Native Trees Naturally Fight Invasives in Some Eastern Forests

Japanese stiltgrass (Microstegium vimineum) spreads along a forest trail. Researchers found evidence of biotic resistance to establishment and dominance of invasive plants in some forests of the East. Photo by Stephanie Worley Firley, U.S. Forest Service.
Japanese stiltgrass (Microstegium vimineum) spreads along a forest trail. Researchers found evidence of biotic resistance to establishment and dominance of invasive plants in some forests of the East. Photo by Stephanie Worley Firley, U.S. Forest Service.

In this modern society, non-stop movement of people and goods means that invasive species will continue to move and spread, too. Recent research indicates that invasive plants can be found in nearly half of the forests of the eastern United States, raising concerns about the sustainability of these ecosystems and the benefits and services they provide. The good news is that some eastern forests seem to have a natural, biotic ability to resist invasion. To understand why, a team of U.S. Forest Service and university researchers looked for clues within “big data” from the Forest Inventory and Analysis (FIA) program.

Using these “big data”—information collected from more than 42,000 FIA research plots surveyed across the East—the researchers used innovative statistical models to study the associations between native trees and invasive plants. Their findings, recently published in Landscape Ecology, suggest that live tree biomass and evolutionary relationships among tree species are key factors for invasion resistance.

“When we studied data at the landscape scale, we found that more native tree biomass and greater evolutionary diversity meant that invasive plants were less likely to be established or to become dominant if they were established,” says Kevin Potter, a North Carolina State University scientist working with the Eastern Forest Environmental Threat Assessment Center. The researchers also found that evolutionary diversity among tree species plays a more significant role in limiting the dominance of invasive species than preventing their establishment.

Greater evidence of invasion resistance emerged in patterns seen in some forests of the Upper Midwest and in and around the Appalachian Mountains. “These regions may exhibit ecosystem characteristics that allow native biomass and evolutionary diversity to more effectively prevent invader establishment and dominance,” says Potter. More research is needed to understand the ecosystem processes and spatial variables at play in these areas.

Previous studies of invasion resistance have focused on species richness — the number of species present in a study area — as a possible indicator of invasion resistance, but results have been inconsistent within and across spatial scales. In this study, researchers also examined the effects of species richness, but found that it is not a landscape-scale indicator of biotic resistance.

The researchers’ use of “big data” across such a large spatial scale and their application of sophisticated evolution-based measures of biodiversity uncover trends that bring new thinking to the issue of forest invasions and the importance of native trees. “In forests, trees comprise the majority of biomass, making them important contributors to biotic invasion resistance,” says Potter. “Our findings provide a better understanding of the nature of this resistance, which can inform invasive species management and policy across landscapes and jurisdictions.”

And with this new thinking comes further inquiry, according to Basil Iannone, a researcher with Purdue University and the study’s lead author. “These findings raise important new questions about how we quantify biodiversity, about the mechanisms by which different metrics of biodiversity impact invasion and other ecological processes, and about how these mechanisms vary across large geographic areas. Answering these questions will provide valuable insights into how to best manage forests and other ecosystems.”

Read the full text of the article.

For more information, email Kevin Potter at kevinpotter@fs.fed.us.

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