Tornadoes, windstorms pave way for lasting plant invasions


EXCERPT: : When tornadoes touch down, we brace for news of property damage, injuries, and loss of life, but the high-speed wind storms wreak environmental havoc, too. They can cut through massive swaths of forest, destroying trees and wildlife habitat, and opening up opportunities for invasive species to gain ground. A new University of Illinois study, published in the Journal of Ecology, shows that large blowdown areas in southern Illinois forests are more heavily invaded and slower to recover than smaller areas. The research guides management decisions for windstorm-prone forests.

"We used satellite imagery and grueling on-the-ground surveys to look at what was happening with invasive plants after a series of windstorms - a tornado in 2006, a derecho in 2009, and another tornado in 2017 - hit southern Illinois forests," says Eric Larson, assistant professor in the Department of Natural Resources and Environmental Sciences at U of I and co-author on the study. "We assume the forest recovers and those invaders get shaded out, but they may not. They could potentially prevent forest recovery or spread into surrounding areas."

... Once she reached the sites, Melissa Daniels [a former graduate student who led the project] identified and measured invasive plant cover and took readings of the tree canopy. It was immediately clear that storm-damaged areas, especially recent ones, were brighter and more open than unaffected sites, offering more light to understory invaders such as multiflora rose, Japanese honeysuckle, Amur honeysuckle, autumn olive, and Oriental bittersweet.

Comparing the storm-affected areas from 2006, 2009, and 2017, invasive species cover decreased and tree cover increased over time. "Since invasive plants decreased over time, some might interpret that as the forest healing on its own, and that they don't need to worry about it. The issue with that is, of our top five invaders, all of them demonstrate the ability to grow under closed canopy conditions. That means that even if they are being shaded out over time, they have the ability to spread into and persist in adjacent forest, potentially affecting forest regeneration," Daniels says.

Not surprisingly, the storm-damaged areas also were significantly more invaded than unaffected matching parcels, even 12 years after the first tornado hit. And larger damaged parcels were slower to recover, both in terms of decreasing invasions and increasing tree cover. The results suggest a couple of practical management recommendations.

"If you need to preferentially spend money on invasive species management, it makes more sense to focus treatment in larger blowdown areas," Daniels says. [...] Although the research focused on forests in southern Illinois ... Daniels and Larson suggest the general patterns - more invasive species and greater persistence in larger canopy gaps - are likely relevant anywhere major windstorms affect forested areas. (MORE - details)

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