Once A Bully, Always A Bully, Invasive Non-Native Plants Tend To Be Aggressive Wherever They Find Themselves

November 12, 1998

When Hurricane Andrew tore through tropical hardwood forests of southern Florida in 1992, it uprooted trees, stripped off leaves, fruits, flowers, and snapped off tree limbs. Opportunities for plants to recolonize were numerous in the wake of this natural disaster. But those most successful were invasive non-natives who had already gained a foothold in the forests before the hurricane struck.

In the November issue of Ecological Applications, researchers Carol Horvitz and colleagues from the University of Miami report on research that suggests that nature preserves may not be as safe for conservation of native species as previously believed.

"We found that in the aftermath of Hurricane Andrew, non-native forest species competed with native forest species for regeneration opportunities, exhibiting the same range of ecological roles as native forest species and competing for particular kinds of regeneration opportunities," said Horvitz.

If invasive species can successfully compete with natives in areas relatively free of human disturbance, explains Horvitz, they present a threat to biodiversity conservation and may considerably alter ecosystem processes.

In the case of several non-indigenous vines, not only did they form denser "blankets" than native vines, but they also inhibited the regeneration of other natives by strangling native tree seedlings and juveniles.

Horvitz points out that Florida's invasive non-natives species exhibit invasive behavior in other regions of the world, suggesting that understanding the ecological roles of such invaders in one region may help predict invasive roles in other areas.

According to the researchers, the ecological roles of invasive, non-indigenous species in forest ecosystems are poorly understood. Some analyses have proposed that such invaders become established primarily in human-disturbed areas. In contrast to these views, Horvitz and her associates suggest that successful invasion may in fact occur in natural habitats when invaders draw upon seeds, juveniles, and other sources they have sown prior to the disturbance.

Compared with native plants, the researchers found that non-native species were very similar in seed mass, and were also recruiting from diverse sources such as banks of pre-established juveniles, dormant seeds, and resprouts from pre-established adults. That meant these non-natives were not restricted to the pioneer type of life history frequently thought to be their primary option.

Horvitz's article is part of a larger series of research presented in this issue of Ecological Applications. Entitled, "Ecological Concepts in Conservation Biology: Lessons from Southeastern U.S. Ecosystems," the series presents a collection of articles which address the applicability of ecological concepts to conservation of Southeastern ecosystems.
Ecological Applications is a quarterly journal published by the Ecological Society of America (ESA). Copies of the above article are available free of charge to the press through the ESA's Public Affairs Office. Members of the press may also obtain copies of ESA's entire family of publications, which includes Ecology, Ecological Applications, Ecological Monographs, and Conservation Ecology. Others interested in copies of articles should contact the Reprint Department at the address in the masthead.

Founded in 1915, the Ecological Society of America (ESA) is a scientific, non-profit, organization with over 7000 members. Through ESA reports, journals, membership research, and expert testimony to Congress, ESA seeks to promote the responsible application of ecological data and principles to the solution of environmental problems. For more information about the Society and its activities, access ESA's web site at: http://esa.sdsc.edu.

Ecological Society of America

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