Even relatively modest heat and precipitation losses could dramatically alter the composition of Earth’s northern forests, jeopardizing their biodiversity-rich ecosystems and eroding their ability to store the carbon pollution that is warming the planet, researchers said Wednesday.
The boreal forests cover much of Russia, Alaska and Canada and are a major carbon sink, but they are threatened by more frequent wildfires and outbreaks of invasive species associated with climate change.
To assess how higher temperatures and less precipitation may affect the tree species most commonly found in forests, a team of researchers from the United States and Australia conducted a unique five-year experiment.
Between 2012 and 2016, they grew about 4,600 seedlings of nine species of trees — including spruce, fir, and pine — in wooded areas of northeastern Minnesota.
With the help of underground cables and infrared lamps, the seedlings were heated around the clock at two different temperatures – one batch 1.6 degrees Celsius hotter than the ambient temperature, the second 3.1 degrees warmer.
In addition, moveable tarps were positioned over half of the plots ahead of storms to capture rainwater and mimic the type of precipitation shifts climate change is expected to bring.
The study, published in Nature, found that even the trees that grew under 1.6°C of warming faced major problems, including decreased growth and increased mortality.
“I thought we would see modest declines — of a few percent — in survival and growth even in the boreal species like spruce and fir, but we saw very large increases in mortality and declines in growth in a number of species .” Lead author Peter Reich told AFP.
The team found that warming alone or in combination with reduced rainfall increased juvenile mortality in all nine tree species studied.
– “Exponential negative effects” –
The 2015 Paris targets committed nations to limit temperature increases to “well below” two degrees Celsius above pre-industrial levels and work towards a safer 1.5°C ceiling.
Wednesday’s research suggests that even this relatively modest warming would have profound effects on boreal ecosystems.
Current government plans envisage that the earth will warm up by up to 2.7 °C in this century.
Previous research has shown that boreal forests are likely to experience both positive and negative impacts from climate change, such as B. a longer growing season in the far north.
The experiment showed that moderate warming – in the 1.6°C sample – enhanced growth of some hardwood species such as maple and oak. These are currently scarce in boreal forests but plentiful in more temperate, southern forests.
However, the team suggested that the southern hardwoods are probably too rare to fill the gap left by other species, such as conifers, which performed very poorly in the experiment.
Reich, director of the University of Michigan’s Institute for Global Change Biology, said that increased CO2 levels would likely have “modest beneficial effects” on some species.
“But as CO2 and temperatures continue to rise, plants will become saturated with CO2, so further increases will have less and less effect,” he said.
“While the negative impacts of climate change will increase exponentially.”
Reich said warming due to poorer plant regeneration would likely affect boreal forests’ ability to store carbon.
“Additionally, more fires associated with warming will also cause greater carbon losses to the atmosphere,” he said.
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