Campaigns for planting massive numbers of trees can backfire, according to a new study that is the first to accurately analyze the potential impacts of policies supporting such schemes.
The analysis, published on June 22 in the journal Nature Sustainability, reveals how efforts such as the Global Campaign to Plant One Trillion Tree and Related Initiatives can lead to more biodiversity loss, and less climate change control.
However, the researchers assert that these efforts could have significant benefits if they include strong support restrictions, such as the ban on replacing native forests with tree plantations.
Great danger and fatal errors
"If the policies to stimulate tree planting are poorly designed or poorly applied, there is a high risk of wasting public money, generating more carbon and losing biodiversity," says Eric Lampen, associate professor of the study, from Stanford University's School of Earth, Energy and Environmental Sciences. And "This is the opposite of what these policies aim at."
There is no doubt that forests have a major role to play in efforts to slow global biodiversity loss and combat climate change by sequestering carbon as a biomass.
So it is not surprising that tree planting plans have been a magnet in recent years with ambitious commitments.
This includes the Bonn Challenge, which seeks to restore an area of forest more than eight times the size of California by 2030, or a trillion tree campaign that seeks to grow as many trees as possible.
A closer look reveals errors in these upbeat plans. For example, roughly 80% of the commitments to the Bonn Challenge involve planting single trees or a limited mixture of trees such as fruit and rubber instead of restoring natural forests.
Usually, these agriculture projects contribute less to carbon sequestration, habitat creation and erosion control than natural forests.
The potential benefit is further diminished if planted trees replace natural forests, rangelands or savannas, which are ecosystems that have evolved to support unique local biodiversity.
Financial support policies
In the new study, researchers critically examined subsidy policies designed to encourage private landowners to plant trees. They took an example of the world's longest and most powerful afforestation support policy, which is a Chilean Decree of Law 701.
The law was in effect from 1974 to 2012 and is now seen as a model for similar policies in a number of South American countries and international development projects.
"Chile's experience can help us understand the climatic, environmental, and economic impacts that may occur when governments push landowners to create huge tree farms," says lead author Robert Hillmayer, associate professor at the University of California Santa Barbara, who worked on studying while obtaining a PhD from Stanford University. ".
Chilean law subsidized 75% of afforestation costs and provided support for running farms. But it has already led to the use of subsidies on forest land, leading to cases where the government has supported the replacement of indigenous forests with profitable tree plantations.
Evidence indicated that the benefits provided by the law reduced the original forest cover by encouraging the establishment of farms on shrub lands or marginal agricultural lands where forests could naturally regenerate.
Given that Chile's indigenous forests are more dense and carbon-absorbing and biologically diverse than newly developed tree farms, subsidies have failed to increase carbon storage and accelerate biodiversity losses.
"Countries should design and implement policies to support natural forests to avoid the unwanted environmental impacts of the Chile program," says Christian Icheveria, associate professor at the University of Concepcion in Chile.
“Future subsidies should seek to promote the recovery of many carbon-rich natural ecosystems and biodiversity that have been lost.”