Droughts and wildfires are nothing new or unnatural; but they are becoming more frequent and more dangerous. Parched moorland, scrub, and heathland are particularly prone to heat and drought, and it doesn’t take much to ignite them. Once alight, they create their own winds and are difficult to stop, with potentiality devastating consequences. Close-packed, unmanaged conifer plantations are also highly vulnerable. With waxy needles and resinous sap, stems close enough to ignite one to another and carpets of dead, dry kindling beneath, fifty years’ growth can be lost in mere minutes. Native British broadleaf woodlands are much less vulnerable to fire because they create the right conditions for their own success: cool shade, high humidity and abundant green foliage. Firebreaks created from belts or copses of broadleaf trees would slow and interrupt the spread of wildfires and provide refuges for wildlife.
In parts of the world where drought and wildfires are commonplace, trees have adapted to the inevitable, as is the case with the fantastic Mulga Acacia (Acacia Aneura).
Any species successfully colonising the deserts of Australia must be tough, resilient and highly adapted. The thornless Mulga Acacia does not bear true leaves but flattened, thick-skinned pointed leaf stalks or phyllodes, covered in tiny hairs, which grow very erect to minimise water loss in the intense midday sun. In very dry periods these phyllodes are shed, reducing water loss and acting as a protective mulch for the soil beneath the tree. Its stomata, through which it respires and exchanges gases with the atmosphere, are hidden.
Sometimes growing as shrub, sometimes as a tree that can reach heights of 15 metres (49 feet), the Mulga Acacia channels the little rain that it receives down to the soil next to the base of its trunk, close to the deep, nitrogen-fixing roots that help to stabilise and enrich the soil. Acacia woodlands and scrub, important bush habitats across much of the continent, are often found close to seasonal stream beds and on slopes and ridges. The seeds are dormant until germination is triggered by fire (a process called serotiny); but the parent tree does not survive the experience; nor does it recover from being cut down. Other serotinous trees include Eucalyptus and Pitch pine.
Unsurprisingly, perhaps, such a key plant has been exploited by equally tough and hardy indigenous Australians for tens of thousands of years. The dark reddish-brown wood was used for shelter and firewood, to make digging sticks, spears and spear-throwers, clubs and boomerangs; and European settlers opening up large areas of bush found it useful for fencing, furniture, carving and for turning objects on a lathe. The phyllodes were and are a valuable source of nutrition for grazing wildlife and stock throughout the year. The gall of a wasp that lays its larvae on the acacia was a bush tucker food of indigenous hunter-gatherers and a gum exuded from branches was regarded as a sweet treat and a useful adhesive. Flour could be ground from the seeds. The yellow flowers attract bees and their honey provides another vital nutritional resource for foraging groups. The Mulga Acacia, the Australian desert and its people seem perfectly suited to one another.