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Invasive plants are considered “pests” to their non-native environments, contributing to a 42 percent decline of endangered and threatened species in the U.S., according to the United States Department of Agriculture.

In a new meta-analysis, researchers from the Smithsonian Environmental Research Center found that invasive plants could potentially be catalysts for fighting climate change in coastal vegetated habitats (CVHs) because the invaders made it easier for the ecosystems to store blue carbon. Habitats that store blue carbon include tidal marshes, seagrass beds and mangrove forests.

Research surrounding carbon storage in CVHs has been shortcoming while research regarding carbon storage in terrestrial forests has been heavily investigated.

An estimated 25 to 50 percent of blue carbon-storing coastal habitats are already lost, making deeper knowledge, management and preservation of these ecosystems crucial due to the threat of climate change.

Blue carbon storage sinks are formed from plant-based pools of biomass that are intertwined with the soil beneath these coastal habitats.

A team of researchers calculated changes within the plant-based biomass when an invader was present by analyzing 104 studies containing 345 comparisons of blue carbon ecosystems with or without invasive plants.

They found that when a powerful invasive species entered the ecosystem, it increased biomass and carbon storage because of its similarity to the native species. The invasive plant species grew larger and faster than its native counterpart, building the habitat more efficiently. The analysis also showed that carbon pools were 40 percent higher in CVHs with invasive plant species compared to carbon pools in CVHs with no invasive species, but the effects varied based on different species.

Ian Davidson, a marine biologist from the Smithsonian Environmental Research Center (SERC), says these species are “ecosystem engineers,” which are efficient and aggressive, helping the biomass skyrocket.  

Davidson worked alongside Christina Simkanin, a marine biologist from SERC, John Devaney, a postdoctoral research fellow at Trinity College Dublin, and Grace Cott, a wetland ecologist from University College Cork.

While the researchers note a large portion of their data consisted of salt marshes, it is significant that the salt marshes benefited highly with a biomass boost of 91 percent because of its invasive counterpart.

The researchers are still hesitant to say invasive species can be heroes in the climate change equation. Invasive species in CVHs still show negative effects, such as biodiversity and habitat loss. Enhanced carbon storage from invasive species is just one positive effect, but negatives of invasions should still be considered.

“Nobody’s advocating, ‘Let’s introduce phragmites, because it grows really fast and great, and let’s increase carbon storage here,’” said Simkanin. “We’re talking about how to best manage systems that are already impacted by humans, and how to do that in terms of what functions you want to preserve or you find most important.”

Some CVH invaders do not contribute to a biomass boost, and are not as efficient or helpful to native species. Invasive animals, for example, have the opposite effect. They trample, eat and destroy CVH biomass—nearly cutting it in half. Biomass of seagrass beds fell by a third when invaded by algae, while mangroves did not show any significant positive or negative effects from plant invaders.

“Ecosystem managers will be faced with a decision to eradicate or control invasive species,” said Cott. “The information contained in this study can help managers make decisions if carbon storage is a function they want to enhance.”

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