Columbia, S.C. ? From the ground, the pine forests near the North Carolina line appear unremarkable – rows of trees that eventually will be chopped down to make way for a housing development.

But hidden among the trees, easily visible only from the air, is a bumper crop of what some experts consider South Carolina’s most lucrative harvest: marijuana.

More than 30,000 marijuana plants were seized in two July busts just south of Charlotte, N.C., bringing the total amount of pot seized this year to 38,000 plants. That’s nearly three times the number confiscated across South Carolina in all of 2005, and nearly as many as were seized statewide last year.

State and federal authorities, and experts in marijuana policies, say that what appears to be a bumper crop of the illicit plants this year is due to two factors: bolder and more sophisticated marijuana growers producing more of the drug, and law enforcement getting better at finding the grow operations.

“The traffickers are doing just larger amounts of grows, and larger crops, in places where law enforcement is doing a better job in finding them,” said John Ozaluk, the federal Drug Enforcement Agency’s top agent in South Carolina.

Much of the marijuana that ends up in South Carolina is grown in Mexico, according to federal officials. But transporting drugs across the U.S.-Mexico border means high costs and security risks, something Ozaluk said has led to more homegrown marijuana.

A 2006 study by Virginia-based researcher Jon Gettman said marijuana was the nation’s largest cash crop, at $35.8 billion over a three-year period, and was the single largest cash crop in 12 states, including South Carolina.