Mangrove migration mapped by ‘historical detective work’

Mangrove migration mapped by ‘historical detective work’

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“You think of Florida as a very tropical place, and it is, but every now and again they’ll get these winter storms and it will go below freezing.”


Dr Hayes said through studying historical weather records they’ve found those cold events used to be more common, however because of climate change they had become more rare.

To get the data they needed the scientists had to rely on a range of contemporary sources, including personal journals, logbooks, photos and maps from the times in question.

“Over the last few hundred years there wasn’t a lot of scientists going through this part of the world looking at mangroves specifically, but what there was was a lot of naturalists, a lot of people in ships keeping logs, and other people travelling and keeping notes of what they saw,” Dr Hayes said.

“You’re looking for simple little lines or references, doing a bit of detective work.”

In many cases the references were simple passing mentions in diaries or logs, however sometimes the team got lucky and found an actual photo of mangroves.

One such example was Fort Matanzas, an old Spanish fort on Florida’s Atlantic coast.

The back of Fort Matanzas taken in: (a) 1900-1915, (b) 1934, (c) 1981, and (d) 2018. Black mangroves (Avicennia germanins) are identified with white arrows on (b) and (d)

“I was inside this fort visiting as a tourist in 2016 and they had a book showing how they had restored it in the early 1900s,” Dr Hayes said.

“And I looked at one of the pictures and said ‘oh, there’s a mangrove there’ and it was, which went against the view at the time that mangroves had not grown that far north.”

Based on their work, the research team created a model of the local ecosystem, and found from the year 2000 to 2100, annual minimum temperatures are predicted to increase by 0.5 degrees per decade.

This would see mangroves move away from areas nearer to the equator where it was consistently hotter, and towards the poles, where there were fewer extreme cold events stopping their encroachment.

Dr Hayes said the model was designed for Florida, but could be adapted to the Australian coastline to explain the behaviour of mangroves here as well.

“Mangroves have already moved down into the farthest southern point in [mainland] Australia, but they’re certainly not in Tasmania yet, it’s still a bit cold for them there,” he said.

“But we can also use it to model other extremes … like what’s happening in the north of Australia, around the Gulf of Carpentaria with its massive mangrove die-off.”

The research has been published in the journal PNAS.

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