Northern Virginians, seeking to preserve lands, streams and wetlands from encroaching development, protected almost 4,000 acres in conservation trusts between 2005 and 2010, a new survey shows.

The survey, conducted by the Land Trust Alliance, reported that more than 10 million acres had been preserved nationwide, with more than 1.1 million acres saved in Virginia, the most in the Southeast region.

The lands, preserved with the help of tax deductions for landowners and public-private partnerships with several area governments, include the quarter-acre Rockwell Field, which adjoins Fillmore Park in Arlington County, Crow’s Nest natural preserve in Stafford County and the Kust family property, a three-acre easement adjoining Alexandria’s Monticello Park that is considered one of the top birding sites in the nation.

Given the dismal economic conditions that started in 2008, the gain pleased Mike Nardolilli, president of Northern Virginia Conservation Trust.

“Generally, in the ebb and flow of things, when the economy is going well, we get more easement donations. When the economy is going poorly, we get donations of fee lands,” Nardolilli said. That’s held true recently, he said, although the trust expects to finish at least one and possibly two more easements before the end of this year.

Land trusts nationwide have protected 47 million acres, an area more than twice the size of all the national parks in the contiguous United States. The Northern Virginia trust, which has been operating for 17 years, holds 98 conservation easements and owns 21 properties in Arlington, Fairfax, Stafford, Prince William and Loudoun counties and in Alexandria, Fairfax City and Falls Church.

Not every donation is accepted by land trusts. The land has to have a conservation value, such as being a breeding place for a rare or important animal or part of an endangered habitat. The identification of a property can be followed by a long process of qualification for tax benefits, addressing property title matters and the like. But for landowners who want to be sure their property is protected in perpetuity, the benefits of a land trust are unequaled.

Donors “generally want to leave a legacy to their community,” Nardolilli said. “Many of them love the land, and they would really like an opportunity to do something with the land other than develop it. Sometimes that’s possible, sometimes it isn’t — but we’ll talk to them about it.”