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Peculiar Patersonia patterns

Published 21 Dec 2023

This story happened to a friend of a friend of a friend of mine.

No, it didn’t. But it happened to Reserve Manager Mike Bretz and Ecologist Nick Fitzgerald after a day in the field setting up fauna cameras at Friendly Beaches Reserve, Tasmania, palawa Country.

Late in the afternoon, Mike and Nick sent the drone up to assess the landscape from a birds-eye view. Flying above masses of pink flowering melaleuca they mapped opportunities for future planned burns before heading north to inspect one of the reserve’s harder-to-reach corners.

Patersonia fragilis 'fairy rings' at Friendly Beaches Reserve, Tasmania. By Mike Bretz.

High above the 121-hectare reserve, they made a curious discovery.

From the controller’s tiny screen, they spotted a strange circular pattern in the vegetation. Then another, and another.

Unable to identify the plant at the centre of these creations (due to the available pixel resolution), they snapped a few pictures and committed to further investigation. Was this a Bush Heritage version of crop circles, they wondered?

“The next trip out there was with a volunteer field assistant surveying our long-term vegetation transects. At the first site, there was one of the circles right next to it.” says Nick.

“The rings don’t look that distinct from the ground. But from an aerial perspective – visible on Google Earth – they’re about 8-10 metres wide, and very obvious.”

Who is the floral alien behind all this landscape trickery?

At plant level, Nick quickly confirmed the flowers at the centre of the mysterious circles: it was the three-petaled Patersonia fragilis, more commonly known as the Purple-flag Iris. The iris forms small dense tussocks and grows extensively in wet coastal heath along Tasmania’s coasts, and can also be found in South Australia, Victoria and New South Wales.

Patersonia fragilis at Friendly Beaches Reserve, Tasmania. By Mike Bretz.

Patersonia fragilis commonly occurs as small, scattered plants throughout the heathland on the reserve, yet in these circles it grows much larger and is the dominant plant. The largest Patersonia tussocks are around the edges of the circular formations,” explains Nick.

The Purple-Flag isn’t the only species growing in the circles. Banksia and tea tree also grow, but they’re not nearly as abundant or dense as they are outside of the circles.

“It’s like something is shifting the balance towards the Patersonia species. I’ve looked at the satellite imagery all up and down the coast, to the north and south of the reserve where there’s extensive heathland, and I can’t see the circles anywhere else. Even within our reserve, they’re confined to the northern corner.”

And, what is the cause of these patterns?

Could it be extra-terrestrial beings, landscape artists (like those responsible for 30 years of major artworks in UK’s wheatfields), hungry marsupials (like those who continue to make regular patterns in Tasmania’s opium fields), or something else entirely?

At this point, we are unsure and that is the beauty of science – a vast realm of continual questioning.

There are a few more promising theories (sorry to the stoned wallabies and UFOs), that Nick and Mike are investigating with fellow scientists.

“We think ours might be more closely related to the subalpine rush circles studied by researcher Jamie Kirkpatrick in Tasmania’s highland grasslands. This research suggests the plants begin growing outwards and muscle out other species in their path. Over time the plants left in the centre begin to deteriorate with age and this inhibits any new growth from occurring – forming a circle.”

Patersonia fragilis 'fairy rings' at Friendly Beaches Reserve, Tasmania. By Mike Bretz.

Professor Kirkpatrick also studied mosaic cyclic succession of Richea acerosa (a common heath plant found in Tasmania’s drier alpine regions) and found that the Richea shrubs grew outwards, suppressing other plants in a circle. Over time the Richea plants declined in the centre of the circle, allowing smaller plants to colonise under the dead shrubs.

This is similar Nick and Mike’s observation of the impeded banksia and tea tree growing inside the Purple-Flag circles at Friendly Beaches, although 15 years of satellite imagery shows the Patersonia circles are not perceptibly expanding in size.

Or, it could be something underground!

Nick also believes the cause of our circles could be linked to the soil, or what lives in the soil. The arid fairy circles found in Australia’s Western Desert are striking patterns formed by gaps in the vegetation. Scientists have proposed various theories to explain the bare compressed circles of earth ringed by spiky spinifex grass, including competition between spinifex plants for scarce nutrient or water resources.

Recently, scientists worked with Martu Traditional Owners to better understand the cause of this phenomenon. Their studies were enlightened by Martu cultural stories and generational knowledge of the area that spans over 60,000 years and found the circles are linked to the underground homes of spinifex termites.

As an organisation grounded in science, we'll continue to monitor and manage this intriguing geometric vegetation. Guided by best-practice methods and in collaboration with fellow researchers we'll get to the middle of this mystery. For now, we just have to appreciate it as one of nature’s beautiful and wondrous creations!

More to come.

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