Minnesota is spending hundreds of millions of dollars conserving private land without ensuring that the money is doing what it's supposed to, a state watchdog agency reported Tuesday.

At issue are conservation easements, in which a landowner is paid to keep a swath of land undeveloped in perpetuity. Advocates say they preserve open space, protect waterways from pollution and provide valuable wildlife habitat.

A report by the Legislative Auditor found that the state isn't adequately watching what's being done with the land -- 600,000 acres across the state, the equivalent of 17 times the surface area of Minneapolis -- and whether the easements are doing what they were intended to do.

"This should not be treated as a passive investment in which we do the deal and put the documents in a drawer," said auditor James Nobles. "There needs to be some level of verification."

Although a spot check found little outright abuse, he said, the inventory of land that taxpayers are paying to protect is rising quickly and problems tend to develop over time.

Leaders of organizations working to protect the land praised the report in some respects but cautioned against clapping a lead backpack of regulation onto a process they say is already subject to plenty of oversight.

"If you do the math, this is an incredible cost efficiency for the state," versus buying land outright, said Kris Larson, executive director of the nonprofit Minnesota Land Trust. "We've leveraged over $80 million in private donations for less than $4 million in state investment."

With money pouring in from the Legacy Amendment, among other factors, the pace of land protection is rising and is expected to continue at a high rate, Nobles said.

Of the "more than 6,600 state-funded conservation easements, more than half ... were acquired from 2001 to 2011," the report says. "During that time, the state spent almost $190 million to acquire, manage and monitor conservation easements."

But the process of doing so is a bit sketchy, he and his staff reported. Among the problems:

• Monitoring to make sure the land is used and maintained appropriately is "not adequate," and there is "longstanding inattention" on the part of the Department of Natural Resources (DNR).

• Deeper than just the question of whether anything is being built on the land, not enough attention is given to whether the dollars are achieving their intended aims: whether protecting land along a river, for instance, is helping keep the water clean.

• The state's relationship with nonprofits out in the field is worrisome. For instance, the nonprofits always list properties they plan to protect with the funds, but then once funds come in, they "often revise the list." State officials, meanwhile, lack authority to review those agreements, though they have the expertise.

Larson, of the Land Trust -- the major nonprofit doing the deals -- said those switches occur because the funding process can last years while nonprofits cope with landowners' changing circumstances and wishes.

"Our mission is totally in line with the state's goals," he said. "We are protecting, for instance, 1,000 acres around a state park to make sure the public investment in that park is buffered."

DNR Commissioner Tom Landwehr submitted a four-page single-spaced letter responding to the report. Although the agency generally agrees with the report's key points, he said, it doesn't always reflect the difficulties involved.

"This report does recommend databases and state agency reviews that may be costly and would need to be funded by the Legislature," he wrote. "Also, the report often fails to identify who would enforce the proposed new requirements and how would they do so as to private holders of conservation easements."

Members of two legislative committees who were present for a summary of the report on Tuesday reacted with a volley of questions, and agreed they need more time to absorb it and weigh solutions.

Reacting to Nobles' point that the DNR has lots of staff who could be eyeballing properties without huge expenditures, Rep. Jean Wagenius, DFL-Minneapolis, said:

"We need more than just a drive-by. We're purchasing the biology here. It's not just whether someone has built a house or road on the land. Is it being maintained as it should? Is it full of invasive species? We need to address that."

David Peterson • 952-746-3285