The number of plants seized by the state's Campaign Against Marijuana Production plummeted this year, in part because drug traffickers shifted production from public to private land, where they more easily blend with legal pot operations, according to the state Department of Justice.

"They're changing their tactics," said Michelle Gregory, a spokeswoman for the justice department.

Weather, the manhunt for murder suspect Aaron Bassler and a truncated growing and eradication season also are factors in the decline, law enforcement officials said.

A total of 2.2 million plants were seized during the three-month CAMP operation this year, half as many as in 2010, Gregory said. CAMP operations concluded last week, she said.

Mendocino County again ranked No. 1 for CAMP pot seizures this year, despite its plant numbers dropping to 341,306, down from 572,680 plants last year. In Sonoma County, ranked 11th, pot seizures fell to 65,545, down from 311,147 in 2010. Lake County's seizures dropped to 123,645 from 374,958.

In 2010, 73 percent of the marijuana plants seized statewide during CAMP operations were on public land.

This year, it was about 60 percent, despite an intensive three-week federal, state and local offensive on pot production in the Mendocino National Forest. The six-county initiative, dubbed Operation Full Court Press, yielded 632,058 marijuana plants and 1,986 pounds of processed marijuana, figures included in CAMP's totals, Gregory said. The operation stemmed from complaints that armed pot growers had taken over public lands, making them unsafe for hikers and hunters.

The numbers indicate that many organized drug operators have shifted production from forests to private land, where they can blend with medical marijuana growing operations, Gregory said. Fresno County law enforcement agencies have reported a spike in large pot gardens in their jurisdictions, she said.

"They're inundated," Gregory said.

Drug traffickers are renting homes and growing pot in the backyards, she said. Some suspects claim to be growing medical marijuana but many don't bother, she said.

There's a similar shift toward growing illegal pot on private land in Mendocino County, said Bob Nishiyama, commander of the Mendocino Major Crimes Task Force.

Operation Full Court Press was highly publicized and drug traffickers likely decided it was safer and easier to hide their marijuana in plain sight, Nishiyama said, noting that medical marijuana gardens are ubiquitous in the county.

Another factor affecting pot seizures this year was the month-long manhunt for Bassler, who was accused of killing Matthew Coleman and Jere Melo in August. Dozens of local, state and federal law enforcement officers were diverted to the effort to catch Bassler, who was hiding out in the woods around Fort Bragg, Nishiyama noted. The search ended with Bassler being shot by law enforcement.

Unseasonably cool weather also affected pot operations, Nishiyama said.

A late winter and cool, wet spring and fall affected pot production, much as it did wine grapes, he said.

The late winter and delayed growing season also reduced the number of days CAMP operated this year by about 20 days, Gregory said.

The various factors that affected marijuana eradication efforts this year are subject to change, including the preference for growing pot on private land, Nishiyama said. He noted that illegal growers in the past shifted from private and public land in response to law enforcement action.