Six people have been arrested in connection with ecoterrorism attacks dating to 1998, including a fire at an Oregon poplar farm set at the same time as a devastating blaze at the University of Washington's Center for Urban Horticulture.

The university fire — one of the Northwest's most notorious acts of ecoterrorism — was set early on May 21, 2001. About 110 miles away in Clatskanie, Ore., fire ripped through buildings and vehicles at the Jefferson Poplar Farm, causing more than $1 million in damage. The Earth Liberation Front, a shadowy collection of environmental activists, claimed responsibility for both fires, which caused no injuries.

The arrests were made Wednesday in New York, Virginia, Oregon and Arizona, and each defendant has been indicted in the Northwest, the U.S. attorney's office said. Besides the tree farm fire, the attacks included three other arsons in Oregon, a $1.2 million fire at a U.S. Department of Agriculture facility in Olympia, and the toppling of a Bonneville Power Administration transmission tower near Bend, Ore., as the millennium drew near.

Assistant U.S. Attorney Andrew Friedman declined to say Thursday what led to the arrests after years of investigation. The FBI and the Building Industry Association of Washington recently began offering $100,000 rewards for information in ecoterror cases.

The FBI estimates that ecoterrorist groups have committed more than 1,100 crimes in the United States since 1976, causing about $110 million in property damage, and the building industry group says $8 million of that damage has been in Washington state since 1996.

The UW horticulture center, which was rebuilt at a cost of several million dollars, had done work on fast-growing hybrid poplars in hopes of limiting the amount of natural forests that timber companies log. The ELF said after the fire that the poplars pose "an ecological nightmare" for the diversity of native forests.

Stanislas Gregory Meyerhoff, 28, and Daniel Gerard McGowan, 31, were charged in the poplar farm fire. They face a maximum sentence of life in prison if convicted of several counts of arson and use of incendiary devices.

Meyerhoff was arrested in Charlottesville, Va., where he attended Piedmont Community College. McGowan was arrested in New York City.

Kevin M. Tubbs, 36, and William C. Rodgers, 40, face up to 20 years each if convicted of a June 21, 1998, arson at the Agriculture Department's Animal and Plant Health Inspection Services facility in Olympia.

Tubbs was arrested in Springfield, Ore., and Rodgers was arrested in Prescott, Ariz.

Sarah Kendall Harvey, 28, an administrative assistant at Northern Arizona University, was arrested in Flagstaff after being charged in a Dec. 27, 1998, fire at U.S. Forest Industries in Medford, Ore. That fire caused an estimated $500,000 in damage. She faces up to 20 years if convicted.

Chelsea Dawn Gerlach, 28, of Portland, Ore., was charged with conspiring to destroy an energy facility and destruction of an energy facility in the Dec. 30, 1999, toppling of the transmission tower. A not guilty plea was entered for her Thursday by a court-appointed attorney. If convicted of the conspiracy charge, she faces up to 25 years.

The other defendants were scheduled to make initial appearances in federal court in the districts where they were arrested.