The leader of one of the county’s largest land conservation groups announced this week that he plans to retire once his replacement is found.

Ralph Benson, executive director of Sonoma Land Trust, oversaw the preservation of about 33,000 acres during the 11 years he was at the helm of the Santa Rosa-based nonprofit organization, more than tripling the amount of land the group has preserved over its 38-year history.

Lands preserved under his watch include more than 6,000 acres around San Pablo Bay, more than 6,300 acres running from the coast near Jenner to the mountains outside Cazadero, and the 1,655-acre Tolay Creek Ranch, which will combine with Tolay Lake Regional Park to create the county’s largest regional park, at just over 3,400 acres.

Benson, 72, said he is stepping down so that, among other things, he can spend more time with his two grandchildren.

“You only get one chance to be a little more involved in their lives,” he said. “It’s been a privilege to work at Sonoma Land Trust with so many members and partners and friends bent on protecting these places for our kids and their kids.”

Benson worked previously for the Trust for Public Land, the large national conservation group, where he was an attorney and later served as chief operations officer.

Benson, who joined the land trust in 2003 and took over its top job, helped grow the relatively small, local group into a well-known and respected conservation outfit in the wider Bay Area. Its protected lands now total more than 48,000 acres, including private property preserved through conservation easements. The group has also modernized its mission, broadening its public outreach and education programs, expanding restoration efforts and developing strategies to address landscape impacts from climate change.

Sonoma County Supervisor Susan Gorin, who has worked with Benson for years, said he was especially successful at building relationships. Those included ties with other land management agencies such as the county’s Regional Parks department and its Agricultural Preservation and Open Space District; with philanthropic organizations that provided needed funds; and with land owners wishing to preserve their land.

“Over the last 10 years, these relationships were important in the donations of land, (and) the protecting of land,” Gorin said.

Denny Van Ness, chairman of the land trust’s board, added: “Ralph brought a real professionalism to the organization. He was able to develop over time a real mission and vision for the land trust.”

Benson’s total compensation in 2012 was $159,885, according to the land trust’s tax records. He plans to remain on the job during the search for his replacement.