Even modest climate change could lead to drastic changes in the northernmost forests

Even relatively modest global warming and associated precipitation changes can significantly alter Earth’s northernmost forests, which are one of the largest nearly intact forest ecosystems on the planet and are home to much of the planet’s terrestrial carbon.

This is the main discovery of a distinctive experiment five-year project, led by a University of Michigan ecologist, who used infrared lamps and heating cables to study the predicted impacts of near-term climate change on thousands of seedlings of nine tree species found in many distant regions. the northern forests, called boreal forests.

The boreal forests of North America contain mainly conifers such as spruce, fir and pine. They are found primarily in Canada and Alaska, but also in parts of northeastern Minnesota, a very small part of Michigan’s Upper Peninsula, and northern Maine. Boreal forests are bounded to the north by tundra and to the south by temperate forest.

In the experiment, saplings from two forest web-sites of the University of Minnesota in northeast Minnesota were heated 24 hours on 24, from early spring to late fall, outdoors without using greenhouses or growth chambers. Two levels of century global warming potential were used: approximately 1.6 degrees Celsius (approximately 2.9 degrees Fahrenheit) and approximately 3 .1 C (approximately 5.6 F) above ambient temperatures.

In addition, movable tarps were positioned over half of the plots before some storms to capture rainwater and mimic changes in precipitation under a changing climate. As a control, some of the trees were grown at ambient temperatures and humidity levels.

The study found that even modest global warming (1, 6°C) caused major problems for many species, including reduced growth and increased mortality. In addition, the decrease in precipitation has amplified the negative effects of warming on the survival of several boreal species.

“Our results pose problems for the health and diversity of future forests. regions,” said UM forest ecologist Peter Reich, lead author of the study slated for publication on August. in the journal Mother nature.

“The current southern boreal forest could reach an end of tipping with even modest global warming, resulting in a major compositional shift with potential negative impacts on regional forest health and diversity,” said Reich, director of the Institute for Global Alter Biology at the School of Environment and Sustainability from the University of Michigan.

“These impacts could reduce the ability of our forests to produce wood, support other plant diversities, mic robians and animals, to mitigate floods and – perhaps most important of all – to remove carbon from the air and retain it in the wood. and soil.”

Plants in mid to high latitudes are likely to experience both positive and negative effects of 21st century climate change, say scientists. In some places, especially in the far north, a longer growing season can stimulate tree growth when moisture is plentiful.

In other places, hotter and drier situations could result in lower tree growth and survival. Observational studies show that both positive and negative trends in boreal forest survival and growth are already underway.

But direct experimental assessments of the effects of global warming on boreal forests across a range of soil moisture conditions are rare and have generally been limited in size, scope and duration, according to the authors of the new study.

The Mother Nature report fills many of these knowledge gaps. The study used the joint manipulation of temperature and precipitation to examine the likely effects of short-term climate change on the mortality and growth of juvenile trees on the two field web pages.

“In the experiment, we subject forest plots to temperatures that we will not see before 40, 50 or 60 years to understand what these impending temperatures will do,” Reich said.

Researchers found that warming alone, or in combination with reduced precipitation, increased the juvenile mortality of nine tree species and significantly reduced the growth of several species of northern conifers – balsam fir, white spruce and white pine – which are common in boreal forests.

At the same time, modest warming has favored the growth of some hardwoods, including some oaks and maples, which are rare in the boreal forest but much more common in southern temperate forests.

However, the new study concludes that hardwoods are probably too rare in the forest southern boreal to quickly fill the void left by the disappearance of the conifers. Therefore, projected near-term climate change will likely shift the current boreal forest to “a new state” of altered composition.

“This new state is, at best, likely to be a more impoverished model of our current forest,” Reich said. “At worst, this could include high levels of invasive woody shrubs, which are already common in the temperate-boreal border and are rapidly moving north.”

The experiment was conducted at two field stations at the University of Minnesota. Reich, who joined the UM faculty in 2021, maintains a joint affiliation in Minnesota and continues to collaborate on the Forest Warming Project.

For the experiment, more than 4 500 seedlings of nine native tree species – five broad-leaved and four needle-leaved species – were were planted in the existing vegetation of grasses, shrubs and ferns on the study web pages. The nine tree species are balsam fir, white spruce, jack pine, white pine, red maple, sugar maple, paper birch, bur oak, and red oak.

Mobile tarps reduced the overall rainfall on selected plots by approximately 30% randomly during the growing season. Since rainfall was above average in all five years of the experiment, the low rainfall treatment actually represented average dry years over the past century, and the control treatments represented generally wet years over the same period. Therefore, the low rainfall treatments were by no means extreme.

Other authors of the Mother Nature article are Raimundo Bermudez, Rebecca Montgomery, Karen Rice, Sarah Hobbie and Artur Stefanski from the University of Minnesota, and Roy Abundant from the Smithsonian Environmental Investigation Center. The research was supported by the US Department of Energy, the Nationwide Science Foundation, the Minnesota Agricultural Experiment Station and the University of Minnesota.

Video: https:// youtu.be/XjCtmK3YhcI

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