Planting trees to store carbon? It has more disadvantages than advantages

Planting trees to offset carbon dioxide emissions is overrated. Large plantations of homogeneous trees are established, especially in tropical regions. It may sound great, but according to researchers its impact is very disappointing: biodiversity is declining, while carbon storage is limited. We can better focus on preserving and restoring existing ecosystems.

It makes sense: trees remove carbon from the air, so if we plant enough of them we will automatically slow climate change. But it’s not that simple, concluded researchers from the University of Oxford, among others. Currently, many forests are planted in the tropics, because trees grow faster there. They can therefore store carbon more quickly. Sometimes a little of the old, fertile forest land is used for this purpose, but more often trees are planted in areas that had never been forests before, but were merely healthy pastures.

It was reduced to one goal
“Tropical ecosystems have great biodiversity and many functions, but we have reduced them to just one purpose: storing carbon.” Write researchers Led by Jesús Aguirre Gutierrez of Oxford university. “Policymakers should not encourage this degradation of ecosystems by planting trees solely to store carbon.”

But many people are not fully aware that creating forests is very bad for nature. It is often believed that planting trees to store carbon also has benefits for biodiversity and also provides financial benefits to local people. But the researchers write that this is not usually the case. Tropical ecosystems have great biodiversity and are important in many areas. This way they ensure that the water quality remains high and the soil is healthy. They are also important for pollinating plants.

Five types of trees
In comparison, carbon sequestering tree plantations are mostly monocultures dominated worldwide by only five tree species: teak, mahogany, cedar, silk oak and acacia. These are used for lumber, pulp or agroforestry. This may be valuable from an economic point of view, but biodiversity is difficult to find. In the Cerrado, a savannah region in Brazil, a 40 percent increase in forest resulted in a 30 percent decrease in plants and ants. These plantations can also directly degrade ecosystems by depleting groundwater, reducing water discharge, and acidifying soil.

Then there’s actually a more important point from the researchers: Even if we do our best, carbon storage in these tree farms is limited. “The current trend of planting trees to store carbon leads to widespread homogenization of a small amount of carbon gain,” the researchers wrote. “An area the size of the US, UK, China and Russia combined would need to be afforested to store one year’s worth of emissions.” This is not possible at all.

Underground carbon storage
Tropical grasslands and savannas are also carbon sinks. When left intact, they store large amounts of carbon underground. Unlike trees, which store carbon mainly above ground, underground carbon sinks are less vulnerable to problems such as drought and wildfires.

Private companies buy carbon dioxide emissions by planting trees. This is much easier and cheaper than reducing their actual emissions. The researchers concluded that the significant increase in the number of tree farms is driven by money, not environmental benefits. Compared to biodiversity or ecosystem function, carbon storage is much easier to measure and monetize.

Preserving the original ecosystem
But the benefits of planting trees for carbon storage are overstated and “may lead to a net negative consequence of carbon storage in terms of reduced biodiversity and ecosystem function,” the researchers wrote.
Instead of focusing on commercial forestry, we should prioritize ecosystem conservation. “Conserving the local ecosystem and maximizing its functions should take priority over the economic focus on carbon storage projects,” the report concludes.