Even small temperature changes will significantly affect North American forests

Gianna Melillo
Thu, August 11, 2022 


Story at a glance

• Increasing global temperatures spell concern for a host of plant and animal species, along with human health.

• New research demonstrates the extent of damage resulting from slight temperature increases on North American tree species.

• Results show that in addition to increased mortality, warming would significantly restrict growth for some species and effects will be compounded by reduced rainfall.

An analysis of more than 4,500 seedlings of nine North American tree species revealed just a slight temperature increase of 1.6 degrees celsius (about 2.9 degrees Fahrenheit) alone, or combined with reduced rainfall, would increase mortality among the trees and significantly restrict growth.

The research, carried out by a team at The University of Michigan, was published in the journal Nature and underscores the precarious situation of North American boreal forests seen throughout Alaska, Canada and parts of Michigan and Minnesota.

These areas are one of Earth’s largest nearly intact forested ecosystems and play a significant role in decreasing human-made carbon emissions; they are located below tundra regions but above more temperate forests.

Over five years, researchers used infrared lamps and soil heating cables to study near-term impacts of warming on the seedlings.

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Several common northern conifer species including balsam fir, white spruce, and white pine exhibited severely reduced growth under experimental conditions, while modest warming did enhance growth for some species more commonly found in southern temperate forests.

However, the enhanced growth of these species is not enough to offset the effects of the vanishing conifers, researchers warned.

In addition to testing the effects of a 1.6 degree celsius warming, researchers also tested outcomes of a 3.1 degrees celsius (about 5.6 degrees Fahrenheit) increase above ambient temperatures. Rainwater tarps were used to test drier conditions and outcomes were compared with control trees grown at ambient temperatures and under normal moisture conditions.

Data showed reduced rainfall exacerbated the effects of slight temperature increases.

“Our results spell problems for the health and diversity of future regional forests,” said study co-author  Peter Reich of the University of Michigan in a statement.

“Present-day southern boreal forest may reach a tipping point with even modest climate warming, resulting in a major compositional shift with potential adverse impacts on the health and diversity of regional forests,” he added.

The resulting consequences could have sweeping impacts on forests’ ability to produce timber, host other plant and animal biodiversity and reduce flooding and carbon in the air.