Mangrove forests that died along a 1,000km stretch of coastline in northern Australia have been emitting methane at rates eight times higher than live trees, according to new research.

Scientists from Southern Cross University have used the site of the mass dieback along the Gulf of Carpentaria to measure methane emissions from mangrove tree stems for the first time.

Forests of mangroves along the coastline died as a result of extreme heat, rainfall shortages and low sea levels in the summer of 2015-16.

The mass mortality is one of the worst cases of forest dieback ever recorded and happened in the same year as the mass coral bleaching on the Great Barrier Reef.

Researchers travelled to the Gulf of Carpentaria in August last year to measure methane emissions from an area of live mangroves, then compared them to those from an area of dead mangroves about two kilometres away.

They found the emissions from the dead trees were eight times higher than those from the healthy trees.

The study’s lead author, Luke Jeffrey, said the purpose of the research was to try to understand what happens when climate stressors, such as heatwaves, cause forest mortality.

He said the results, published in New Phytologist, had “significant implications” for greenhouse gas emissions from coastal habitats, given global heating made it more likely such catastrophic diebacks would occur more often into the future.

Methane is about 34 times more potent as a heat-trapping gas than CO2.

“Because methane is such a potent greenhouse gas, for every molecule of methane released, about 34 molecules of CO2 need to be consumed by mangroves simply to break even,” Jeffrey said.

“When you consider the mangrove system is now dead and not drawing down CO2, this is a pretty significant imbalance.”

In most cases, carbon storage by trees would outweigh their methane emissions, Jeffrey said.

But understanding the process that drives methane emissions from trees, and the extent to which mortality events could increase emissions, was an important consideration for policies such as offsetting.

“We’re currently in a world where corporations or governments plan on planting trees to offset emissions,” he said.

“Therefore, it’s important to know if these numbers will add up or if they might be underestimating the balance of the carbon the trees will capture versus how much methane they will emit as a byproduct.”