The Vineyard could see as many as 7,032 more homes on its 17,475 remaining acres of developable land, officials from the state Executive Office of Environmental Affairs (EOEA) said at an Island forum held Thursday night.

"That's a relatively short time frame to be faced with some tough choices," said Christian Jacqz, director of Massachusetts Geographic Information System, in a presentation to Island officials at the Howes House in West Tisbury.

Mr. Jacqz used GIS equipment and data compiled by the Martha's Vineyard Commission to paint a picture of an Island development capacity. The six Island towns were the last of the state's 351 municipalities to be presented with information about buildout, or full development allowed under current zoning, and its effects.

This three-tiered community preservation effort - involving the state legislature, governor and EOEA - places control, information, planning resources and funds within the reach of Massachusetts towns willing to tackle issues of open space, affordable housing conservation and transportation.

"It allows the towns to chart their own destiny and control quality of life on the Vineyard," Thomas Durand, secretary of the EOEA, said in a conversation with the Gazette this week. "It allows us to ask ‘what's our carrying capacity and what steps can we take today to impact the effect on growth, transportation, conservation and development."

The 7,032 more residences would be added to a stock of 14,299 current homes - a number that already grew by 50 per cent in the last decade. And, of course, the new homes would bring more people - roughly 13,000 of them. Some 60 per cent of those transplants would only live on the Island part-time.

"Assuming you want that magnitude of growth, what do you need to do to provide for that within the infrastructure?" Mr. Jacqz asked.

The new year-rounders would funnel another 1,000 students to a school system already accommodating 2,500 Island youth.

Sixty-seven miles of roadway would have to be laid to offer access to all the new homes.

"And this is just in subdivisions. It's not counting the strain on existing major roadways," Mr. Jacqz said.

The Vineyard's largest ponds and lakes would not fare well with the potential increase in density. Septic systems from new homes would dump into Tisbury Great Pond 66 per cent more nitrogen than recommended for safe swimming and a healthy fish supply. Lagoon Pond would get 23 per cent more, Chilmark Pond 73 per cent more and Squibnocket 46 per cent more than recommended. Only around Menemsha Pond would development not lead to nitrogen loading above suggested limits. Denitrifying systems could, however, significantly curb loading around those watersheds.

Residents currently drain 2.5 million gallons of water from Island aquifers a day. At buildout, usage could jump to four million gallons each day.

"You must think about water supply beyond community boundaries," Mr. Jacqz said. "We're, in essence, sticking our straws into the same glass of water."

The Island's 60,000 acres include 38,000 acres that provide habitat for species in need of protection - among which about 8,000 are threatened by possible development.

None of the buildout numbers, however, take into account the expense of land and homes on the Island. If nothing else, the cost of living on-Island may slow growth - particularly for the middle class, to say nothing of low-income residents.

Median home prices currently soar 85 per cent above state averages - reaching $767,900 in Aquinnah, a jump of 160 per cent since 1990. According to U.S. Census data, home prices increased by at least 50 per cent in every Island town in the last decade. Even renters pay 30 per cent above average state rates.

While expenses stretch beyond reach, earning potential for most remains stagnant. Vineyard wages register about 25 per cent below comparable salaries in Massachusetts.

State officials admitted that the buildout information could never predict which landowners are unwilling to sacrifice large parcels of land for development. The data also cannot account for limitations of the land - steep gradients and other topographical features that make certain parcels undesirable for development.

And, as Mr. Jacqz noted, building rates always slow dramatically as a community reaches capacity.

Officials from each town on Thursday night received a series of maps detailing development constraints for each town and highlighting available land. The maps reveal zoning districts, districts of critical planning concern and areas protected by wetland protection bylaws. Islandwide statistics were broken down town by town.

The community preservation initiative aims to put growth control in the hands of town leaders. Each town can access up to $30,000 in contracted planning expertise under an executive order from the governor's office. Nearly half of Massachusetts communities have already signed on to the community development plan.

Leaders of Vineyard conservation groups ended the presentation by outlining conservation efforts on Martha's Vineyard.

"Conservation groups are nibbling away at the edges of buildout," said Brendan O'Neill, executive director of the Vineyard Conservation Society. "Changes are occurring, and it's a product in the pipeline. We're not going to go out and buy lots on a subdivision."

Dick Johnson, executive director of Sheriff's Meadow Foundation, said the Conservation Partnership of Martha's Vineyard - namely Sheriff's Meadow, The Nature Conservancy, the Martha's Vineyard Land Bank, the Vineyard Conservation Society and The Trustees of Reservations - focused on protecting larger parcels of land, specifically those larger than 20 acres. So far, the groups combined have secured 1,800 acres of Island land.

Mr. Johnson stressed the importance of town regulatory bodies and conservation groups working together.

"It's like weaving. If you don't have both groups working together, ultimately the fabric will be weaker," Mr. Johnson said.