Looking up from Corbett's Glen toward an office park, you can see a few balloons floating in the air, clearly visible through the naked treetops on this December morning. It's cold, but the snow that fell a few days ago is starting to melt. Allens Creek is flowing quickly and the constant trickling provides a pleasant ambience.

Members of the Penfield Planning Board are walking near a particularly scenic portion of the creek called Postcard Falls. They're using the balloons to judge the visual impact a controversial office park expansion might have on the Glen. Standing next to the small waterfall, one balloon is clearly visible. Each balloon represents the top corner of a building.

Nightingale Properties wants to expand the Linden Hills office park in Penfield, adding three new buildings - one of which would be in Brighton - totaling 72,000 square feet. The balloons were put up by a developer for the benefit of the Penfield Planning Board.

The property sits right along Corbett's Glen, however, and residents and environmentalists say the proposal is too intense for the site. They fear the expansion will intrude on the park, marring the view from its footpaths and disrupting or harming important animal habitat.

This is one of two battles being fought over environmentally sensitive properties in Brighton. On the other side of town, just off South Clinton Avenue, Anthony J. Costello and Son Development wants to build town houses, loft apartments, and single-family homes along the north side of the Erie Canal, amounting to more than 330 new residential units. Environmentalists and nearby residents are resisting the project, which developers are calling The Reserve at Brighton.

The property is former pasture, now grown with tall grass and scrub. It provides habitat for grassland birds, whose national numbers have been declining. And the project could also intrude on a breeding colony of chorus frogs, which live in neighboring wetlands and marshes.

While both proposals have specific environmental concerns, there are other questions that need to be asked: Are these projects necessary? Is there a real need for new residential or commercial space? Monroe County's population is not growing and the job market is sluggish.

"We just keep building because we can," says former Rochester Mayor Bill Johnson, now a public policy professor at RIT. Johnson is also a sprawl and smart growth researcher.

From 2000 to 2006, Monroe County's population shrank by over 5,000 people to about 730,000. But during that same period, 9,469 building permits were issued for single-family homes. More still were issued for new town homes and apartment buildings. And under those permits, over 12,500 new residential units - homes, apartments, and town houses - were added countywide. Currently, there are more homes for sale across the county than there are buyers, says John Antetomaso, president of the Greater Rochester Association of Realtors.

In Brighton, the population has been essentially fixed at 34,500 since 1990. Yet between 2000 and 2006, the town issued 96 residential building permits, adding 410 residential units, says town planner Ramsey Boehner.

But town officials say there is a demand for new housing from current and potential residents. Newer, bigger homes would draw out-of-towners and may also appeal to current residents who want bigger homes but don't want to leave Brighton, says Supervisor Sandra Frankel.

Many of the homes on the market in Brighton are older and between 1,100 and 1,800 square feet. It's hard to find a 2,200-square-foot, four-bedroom colonial for sale in the town, says Brighton realtor Rome Celli.

Frankel says The Reserve is the first major housing development proposed in the town in many years and that she's had many people ask for a greater variety of housing.

New housing in Brighton, such as The Reserve, may be attractive to University of Rochester staff recruits, say college officials. Many university staff and faculty, as well as Strong Memorial Hospital personnel, choose to live in Brighton, particularly because of the schools and the town's proximity to the university campus and medical center facilities, officials say.

But if out-of-towners do come, where will they come from? Will they simply be residents of the city or nearby towns and villages, moving from one development into another?

Shifting is a bigger concern with the Linden Hills proposal, at least among Brighton officials. It would add a considerable amount of class A office space. There is conservative demand for that category of office space, which is generally newer with state-of-the-art systems, says Kimberly Schafer, director of marketing and research for the C.B. Richard Ellis real estate firm's Rochester office.

Most existing office parks can't accommodate tenants that want to expand, so the tenants look elsewhere. So to some degree, occupants are simply moving from one office park to the next. For example, when a new 45,000-square-foot office building was finished on Route 96 in Perinton, Merrill Lynch moved in, consolidating its city and suburban locations and leaving both previous offices vacant.

The major benefit Penfield would see from the Linden Hills project, says Penfield Supervisor George Wiedemer, is the addition to the tax base. There is "no overabundance" of office development in Penfield, he says.

There is currently about 2.5 million square feet of class A office space in the city and 8.1 million square feet in the suburbs - occupied and vacant - according to a C.B. Richard Ellis study released in April 2007.

After sitting in the single digits during the late 1990's, class A office vacancies shot up in 2001 - in the suburbs the rate was 9 percent, while it was over 14 percent in the city. By 2002, the suburban rate had increased to just under 14 percent. Those numbers held steady until 2006, the last year of data in the report, when the suburban rate dropped to about 9 percent. The city's rate stayed at about 14 percent that year.

Those numbers are considered healthy, Schafer says. Anything in the single digits, she says, is generally considered "no vacancy."

Vacancies are a bigger problem in the older, smaller, downscale offices primarily found in the city, known as classes B and C. Many of the former tenants have left for the suburbs. In downtown Rochester, there's a 36-percent vacancy rate for class B and C office space. In some cases, underutilized office buildings have been converted into apartments. The Medical Arts Building and Buckingham Commons are examples.

Part of the problem, Johnson says, is a lack of needs-assessment in speculative development - things like housing tracts and office parks - which are often built without a specific occupant in mind.

The Rochester area needs a regional approach to zoning and land use, Johnson says. Each municipality has the right to determine how its land is used, but residents and leaders tend to view their community as an island, and not part of a greater system. The system that's in place doesn't give planners a good view of the overall picture, Johnson says. And so one municipality repeats what may already exist in abundance somewhere else. And at some point, he says, there will be surplus capacity.

In a sense, that's what's happening with Medley Centre - the former Irondequoit Mall - and newly constructed shopping plazas in Webster, says Johnson. Webster's plazas are thriving, while Medley Centre has a high number of vacancies. The mall and the shopping centers serve the same purpose and, most likely, the same shoppers. And because they are close, they are competing for both tenants and customers. This situation isn't new to Medley Centre. Oft-cited reasons for the decline of Irondequoit Mall include the expansion of Eastview Mall and the merger that led to the Mall at Greece Ridge Center.

It's not just retail. When new tenants move into an office building or people buy new homes, they are simply relocating from the city or another town or village in the Rochester area.

"Everybody's essentially appealing for the same market," Johnson says.

There are good reasons why Rochester's communities should stop competing and start working together: the impact on built communities and the impact on open space and the environment.

Places like Brighton, Rochester, Gates, and Irondequoit are almost entirely built out. They have water and sewage systems, street and sidewalk infrastructure, and services such as their own police departments. But if people or businesses leave a developed community for a less-populated one, those who remain must make up the difference for the cost of things like police or fire services.

And residents shifting from developed communities into more rural communities like Mendon, Rush, Webster, or Wheatland, stress those towns, too. Often, the towns have to expand public water, sewers, and other services to new subdivisions or commercial areas. Roads have to be rebuilt to handle more traffic and schools have to make more space for a growing student body.

But the most visible impact has been on the land. Considerable amounts of open space have vanished in places like Webster and Pittsford. But it's not just what the homes and offices are built on. What they're built next to matters as well.

The Reserve at Brighton would be built on 63 acres of grasslands. In its current, undeveloped state, the land is a mix of open field filled with tall grass and weeds, tall trees, and rows of brush. Robins, finches, and sparrows flit about, and red-tailed hawks perch in the trees. Hedgerows along the canal provide berries for food and cover for nests.

The housing project, which includes several 75-foot tall, multiple-story buildings, will likely wipe that habitat out, says Jay Greenberg, a Brighton resident and member of the Rochester Birding Association.

"The development that's presently proposed would decimate the former pastures," he said during a November 14 Brighton Town Board meeting.

But it's not just the birds that residents and environmentalists are worried about. The property borders wetlands and marshes, home to several sensitive amphibians, including gray tree frogs and western chorus frogs. Nancy Chalker Tennant, of the Rochester Sierra Club, says The Reserve would be located next to the only breeding colony of western chorus frogs within 10 miles of the city of Rochester.

Nationally, the frogs are in decline, largely because of habitat loss or changes, says Sara Rubin, a member of the Brighton Conservation Board.

Linden Hills would be built on just over 20 acres of land directly bordering Corbett's Glen Nature Park, located between Penfield Road and Linden Avenue in Brighton.The park is an environmental success story. In the 1930's, a sewage treatment plant was built next to the property and Allens Creek. It operated for decades and left the Glen in disaster. Restoration efforts began in the 1980's. In 1999, Brighton, with the aid of the Genesee Land Trust, purchased the first part of the park. Brighton later purchased another chunk of land in the Glen, giving permanent protection to a total of 52 acres.

Corbett's Glen is a peaceful, idyllic valley. Squirrels and chipmunks scurry about the brush, while birds dart from tree to tree. Allens Creek cuts through the south side of the park.

The visual impact of the Nightingale project is a major concern. The new buildings - there is a 54,000-square-foot office building on the site - will mar the park's natural atmosphere, say residents, park users, and environmentalists. In addition, the lighting will be intrusive and the increase in traffic will create unwanted noise and contamination, says Jean Baric, a Penfield resident living next to the park and a leader of the Allens Creek-Corbett's Glen Preservation Group.

The other major concern is the impact on Allens Creek. The stream, a tributary of Irondequoit Creek, is a major trout and salmon stream, says Matt Sanderson, a biologist with the Department of Environmental Conservation's Bureau of Fisheries. Chinook and Coho salmon, along with steelhead and brown trout, make seasonal migrations through the stream. They spawn in select areas where there is clean gravel and good quality water, Sanderson says.

One of those areas is near the creek's three waterfalls in Corbett's Glen, Baric says. And runoff from additional development could change the characteristics of the creek, she says. Contaminants like antifreeze and salt could wash into the water. And water streaming off the parking lot surface could increase the creek's temperature.

There's a stormwater management system in place that's meant to cool the runoff and discharge it into a wetland before it goes into the creek, and studies show that it is working, says Doug Fox, Penfield's planning director. But some water also streams directly from the property into the creek, Baric says. And more buildings and parking could mean more water running off the property. Since the runoff is warmer than the creek water, it could raise the stream's temperature and impact spawning, she says.

The three new buildings and accompanying parking are too dense for the property, Baric says. And the Penfield Planning Board agrees. In an October letter to the developer, it said the development was too intense and may have to be scaled back. It also said the developer may have proposed too much parking.

The zoning, however, allows for "maximum development," even though it borders on sensitive areas and residential neighborhoods.

"We are all living with the consequences of very poor zoning," Baric says.

A group of neighbors is talking with both Brighton and Penfield officials about purchasing the undeveloped property and preserving it as open space. A special tax district would be established to pay for it. The owner "seems open to working with the neighbors," Baric says, but any talks have been superficial. The group may intensify its push after the New Year, she says.

The projects are not set in stone just yet, but The Reserve at Brighton is furthest along. The town board has approved the scope of the draft environmental impact statement - an outline of what the developer needs to consider during the environmental review. It's now up to Costello to submit the environmental review to the board, which will then hold a public hearing. The comments will be sent to Costello for use in preparing the final environmental review. Once it's satisfied, the town adopts the review's findings, and then decisions on the site plan can be made.

The town will also have to decide whether to allow zoning changes for the proposal. Costello wants the property rezoned to allow for waterfront residential building. He also wants changes that would allow for taller buildings. Since it would be an incentive-zoning proposal, Brighton, in turn, may require a certain amount of open space or canal-side amenities like a launch for non-powered boats.

Linden Hills is still in the conceptual stages. Nightingale Properties submitted several alternative designs, but only one was formally presented to the towns of Penfield and Brighton. Penfield is leading the project since the bulk of the proposal is on its side of the town line. No formal application has been submitted to either town, though boards have been preparing for one by examining the site and associated issues and concerns.

Both projects have considerable amounts of review to complete before work can begin. And now, when the projects are in environmental review stages, is the time when citizens can have the most impact.

Baric says it's not a question of whether the Linden Hills project will affect the Glen, but "How bad will it be?"