Months before the economy crashed, the housing bubble burst, and development nationwide slowed to a trickle 10 years ago, a group of Marple Township commissioners and residents gathered to map out the Delaware County municipality's future.

"Marple Township will continue to be a desirable place to live," the group wrote in December 2006. Its retail sector "viable." The township would draw "more affluent residents," it said, attracted by "proximity to major means of transportation, aesthetic features, and the township's progressive planning initiatives."

Yet the team acknowledged a growing problem: "Marple Township will experience modest growth pressure. ... Growth will be limited by the lack of available land." Population was on an upswing. The baby-boom generation was aging, and housing accommodations for senior citizens would be needed, the authors wrote.

Eight years later, developer Stephen Sudhop read that report, his lawyers say, and decided to fill the void. He bought land, made a plan, and proposed in 2014 a 650-unit active-adult retirement community, embellished with a clubhouse, a fitness center, a Main Street, and some untouched woodlands. To make it work, however, Sudhop would need a zoning ordinance amendment.

Initially, Sudhop now alleges in a lawsuit, he had officials' support. But there were delays, zoning issues, and eventually, residents' opposition. Two years later, Sudhop got a surprising decision: Marple's planners unanimously denied recommending his plan.

Like other communities across the Philadelphia region, Marple found itself in the middle of a tug-of-war between dueling interests: the need to preserve what's left of its open space while also growing to meet the demands of an increasing population.

Towns and counties are at a critical moment: After decades of development, many now realize they are dealing simultaneously with less open space, more residents, and heightened concern among constituents about what is done with the empty acres that remain.

"There's less land out there to develop now," said Patty Elkis, director of planning at the Delaware Valley Regional Planning Commission (DVRPC). "People are getting savvier about what they want from their community and demanding more from their officials to make sure it's more of a development that fits."

For planners at all levels, there are hard decisions: As the region becomes increasingly attractive, can officials approve projects that entice residents, boost the economy, and increase the tax base while still preserving enough space and preventing traffic and environmental damage?

For developers in some areas, meanwhile, there is an uphill battle to win permits and zoning approval, often featuring push-back from residents and scrupulous requirements from officials.

The result: a possible cooling effect. In the 1990s, development of untouched land in the nine-county area (including Mercer) occurred at the pace of one acre every 45 minutes, according to the DVRPC. Today, it's one acre every 177 minutes.

Part of that is a natural slowdown after the recession, observers say: a trend toward redevelopment. But open space lingers on the minds of many.

"We had a building boom in the late '90s, early 2000s, for residential, and in many ways that greatly benefited our county," said John P. McBlain, a councilman in Delaware County, where pitched battles over developments and open space have been fought. "But I think now that pendulum swung back and we're looking toward preservation."

Across the region, no town or county has treated open space the same. Some, such as Chester County, have acquired farmland through easements. Bucks County has seen voters approve nearly $180 million in open-space bonds.

According to 2011 figures from the DVRPC, the most recent available, Burlington County has by far the greatest amount of protected space: 40 percent of all land, due primarily to protection of the Pinelands. Delaware County ranks the worst, protecting 10.6 percent.

Determining how the counties stack up when it comes to open space can be difficult, officials say: Each county's unique geography, terrain and age makes a fair contrast nearly impossible.

Still, the dwindling supply of open space in Delaware County — in 2011, just 13,000 acres were protected — has forced developers, residents and officials into court over the remaining land. At least three prominent open-space complaints have been filed within the last two years. In one, residents faced off against Concord, challenging its preliminary approval of a project proposed by Eastern States Development and the McKee Group on land in the Beaver Valley. The two others are against Marple: the one, filed by Sudhop; the other, filed by Jenkintown developer Bruce Goodman, who bid $47 million in 2014 for 213 acres owned by the Archdiocese of Philadelphia.

Like Sudhop, Goodman claimed in his lawsuit that his plans for 318 homes and nearly one  million square feet of retail and business space were denied by Marple's commissioners after years of promises and delays. Last year, Goodman sued to recoup the $7 million he spent on the land. Meanwhile, Sudhop sued around the same time, requesting declaratory relief — essentially, clarification — about a zoning-laws dispute.

Neither Marple lawsuit has been resolved. Marple Board of Commissioners President Joseph Rufo declined comment. The township solicitor could not be reached.

"There was no indication that [officials] had displeasure with [Sudhop's development]," said Vince Pompo of the West Chester law firm Lamb McErlane, one of Sudhop's lawyers. "... It just so happens that around the same time, there were other major developments that started to be pursued in the township, and that citizens started to come before the township not being happy with the proposals."

Some of the push-back against large developments has been led from the ground up.

In Delaware County, a few dozen residents have mobilized over the last five years to create opposition groups against the three developments that have resulted in lawsuits.

So far, they have tracked at nearly 100 percent success: In Concord Township, after opposition for years from a group called Save the Valley, a proposal to transform 240 acres into 150 homes collapsed in November, allowing environmental groups to buy the land.

Similar groups in Marple — Save Marple Greenspace and Paxon Hollow Greenspace — put similar pressure on officials. Finally, after months of protests and storming meetings, officials voted "no" on both Sudhop's and Goodman's proposals.

"People have finally woken up to the fact that, in our region, we're not getting any more open space," said Ken Hemphill, a Concord resident who has been involved with all groups.

"Once you lose this open space, you can't tear a shopping center down and replant a forest."