When trees at the edge of a woodland are cut down, more sunlight pours into the forest. More wind comes through. The days are hotter, the nights are colder. Birds and wildflowers who seek refuge from those harsh conditions in the deep woods may die or move out.
That scenario may be played out in the Middlesex Fells Reservation if The Gutierrez Co. goes ahead with plans to widen nearby roads to improve traffic flow near the proposed Stoneham Executive Center.
The Fells is not an untouched wilderness, but it is home to several habitats that are unusual in this area, and because it is close to local universities, it is also a convenient laboratory where biologists can study changes in living systems.
The building of the Stoneham Executive Center could change the ecology of the Fells. The 914,000-square-foot office park will sit on a site that is already developed, the former Boston Regional Medical Center, but the increase in use will draw more traffic, and Gutierrez Co. has proposed widening several roads and intersections in the area to help traffic flow more smoothly. That could change the nearby woodlands and also isolate plant and insect communities from one another.
In a separate project, the MWRA is considering putting a covered reservoir in the Fells, which would disrupt the wildlife in the immediate area. Recreational use also has an impact, as human visitors bring in weed seeds and disease germs, and new trails are cut to accommodate hikers.
All these small changes and temporary disruptions may add up to permanent changes in the area, biologists say
The changes may permanently disrupt habitat by:
Plant ecologist Brian Drayton said that the Fells is one of the largest tracts of undeveloped land inside Route 128, and for an ecologist, size counts: "The larger the tracts of land you have, the more variety and potential there is for wildlife and vegetation to diversify, " he said. "A bigger area can support more things."
That diversity is important, he said. "I think there is a big argument to be made people are healthier when there is a lot of diversity around," he said. "There is a real positive value to being surrounded by lots of things that arenít humans."
Drayton, who did a census of the plants in the Fells while working on his doctorate in biology at Boston University, said that the Fells includes a number of different habitats. Some, such as oak forest, are common, while others, such as stream banks, are relatively rare.
"The area around the Virginia Wood is pretty unusual," Drayton said. "There is a stream bank, kind of a flood plain area, along Ravine Road, and there is that beautiful stand of hemlocks-there is nothing quite like that elsewhere in the Fells."
In a 1993 study, Drayton counted the different species plants in the Fells and compared that census with another done in 1894. The result: The number of plant species in the Fells had declined from 422 to 324.
Some of that is natural, he said. For instance, when the MDC stopped mowing an open field near Medford High School, trees began taking over, and some of the butterfly species that had lived there disappeared.
But Boston University biologist Richard Primack, who was Draytonís advisor on the 1993 census, said that the types of species being lost tells the biologists what is going on in the Fells. Most striking to him was the loss of wildflowers, orchids, and other species that live in moist woodlands or the banks of streams.
"There are a lot of species that require a clean, undisturbed stream to complete their lifestyle," he said. "Anytime you have more development, more runoff into streams, you lose species. The effects are subtle."
Primack believes that species are lost in bursts, several at a time, rather than gradually, and that even a temporary disruption, such as that caused by construction, can cause species to disappear forever.
"The Middlesex Fells is very isolated," he said. "It is difficult for species to come back, especially wildflowers, but that is true of insects, too."
For example, Drayton said, wildflowers such as violets and bloodroot drop their seeds on the ground, and some of the seeds are picked up and carried to new locations by ants. If a road is built nearby, the ants cannot cross it, and if the original plants die, they will not be replaced. "Hard, dry places act as barriers to the movement of species," Drayton said.
The Fells is already isolated because it is surrounded by developed land, but widening roads or building new trails could also isolate different parts of the reservation from each other.
Another type of change comes when new trails are cut through wooded areas, or trees are cut at the edge of a forest. "The more edge you create, the more things can get in," Drayton said, including heat, light, humans, and pests. These "edge effects" can affect the wooded area for up to half a mile, Drayton said, and if the surrounding areas are cut on several sides, the entire ecosystem changes. The deep-woods warblers and wildflowers will be gone, never to return.
While nothing Gutierrez has proposed is that drastic, the developer and the MDC have agreed that Gutierrez should widen the Fellsway East southbound where it meets Pond Street. That would slice a narrow strip out of the Crystal Springs area, creating just the sort of edge effect Drayton was talking about.
The swath of woods immediately surrounding the SEC site has already been heavily disturbed, Drayton said, although he added "It would be worth having a botanist go through there one more time" to look at the species there.
Virginia Wood, which is on the other side of Ravine Road, is a different matter. In addition to the hemlocks, the wood includes a ravine that contains several species that are unusual in this area. "It is a fairly rich, moist area that is unusual," he said. "I doubt there is anything of great rarity on global scale but as a habitat it is unusual near Boston. That is an area that needs to be treated carefully."
The Fells will always be surrounded by roads and infiltrated by humans, but Drayton feels that its neighbors should tread lightly on the land. "This is not wilderness, but it is rich," he said, "and there is a kind of beauty and complexity that I think people need. That is why I would protect it."