Take a close look at the coppicing trees in the old photo above. Notice anything unusual?
Perhaps it looks like any other stand of burnt mallee? Perhaps it does. But most of the trees aren’t resprouting after a fire. They aren’t recovering from drought, insect attack or damage by humans either. What could have caused the damage? The photo below of dead foliage on Mallee Tea-trees (or Green Tea-trees), Leptospermum coriaceum, provides a clue.
The impact on the vegetation was dramatic. Thousands of hectares of mallee scrub and heathland were devastated, especially in the interdune swales.
When I wrote the story, I knew of only two photos of the frost-killed trees, in an out-of-print book: ‘Mediterranean Landscapes in Australia, Mallee Ecosystems and Their Management’. According to some of my students, information that isn’t on the web doesn’t exist. Only digital information is accessible. So it’s time to bring imagery of that frosted landscape back from the dead.
Ancient photos unearthed
In 1982, David Cheal worked as a plant ecologist at the National Parks Service of Victoria. He knew Wyperfeld National Park well and took many photos after the big frosts. These are his photos, scanned from old slides and photoshopped a trifle to remove the dust and blemishes. As far as I know, David’s photos are the only publically available, digital images of ‘the cold that killed the mallee’.
The tall green trees in the photo above are Cypress-pines, Callitris gracilis and C. verrucosa. Cypress-pines are tough as floorboards. The frosts didn’t harm them. Eucalypts were more sensitive. The coppicing eucalypts in the top photo grew in a swale where the frost was most severe. They responded as they would after a fire, resprouting from the lignotuber at the base of the trunk.
You may be wondering why the ground layer in the top photo is so open and devoid of leaf litter. The site was hit by a double whammy of disturbances: first by fire and then, a year and a half later, by frost.
After the fire, the trees resprouted from the base and Wheel-fruit plants (Gyrostemon australasicus) regenerated from seed. The frost killed the tops of the Wheel-fruit – they’re the wispy herbs in the foreground – and killed most of the resprouting foliage on the eucalypts. You can see the frost-killed leaves at the base of the trees on the right of the photo. The trees then resprouted once again, creating a second green flush of coppice regrowth. You just can’t keep a good mallee down.
Mallee Tea-trees followed the eucalypts’ example. Across thousands of hectares, the aerial shoots were killed and the shrubs resprouted from the base. Slowly they grew to dominate the mallee heathlands once again. A photo David took in 1993 shows recovering tea-trees 10 years after the frost. The frost-killed branches still stand above the new flowering shoots.
Not all plants are as hardy as mallee cypress-pines, eucalypts and tea-trees. As described in the earlier story, the biggest loser was Desert Banksia, Banksia ornata. In 1986, Terry O’Brien and colleagues wrote:
With the exception of sporadic survivors, all adult [Banksia] ornata in frost-affected swales were eliminated.
Now we can see those swales of dead Banksias, thanks to David Cheal’s old slides. The scenes below extended across thousands of hectares. The large-leaved shrubs are Desert Banksias, the fine-leaved shrubs Mallee Tea-trees, and the tall green trees are cypress-pines and eucalypts.
Unlike the eucalypts and tea-trees, Desert Banksias didn’t resprout and few seedlings emerged. Across vast areas of the mallee, the banksias disappeared.
In many parts of the Park, the only surviving adult [Banksia] specimens are now located on dune crests and upper dune slopes above the level affected by the frosts.(O’Brien et al. 1986)
In David Cheal’s words: “The frosts were … one of those rare stochastic ‘natural’ events that have impacts for centuries. We talk about these events in ecology and hypothesize about their long-term impacts but we then usually forget about them and interpret landscape patterns in terms of the current climate and other conditions … We should never forget the long-term impacts of major perturbations on landscape patterns. Extreme events matter, and may matter for a very long time afterwards.”
We humans are visual creatures. Imagine reading about pandas without ever seeing a photo of one. Would you be convinced of their alleged cuteness? I doubt it. ‘Nah’, one might reply, ‘I’m sure my kids are way cuter than those hairy things’.
Imagine reading about a huge ecological event of which all traces had long disappeared. Would you consider it critical, pivotal, or merely interesting? Imagine trying to convince future readers of the impacts of climate change, without photos to demonstrate changes. A futile endeavour?
Photos of ecological changes are incredibly important. They generate our interest, trigger our emotions and spur our engagement. If a Banksia died in the mallee and nobody snapped … would anybody care?
I am indebted to David Cheal for kindly allowing me to share his valuable photographs of the frosted mallee, and for proof-checking this post.