Circumvent the hungry herbivores to restore ecosystems

November 29, 2023

Re-establishing the planting of trees, grasses and other vegetation is essential for restoring degraded ecosystems, but a new survey of almost 2,600 restoration projects from nearly every type of ecosystem on Earth finds that most projects fail to recognize and control one of the new plants’ chief threats: hungry critters that eat them.

A crab in the reeds. Photo credit: Brian Silliman, Duke University.

The majority of the projects surveyed took steps to exclude competing plant species, yet only 10% took steps to control for, or exclude, herbivores that graze on budding flora. By not protecting plants in their early stages, conservationists are missing opportunities to significantly speed restoration. Fencing, for example, can keep herbivores away until plantlings mature and become less vulnerable. Introducing or increasing predators to keep herbivores in check can also bolster plant re-growth by roughly 100-400%. Those gains are equal to, or greater than, the gains realized by excluding competing plant species, this new survey shows, which was conducted with input from an international team of researchers.

Jonathan Lefcheck, a research scientist with the University of Maryland Center for Environmental Science (UMCES), co-authored the study, which was published November 3 in Science. Lefcheck has been a contributor to restoration in the Chesapeake region, from demonstrating the value of nutrient reductions in promoting healthy underwater grasses in the Bay to helping achieve the largest seagrass restoration in the world, on the Eastern Shore.

“There is a huge focus on restoration now, so much so that the UN has declared this the Decade of Ecosystem Restoration and set lofty goals in terms of getting ecosystems back to where they once were,” said Lefcheck. “There is also a huge emphasis on restoration methods: we’ve seen an explosion in different approaches and technologies that improve outcomes and make restorations more efficient and more cost-effective. Our study demonstrates that herbivores are the primary determinant of restoration outcomes globally, from terrestrial to marine and aquatic ecosystems and across different organisms and methods.”

Failing to consider the herbivore impact has led to less success than could be achieved, especially in light of aspirational national and international targets, he said. The survey’s findings have far-reaching implications for efforts to restore vegetation in a time of climate change.

“Herbivores’ effects were particularly pronounced in regions with higher temperatures and lower precipitation,” said Brian Silliman, a Duke University Distinguished Professor of Marine Conservation Biology. “If we want more plants, we have to let more predators in, or restore their populations. Indeed, the decline of large predators, like wolves, lions, and sharks that normally keep herbivore populations in check, is likely an important, indirect cause of high grazing pressures.”

Once a planting is established, the herbivores are essential, too, Silliman added. “Plants just need a small break from being eaten to restart making ecosystems. Once established, herbivores are key to maintaining plant ecosystem diversity and function.”

Additional Information

The team was led by Qiang He, a professor of coastal ecology at Fudan University and a former postdoctoral research associate of Duke University Professor, Brian Silliman.   

Researchers from Northeastern University, Northern Illinois University, the Smithsonian Environmental Research Center, the University of Florida and Sonoma State University also contributed to the study. Additional co-authors came from the University of Canterbury (N.Z.), Aarhus University, Pusan National University, the Instituto de Investigaciones Marinas y Costeras, East China Normal University, Peking University, Nanjing University, the Royal Netherlands Institute for Sea Research, the University of Groningen, the Chinese Academy of Sciences, Lanzhou University and Yunnan University. 

Funding was provided by the National Key Basic Research Program, the National Natural Science Foundation of China and the Global-ERCaN project of the Chinese Academy of Sciences.