Instead of planting trees, keep forests healthy

Many scientists support the idea that large-scale tree-planting will help to mitigate climate change and global warming. But in a new Perspectives article, two leading experts say the idea of planting trees as a substitute for the direct reduction of greenhouse gas emissions could be a pipe dream.

Jonathan Overpeck is dean of the University of Michigan School for Environment and Sustainability and an expert on paleoclimate and climate-vegetation interactions. His co-author, University of Arizona’s David Breshears, is a top expert on tree mortality and forest die-off in the West. 

According to the researchers, instead of wasting money by planting lots of trees in a way that is destined to fail, it makes more sense to focus on keeping existing forests healthy so they can continue to act as carbon sinks, removing carbon from the atmosphere through photosynthesis and storing it in trees and soils. “We can’t plant our way out of the climate crisis,” said Breshears.

The researchers hope the role of the world’s forests, and specifically the urgent need to protect existing forests and keep them intact, is thoroughly debated at the COP26 climate change conference in Glasgow this November.

“Policymakers need to enable new science, policy and finance mechanisms optimized for the disturbance and vegetation change that is unstoppable, and also to ensure that the trees and forests we wish to plant or preserve for the carbon they sequester survive in the face of climate change and other human threats.”

“Failure to meet this challenge will mean that large terrestrial stores of carbon will be lost to the atmosphere, accelerating climate change and the impacts on vegetation that threaten many more of the ecosystem services on which humans depend.”

Overpeck and Breshears explained that keeping forests healthy will require a new approach to forest management, one that they call managing for change. The first step of this approach is to acknowledge that large-scale vegetation changes are inevitable.

“Even in a world where climate change is soon halted, global temperature rise will likely reach between 1.5 and 2 C above pre-industrial levels, with all the associated extreme heat waves that brings, and thus global vegetation will face up to double the climate change already experienced,” wrote the researchers.

The next step is to manage forests proactively for the vegetation changes that can be anticipated, instead of trying to maintain forests as they were in the 20th century, explained Overpeck and Breshears.

Managing for change means, for example, more aggressive thinning of forests to reduce the buildup of fuels that stoke massive wildfires. Furthermore, the experts point to a big opportunity to improve the ability of forests to store carbon through increased use of biochar, a form of charcoal.

Biochar is produced by exposing organic waste matter, such as wood chips or manure, to heat in a low-oxygen environment. Overpeck noted that large amounts of wood generated during forest thinning projects could be converted to biochar, then added to forest soils to improve their health and increase the amount of carbon that is locked away.

“Thinning of forests, conversion of the removed wood to biochar and burial of the biochar in forest soils is a way to bring new jobs to forested rural areas while allowing forests to play a bigger role in keeping carbon out of the atmosphere and thus fighting climate change,” said Overpeck. “Forest carbon management could be a boon for rural areas in need of new economic engines.”

In the long run, according to the researchers, such projects are likely to benefit forests and enhance their ability to store carbon far more than massive tree-planting campaigns conducted without appropriate management strategies.

“Tree-planting has great appeal to some climate activists because it is easy and not that expensive,” said Breshears. “But it’s like bailing water with a big hole in the bucket: While adding more trees can help slow ongoing warming, we’re simultaneously losing trees because of that ongoing warming.”

The study is published in the journal Science.

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By Chrissy Sexton, Earth.com Staff Writer