The good intentions behind tree plantations to offset against carbon emissions may be counterproductive, according to researchers of an Oxford study.
Writing in the journal ‘Trends in Ecology and Evolution’ scientists have argued that the “well-intended” plantations might come with costs for biodiversity and other ecosystem functions.
Researchers say we must “prioritise conserving and restoring” intact ecosystems.
Lead author of the study, Dr Jesús Aguirre-Gutiérrez said: “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.”
Although offset schemes can be palatable to eco-conscious consumers and companies, many environmental organisations have questioned whether it is meaningful action.
Celebrities and tycoons including Prince Harry, Elton John, and Amazon founder, Jeff Bezos, have all said they have used offsetting to cancel out the greenhouse gases emitted by activities such as flying in private jets.
Authors at the Environmental Change Institute argued single species plantations are harmful to biodiversity and put forests more at risk of fire, while they do little to suck up greenhouse gases.
Instead, the authors said we should prioritise conserving and restoring intact ecosystems. Although some tree plantations involve reforestation of degraded land, in many cases they involve afforestation – planting forests in undegraded and previously unforested regions such as grasslands.
Tropical ecosystems are highly biodiverse, and provide multiple ecosystem services, such as maintaining water quality, soil health, and pollination.
In comparison, carbon-capture plantations are usually monocultures and are dominated by just five tree species, teak, mahogany, cedar, silk oak and black wattle, grown for timber, pulp, or agroforestry.
The Mail Online reports the result is that these plantations usually support a lower level of biodiversity.
For instance, in the Brazilian Cerrado savannah, a 40 percent increase in woody cover reduced the diversity of plants and ants by approximately 30 percent. Tropical grasslands and savannahs are already carbon sinks and, unlike trees, are less susceptible to disturbances such as drought and fire.
These plantations can also directly degrade ecosystems by reducing stream flow, depleting groundwater, and acidifying soils.
Dr Aguirre-Gutiérrez added: “The current trend of carbon-focused tree planting” is creating monocultures for “little carbon gain”.
The authors also say that there are considerable financial incentives for private companies to offset their carbon emissions by investing in carbon capture and carbon is “easy to measure and monetise”.
The research was supported by the Natural Environment Research Council, the John Fell fund from the University of Oxford, and the Trapnell Fund.
