Climate crisis: Polar forests and tropical deserts

Forests from the Arctic to the Amazon are transforming at a ‘shocking’ rate due to the climate crisis, with trees advancing into the previously barren tundra in the north while dying from the increasing heat farther south, researchers have found .

Global warming, along with changes in soils, wind and available nutrients, are rapidly altering the composition of forests, making them much less resilient and prone to disease, according to a series of studies that examined the health of trees in the world. North. and South America. .

Many forest areas are now becoming more susceptible to violent wildfires, leading to the release of more greenhouse gases from these vast carbon stores, further warming the planet. “It’s like humans struck a match and now we see the result,” said Roman Dial, a biologist at Alaska Pacific University.


The woods are moving

Dial and his colleagues found that a patch of white spruce in northwest Alaska “jumped” north into an area of ​​arctic tundra that hasn’t had such trees in millennia. The scientists’ new research paper, published in Nature, estimates spruce trees are advancing northward at a rate of around 4 km per decade, aided by warmer temperatures and changes in snow and winds influenced by melting sea ​​ice in the region.

“It was shocking to see trees there. Nobody knew them, but they were young and growing fast,” said Dial, who first saw the tree shadows in satellite images and then made a journey in a single-engine plane, followed by a five-day trek, to find and study the advancing forest

“Trees were basically jumping over mountains in the tundra. According to climate models, this was not supposed to happen for a hundred years or more. And yet it is happening now.

The Arctic is warming several times faster than the global average, and the appearance of dark conifers on the once-pristine white tundra threatens to absorb, rather than reflect, more sunlight, causing further warming. Trees can also disrupt the migration of various local species. “These trees move very quickly,” Dial said.

Other research detects more changes

Further south, separate research has revealed that a transformation is underway at the boundary between boreal and temperate forests, with spruce and fir species increasingly unable to cope with warmer conditions. Scientists estimate that even small amounts of additional heat, caused by human activity, could lead to the death of up to 50% of trees in the traditional boreal forest in some places, and the stunting of many other trees.

“Boreal species are doing very poorly with even modest warming. They grow more slowly and have higher mortality,” said Peter Reich, a researcher at the University of Minnesota and co-author of the research. “Intuitively, I thought they would do a little worse with 1.5° C of warming, but they are doing much worse, which is worrying.”

Polar forests and tropical deserts?

Reich and his colleagues spent five years raising nine different tree species from seedlings in different conditions in northern Minnesota, subjecting them to different amounts of heat and water. Boreal species have been found to suffer when soils dry out due to heat, while other more temperate species, such as oak and maple, can cope better and may slowly move towards the boreal zone as the world warms. .

“Given the rapidity of climate change, we could have a period of 50 to 150 years where fir trees and spruce trees for thousands of miles, even from Siberia to Scandinavia, are not regenerating, so you will have this new strange system of invading shrubs that will not provide us with the economic and ecological services that we are used to,” Reich said.

The impact of the climate crisis is also being felt in the heart of the Amazon, another study points out. Scientists have raised concerns that the huge rainforest ecosystem is at risk of tipping over into a new altered state, eventually becoming savannah, and the new research has found that a lack of phosphorus in Amazonian soils could have “significant implications” for its resilience to global changes. warming up.

By Oliver Milman. Articles in English

Leave a Comment