"Night crawlers [Lumbricus terrestris] and the slightly smaller red worms [also called leaf worms or beaver tails, Lumbricus rubellus], have the most damaging impacts to the soil, litter layer, and plants in forests that were historically earthworm-free," Loss says.
"Everyone has probably heard at one time or another that earthworms have really positive effects in breaking down soil and making it more porous," Loss explains. "This is true in agricultural and garden settings but not in forests in the Midwest which have developed decomposition systems without earth worms."
Because the forested areas of the Midwest U.S. were once covered in glaciers, there are no native earthworm species present in the soil. "These earthworm-free forests developed a slow fungus-based decomposition process characterized by a deep organic litter layer on the forest floor," Loss says.
Earthworms feed on this layer of leaf litter and make it decompose much faster, Loss explains. "As a result, we see the loss of sensitive forest-floor species such as trillium, Solomons seal, sarsaparilla and sugar maple seedlings and a shift in dominance to disturbance-adapted species like Pennsylvania sedge."
One result is reduced nest concealment for the ovenbird and increased predation by squirrel and bird predators.
The researchers found no decline in three other species of ground-nesting birds included in their surveythe hermit thrush (Catharus guttatus), black-and-white warbler (Mniotilta varia) and veery (Catharus fuscescens)nor did they find a correlation between ovenbird decline and invasive worms in other forest types, such as red oak, paper birch and aspen.
"Our results suggest that ovenbird density may decline by as much as 25 percent in maple-basswood forests heavily invaded by invasive earthworms," the researchers conclude. "Maple-basswood forests are among the preferred ovenbird habi
|Contact: Lindsay Renick Mayer|