Invading plants boost blue carbon

Exotic plants invading coastal areas can substantially boost the carbon storage capacity of such ecosystems, a meta-analysis of 104 studies has found.

The analysis, published in the journal Global Change Biology, found that in some instances invading species – conventionally regarded as harmful – boosted the carbon storage potential of salt marshes, mangrove woodland and seagrass beds by as much as 117%, more than doubling the “natural” capacity.

The finding, from a team led by Ian Davidson from the Smithsonian Environmental Research Centre (SERC) in the US, could point to a way to mitigate the carbon storage loss arising from the destruction of about 8000 square-kilometres of coastal wilderness each year.

Such landscapes are considered important components of the planet-wide effort to sequester as much carbon as possible. Coastal ecosystems such as marshes and mangroves can trap and store carbon at a rate 40 times higher than that of rain forests. The result is referred to in climate change discourse as “blue carbon”.

However, the benefits of blue carbon storage are being dramatically eroded, with an estimated 25 to 50% of suitable ecosystems already lost.

Davidson and colleagues found that in some cases exotic species turbo-charged the storage ability of remaining ecosystems – but stop well short of advocating deliberate introductions.

In part, this is because the results across the studies included in the analysis weren’t consistent.

The biggest boosts came when the primary invading species was similar to those already established – a new mangrove moving into a mangrove forest for instance, or a new reed into a reed bed. Davidson’s team calls this type of plant “ecosystem engineers”.

“When you have these essentially ‘ecosystem engineers’ come into the system, not only are they helping build habitat, they seem to be doing it more aggressively and more efficiently,” Davidson said.

This is particularly the case with salt marshes, he adds, where invaders boosted blue carbon by an average of 91%.

The beneficial effect, however, did not carry through in situations wherein the invading plant was very different to the native species. In these cases, the storage capacity of the ecosystem decreased on average by more than a third.

Even in the positive examples, the researchers caution against seeing invasive species as unlikely or accidental heroes. The boost to carbon storage capacity did not necessarily outweigh negative effects such as loss of habitat and biodiversity.

“Ecosystem managers will be faced with a decision to eradicate or control invasive species,” says co-author Grace Cott.

“The information contained in this study can help managers make decisions if carbon storage is a function they want to enhance.”