Dead oaks provoke ecological enigma
Winds gusting to 50 mph swept over Martha's Vineyard Saturday night and again on Tuesday, knocking out power in some spots, and littering up-Island roads with branches of dead oak trees -just a taste of the mess that would occur if a hurricane tracked directly over Martha's Vineyard. Tens of thousands of dead oak trees that have been killed over the last four years of caterpillar infestations could come tumbling down in a big blow. Some would fall across roads, creating a headache for town highway departments, but these would only be a tiny fraction of the total.
Most oaks survived the initial caterpillar infestations of 2005 and 2006, but the defoliation in 2007 was followed by a severe drought and many trees didn't get the boost they needed to re-leaf as they had the two previous years. "It's the worst possible scenario if there's a dry time after the defoliation - it's just too much for them," said Tom Robinson of Island Timber.
Up-Island, the greatest concentration of dead trees is on private property just west of the intersection of North and State roads in North Tisbury. It's most visible eight tenths of a mile up North Road, where the road rises and curves gently to the right around the shoulder of a hill. Along a ridge about a half-mile off to the south is a sea of grey, starkly noticeable this summer against the surrounding green. Known as Middle Ridge, this is the epicenter of the great defoliation and die-off of the oaks that dominate up-Island woodlands.
Photo by Ralph Stewart
Owned by the Woods family, the property visible from the road is part of a 512-acre wildlife refuge with conservation restrictions held by the Nature Conservancy (TNC). It abuts the Polly Hill Arboretum, the Agricultural Society's fairgrounds, and Panhandle Road along its eastern edge, and to the west it runs up against the Land Bank's Waskosim's Rock Reservation, where walkers can get a firsthand taste of the devastation wrought by the marauding bugs. It's surreal to be walking through thick green woods and suddenly find yourself under skeletal oak trees with the sun shining through as if it's the middle of winter.
Matthew Pelikan, Director of the TNC's Islands Program, said that about 200 acres of the Woods property is completely defoliated. Tim Boland, executive director of the Polly Hill Arboretum (PHA), said, "Right now, it looks like 30 to 40 percent of our natural areas are impacted by the caterpillar and at least 30 percent are outright dead trees." To the untrained eye, the mortality at Waskosim's Rock looks to be a bit less.
The extensive caterpillar carnage on Middle Ridge was abetted by two factors. First, there are no open fields or roads to break up their progress through the woods. Second, "Trees that were higher and farther away from the water table, along the ridgeline where there is higher elevation morainal gravel really suffered," said Mr. Boland.