The blades on the 660-kilowatt turbine are 47 meters in diameter. This particular model—a Vesta V47—is a fixed rpm machine. No matter how hard the wind blows, it always spins at the same speed; the individual blades rotate and feather to compensate for increased velocities. At 6 to 7 mph, wind begins to generate enough force to spin the propeller, Stern explains, though this produces minimal electricity. When the wind reaches 12 mph, the turbine produces at 40 percent capacity. Output increases until the wind reaches an optimal speed of 20 to 22 mph. Little to no additional energy is produced at higher speeds. At a certain point, around 45 mph, the wind becomes too potent and the turbine automatically shuts down.

Installed in 2001 at a cost of $753,000, the turbine, known as Hull 1, generates approximately 1,600 megawatt-hours annually, enough to power about 150 households. Farther down the peninsula sits Hull 2, the town’s second wind turbine. With a blade diameter of 70 meters, it is “a newer, bigger model, with three times the capacity without being three times as large,” Stern enthuses. Together, the two turbines provide 11 percent of the town’s electricity needs.

But overall, Stern is unimpressed. “Two machines up in 10 years? I don’t think it’s a success. We gotta put more of these things up.” To that end, the town is developing a plan to install four 3.6-mega-watt wind turbines just off its northern shore. Once operational, the combined turbines would produce enough juice to power the entire 11,000-person community.

Such projects will shape the skyline in years to come, a highly visible manifestation of wind’s influence on the Boston landscape. But Hull is fortunate, its seaside location providing the consistent breezes needed to make these efforts viable. Farther inland, dense forest and a rumpled topography slow down air flow into an irregular and temperamental force. Here wind’s power is not evidenced by man-made structures; it’s in the trees overhead.

In the forests of the Northeast, wind is a squirrelly sprite that vacillates between calm and fury, depending on the weather. And its effects shape the very structure of the woods. “The dominant disturbance factor in most northeastern forests is the wind regime,” says Charlie Cogbill, an ecologist specializing in historical ecology who is currently working on a Hubbard Grant at the Harvard Research Forest in Petersham, Mass.

As wind velocity increases, it first rustles leaves and twigs, then small branches. Large branches start moving at 25 mph. Entire trees begin to sway around 30 mph. By the time speeds hit 40 mph, limbs begin to shear off. And the primary interface for this damage is in the canopy. “That’s the delivery point, where all the action is,” Cogbill says.

“As the average wind speed goes up, the canopy becomes more shaped, more ragged, more damaged,” he explains. “The trees that grow up and out of the canopy, the emergents, are in the windier spots. Their tops tend to get abraded and broken. A classic is yellow birch. They can last a long time, but the canopies of older trees are almost always bushy-topped as the uppermost boles are snapped off by the wind.”

It’s a different world down below on the forest floor, where air movement is minimal beneath the sheltering canopy. “High wind speeds seldom if ever penetrate the understory and rarely affect saplings, even the most vulnerable species,” Cogbill explains.

Which is true—until the wind punches a hole through the canopy’s protective layer.

Trees start getting knocked down when the wind begins to exceed 50 mph, though a variety of factors—rot, disease, age—all play a role in whether a particular tree succumbs at a given wind speed. “Wind is a mortality disturbance,” Cogbill notes. “On average, at any given point in the landscape, you’d expect wind to be a mortality factor once every 100 years.”

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