Centre, 2002|
||World Agroforestry Centre, 2002|
|Malaysia||Present||Introduced||World Agroforestry Centre, 2002|
||World Agroforestry Centre, 2002|
||World Agroforestry Centre, 2002|
||World Agroforestry Centre, 2002|
|Singapore||Present||Introduced||Chong et al., 2009||Cultivated|
||World Agroforestry Centre, 2002|
||World Agroforestry Centre, 2002|
|Botswana||Present||Introduced||Buss , 2002|
|Congo Democratic Republic||Present||Introduced||
||World Agroforestry Centre, 2002|
||World Agroforestry Centre, 2002|
|Kenya||Present||Introduced||Spiers & Stewart, 1992; Kalinganire et al., 1996; World Agroforestry Centre, 2002|
||World Agroforestry Centre, 2002|
|Mauritius||Present||Introduced||World Agroforestry Centre, 2002|
||Kalinganire & Hall, 1993|
|Saint Helena||Present||Introduced||ISSG, 2015||Cultivated|
|South Africa||Present||Introduced||Invasive||Henderson , 2001; World Agroforestry Centre, 2002|
|-Canary Islands||Present||Introduced||DAISIE, 2015||Cultivated|
|Tanzania||Present||Introduced||Mbuya et al., 1994; World Agroforestry Centre, 2002|
||World Agroforestry Centre, 2002|
||World Agroforestry Centre, 2002|
|Zimbabwe||Present||Introduced||Invasive||Buss , 2002; Nyoka , 2002; World Agroforestry Centre, 2002|
|USA||Present||Introduced||World Agroforestry Centre, 2002|
||Gilman & Watson , 1993|
|-Florida||Present||Introduced||Gilman & Watson , 1993; USDA-NRCS, 2004|
|-Hawaii||Present||Introduced||Invasive||Nelson & Schubert, 1976; Cronk & Fuller , 1995; PIER, 2002|
CENTRAL AMERICA AND CARIBBEAN
|British Virgin Islands||Present||Introduced||Acevedo-Rodriguez & Strong, 2012||Tortola|
|Costa Rica||Present||Introduced||Morales, 2014||Cultivated|
|Cuba||Present||Introduced||Oviedo et al., 2012||Potentially invasive|
|Dominican Republic||Present||Introduced||Acevedo-Rodriguez & Strong, 2012||Cultivated: potentially invasive|
|Guadeloupe||Present||Introduced||Acevedo-Rodriguez & Strong, 2012||Cultivated|
|Haiti||Present||Introduced||Acevedo-Rodriguez & Strong, 2012||Cultivated|
|Jamaica||Present||Introduced||Invasive||World Agroforestry Centre, 2002; PIER, 2002; IABIN, 2003; Anon, 2003|
|Montserrat||Present||Introduced||Acevedo-Rodriguez & Strong, 2012||Cultivated|
||USDA-NRCS, 2004; Acevedo-Rodriguez & Strong, 2012|
|Brazil||Present, few occurrences||Introduced||Baggio et al., 1997; Ziller & Rosa , 2001; I3N-Brasil, 2014|
|-Espirito Santo||Present||Introduced||Invasive||I3N-Brasil, 2014|
||Ziller & Rosa , 2001; I3N-Brasil, 2014|
|-Rio Grande do Sul||Present||Ziller & Rosa , 2001|
|-Santa Catarina||Present||Introduced||Invasive||I3N-Brasil, 2014|
|-Easter Island||Present||Introduced||Invasive||Meyer, 2008|
|-Galapagos Islands||Present||Introduced||Invasive||Charles Darwin Foundation, 2008|
|-Madeira||Present||Introduced||DAISIE, 2015||Cultivated and naturalized|
|Spain||Present||Introduced||DAISIE, 2015||Cultivated and naturalized|
|Australia||Present||Native||Boland et al., 1984; World Agroforestry Centre, 2002|
|-Australian Northern Territory||Present||Introduced||
|-Lord Howe Is.||Present||Introduced||PIER, 2002; Orchard, 1994|
|-New South Wales||Present||Native||Invasive||
natural and planted
natural and planted
||Sun et al., 1995|
||Weeds of Australia, 2011|
|Cook Islands||Present||Introduced||PIER. 2002|
|French Polynesia||Present||Introduced||Space & Flynn , 2001; PIER, 2002; PIER, 2015|
|Micronesia, Federated states of||Present||Introduced||PIER, 2002|
||Webb et al., 1988|
|Norfolk Island||Present||Introduced||PIER, 2002|
|Papua New Guinea||Present||Introduced||
|Solomon Islands||Present||Introduced||PIER, 2015||Cultivated|
|Tonga||Present||Introduced||Invasive||Space & Flynn , 2001; PIER, 2002|
History of Introduction and SpreadTop of page
G. robusta has been introduced to other parts of Australia outside its native distribution range, and is now regarded as invasive around Sydney and is a known weed in the Blue Mountains of New South Wales (BMCS, 2002). It has also been introduced to warm temperate, subtropical and tropical highland regions around the world commencing in the mid to late 1800s, and it is now widely planted in India, Sri Lanka, Central and South America and many countries in Africa (Harwood, 1989). It performs poorly in lowland tropical environments. In Hawaii, it was introduced in 1880 from Australia (Motooka et al., 2003). In the West Indies, G. robusta appears in herbarium collection made in 1899 in Guadeloupe, 1916 in Puerto Rico, 1928 in Dominican Republic and 1932 in Jamaica (US National Herbarium).
Risk of IntroductionTop of page
The risk of introduction of G. robusta is moderate to high. This species has been widely planted in warm temperate, subtropical and tropical regions of the world and it is a prolific seed producer. It behaves as a weed in drier mesic pastures, disturbed areas and forests and it can be found naturalized principally in areas near cultivation (Harwood et al., 1997; ISSG, 2015; PROTA, 2015).
HabitatTop of page
In its native range, G. robusta is commonly found in small, discontinuous stands along the banks of rivers and streams, usually within 30 m of the water's edge, in areas with generally moderate to good soil fertility and water availability. 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. Habitats invaded by this species in South Africa include forest edges, coastal forests, disturbed sites, savannah and riparian areas (Henderson, 2001). It is very popular in agroforestry systems and often planted to provide shade for tea and coffee plantations (Harwood et al., 1997).
Habitat ListTop of page
|Coastal areas||Present, no further details||Harmful (pest or invasive)|
|Coastal areas||Present, no further details||Natural|
|Coastal areas||Present, no further details||Productive/non-natural|
|Cultivated / agricultural land||Present, no further details||Harmful (pest or invasive)|
|Cultivated / agricultural land||Present, no further details||Natural|
|Cultivated / agricultural land||Present, no further details||Productive/non-natural|
|Disturbed areas||Present, no further details||Harmful (pest or invasive)|
|Disturbed areas||Present, no further details||Natural|
|Managed forests, plantations and orchards||Present, no further details||Harmful (pest or invasive)|
|Managed forests, plantations and orchards||Present, no further details||Natural|
|Managed forests, plantations and orchards||Present, no further details||Productive/non-natural|
|Natural forests||Present, no further details||Harmful (pest or invasive)|
|Natural forests||Present, no further details||Natural|
|Natural grasslands||Present, no further details||Harmful (pest or invasive)|
|Natural grasslands||Present, no further details||Natural|
|Riverbanks||Present, no further details||Harmful (pest or invasive)|
|Riverbanks||Present, no further details||Natural|
Biology and EcologyTop of page
The chromosome number reported for G. robusta is 2n = 20.
No records of hybrids between G. robusta and other species of Grevillea have been published. Isozyme studies of natural populations and land races (Harwood et al., 1997) established that the species has a moderate level of allozyme heterozygosity in natural populations. The genetic diversity of individual populations varied little, and did not appear to be related to their ecological characteristics (araucarian vine forest or riverine habitat types) or their geographic locations. Between-population differences accounted for 17.9% of the total genetic variation. It appears that genetic exchange between populations has been maintained, despite the pattern of natural distribution in small, separated populations. African land races of G. robusta are descended from initial introductions in the late 1800s and early 1900s and have developed in different countries in partial or total isolation from one another, and mean heterozygosity and other genetic diversity measures were substantially lower for the African land races than for the natural populations. The complete absence of a common allele in the two Madagascar populations suggested that these populations were derived from a very narrow genetic base. Provenance-progeny trials testing seed collections from across the natural range have recently been established in several countries including Australia, Kenya and Rwanda.
Physiology and Phenology
Flowering commences in October in lowland occurrences in the native range, and seed is mature by the end of December. At high elevations, flowering and seed production occur 4-6 weeks later (Harwood, 1992a). In the equatorial highlands where rainfall distributions are bimodal, flowering is much less synchronized. In western Kenya, for example, there are two main flowering peaks in March-May and August-October, with some trees flowering throughout the year (Kalinganire et al., 1996). In its native range, the species is partly deciduous, losing much of its canopy in the dry spring months (September-October) and recovering in early summer. In the equatorial highlands there is no clear seasonal pattern of foliage loss.
Under favourable conditions, flowering and seed production of G. robusta commence at age 2-3 years (Kalinganire et al., 1996). In subtropical and warm temperate latitudes, first flowering may occur at 4-6 years (Swain 1928). Flowering in the native range occurs for a few weeks in October-November but in equatorial latitudes the species may flower at any time of year and in Jakarta, Indonesia, it does not flower (World Agroforestry Centre, 2002). There are about 40,000 viable seeds/kg. The species seeds heavily and regenerates strongly after site disturbance in rainforests and along riverbanks.
The breeding system in natural populations was found to be highly outcrossing in isozyme studies of progeny arrays (Harwood et al., 1992). Multi-locus estimates of outcrossing rates of 0.97 and 0.86 were obtained for two natural populations. Observations and experimental studies in a planted stand in western Kenya (Kalinganire et al., 1996) confirmed that the species is fully outcrossing and self-incompatible, and that nectivorous birds are the principal pollinating agents in Kenya, as was found in Australia (Brough, 1933). According to the World Agroforestry Centre (2002) pollinating agents also include honeybees and tree-living marsupials (Phanlangeridae) but Kalinganire et al. (2001) report that ants and bees are nectar robbers that rarely come into contact with the stigmas. The period from the start of inflorescence development to anthesis is about 40 days. Stigmas become receptive 1 day after anthesis, and the period from fertilization to fruit maturity is about 60 days. Hot, dry weather stimulates seed release once the fruits are mature. G. robusta may also vegetatively reproduce by root suckering (World Agroforestry Centre, 2002).
The distribution is in the warm humid to warm sub-humid climatic zones. Climatic analysis of the natural occurrences and locations where the species is successfully grown as an exotic has been carried out by Harwood and Booth (1992) and a modified description of climatic requirements was prepared by CSIRO (Booth and Jovanovic, 2000). Within its natural distribution range, climate varies widely because of the substantial altitudinal range (0-2500 m) and the rainfall gradients created by prevailing weather systems interacting with rugged topography. Mean annual rainfall is in the range 700-2400 mm, but droughts of 6 months or longer will cause death or damage to established trees, although towards the hotter extremes of the tolerated temperature range, the dry season should be no longer than 4 months for good growth.
. It has some resistance to frost, as during the winter months in temperate latitudes, G. robusta can survive temperatures down to -8°C with little or no damage, but milder frosts of only -2°C or so will cause damage during the growing season.
While it occurs naturally along riverbanks and will survive short periods of flooding by moving water, G. robusta will not grow on poorly-drained, swampy sites where waterlogging occurs for more than a few days at a time. The species is more common on rather fertile soils such as those derived from river alluvia or basalts but will grow on shallower, less fertile soils derived from sedimentary material. Best growth is obtained on sandy loam, loam and clay loam soils and it performs poorly on heavy clays. The pH range for good growth is around 4.5 to 7.5. In highly acid soils, symptoms of boron deficiency (Smith, 1960) and manganese toxicity (Child and Smith, 1960) have been observed. While the species is frequently planted as a windbreak around plantations of food and cash crops, it cannot withstand severe gales or persistent strong winds without damage to the branches. Even low-intensity ground fires will kill seedlings and young trees.
G. robusta is present in riverine gallery rainforest of the Castanospermum australe (black bean) alliance, the natural vegetation along larger Australian rivers. The frequency of mature trees has, however, been reduced across much of the natural range as a result of past logging and land clearance. G. robusta is also associated with river she-oak (Casuarina cunninghamiana) along smaller streams where rainforest has not developed. The second major habitat type for the species is the Araucarian vine forests and vine thickets dominated by Araucaria cunninghamii. These forests contain rainforest elements but are subject to occasional fires. The species is not known to form symbiotic associations with soil bacteria or mycorrhizal fungi, although it develops proteoid roots that are believed to enhance nutrient uptake.
Latitude/AltitudeTop of page
|Latitude North (°N)||Latitude South (°S)||Altitude Lower (m)||Altitude Upper (m)|
Air TemperatureTop of page
|Parameter||Lower limit||Upper limit|
|Absolute minimum temperature (ºC)||-8|
|Mean annual temperature (ºC)||13||24|
|Mean maximum temperature of hottest month (ºC)||25||38|
|Mean minimum temperature of coldest month (ºC)||6||16|
RainfallTop of page
|Parameter||Lower limit||Upper limit||Description|
|Dry season duration||0||7||number of consecutive months with <40 mm rainfall|
|Mean annual rainfall||700||2400||mm; lower/upper limits|
Soil TolerancesTop of page
Notes on Natural EnemiesTop of page
In the humid tropical lowlands and other regions with high humidity, G. robusta is vulnerable to attack by fungal diseases such as Botryosphaeria dothidea in Guatemala (Schieber and Zentmeyer, 1978) and Corticium salmonicolor [Erythricium salmonicolor] in Karnataka, India (Nayar, 1987). Pathogenic fungi such as a Amphichaeta grevilleae [Seimatosporium grevilleae] (Loos, 1950; Venkataramani, 1954), Cercospora sp. (Chiddawar, 1956) and Phyllosticta sp. (Rao, 1961) have been observed to cause considerable damage to leaves and stems of young plants in Sri Lanka. In lowland environments in the Caribbean, G. robusta is severely attacked by the scale insect Asterolecanium pustulans (Martorell, 1940), effectively precluding its use there. Attack by termites can be a problem when the species is planted on dry sites in Africa.
Means of Movement and DispersalTop of page
The seeds of G. robusta are dispersed by wind (Smith, 1998). G. robusta has gained widespread popularity in warm temperate, subtropical and tropical highland regions of many countries, originally as a shade tree for tea and coffee and now as an agroforestry tree for small farms (Harwood, 1989) and intentional introduction is the principal means of long-distance dispersal.
Pathway CausesTop of page
|Agriculture||Extensively planted as “shade tree” in tea and coffee plantations||Yes||Yes||Harwood et al., 1997|
|Escape from confinement/ garden escape||Prolific seed producer. Escaped from cultivation||Yes||Yes||Orwa et al., 2009|
|Forestry||Common element introduced in agroforestry systems||Yes||Yes||Orwa et al., 2009|
|Hedges/ windbreaks||Often planted to be used as windbreak tree in plantations||Yes||Yes||Orwa et al., 2009|
|Ornamental purposes||Ornamental shade tree||Yes||Yes||Orwa et al., 2009|
|Timber trade||G. robusta yields a medium-weight hardwood||Yes||Yes||Orwa et al., 2009|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
Economic ImpactTop of page
Its use as tea shade has been largely discontinued in Kenya and Rwanda because of the risk of Armillaria and other root pathogens spreading from dead G. robusta roots to those of the tea plants (Tea Research Institute of East Africa, 1969).
Environmental ImpactTop of page
G. robusta drops much leaf and fruit litter (Gilman and Watson, 1993). Its leaves produce an allelopathic substance that inhibits the establishment and development of native species. G. robusta also causes changes in patterns of nutrient cycling (ISSG, 2015).
Smith (1998) reports allelopathic effects that restrict the growth of other plants including other individuals of G. robusta. Webb et al. (1967) considered that an auto-allelopathic compound associated with the living roots of G. robusta was responsible for the poor performance of plantations in Australia. The good growth of many successful plantations and woodlots in Africa suggests that in most plantations such an effect is minor, if present at all. Henderson (2001) regarded G. robusta as a potential transformer of habitats.
Social ImpactTop of page
The sap of G. robusta is an irritant to skin and eyelids (Henderson, 2001) and its pollen may trigger hay fever (Motooka et al., 2003).
Risk and Impact FactorsTop of page
- Competition - shading
- Pest and disease transmission
- Altered trophic level
- Damaged ecosystem services
- Ecosystem change/ habitat alteration
- Modification of nutrient regime
- Modification of successional patterns
- Negatively impacts human health
- Reduced native biodiversity
- Has high reproductive potential
- Highly adaptable to different environments
- Highly mobile locally
- Invasive in its native range
- Long lived
- Proved invasive outside its native range
- Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
Likelihood of entry/control
- Highly likely to be transported internationally deliberately
UsesTop of page
G. robusta is a common element in agroforestry and forestry applications, and is one of the most important trees for agroforestry in the tropical highlands of East and central Africa (Harwood, 1992b). It is commonly planted as a boundary tree around the perimeter of small farms, in a single row at 2-2.5 m spacing. It is also planted in rows between small fields, and as scattered individuals over crops such as coffee and maize (Spiers and Stewart, 1992). G. robusta has been planted as a component of contour rows in a number of farming systems that aim to conserve soil on sloping lands in the tropical highlands (e.g. Neumann, 1983). The use of the leaves as a mulch is frequently advocated and practised, and studies have shown that this can reduce soil losses on sloping land (Omoro and Nair, 1993).
The dense, brilliant golden-yellow or orange flower heads, attractive silver, fern-like leaves and symmetrical crown encourage widespread and increasing use of the species as an ornamental. It is used in many tropical and subtropical countries for park and roadside plantings. In the UK and Europe it is commonly available as an indoor plant. In Australia, other Grevillea species and interspecific hybrids are commonly grafted onto rootstocks of G. robusta to produce ornamental planting stock. This practice takes advantage of the resistance of the root system of G. robusta to Phytophthora cinnamomi and its non-susceptibility to phosphorus toxicity, which is a problem for most other Grevillea species (Burke, 1983).
From the late 1800s onwards, G. robusta has been planted extensively as high shade for tea and coffee plantations, and this use continues in many countries. The trees are often pollarded to produce a spreading crown, and have a typical working life of 40-50 years before they become senescent and must be replaced (Rao 1961). Shade trees of G. robusta provided effective protection against frost that caused extensive damage to open-grown coffee plants in southern Brazil at planting densities of 71 and 119 trees per hectare, but not at 26, 34 and 48 trees per hectare (Baggio et al., 1997), and the economic productivity of coffee and G. robusta wood at 34, 48 and 71 trees per hectare was greater than that of coffee in unshaded plantations. Only at 119 trees per hectare was there a significant (15%) reduction of total coffee production to age 10 years, relative to unshaded stands.
The sawn timber is of medium strength and is used for furniture, packing cases, flooring, panelling, plywood and the manufacture of small wooden items such as pencils (Bolza and Keating, 1972; Skolmen, 1974). The wood produces short-fibre pulp of acceptable quality (Ghosh, 1972) but has not been used for pulp production on a commercial scale. Poles are used for house construction, scaffolding and rafters in rural areas (Spiers and Stewart, 1992). The branches and twigs are used for firewood and charcoal (Mbuya et al., 1994).
In addition to their use as a soil mulch, the leaves of G. robusta are used by some farmers in the Embu district of Kenya as a fodder supplement for cattle in the dry season when other fodder sources are scarce (Spiers and Stewart, 1992). They are also used as bedding in livestock stalls. The leaves contain a number of useful chemical compounds, in particular rutin which has pharmacological applications (Cannon et al., 1973). However, the rutin concentration of 0.6% of leaf dry weight is too low to be of commercial value. The gum produced from the wood of trees that are stressed or wounded may have commercial value (Anderson and de Pinto, 1982).
Uses ListTop of page
Animal feed, fodder, forage
- Boundary, barrier or support
- Erosion control or dune stabilization
- Graft stock
- Shade and shelter
Human food and beverage
- Carved material
- Miscellaneous materials
- Source of medicine/pharmaceutical
Wood ProductsTop of page
For light construction
Industrial and domestic woodware
Sawn or hewn building timbers
Prevention and ControlTop of page
G. robusta is vulnerable to fire, which may be used as a means of control. Also, grazing with goats can contribute to the control of G. robusta (PIER, 2002). Herbicides such as triclopyr ester, picloram and glyphosate may be used against G. robusta, with modes of application including basal bark applications, cut surface, frill cut and continuous frill techniques, though it appears to be resistant to 2,4-D and dicamba (PIER, 2002). Smith (1998) reports that biological control has not been investigated on Hawaii because of conflicts with forestry and farming industries.
ReferencesTop of page
Acevedo-Rodríguez P, Strong MT, 2012. Catalogue of the Seed Plants of the West Indies. Smithsonian Contributions to Botany, 98:1192 pp. Washington DC, USA: Smithsonian Institution. http://botany.si.edu/Antilles/WestIndies/catalog.htm
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ContributorsTop of page
13/04/15 Updated by:
Julissa Rojas-Sandoval, Department of Botany-Smithsonian NMNH, Washington DC, USA
Top of page
- = Present, no further details
- = Evidence of pathogen
- = Widespread
- = Last reported
- = Localised
- = Presence unconfirmed
- = Confined and subject to quarantine
- = See regional map for distribution within the country
- = Occasional or few reports