Some climate activists advocate large-scale tree-planting campaigns in forests around the world to suck up heat-trapping carbon dioxide and help rein in climate change.
But in a Perspectives article published May 21 in the journal Science, a University of Michigan climate scientist and his University of Arizona colleague say the idea of planting trees as a substitute for the direct reduction of greenhouse gas emissions could be a pipe dream.
“We can’t plant our way out of the climate crisis,” said Arizona’s David Breshears, a top expert on tree mortality and forest die-off in the West.
His co-author is Jonathan Overpeck, dean of Michigan’s School for Environment and Sustainability and an expert on paleoclimate and climate-vegetation interactions.
“Tree-planting has great appeal to some climate activists because it is easy and not that expensive,” Breshears said. “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 authors favor 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, according to the researchers.
At the same time, emissions must be reduced as much as possible, as quickly as possible, they say.
Overpeck and Breshears describe their approach to forest management as “managing for change.”
As a first step, policymakers and land managers would acknowledge that additional large-scale vegetation changes are inevitable.
Managing for Change
Climate change has been implicated in record-setting wildfires in the western United States, Australia and elsewhere, as well as extensive tree die-offs that are largely due to increasingly hot, dry climate extremes.
Those trends are expected to accelerate as the climate warms, according to Overpeck and Breshears.
“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,” they write.
At the same time, deforestation continues to expand globally and is especially damaging in tropical forests, which hold vast amounts of biodiversity and sequestered carbon.
The next step the authors propose is managing forests proactively for the vegetation changes that can be anticipated, instead of trying to maintain forests as they were in the 20th century.
Managing for change means, for example, increased thinning of forests to reduce the buildup of fuels that stoke massive wildfires.
It also means selectively replacing some trees — after a wildfire, for example — that are no longer in optimal climate zones with new species that will thrive now and in coming decades.
Such activities, where needed, would inevitably increase the costs of forest management. But the authors argue such costs should be considered a prudent investment in carbon sequestration.
Overpeck sees a big opportunity to improve the ability of forests to store carbon through increased use of biochar, a form of charcoal produced by heating organic waste matter — such as wood chips, crop residue or manure — in a low-oxygen environment.
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. This activity could bring jobs to rural areas, Overpeck said.
In the long run, such projects are likely to benefit forests and enhance their ability to store carbon far more than massive tree-planting campaigns alone, Overpeck and Breshears said.