Ask anyone who's tried to cut down pesky bamboo shoots or rid his garden of purple loosestrife: Invasive plants can be a major hassle.
Scientists have long believed that invasives thrive as well as they do because they have escaped the natural predators in their native homes. But a study released today says that's only part of the reason.
Scientists at Georgia Institute of Technology say that invasive plants have succeeded because they are sharing their new homes with the enemies that evolved along with them.
The researchers examined 63 studies documenting the effects that native and nonnative grazing animals have on more than 100 native and invasive plants. They studied grasslands, forests, deserts, marshes and other habitats.
Their conclusion: When animals such as sheep, goats, cattle and horses are introduced to new habitats, they are less effective than native animals, such as bison and elk, at combating the spread of invasive plants.
The study, published in today's edition of Science, was not aimed at finding ways to control bamboo or kudzu, invasive Asian imports that are choking waterways and backyards, said senior author Mark Hay, an ecologist at Georgia Tech.
But the results show how humans and animals have played a major role in spreading invasive plants, he said.
The findings also bolster arguments for reintroducing more animals such as bison and wolves to Western states, and beavers to East Coast wetlands. Human influences are too pervasive for conservation officials to merely set land aside and hope for the best, Hay said.
"We act as if we were to leave things alone they will get better. But with six billion people living on the Earth right now, that's not going to work," Hay said. His co-authors are John D. Parker, a researcher at Cornell University, and Deron E. Burkepile, one of Hay's graduate students.
The researchers say the pattern can be traced to the 1600s, when European colonists began altering the landscape by replacing native bison and elk with imported cattle, sheep, horses, pigs and goats.
Since early times, the animals have been eating up the native grasses, damaging habitats and opening the door for European grasses that were among the earliest invasive plants here. The pattern continues to this day, scientists say.
Natural enemies
"The notion has always been that these organisms are spreading because they've escaped their natural enemies, but the problem is that they're following their natural enemies," Hay said.
