Three reasons tropical Aussie forests are becoming unrecognisable

Trees in Queensland's beautiful Wet Tropics can disappear under a weighty vine in just one year.

Vines are swamping forests around Australia’s Wet Tropics, stunting the growth of trees before they can reach their full height. The rapidly changing climate has tipped conditions in favour of woody liana that chokes low-elevation foliage below.

It means that in just a year, fast-growing vines can grow over a tree. Their weight is often so great that trunks beneath will bend and break. Professor Andy Marshall from the University of Sunshine Coast’s Forest Researcher Institute explained the vines transform the regions they take over into something “very different” to what most people think of as forests.

“If you look at them, you can see isolated trees, or the crowns of some trees popping out for the top of the vines, but essentially it’s a big mass of vines and thorny vegetation that’s about the tenth the height of a regular forest,” he told Yahoo. “For all intents and purposes it doesn't look like a forest, it looks like a thicket.”

Two images showing vines swamping trees in the Wet Tropics.
Forests in Queensland's Wet Tropics are being rapidly changed by vines. Source: Andy Marshall

Other hotspots for vines were low-elevation forests in East Africa, Vietnam, Colombia. Under the dense growth they are humid and filled with bugs.

“We have to get on our hands and knees and get underneath the vegetation to mark and measure the vines. There’s a lot of marsh flies, a lot of mosquitoes, even birds. It’s quite lively,” Marshall said. “Although these places look very unhealthy, the vines do actually help maintain biodiversity that can help the forest in the future.”

Three conditions causing low-lying forests to be consumed by vines

Forests in Queensland's Wet Tropics region were among 556 locations studied across 44 countries over 20 years by researchers. They identified three key factors that are helping the vines outcompete other plants:

  • A mean annual temperature above 27.8 degrees.

  • Rainfall is less than 1614 mm.

  • Forest already disturbed by logging.

Researchers found the vine is better able to deal with climate change than larger trees, and once the invasive plant swamps trees below, they are unable to soak up and store carbon. While the vines can be enormous, they don’t have the same “massive” trunks as the trees they outcompete and therefore can’t store as much carbon.

Professor Andy Marshall underneath some vines in Africa.
Professor Andy Marshall had to crawl amongst thick vines among mosquitoes and marsh flies. Source: Ruben Mwakisom

The question scientists must now consider is what to do with the vines. Cutting them could help restore biodiversity of foliage, but rapidly removing them could hard the creatures that have evolved to live beneath them.

More disturbance of forests is expected to continue, particularly around Queensland. The state is home to some of the most extensive land clearing in the developed world, and it is increasingly being impacted by severe cyclones that can impact forests because of climate change.

“The forests look like they're really struggling. And in fact they are. So now the challenge is to know what to do about it,” Marshall said.

The University of the Sunshine Coast-led study has been published in the journal Global Change Biology.

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