Lecture examines invasive species

10/07/08 - While there is much research on how invasive species affect their native counterparts, there is little on how they can affect the ecosystem as a whole.Bernard Blossey, an ecology professor from Cornell University, intends to change all that by studying which species negatively affect eastern forest ecosystems, and in what capacity. He spoke yesterday in the University of Rhode Island's Coastal Institute.

Blossey's lecture, titled, "How Worms, Weeds, Slugs and Deer Shape our Eastern Forests," examined the different ways these organisms can affect ecosystems.

Blossey said classifying, quantifying and managing detrimental invasive species in the ecosystem is difficult. Just because an invasive species is surviving in an ecosystem does not necessarily mean it harms the habitat. In some situations even native species, like the white tailed deer, can disrupt the balance of an area simply by being overpopulated or fenced in by human construction.

"When they ask the question, 'who is the most important actor,' we very often do not know," he said. "What sets a white flowering [green] plant- apart from another white flowering green plant, other than its origin? Is there something fundamentally different between the two species? Why do we worry?"

Blossey said an invasive plant is usually only an issue if it becomes dominant in the habitat and crowds the other native plants. Garlic mustard, he said, was considered detrimental because it flourished in vast numbers and grew very quickly, and it was believed at the time that it would spread like wildfire.

Instead, he said, it stayed in the areas it started growing in, and was not as big of a problem as initially thought.

Native white-tailed deer are a much bigger concern, Blossey said, and since they have been corralled into much smaller areas and their natural predators have been severely reduced, their food sources have dwindled drastically.

Combined with the fact deer always prefer the biggest and most sexually developed flowers, they can inhibit the growth of the next generation.

He showed pictures of areas fenced off from deer and the unfenced counterparts. The fenced-in areas had normal vegetation growth, while the other side was virtually barren.

"Now I'm going to gross out some people because this is what I believe has to happen," he said. "This,[points to buck] plus this, [points to doe] equals venison. I think what has to happen is we have to teach hunting as a civic duty."

Blossey encouraged the crowd to talk to their local municipalities about allowing hunting in urban areas and local parks. He said that venison is a viable food source because it has a low carbon impact, it's completely organic, locally grown and has no transportation costs.

"It's a win, win, win situation," he said.

Blossey said that if the deer population is significantly reduced, it would give native plants a level playing field. Because they have longer reproductive cycles than the invaders, more of the native species being eaten results in fewer plants being reproduced the following year. The shorter cycles of the invasive plants make them more abundant and less vulnerable to deer. He said this is evident when deer have been removed from certain areas that were later fenced off.

"They went in [the area], got sharpshooters for a couple of weeks, took 400 deer out, two years later they took another 300 deer out, and then the [native] vegetation rebounded," he said. "So they now have to go in and do this periodically and cull the herd."

Blossey does not expect human casualties to be an issue when hunting in populated areas. He said reports of hunting accidents get sensationalized in the media and scare people into believing that hunting causes a lot more deaths than it actually does. He added since bows and arrows would be used primarily in populated areas, injuries would not be likely, or life threatening.

"I think it's much more of a perception that there's a lot of dangers because people are flinging arrows left and right," he said. "People just don't do that. You really shoot at very short distances."

Blossey said that another contributing factor is the European-based surface dwelling earthworms that eat the mulch and compost on surface soil. While in Europe, this actually helps plant growth and development, in the American eastern forests this can upset the natural balance. He said earthworms are called ecosystem engineers, as they help to shape the environment around them. In this way, they can also aid in the growth and expansion of invasive plant species from the same area as the European earthworms, such as garlic mustard, and cutoff reproductive cycles of native plants.

"So I have a standing award ... it's at $1,000 right now," he said. "If anyone can show me a site where garlic mustard grows and there are no earthworms. Nobody has ever claimed this award."

Blossey said foreign slugs impact native vegetation because when their larvae eat certain seedlings, stifling growth and spread of native plants.

He said when he and a team of researchers, through a federal grant, surveyed an area near West Point, N.Y., they found hundreds of Arion subfuscus, or dusky slugs, in the surrounding areas.

Blossey said that regardless of whether the slugs are native or invasive, they have very selective eating habits. While the verdict is still out on how these picky eaters affect the ecosystem, Blossey said the data will show if their diets effect any more plant species' abundances and whether they are crucial to maintaining the habitat's homeostasis.