Scientists warn world in danger of failing to see the good from the trees

Scientists have warned a number of national tree planting strategies in the tropics in an effort to stem the loss of forest could be having a negative effect on the environment.

The team from the University of Maryland Baltimore County (UMBC) examined the increase in tree cover across the global tropics between 2000 and 2012. The results found tree cover gains during that period were equally attributable to natural forest regrowth and the creation of tree plantations. The most common tree plantation species were rubber, eucalyptus, and oil palm.

They said that the scientific community recognised trees store carbon, filtre the air, create habitat, and supply a host of other benefits for animals and people. Planting the right trees, in the right places, in consultation with local communities, can support goals like addressing climate change and improving lives. However, the research led by Matthew Fagan, assistant professor of geography and environmental systems at UMBC, finds that some trees planted in the tropics may be doing more harm than good.

“Tree plantations are not always harmful to the environment, and even much-maligned oil palm can be farmed sustainably, Fagan explained. However, the study found that 92 percent of new tree plantations were in biodiversity hotspots, threatening a range of plant and animal species. Also, 14 percent of plantations were in arid biomes, where trees are unlikely to thrive and likely to damage existing ecosystems. And tree plantations had encroached into 9 percent of accessible protected areas in the humid tropics, such as national parks.

“Ecologists have been sounding the alarm on this for over a decade,” Fagan added. “But no one’s had a hard number about how much this is actually happening.”

In recent years, dozens of nations have committed to restoring large areas of forest. Tree plantations make up 45 percent of commitments to the Bonn Challenge, an international initiative to restore degraded and deforested landscapes. But Fagan is concerned that these plantations may have unintended consequences.

For example, China has undertaken a massive tree-planting effort at the edge of the Gobi desert, and many African countries have committed to planting trees at the transition between the Sahara desert and Sahel grassland. The goal is to prevent desert expansion, but the plantings can cause harm. Disturbing the soil releases carbon, and trees are water hogs. They end up “killing off the grassland that was there, and then they often die of drought,” Fagan says. In these situations, tree planting is lose-lose.

Similarly, in Brazil, soy farmers moved out of the Amazon and into the Cerrado, one of the world’s largest savannas. Pine and eucalyptus tree farms followed. The Cerrado supports a wealth of biodiversity, and the carbon it stores underground rivals rainforest carbon sequestration, Fagan explains. Tree crops in the Cerrado may count toward Brazil’s reforestation commitment but could actually be a step backward in mitigating climate change and biodiversity loss.

“In the U.S., we have a huge area of relatively wet woods, and we tend to idolise planting trees as sort of the ultimate environmental act,” Fagan explained. “But there’s a lot of value in grasslands and savannas that we don’t necessarily see. And when you plant trees, you essentially destroy that ecosystem.”

In response to his team’s new research, Fagen added: “I would really like to see governments around the world reassess their restoration plans, or at least be more transparent when their plans involve tree planting, especially in areas that may not be appropriate for planting trees.”

Fagan’s new paper also revealed the extent to which tree plantations are invading protected areas. The problem was so bad that he had to overhaul the algorithm his team used to differentiate between data representing natural forest regrowth and tree plantations.

“It was very disturbing to see there were just so many parks that were compromised,” Fagan said.

“In the end, the tropics is a much more modified place than we were expecting,” He added. “There’s a whole host of reasons that we see these encroachments, but they’re definitely happening all over the world. We see a steady erosion of these parks by plantations, and the industry is just getting started.”

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