Our Bushland Diary

Friday, May 20, 2011

seasons of ancient trees

May brings warm clear days interspersed with showers.  The Western name for this season is Autumn, traditionally a time when deciduous trees lose their leaves after a show of fire and earth colours.  Why do trees lose their leaves?  Recycling nutrients, avoiding snow or extreme heat, protecting their roots with the fallen leaves are some of the reasons that science has illuminated.  In many of the colder climates of the Northern Hemisphere, trees have bare branches during Winter, and seem to come back to life with a flurry of flower buds and leaves in Spring.

In Western Australia, trees behave very differently to those of the Northern Hemisphere.  Our local native trees don't lose their leaves in Autumn.  Instead, many of them, such as the Firewood Banksia (Banksia menziesii), start flowering.  This beautiful tree has thick leathery leaves of blue-green about 20cm long. The “flower” is actually an inflorescence, composed of hundreds of tiny flowers packed close on a single cone.  When in bud, the inflorescence is pinkish green.  The flowers start opening from the base of the cone and slowly work their way to the top, changing colour from a silvery reddish pink to bright yellow over several weeks.  (That's the usual colour form.  See this post from May 2009 to view photos of the other, rarer, colour forms.)  The spent flowers darken to a shaggy brown, then fall off to reveal the hard woody cone in the middle.

Banksia menziesii - four "flowers" in different stages of development
Firewood Banksia belongs to an ancient family of plants called Proteaceae, along with Grevilleas, Hakeas, Dryandras and Synapheas. The plants in this family are usually pollinated by birds and small mammals such as the tiny Honey Possum, rather than insects.

Next time you're visiting the WA Museum, have a look at the fossil Banksia on display in the "Diamonds to Dinosaurs" exhibition.  It's a rather sobering experience to view leaves and flower cones from millions of years ago, set in stone – they are almost identical to what you can see alive in the bush today. 

[The above is an edited extract from an article published in local newspaper "Windows on Ellenbrook" in May 2008.  Photo and text by L. Dalgliesh]

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