In a commentary written for the journal Science, Professor Karen Holl acknowledges the benefits of planting trees but cautions against the belief that it is a solution for climate change and environmental degradation.
Along with study co-author Professor Pedro Brancalion, Professor Holl reports that the issue of climate change is too complicated for one single solution, and even millions of new trees should be looked at as one part of a “multifaceted environmental solution.”
“We can’t plant our way out of climate change,” said Professor Holl, who is a leading expert in forest restoration at UC Santa Cruz. “It is only one piece of the puzzle.”
“Trees are deeply entrenched in the human psyche. It’s very satisfying to go out and put a tree in the ground. It’s a concrete, tangible thing to do.”
However, major initiatives for planting trees like the Trillion Tree Campaign must be approached with a commitment to long-term management, explained Professor Holl.
“Planting trees is not a simple solution. It’s complicated, and we need to be realistic about what we can and cannot achieve. We need to be thoughtful and plan for the long term.”
While planting trees cannot reverse climate change, they still come along with many benefits. Trees improve water quality, reduce erosion and flooding, provide food and shelter for wildlife, and improve air quality.
At the same time, tree-planting has the potential to harm native ecosystems and species and reduce water availability.
The researchers recommend specific principles to guide forest enhancement initiatives, such as planning ahead to resolve conflicting land-use goals to ensure maximum effectiveness over the long term.
“Much of the land proposed for tree planting is already being used to grow crops, harvest timber, and other subsistence activities, so tree planting initiatives need to consider how landowners will earn income,” said Professor Holl. “Otherwise, activities such as agriculture or logging will just move to other lands”
Professor Holl applauds the widespread enthusiasm for “increasing forest cover,” but emphasizes that it is not the same thing as planting more trees.
“The first thing we can do is keep existing forests standing, and the second is to allow trees to regenerate in areas that were formerly forests,” said Professor Holl. “In many cases, trees will recover on their own–just look at the entire eastern United States that was deforested 200 years ago. Much of that has come back without actively planting trees.”
“Yes, in some highly degraded lands we will need to plant trees, but that should be the last option since it is the most expensive and often is not successful. I’ve spent my life on this. We need to be thoughtful about how we bring the forest back.”
Professor Holl explained that slowing the pace of climate change requires a comprehensive strategy that starts with burning less fossil fuel.
“Trees are a small piece of what needs to be a broader strategy,” said Professor Holl. “We’re better off not releasing greenhouse gases to begin with.”
The research is published in the journal Science.