Thursday, May 5, 2011

Kurrajong - The Perfect Shade Tree

Brachychiton populneus
Kurrajongs are dry rainforest trees which take the “dry” more literally than most. We see them far out on the western plans, as in this specimen in a Western Downs town which is doing such a good job of shading a cool Queensland-style house.

Their deep roots help them survive droughts. Deep roots also mean (as with other dry rainforest trees) they are less likely to create problems for buildings and other structures. However the roots do seek water, so should not be planted closer than 3.5m to water pipes or sewage lines.

Another part of the secret of kurrajongs’ drought survival is the capacity to drop their leaves in dry winters. The degree of leaf drop depends heavily on the availability of soil moisture, so in wet winters they may lose very few of them. This photo was taken near Toowoomba in June 2008, which was probably the driest of all the dry times in our recent long drought.

The species can grow tall, as shown in this bushland example, also near Toowoomba. Usually, rainforest species only grow this shape if surrounded by other trees. It is possible that this very old tree spent its youth in a quite different environment from the grassy eucalypt woodland you can see in this modern photo. A great deal of such country, along the Great Dividing Range and the valleys to the west of it, was once dry rainforest. It was cleared so long ago that we have forgotten it was ever there. The shape of this tree may indicate that this was the case here.

Kurrajongs have a very pretty flower, and unlike some of the other Brachychiton species (notably the flame tree Brachychiton acerifolius), they don’t link flowering with leaflessness.
This photo was taken in October, and the tree had a shady green canopy.
While mature trees can put out a great show of flowers, it won’t happen every year, so the kurrajong’s ornamental qualities are largely based on its cool green canopy.

As with many Australian trees, their juvenile leaves differ from the leaves on older trees. These leaves are from a very young tree.

The shape on the right is the one we most commonly see, while the one on the left only occurs on mature trees.

I photographed this paddock of kurrajongs at Gilgandra. They were neatly pruned, and I wondered why. Then we drove on to visit the Dubbo Western Plains Zoo, where we watched giraffes being fed with kurrajong leaves. No doubt this explained the mystery!

The photo is such a good demonstration of the results that we can get from pruning most of our dry rainforest tree species. You can see how well these Australian native trees would grace a formal garden. They can be kept to a size suitable for the suburbs, and make very good street trees, as seen in Goondiwindi.

This young kurrajong in Crows Nest is being groomed for the job.

Pastoralists have long recognised the value of kurrajong leaves as emergency drought fodder for their stock. Unfortunately they have all too often solved their problem by cutting down whole trees, a curiously short-sighted solution. The result is that, while we see many young trees in the Toowoomba district, large, old ones are rare.

Kurrajongs are host trees for one of our larger butterflies, the tailed emperor (Polyura pyrrhus sempronius). We caught this delightful pair “kissing” in the bushes at Kwiambul National Park last weekend. (Butterflies kiss with their antennae.)

Brachychitons are recognised as being fire resistant. A row of them on a fenceline downhill from the house, in bushfire-prone areas, could make all the difference (though of course no tree will resist a very large bushfire). A green canopy catches sparks, and might just be the factor that saves a house from catching alight.
A “home among the kurrajongs” is a very Australian image, and considerably safer than the one among the gum trees which is celebrated in the well-known song.
Kurrajongs can be transplanted at up to 8 years old.


Stan Lusby said...

Thanks for the info. I witnessed Kurrajong in the drought of 1966. I had only been in the country for five weeks as a young immigrant surveyor and wondered then why they were not used in swathes as fire retardant protection for human settlements against the eucalypt killer fires like you have in NSW at the moment.

"Ignorance is not lack of knowledge but the mischievous desire to ignore."

Stan Lusby
Hsven Street
South Island NZ

Patricia Gardner said...

Hi Stan.
I am interested to hear your point of view. This is certainly a tree that performs well in the drought.
We do see Brachychitons used as minor firebreaks far more than you would have seen in here in 1966.
The problem with them is that they are not useful, in enough other ways, for it to be regarded as financially viable to sacrifice the amount of land that would be needed for firebreaks on a scale would have any effect on the kind of fire they're having in NSW at present. A hot fire in Eucalyptus country can jump many kilometres through the air to another stand of eucalypts. One would need great, long belts of kurrajongs many kilometres wide - not really a practical proposition.
A nice thought, though.

Anonymous said...

Hi Trish
I am planning to grow kurrajongs as an ember catch break around our house in the Adelaide Hills. Can the kurrajong tolerate frosts?
Thanks in advance.

Patricia Gardner said...

Hi Jules.
They are said to be able to tolerate frosts to at least -5°C.
do you know how cold your frosts are?
If you haven't already done it, next winter you might like to leave a maximum-minimum thermometer outside overnight in winter, in selected places (on a stake so it sits a few inches above the ground).
there are always quite wide variations in the temperatures around any given site, depending on the degree of slope and the amount of shelter. It is likely even to include some frost-free spots. Knowing your frosts can be a useful tool in choosing the right plants for the right places.
Of course another way of discovering whether a plant is likely to survive in your area is to find out if it grows naturally there. Choose a site with similar slope, aspect and degree of shelter, and Bob's your uncle!
Here's hooping Kurrajongs work for you!