Ecologists have warned that monoculture tree-planting initiatives are endangering tropical biodiversity while providing just a minor climatic benefit, and that ecosystems such as the Amazon and Congo basin are being reduced to their carbon value.
Unintended Consequences
A recent study published in the journal Trends in Ecology & Evolution said that the growing popularity of commercial pine, eucalyptus, and teak plantations in the tropics for carbon offsets is having unintended consequences such as drying out native ecosystems, acidifying soils, crowding out native plants, and accelerating wildfires.
"Despite the broad range of ecosystem functions and services provided by tropical ecosystems, society has reduced the value of these ecosystems to just one metric - carbon," the paper reads. "It is broadly assumed that maximizing standing carbon stocks also benefits biodiversity, ecosystem function and enhances socioeconomic co-benefits - yet this is often not the case."
According to Jesús Aguirre-Gutiérrez, an ecologist at the University of Oxford who led the study, the scientists decided to speak out after seeing a surge in commercial plantings in the tropics.
"These schemes are a win for the company planting these trees but not for biodiversity. This is the start of this phenomenon, hence the seriousness of the situation," he added.
The study said that a plantation the size of the United States, China, Russia, and the United Kingdom would have to be planted in order to sequester one year's worth of emissions.
While plantations are frequently more economically viable than standing forests, the paper emphasizes that they frequently support lesser levels of biodiversity.
For example, in the Brazilian Cerrado savanna, a 40% increase in woodland cover reduced plant and ant diversity by roughly 30%.
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Restoration of Native Forest
Tree planting has been hailed as a critical strategy in combating global warming, with hundreds of public and private programs underway to rapidly increase forest cover around the world in order to attain net zero targets.
However, research shows that the environmental benefit is strongly reliant on the extent and style of restoration and that large expanses of land are required.
A 2019 study revealed that enabling natural forests to regrow might return 40 times as much carbon as planted.
Scientists have urged governments to prioritize the conservation and restoration of native forests over commercial monocultures, warning that planting swaths of non-native trees in tropical regions threatens important flora and fauna with negligible climate impact.
According to Thomas Crowther, an ecology professor at ETH Zurich who co-authored a report that discovered there are 900 million hectares (2.2 billion acres) of land outside urban and agricultural areas suitable for forests, prioritizing the carbon value of an ecosystem over all else is incorrect.
He stressed that once we appreciate one aspect of nature more than the others, we incentivize its perpetuation at the expense of the others. Historically, people have valued the parts that we use for food, wood, medicines, and so on, but we are now doing the same with carbon.
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