Weed threat to Pilbara national parks

Tom ZaunmayrPilbara News
It may be photogenic, but stinking passionflower is choking native vegetation in Millstream-Chichester National Park.
Camera IconIt may be photogenic, but stinking passionflower is choking native vegetation in Millstream-Chichester National Park. Credit: Picture: Tom Zaunmayr, Tom Zaunmayr.

A South American invader is threatening the ecology and amenity of the North West’s most renowned national parks as existing control methods struggle to halt its aggressive growth.

Passiflora, or stinking passionflower, has already overrun the Jirndawarranha Pool’s surrounds in Millstream-Chichester National Park, and has been found in low densities near Karijini and in Murujuga National Park.

In the Kimberley, blankets up to one metre thick have been found in areas such as Giekie Gorge and it is overtaking freshwater crocodile nesting grounds.

Two projects, funded through the National Environmental Science Program and Gorgon’s Barrow Island net conservation benefit scheme, are working on understanding the impact of pasiflora and finding an effective control.

Water lilies are starving Jirndarrawanha Pool of oxygen.
Camera IconWater lilies are starving Jirndarrawanha Pool of oxygen. Credit: Tom Zaunmayr.

CSIRO senior research scientist Bruce Webber said the weed was putting some of WA’s best-known national parks under threat.

“The first few phases of research established very quickly that biological control is really the only feasible way to manage passiflora in Australia — there is simply no other solution which has long-term real impact,” he said.

“Over the next few months, we are about to roll out a big monitoring station system across the Kimberley and Pilbara to give us much better insight into how the plant grows, when it does well and when it does not.

“What we see in drier areas in the Pilbara and the Kimberley ... is it gets up in the tree canopy and makes a huge load of dry, dead material.

“It doesn’t break down as much as native flora might ... so when fire comes through, it torches the canopy at an intensity far greater than what the fire itself might do otherwise.”

Mr Webber said use of existing control methods in Millstream was inefficient but necessary to maintain amenity of tourist and culturally significant areas.

VideoA boost in eco-tourism means visitors to Karijini are getting back to nature without ruining it.

Department of Biodiversity, Conservation and Attractions regional nature conservation leader Coral Rowston said under ideal conditions, passiflora was blanketing areas and reaching the canopy within three months.

Ms Rowston said rangers were trialling management by fire as a control measure.

“Fire is thought to promote the stinking passionflower regrowth, but at the same time, fire takes it out and gives us an environment where it is easy to spray the regrowth,” she said.

“We have a site set up where we are monitoring how long it takes to grow, how long it takes to hit the canopy, to flower, to seed, to give us an indication of how long we have after fire to control it.

“A biological control would be a godsend for us.”

Ms Rowston said volunteer groups and rangers were brought into the park occasionally to help with control efforts.

“People are more than welcome to volunteer with us to keep it under control,” she said.

Ms Rowston said volunteers were also helping clear water lilies from Jirndawarranha Pool.

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