Mystery over why hundreds of trees are 'foaming' in heavy rain

Hundreds of foaming trees amid a huge dumping of rain in drought-affected areas have left people baffled as to what is causing the phenomenon.

A woman from Crescent Head, in NSW Mid North Coast region, posted a picture on Facebook of a gum tree in the heavy rain with white foam dripping down the trunk.

“It was raining sap,” she wrote.

“On the big gum it was pouring out.”

People were left scratching their heads as to what caused the mysterious reaction to the much-needed rainfall.

“I have seen it numerous times and never knew what it meant,” one commented.

“It’s crying with happiness,” another said.

A woman said hundreds of trees started foaming as heavy rain fell. Source: Facebook
A woman said hundreds of trees started foaming as heavy rain fell. Source: Facebook

Associate Professor Charles Warren, plant scientist at the University of Sydney, told Yahoo News Australia the snow-like effect on the trees was a natural phenomenon that occurred after long dry spells.

“Essentially what’s happening is as rain falls on trees it’s dissolving chemicals off the leaves and bark and the compounds the trees produce act as a natural soap,” he said.

“Because of it acting like a detergent, water will then basically foam up as it’s running down the tree trunk.”

Mr Warren said the chemicals were produced mostly by eucalyptus trees to defend themselves against microbes and herbivores.

“You see the foaming much more after a dry spell because it gives the chemicals time to accumulate on the leaves,” he said.

“It’s quite a common phenomenon but it’s really spectacular.”

NSW hit with best rain dumping in months

Crescent Head is expecting up to 20mm of rain again on Saturday after parts of the state received some of the best rainfall in months on Friday.

Sydney was expected to receive up to 25mm on Friday with up to 50mm forecast for parts of the state.

The Northern Tablelands, Northern Slopes, Northern Rivers, Mid North Coast and Hunter all received significant downpours.

Falls of up to 50mm will be the state's most significant rainfall since September last year, with rain expected to continue falling into the weekend.

The NSW SES on Friday morning said it had responded to more than 250 calls for help since Wednesday afternoon, mostly for leaky roofs.

Heavy rain begins to fall near Tamworth. Photo: Brook Mitchell
Heavy rain falls on drought and fire-ravaged country near Tamworth in NSW. Source: Brook Mitchell

The NSW Rural Fire Service on Thursday welcomed the rain on large firegrounds but warned it wasn't the end of the crisis.

"It won't put all these fires out but certainly it's slowed them right down and I think it's given a significant morale boost," RFS deputy commissioner Rob Rogers told the Seven Network on Friday.

"We've had rainfall on most fires now – at least 10mm – and particularly in the south in areas where it's harder to get to, in the Kosciuszko ranges. They're the ones we're quite happy there's been some rainfall."

On Friday morning, there were 82 NSW bushfires burning – down from 88 on Wednesday evening – after significant rain gave firefighters favourable conditions to strengthen containment lines.

About 30 fires remained out of control.

On Thursday, there were still 1700 firefighters on the ground.

- with AAP

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