The Perfect Windbreak

Scrub Wilga
Geijera salicifolia
Family: RUTACEAE
It was so cold on the Darling Downs west of Toowoomba yesterday! The weather report told us the maximum temperature was 14°, and there was a dry, bone-chilling breeze.

However at Irongate Reserve, in the sunny clearings sheltered by the scrub, the weather was delightful. The little birds and butterflies were going about their business as usual, and we felt we could ignore the wind, which was merely providing the musical accompaniment, singing its she-oak song well above our heads.
One of the most effective windbreak trees at Irongate is the scrub wilga.
(Don't confuse it with the very narrow-leaved common wilga, Geijera parviflora, which also occurs at Irongate, but is better known from the plains further west).
The scrub wilga’s great virtue is the density of its dark-green canopy, which it maintains year-round and through the worst droughts. Like so many of our dry rainforest/vine scrub species, scrub wilgas have very deep roots which make use of deep-down groundwater. This lets them be even more resilient in droughts than some of our toughest eucalypts. Over the last few years we have seen Eucalypts dying in paddocks west of Toowoomba, while the nearby “scrub trees” were looking as lush and green as ever.
Here are some roadside specimens growing near Mt Tyson, showing the typical canopy-to-the-ground formation of younger trees, which makes them such good windbreaks. As you can see, they are very happy snuggling up close to the mountain coolibah Eucalyptus orgadophila, making a little clump with obvious bird-appeal.



This garden-grown specimen at Gowrie Junction is known to be 27 years old.






With age, the plants develop into pretty little shade trees. I had thought that pruning by cattle must help with the shape (as pruning by sheep does with the common wilga) but I have been assured by a cattle farmer that cattle won’t eat the leaves of scrub wilgas. They are often left in paddocks as shelter for cattle.
This one has had a hard life, with the soil around it well-compacted by stock.
Paddocks in this district were first cleared about 1880, and it is possible that this tough little tree has been roughly this shape and size for 120 years or so. With many of our vine scrub tree species, growth in tough conditions is very slow indeed, and some very old trees are deceptively small. If this one became part of somebody’s garden, and its soil give a bit of extra care, it would probably start to grow again.
Like many of our local native trees, scrub wilgas are very long-lived. The one at the foot of this article grows at at Gowrie Junction. It has never been dated, but could well be 300 years old.
Don't believe the story - usually told as a justification for planting foreign species - that Australian natives are "short-lived"! (It's partly true, of course. The short-lived species are indeed short lived!!! However, only someone who doesn't know much about Australian natives could think that Australia is more richly endowed with short-lived species than any other part of of the world.)
I imagine, though, that a gardener who wanted a little shade tree, could discourage the early tendency to low branching, by judicious use of the secateurs.
Scrub wilgas have a long flowering season. They were beginning to come out in early April, and are at their best around the district in June and July. They are a mass of flowers at Irongate at present, providing food for insects, which in turn provide useful over-winter food for many little birds. The shiny black seeds which follow will provide a further food source.
Botanists tells us that there two varieties (a broad-leaved one, var. latifolia, and a narrow-leafed one, ver. Salicifolia) however here above the Great Dividing Range we notice that there seems to be a continuum. Close to the range they are broad-leafed, and as we move west they become progressively narrower in the leaf.






This is what the leaves look like at Highfields....











...and this is a photo I took at Jondaryan in April. Note the much narrower leaves....









...while the ones at Irongate are somewhere in between.

This picture shows the deep grey twiglets, which, together with the dark canopy, give the whole tree a rather dark look from the far. This must be part of the reason why the local common name for this tree is “black alley”.




The crushed leaves have a delicious plum-pudding smell. This plant is in the same family as citrus trees, and like them is a host plant for our largest native butterfly, the orchard butterfly (Papilio aegeus).
I am told that the butterflies grow larger on their native host plants than they do on introduced citrus species.
Irongate Reserve is in Wallingford Road, between Pittsworth and Mt Tyson.