Silky Oak, Southern Silky Oak
This species occurs in northern New South Wales and southern Queensland from near the coast to about 150 km inland. It is now relatively rare in its natural state. The latitudinal range is 26-30o S and the altitudinal range from near sea level to 1100 m. (QLD, NSW)
A fast-growing, single-stemmed tree usually 20-30 m in height and about 80 cm in diameter but sometimes larger. The dark grey bark is furrowed in a lace-like pattern. Young branchlets are angular, ridged and maybe slightly hairy. The fern-like foliage is very distinctive. The leaves are 10-34 cm long and 9-15 cm wide, pinnate to bipinnate, green on the upper surface and pale and silky below. The bright orange flowers, about 2 cm long, are borne in many pairs along the flower spikes, in October to November. Fruits are two-seeded follicles (a dry fruit which splits to release the seeds), 2 cm long. Seeds are 13-19 mm long and 8-10 mm wide with a papery wing around the brown central seed. Mature seed is found in December and January. There are about 42 000 viable seeds per kilogram and they germinate readily without pre-treatment.
Ecology/Way of Life:
The climate is warm, humid to sub-humid but varies considerably because of the altitudinal range. Only occasional frosts occur in most localities but this species will tolerate temperatures as low as -8o C. Mean annual rainfall is 750-1700 mm with a summer maximum. Trees growing on stream banks have better access to soil moisture than indicated by the rainfall data; it is typically found along streams but also on dry hillsides. It grows in rainforest often associated with Araucaria spp. (hoop pines and others) and on riverbanks with Casuarina cunninghamiana. It is commonest on rather fertile soils derived from river alluvium or basalt but its special proteoid roots enable it to tolerate less fertile conditions. Proteoid roots, typical in this family, are short, densely clustered lateral roots involved in extracting mineral bound nutrients in infertile soils.
Interaction with Humans/Threats:
Grevillea robusta is popular in warm temperate and tropical highlands of many countries, formerly a shade tree for tea and coffee and now as an agroforestry tree for small farms. It is very common on small farms in the Kenyan highlands where it apparently less competitive with maize and other crops than other tree species. It provides timber, poles, firewood and leaf mulch and is very easy to propagate and manage. Its use in Australia in earlier days for furniture has been curtailed due to the diminished supply from natural stands. It is an attractive ornamental and is also used as an indoor plant in Europe. The flowers are a rich source of nectar for honey plant. It has the potential to become a weed and has caused some problems in Hawaii.
Grevillea robusta was named in 1830 by the explorer and botanist, Allan Cunningham; the genus name honours Charles F. Greville (1749-1809), co-founder of the London Horticultural Society; the species name, from the Latin robustus = hard, strong or robust, refers to the large size of this species of Grevillea, many of which are shrubs.
Boland, D.J., Brooker, M.I.H., Chippendale, G.M., Hall, N., Hyland, B.P.M., Kleinig, D.A., Johnston, R.D. and Turner, J.D. 1984. Forest trees of Australia. 4th ed. Nelson and CSIRO, Melbourne. 687p.
Doran, J.C. and Turnbull, J.W. (eds.) 1997. Australian trees and shrubs; species for land rehabilitation and farm planting in the tropics. ACIAR Monograph no. 24. Australian Centre for International Agricultural Research, Canberra. 384p.
Harwood, C.E. 1989. Grevillea robusta: an annotated bibliography. CSIRO, Canberra and International Council for Research in Agroforestry (ICRAF), Nairobi.
Harwood, C.E. (ed.) 1992. Grevillea robusta in agroforestry and forestry. International Council for Research in Agroforestry (ICRAF), Nairobi. 190p.
Topics:Honey Soils Timber Plant structure Agroforestry Firewood Ornamental Fodder Firewood Germination
Text & map from Australian Trees and Shrubs, courtesy Australian Centre for International Agricultural Research; text edited by J. Turnbull; photo courtesy David Lea.
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