Moreno-Mateos noted that numerous studies have shown that specific wetlands recover slowly, but his meta-analysis “might be a proof that this is happening in most wetlands.”

“To prevent this, preserve the wetland, don’t degrade the wetland,” he said.

Moreno-Mateos, who obtained his Ph.D. while studying wetland restoration in Spain, conducted a meta-analysis of 124 wetland studies monitoring work at 621 wetlands around the world and comparing them with natural wetlands. Nearly 80 percent were in the United States and some were restored more than 100 years ago, reflecting of a long-standing American interest in restoration and a common belief that it’s possible to essentially recreate destroyed wetlands. Half of all wetlands in North America, Europe, China and Australia were lost during the 20th century, he said.

Though Moreno-Mateos found that, on average, restored wetlands are 25 percent less productive than natural wetlands, there was much variation. For example, wetlands in boreal and cold temperate forests tend to recover more slowly than do warm wetlands. One review of wetland restoration projects in New York state, for example, found that “after 55 years, barely 50 percent of the organic matter had accumulated on average in all these wetlands” compared to what was there before, he said.

“Current thinking holds that many ecosystems just reach an alternative state that is different, and you never will recover the original,” he said.

In future studies, he will explore whether the slower carbon accumulation is due to a slow recovery of the native plant community or invasion by non-native plants.

Coauthors with Moreno-Mateos and Power are Francisco A. Comin of the Department of Conservation of Biodiversity and Ecosystem Restoration at the Pyrenean Institute of Ecology in Zaragoza, Spain; and Roxana Yockteng of the National Museum of Natural History in Paris, France. Moreno-Mateos recently accepted a position as the restoration fellow at Stanford University’s Jasper Ridge Biological Preserve.

The work was supported by the Spanish Ministry for Innovation and Science, the Spanish Foundation for Science and Technology and the National Center for Earth Surface Dynamics of the U.S. National Science Foundation Science and Technology Center.