“Warm loving” trees like rimu could expand their range as the climate warms, forcing cooler-preferring plants out. New Zealand’s unique beech forest could be squeezed up and out by other natives like rimu as the world heats up, new studies suggest. Source: Stuff.co.nz
Rimu and other warmer-loving podocarp forest trees would likely have an advantage and spread out in the South Island under climate change over plants that favour the cool, said Victoria University researcher Matt Ryan.
His analysis is part of a larger body of work looking hundreds of thousand of years into the past for clues of the potential consequences of the expected 2 to 4 degree rise in temperatures by the end of the century.
Cores dug up from under the ocean and on land allows Ryan to see the exactly the types of plants and forests that thrive when temperatures warm and become rare when they drop.
Mr Ryan is one of the researchers connected to the Keep A Cool World community climate change events, being held in Wellington on Thursday and Sunday.
He has spent his PhD putting together one of the clearest pictures yet of how New Zealand’s temperatures and plant life differed over the past half million years.
“I look at tiny little pollen grains that have been flushed out from major rivers, and can reconstruct vegetation change,” he said.
The types of tiny plankton also found in these Westland cores allowed Mr Ryan to work out what the temperature of the ocean was at that time period.
Over the thousands of years, sediment including this pollen and plankton steadily builds up in layers on the ocean floor and “levees” of undersea canyons, the latter where Ryan drilled his cores.
“I’m looking towards these intervals that have been particularly warm at these times,” he said.
At one of these warm times, more than 400,000 years ago when the earth’s orbital conditions were similar and carbon dioxide levels high, Mr Ryan found the forests were fundamentally different to what we see today.
“Now we have big tall conifer trees all along the beautiful West Coast of the South Island, but at this time period we actually had this big increase in this really drought- and frost intolerant type of tree. It was really, really warm,” he said.
Mr Ryan said the results of his crown research institute-supported study, which won a international postgraduate student prize last month, could hold lessons for us on how the unprecedented carbon dioxide rise in the atmosphere would impact the country.
“Some species won’t be able to tolerate the conditions that will be occurring,” he said.
“There are these things that limit it, but potentially we could see a difference in forest structure.
“But these past periods of warming are not going to compete with how fast as it’s changing now.”
