Studying sturdy surviving elm trees
Wednesday August 22, 2012
PITTSFIELD -- A lone American elm stands 50 feet tall on a thin strip of roadside grass in a quiet neighborhood off South Street.
In an area that used to be dense with the species -- South Street was once lined with them -- the otherwise unremarkable tree on Elizabeth Street is now one of a handful in the Berkshires that seems to posses a natural resistance to Dutch elm disease, which ravaged the American elm population during the mid-20th century.
Tom Zetterstrom, a member of Elm Watch, an organization dedicated to protecting the remaining American elms in the region, is working with scientists from the Nature Conservancy who hope the Elizabeth Street tree and others like it can be tapped to breed new lines of Dutch elm disease-resistant American elms that can eventually be reintroduced to their natural forest habitat.
"It's either good luck or good genes -- either way, it's a minor miracle that there is a tree like this here," Zetter strom said Tuesday as he worked with Nature Conser vancy intern Michelle Grohe to document the tree's location, condition and age.
In contrast, Zetterstrom pointed to a much smaller American elm in the distance that is already showing brown, dead leaves around its crown -- signs of an apparent Dutch elm disease infection.
On Tuesday, Zetterstrom and Grohe traveled between 16 disease-resistant American elms in Dalton, Lanesborough, Lee, Lenox, Pittsfield and Stockbridge -- all identified by Zetterstrom, who has photographed the trees, which he finds aesthetically exciting, for the better part of two decades.
The targets were all described as "exceptionally large American elms growing ... where they are surrounded by smaller elms displaying the disease."
Christian Marks, the scientist at the Nature Conservancy spearheading the project, said the next step is for conservancy personnel to return to the trees to collect pollen that will then be crossed with other DED resistant elms.
The offspring of those crosses will be planted at three different sites in Vermont, and once they are big enough, will be tested to see if they are indeed resistant.
"We'll keep the best ones and restore them to the wild," Marks said.
It's a long-term project that Marks said is unlikely to yield real results for at least 10 years. But he said the American elm is an important species, particularly in forest flood plains, where no other tree in the Northeast fills the dominant, canopy role that the elm did.
The tree still grows in the habitat, but they are killed off by Dutch elm disease before they fully mature.
"These trees that used to be the biggest trees are now the smallest," he said. That has hurt bird and insect species, he said.
Marks said there are already seven American elms being bred that are disease-resistant. But he said that they have all been cloned from the same seven trees, can't produce new resistant trees naturally, and don't offer the necessary biodiversity to repopulate forests.
By the end of his project, Marks said he hopes to collect samples from between 40 and 50 individual resistant elms that can be bred and introduced to forest flood plain environments, offering enough of a genetic mix for the tree to once again take up its dominant role in the ecosystem.
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