Invasive plants can stimulate blue carbon storage

"We were aware of the effects of invasions on other facets of these habitats, but it was the first time we explored blue carbon storage," said Ian Davidson, biologist of marine invasions at the Smithsonian Environmental Research Center (SERC). author of the new study. Although blue carbon has become a buzzword in climate change circles, it has not emerged in many invasive species discussions, particularly in the marine domain.

The newspaper, published Monday, October 1 at Biology of global change, is the first meta-analysis to exclusively examine marine habitats to address the issue of invasions and carbon storage. Previous research on carbon storage has focused on terrestrial environments such as forests. But swamps and mangroves can store carbon about 40 times faster than forests. And over the last century, biologists have estimated that the world has lost 25 to 50 percent of its blue carbon habitat, and an additional 8,000 square kilometers disappear each year. Understanding these ecosystems is essential as policy makers work to mitigate climate change and the impacts of invasive species.

"This is now part of global climate change solutions for carbon credits in forests," said Christina Simkanin, co-author, also a marine biologist at SERC. "But for blue carbon habitats, the marine version has been slower to materialize."

<a href = "https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/hires/2018/2-invasiveplan.jpg" title = "This wetland of Maryland is covered with Phragmites reeds, light brown stems that grow higher than native grasses. However, marshes and other coastal ecosystems are excellent at storing "blue carbon" and some invasive Phragmites could more than double that capacity. Credit: Gary Peresta / Smithsonian Environmental Research Center ">

Davidson, Simkanin and two Irish-based biologists (Grace Cott, Wetland Ecologist at University College Cork, and John Devaney, postdoc at Trinity College Dublin) partnered to conduct the study. They collected data from 104 different studies, covering 345 comparisons around the world. Each study compared an invaded blue-carbon ecosystem with a similar non-invaded ecosystem. Scientists used the data to calculate the magnitude of the change in plant biomass or soil carbon at each location in the presence of an invader. Over time, plant-based biomass ponds can be converted into valuable blue carbon storage "sinks" that are enclosed in soils beneath these habitats.

But when the researchers analyzed the numbers, they discovered that invasive species did not fall into one camp. When the most powerful plants have invaded – the ones that Davidson called the "ecosystem engineers" – biomass has skyrocketed. With an increase of 117%, they more than doubled the biomass and carbon storage potential of an ecosystem. The reason, according to the authors, is that most of these plants were similar to the species they have usurped (a new type of mangrove tree entering a mangrove forest, for example, or a reed like Phragmites enter a salt marsh). As invaders become larger and faster than native species, the ecosystem as a whole could store more carbon.

"When" ecosystem engineers "get into the system, not only do they help create a habitat, but they seem to do it more aggressively and more effectively," Davidson said.

However, not all plants were so useful. When more dissimilar plants took over, such as algae invading a seagrass, the biomass decreased by more than a third. And animals have reduced biomass by almost half, leaving ecosystems much weaker as blue carbon sinks.

"The introduced animals will essentially eat, stomp, cut and destroy the biomass," Davidson said.

Salt marshes appeared to draw the largest amount of biomass from their invaders, about 91% on average. This is partly due to the fact that most salt marsh invaders have fallen into the category of "ecosystem engineers". However, the authors pointed out that salt marshes constituted a large part of the data they could analyze. Herbaria and mangroves received much less attention, so the researchers did not have as much information to pull.

The authors also warned against considering invasive species as unlikely heroes. Carbon storage is a parameter that some invaders could improve, but managers must still consider other impacts that invaders may have, such as biodiversity loss or shrinkage of habitat. The real question, according to the authors, is how to manage the environments in which an invasive species has already established and evaluate the real costs and benefits of eradication.

"No one advocates, let's introduce Phragmitesbecause it is growing very fast and we are increasing carbon storage here, "said Simkanin. want to preserve where you find the most important. "

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

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More information:
Ian C. Davidson et al, Differential effects of biological invasions on coastal blue carbon: global review and meta-analysis, Biology of global change (2018). DOI: 10.1111 / gcb.14426