In National Parks, Reserves, and on private property in south-western Australia, grasstrees are under termite attack, rotting, breaking off, and toppling over, due to vast accumulation of thatch. The grasstree in this photograph, with heavy thatch removed by hand to show the decay underneath, is typical of thousands.
View image of grasstree rotting under long fire exclusion in Yalgorup National Park, Western Australia (38kbs).
Had grasstrees been covered by heavy thatch when Europeans first arrived, there would have been no reason to call them ‘blackboys’, since the black stems would have been largely hidden. Only rarely would they have produced a flower stalk, usually weak and twisted, quite unlike a spear. More likely popular names with British settlers would have been ‘greybeards’, or ‘haystack trees’. Early sketches and paintings consistently show them, quite clearly, as recently burnt, with black stems, little thatch, and a prominent flower stalk, like a spear.
As a rule of thumb, a grasstree thatch fire lasts as long in minutes as it has been unburnt in years. A three year old thatch will flare for only a few minutes, doing little damage to the green crown. A thirty year old thatch will burn for half an hour or more, reaching an incandescent thousand degrees Celsius.
Such fierce thatch fires often kill the grasstree immediately, because the protective mantle of old leaf bases is rotted away. Where dead eucalypt leaves, or casuarina needles have formed a ‘birds nest’ in the green top, the rot is exacerbated, the green top is reduced in size and vigour, and the eventual fire may completely burn the green top. If the grasstree survives the immediate fire effect, it is forced to live on starch reserves until a new top can grow. Complete replacement of the top can take a year, and the plant may die in the meantime, if its starch is exhausted.
If grasstrees are burnt more often, when the thatch is small, they flower and seed profusely, the protective mantle remains intact, the green top remains largely unburnt, nutrients in the thatch are recycled, and soil pH around the base is raised. The needles become obviously greener, longer, and thicker. Fire scars on some grasstrees along the old railway track in John Forrest National Park show annual burning by railway gangs when the railway was operating from the 1890s to the early 1960s. These grasstrees obviously survived. Now, under long fire exclusion, they are beginning to die.
There is a serious conservation problem with these old icons of the bush. Although still plentiful, the possibility of mass collapses and local extinctions cannot be ruled out. Grasstrees are like the Miner’s Canary – they are warning us that something is amiss in our bushland. The West Australian Government’s”Threatened Species Unit’ has been informed, but, apart from asking me to fill in a form, I am unaware of any action on their part. Perhaps the concept of ‘common and endangered’is too intellectually audacious for those accustomed to the familiar mantra of ‘rare and endangered’. But would a miner be wise to ignore his canary falling off the perch, because canaries are still plentiful?
By David Ward, Retired Senior Research Scientist with the Department of Conservation & Land Management, Western Australia, and formerly Visiting Senior Research Fellow at Curtin University School of Environmental Biology.
Copyright David Ward, 30th June 2005