What is silky oak

Different birds will visit the tree at different times — honeyeaters for the nectar and cockatoos and lorikeets for the seeds, Where is Silky Oak found? Fast facts: Indigenous people used to make a sugary drink from silky oak flowers by dipping the whole flower heads into water to wash the nectar off. Silky Oaks have large shallow roots that will grow towards water and can become a problem if they are growing too close to buildings or pipes. Silky Oaks — the full story The Silky Oak Grevillea robusta is a very popular native tree in Australian gardens and can grow to 20 metres and live for up to years.

Different birds will visit the tree at different times — honeyeaters for the nectar and cockatoos and lorikeets for the seeds, Did you know? Tips to help Backyard Buddies. Habitats invaded by this species in South Africa include forest edges, coastal forests, disturbed sites, savannah and riparian areas Henderson, It is very popular in agroforestry systems and often planted to provide shade for tea and coffee plantations Harwood et al.

Genetics The chromosome number reported for G. No records of hybrids between G. Isozyme studies of natural populations and land races Harwood et al. 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 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. 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 weeks later Harwood, a.

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.

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. Reproductive Biology Under favourable conditions, flowering and seed production of G. In subtropical and warm temperate latitudes, first flowering may occur at years Swain 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, 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.

Multi-locus estimates of outcrossing rates of 0. Observations and experimental studies in a planted stand in western Kenya Kalinganire et al. According to the World Agroforestry Centre pollinating agents also include honeybees and tree-living marsupials Phanlangeridae but Kalinganire et al.

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. Environmental Requirements 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 and a modified description of climatic requirements was prepared by CSIRO Booth and Jovanovic, Within its natural distribution range, climate varies widely because of the substantial altitudinal range m and the rainfall gradients created by prevailing weather systems interacting with rugged topography.

Mean annual rainfall is in the range 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. While it occurs naturally along riverbanks and will survive short periods of flooding by moving water, G. 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. In highly acid soils, symptoms of boron deficiency Smith, and manganese toxicity Child and Smith, 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. Associations G. The frequency of mature trees has, however, been reduced across much of the natural range as a result of past logging and land clearance.

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.

In the humid tropical lowlands and other regions with high humidity, G. Pathogenic fungi such as a Amphichaeta grevilleae [ Seimatosporium grevilleae ] Loos, ; Venkataramani, , Cercospora sp.

Chiddawar, and Phyllosticta sp. Rao, have been observed to cause considerable damage to leaves and stems of young plants in Sri Lanka. In lowland environments in the Caribbean, G. Attack by termites can be a problem when the species is planted on dry sites in Africa.

The seeds of G. 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. Its leaves produce an allelopathic substance that inhibits the establishment and development of native species. Smith reports allelopathic effects that restrict the growth of other plants including other individuals of G.

Webb et al. 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 regarded G. The sap of G. It is commonly planted as a boundary tree around the perimeter of small farms, in a single row at It is also planted in rows between small fields, and as scattered individuals over crops such as coffee and maize Spiers and Stewart, Neumann, 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, 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. This practice takes advantage of the resistance of the root system of G.

From the late s onwards, G. The trees are often pollarded to produce a spreading crown, and have a typical working life of years before they become senescent and must be replaced Rao Shade trees of G. 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, ; Skolmen, The wood produces short-fibre pulp of acceptable quality Ghosh, 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, The branches and twigs are used for firewood and charcoal Mbuya et al.

In addition to their use as a soil mulch, the leaves of G. 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.

However, the rutin concentration of 0. The gum produced from the wood of trees that are stressed or wounded may have commercial value Anderson and de Pinto, Due to the variable regulations around de registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control.

Pesticides should always be used in a lawful manner, consistent with the product's label. Also, grazing with goats can contribute to the control of G. Herbicides such as triclopyr ester, picloram and glyphosate may be used against G.

Smith reports that biological control has not been investigated on Hawaii because of conflicts with forestry and farming industries. Catalogue of the Seed Plants of the West Indies. Smithsonian Contributions to Botany, pp. The agronomic and economic performance of banana, bean and tree intercropping in the highlands of Burundi: an interim assessment. Agroforestry Systems, 31 3 Gum exudates from the genus Grevillea Proteaceae. Carbohydrate Polymers, Anon, Alien invasive plant species of Jamaica.

Clearing house mechanism. Productivity of southern Brazilian coffee plantations shaded by different stockings of Grevillea robusta. Agroforestry Systems, Binggeli P, Invasive woody plants. BMCS, Schedule 6, Weeds of the Blue Mountains. Blue Mountains Conservation Society, Australia.

Forest trees of Australia. Bolza E, Keating WG, African timbers - the properties, uses and characteristics of species. Booth TH, Jovanovic T, Brough, P, The life history of Grevillea robusta Cunn. Burke D, Growing grevilleas. Sydney, Australia: Kangaroo Press.

Buss CM, The potential threat of invasive tree species in Botswana. Phenolic constituents of [the leaves of] Grevillea robusta Proteaceae. The structure of robustol, a novel macrocyclic phenol. Australian Journal of Chemistry, 26 10 ; 50 ref. Charles Darwin Foundation, Database inventory of introduced plant species in the rural and urban zones of Galapagos. Galapagos, Ecuador: Charles Darwin Foundation. Chiddarwar PP, A new species of Cercospora on an economic host. Current Science, 25 8 Child R, Smith AN, Manganese toxicity in Grevillea robusta.

Nature, Lond. A checklist of the total vascular plant flora of Singapore: native, naturalised and cultivated species. Plant invaders: the threat to natural ecosystems. European Invasive Alien Species Gateway.

Plant resources of southeast Asia. Auxillary plants. Leiden, Netherlands: Backhuys. Ghosh KL, Pulping characteristics of Silver Oak [Grevillea robusta]: unbleached kraft paper for wrapping and packing purposes. Indian Pulp and Paper, 26 11 ; 12 ref. Grevillea robusta: silk-oak. University of Florida Extension.

Fact Sheet ENH Harwood CE, Grevillea robusta: an annotated bibliography. Grevillea robusta in agroforestry and forestry: proceedings of an international workshop. Natural distribution and ecology of Grevillea robusta. In: Harwood CE, ed.

Grevillea robusta A. No 11, Auxiliary Plants. The Netherlands: Backhuys Publishers; Isozyme studies on the breeding system and genetic variation in Grevillea robusta. Status of Grevillea robusta in forestry and agroforestry. Genetic differentiation in natural provenances of Grevillea robusta. Australian Journal of Botany, Harwood CE, Owino F, Choose one of the following categories to see related pages:.

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