This spic-and-span all-terrain vehicle is probably not carrying weed seeds. Is that why the driver is grinning? Photo: Oak Ridge National Laboratory

The weed machine
Roads are built to carry people into forests, generally for an economic purpose, like logging or mining, or for camping, hunting and other fun. But these roads don't just carry logs or people lugging chain saws or tents. Roads can also carry weed seeds. Weeds, grandly known as invasive species in the ecology biz, are considered a prime destroyer of habitat, so any increase in weeds worries those concerned with the biological integrity of natural areas.

While hiking boots can carry weed seeds along foot trails, cars and trucks are probably a larger source, since they carry more mud for more distance. On the marginal logging roads that are so common in national forests, a new potential carrier is the increasingly popular all-terrain vehicle (ATV).

The prospect that ATVs are channeling weeds into forests got a lift from new research by Tom Rooney, an assistant scientist in the botany department at the University of Wisconsin-Madison, who studied the Chequemegon-Nicolet National Forest in Wisconsin (see " Off-Road Vehicles ..." in the bibliography).

Rooney began the research by walking along ATV trails -- built on old logging roads. Every 100 meters, he looked for invasive species, and found them growing at nine stops out of 10.

While the seeds of those invasives could have hitchhiked on hiking boots or in animal bellies, Rooney found evidence implicating ATVs. He scraped mud from the vehicles' wheel wells, froze the mud to simulate winter, and allowed any seeds to sprout. In 66 percent of the mud samples, at least one plant sprouted.

Although Rooney did not try to identify those plants, he did conclude that ATVs can carry live seeds, and found no reason why the cargo would not include weed seeds.

"Reed canary grass (yellow stalks) and purple loosestrife are invasive plants that grow rapidly in wetlands. Could ATVs distribute their seeds in natural areas? Photo: U.S. Department of Transportation

Luck of the draw
Once an exotic seed reaches the forest, the ecological impact depends partly on chance. "Imagine being in Northern Wisconsin," Rooney says. "In some areas, you will be traveling through aspen that's 10 to 15 years old. Or you'll be along a lakeshore, or a wetland, or a mature forest. Given these different types of habitat, the ecological impact depends on the species that are invading." Reed canary grass, for example, can invade and dominate wetlands, while garlic mustard can overwhelm mature forest, but not wetlands or open habitat.

There is no question that road-borne invasives can change the landscape, however. "Where people have looked at invasions, they find they go in 100 meters from the road," Rooney says. That number is significant in view of the fact 50 percent of the land in the lower 48 states is within 400 meters of a road.

The findings are cause for concern, says Rooney, especially since:

ATV sales have risen more than 10 percent a year for five years, according to the industry publication Dealernews,

182,000 off-road vehicles are registered in Wisconsin alone, and

ATVs can reach deep into the forest.

Will ATVs intensify the impact of habitat fragmentation in national forests? Perhaps. Already, Rooney says, two highly invasive plants, leafy spurge and spotted knapweed, are established in the Chequemegon-Nicolet National Forest. And even if they did not originally arrive on four-wheelers, ATVs can still spread them. Thus in designing new ATV trails, Rooney says, it would make sense to link existing trails rather than cut through untouched forest.

What can you learn from a spotted salamander?

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