Tree of Merit: Silky Oak
(Grevillea robusta)
Silk y oak (Grevillea robusta) is a much-loved Australian
native. Mostly known for its strong timber, it is used exten-
sively for furniture and woodworking. This upright tall tree
(up to 35m/115 feet) can be found f rom Far Nor th New South
Wales to Mar yborough in Queensland out west to the Bunya
Mountains. It is grown in most countries around the world
not just for its timber but for its beautiful features.
The tree has three distinguishing features that make it a favor-
ite ornamental as both a street tree and a park specimen tree.
( Within Australia it is also used extensively for revegetation of
natural areas.) Its silver fernlike leaves can grow up to 40 cm
(16 in) long; they are dark green above and white/silver under-
neath. The golden orange f lowers with comb-like inf lorescences
are seen in October. It is easily propagated f rom seed, so there
is no need for cut tings. F inally, its dark grey to black , deeply
f issured bark is another feature that stands out with this tree.
In moist climates, silk y oak is evergreen, but in drier areas it
turns deciduous. Due to its ultimate height it is not suitable in
all street tree planting sites. For the best health it prefers ade-
quate space to grow without compaction or root disturbance,
which can be rare to f ind in urbanized areas. It is only under
stressed conditions that this tree requires maintenance for the
removal of deadwood—making it a per fect park specimen tree.
The tree does star t to hollow out f rom the longicorn beetle at
around 40 years of age. The beetle eats at the hear t wood but
rarely does this impact the structural integrit y of the tree unless
root decay connects up with the internal decay over time. This
decay will be ref lected in the fair to poor health of the can-
opy—and this symptom will give the arborist enough time to
assess the extent of the decay using a sounding hammer. It
is preferable to keep the tree as long as possible if no target
exists due to its habitat value for insects and small reptiles.
by Sitara Gare, Arboriculture Coordinator,
Brisbane City Council, Australia
Sitara Gare is an
Arboriculture Coordinator
for Brisbane City Council,
Australia's largest munic-
ipal council. Her arbori-
culture passions lie in edu-
cating the public about all
the benefits of trees.
Photos top to bottom: showy flowers,
interesting seedpods, fernlike foliage, and
fissured bark. Photos on this page courtesy of
selectree.calpoly.edu
www.urban-forestry.com 39
