JOHNSTOWN -- Joggers, walkers and bicyclists using the James Mayer Riverwalk Trail here probably know there's a river running alongside it -- simply by the trail's name. That might be the only way to tell, though, as Japanese knotweed, an invasive, exotic plant, has grown so tall and so thick along the Stonycreek River that it's impossible to see through or over.

	Natural Biodiversity Conservation Strategy Knotweed lines the Stonycreek River in the Moxham section of the James Mayer Riverwalk Trail in Johnstown. Click photo for larger image.

Kylie Daisley, projects manager with Natural Biodiversity Conservation Strategy, worked to change that last month, as she and a group of volunteers set out with long, red-handled loppers and a weed-whacker with a large, metal blade on it -- chopping down bamboo-like plants one stalk at a time.

It would be too difficult to get rid of all the knotweed, originally brought into this country as an ornamental plant for gardens, because of the steep riverbanks. Instead, Daisley had the workers simply cut the tall, leafy stalks back several feet away from the path.

They left the remnants -- piles and piles of leaves and stalks -- where they lay.

"If you move it anywhere else, it has the potential to contaminate that area," Daisley said. "Mowing it or chipping it is a bad idea because you're just putting it in little pieces that each one can grow into a new plant."

Wiping sweat from her face with her gloved hands, Daisley bent to chop each stalk of knotweed individually.

"The reason it's so arduous is you can only cut one at a time," she said.

The fibrous stalks, which are segmented like bamboo, have purple speckles on them, and can be as thick as 1¹/₂ inches around. If they weren't hollow, it would take saws to cut them down. Long spikes of white flowers bloom in late July.

Unlike bamboo, though, knotweed becomes brittle once it's dead and can't be used for furniture. Some groups, though, are experimenting with making it into paper, and it can also be used for cooking, though only when it's young. Daisley compared it to rhubarb, saying it can be made into jam and pie.

Natural Biodiversity, supported by the Westsylvania Heritage Corp., is an organization dedicated to protecting plant and animal diversity in the environment. The group targets invasive plant species, and Japanese knotweed is at the top of the list because of its prevalence in the Kiski-Conemaugh River Basin.

More than 100 years ago, when people realized how quickly knotweed can grow -- it reaches heights up to 12 feet in just one season -- they thought it would work well to stabilize hillsides along railroad tracks. What they didn't know, though, was that knotweed grows so quickly and so densely that it forces native species out of the area. And it doesn't do well to protect soil erosion anyway because of its bulky root system.

"It turned out to be a lousy thing," said Mike Quinn, a facilitator with the Conemaugh Valley Conservancy. "All trail groups have that as an issue."

The knotweed can be so tall that it forms a canopy over walking and biking trails, blocking out breezes and sunlight.

"It does impact the view shed. You can't see the river, and it feels like it's closing in," Quinn said.

On the four-mile section of the conservancy's West Penn Trail in Saltsburg, Natural Biodiversity started a demonstration site to get rid of the knotweed, and they've been at it there for five years.

"It's a constant commitment," Quinn said.

Besides its core of 25 weed-whackers, Natural Biodiversity also has a group of weed-watchers, who monitor local trails and river basins for infringing invasive plants.

Other non-native, invasive plants that cause problems locally include multi-flora rose, which was used in agriculture to set up a living fence to contain livestock; tree of heaven and garlic mustard.

Japanese knotweed, with wide, spade-shaped leaves, needs very little soil to grow, and can grow in the worst soil conditions. Natural Biodiversity started battling knotweed with demonstration sites in 2000, spraying the knotweed with herbicide twice each year -- once in the spring and again in the fall. But now, using the weed-whackers program, Daisley said, they skip the spring spraying and instead cut the knotweed down. Using that method, they had a 93.59 percent reduction in knotweed density over a one-year period at a demonstration site.

"It's pretty impossible to eradicate it," she said.