Global Warming Killing Island Trees?

Submitted by VT on Mon, 11/02/2009 - 10:13.

W. Tisbury

You can see it from the road, even in the middle of summer, a bald spot in the rolling green canopy of oak leaves. The 500 acres of dead oak trees in West Tisbury may be what's left of a caterpillar invasion, or a drought or both but, maybe a harbinger of things to come in a world that is slowly getting warmer.

From today's Globe: WEST TISBURY - Ever since a vast tract of Martha’s Vineyard forest died two years ago, visitors who stumbled upon the graveyard of gray stalks have called it eerie, bizarre, and sad.

Now scientists are calling it something else: a possible climate change lesson.

“Climate change will drive changes in the forest,’’ said Harvard’s Foster. “But they will be more rapid if the forest is also impacted by bugs.’’

The 500 acres of dead oak trees were the epicenter of an islandwide infestation of caterpillars that munched their way through millions of leaves for three consecutive springs ending in 2007. Then a severe summer drought hit the island, finishing off tens of thousands of the weakened trees.

“I have never seen anything like what has happened on Martha’s Vineyard in New England,’’ said David Foster, a Harvard University ecologist. “Usually you walk through forests and see some dead trees, but here, it’s hundreds of acres and almost all of the trees in it are dead.’’

Ordinarily, such catastrophic damage would be chalked up to bad luck. But Foster, who is also director of Harvard Forest, the university’s experimental forest in Petersham, and other researchers recently discovered a vast die-off of Cape Cod coastal oak trees 5,000 years ago during an abrupt warming period. They found evidence of the forest’s demise in sediment samples from under lakes and ponds, and they speculate that the ancient - and far smaller contemporary - episodes may have roots in the same type of one-two climate punch: more-active bugs coupled with an intense drought.

Scientists predict that in a warming world, insects will thrive, and droughts and other extreme weather will become commonplace. With the prospect of more numerous bugs feasting on weakened trees, Foster wonders whether the recent die-off is a harbinger of more catastrophic ones in the future. While the dead trees will certainly be replaced by new ones, what species repopulate forests has ramifications for everything from lichen to leaf-peepers.

“These trees control the foundation of an ecosystem,’’ said Foster, whose group has just been awarded $100,000 from the National Science Foundation to study the Vineyard forest. “What happens when they collapse? We are trying to understand how everything in that forest copes.’’...(more)