Thursday, September 1, 2011

Mountain Coolibah

Eucalyptus orgadophila
Just west of Toowoomba, on the blacksoil slopes, is Mountain Coolibah Country. Where you see them growing naturally, you know that the soil pH is approximately neutral, and, compared with soils further west, has a good proportion of phosphorus

Here’s a typical tree. Mountain coolibahs always seem to have a bit of a lean, in the main trunk, and then lesser branches have grown out of the upper side of the leaning trunk. The dark grey fibrous bark persists on the lower trunk, but the beautiful pale branches shed their bark every spring.

The mountain coolibahs are flowering at present. The flowers are not conspicuous, but the air around them is humming with the sound of the European honeybees, gathering the nectar and pollen.

If you live in mountain coolibah country, and want to plant a Eucalypt, you can hardly do better than this tree. It’s very resistant to both frost and drought, koalas love the leaves, and it's a good honey tree. Older trees make good hollows, which are safe havens for gliders and other shy bush creatures.
The hollows are also a popular habitat for our most drought-hardy orchid, the beautiful black orchid of the west, Cymbidium canaliculatum, which survives drought by sending its great mass of roots deep into the hollows of this tree.

As a young thing, mountain coolibah has these pretty blue-green leaves. Note that they are broader than the adult leaves, and have rounded ends with a distinctive notch.

In the original mountain coolibah woodlands, kangaroo grass Themeda triandra, which is now so fashionable for landscape gardening in the cities, was the dominant grass. Overgrazing has caused it to be supplanted by Queensland bluegrass, Dichanthium sericeum. Planting kangaroo grass with this tree in a garden setting would be a nice touch.

It is a fire-resistant tree, and can be part of a “fire ecology”, that type of local vegetation whose health is maintained by regular burning. However when fire is not a regular event in its environment, it shares its root-space with “scrub trees” - those small, shady dry rainforest trees such as scrub wilga Geijera parviflora, and gumby gumby Pittosporum angustifolium, which love to grow on the same soil.

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