LIVERMORE — The Alameda County Board of Supervisors last week voted to allow South Livermore Valley winery operators to erect larger agricultural buildings on their land, a decision supporters hope will help the local industry prosper and keep open space as farmland.

Acting as the county's Community Development Agency, the board voted 4-0 Dec. 15 to alter the East County Area Plan to give winery operators more space on their land to erect the buildings, which must be used to house farm implements and horticultural products.

Laura Mercier, executive director of the Tri-Valley Conservancy, called the decision vital to the success of the South Livermore Valley area agricultural wine economy.

"It will facilitate commercial agriculture businesses to succeed," Mercier said in an interview.

Mercier, whose organization works to protect agricultural land and open space in the Tri-Valley, said the vote's provision that enables winery operators to build agricultural buildings on 2.5% of their land — instead of the current 1% for nonresidential structures — was key. The previous codes allowed for buildings of about 20,000-square-feet, while winery operators typically need 40,000 to 60,000 square feet to store equipment and supplies.

"We believe it has prevented mid-sized wineries from relocating inside the South Livermore Valley," Mercier said.

The vote does not allow for the construction of event centers necessary for the wine-tasting and tourism industry. Mercier said the subject of agri-tourism is just beginning with the supervisors and open space advocates. Whether a hotel would be necessary in downtown Livermore to support tourism in the area's growing wine business will be discussed as well.

"We need to turn this into a place that supports overnight guests," Mercier said. "That's down the road."

During the board's meeting on Dec. 15, six people spoke in favor of the change. No one spoke against it.

Tamara Reus of Friends of Open Space and Vineyards said that she was for the change as long as event centers were not included. Prior to the board's vote, she stated that the changes provided a "workable solution that fits the goals of the wine country to be a productive agricultural wine country and still maintain the goals of the South Livermore (Valley) Plan."

Rancher Chuck Moore, chair of the Alameda County Agricultural Advisory Committee, supported the change for the wine industry, but hoped it would broaden. Moore owns an equestrian center in Castro Valley.

"I just hope in this we don't forget about other areas of the county that need to enhance their agriculture," Moore said.

Supervisor Scott Haggerty, whose office worked with land preservationists on the change, called it a "great step toward helping to increase agriculture in the East County."

County officials noted that they will make sure the board's decision adheres to the provisions of Measure D, which voters approved 20 years ago to protect agricultural lands and wildlife, or whether it needs to be put on the ballot for the public to approve.

But some of the satisfied open space advocates who spoke during the public meeting said that a ballot measure likely wasn't necessary because the new policy was a technical change.

"This (change) would enhance agriculture, which is one of the expressed purposes of Measure D," Sierra Club leader Dick Schneider said.