Posted by Beth Daley June 13, 2010 06:23 PM
http://www.boston.com/lifestyle/green/g ... dutch.html
For so many years, the story of Dutch elm disease was one only of tragedy: Before this century began, 100 million of the graceful, arching American Elm trees found in cities and forests were dead. Headway has been made to re-establish the shade tree on urban streets through the introduction of disease-resistant elm trees. But there was less emphasis to repopulate low-lying forests where the trees helped slow floodwaters to nearby communities and provided shade and habitat for the floodplain ecosystem.
-------------------------------------------------“American elms along the Connecticut River once grew up to eight feet in diameter, but today most are killed by (Dutch Elm Disease) at diameters of less than one foot,” explained Christian Marks, floodplain forest ecologist for The Nature Conservancy. “Without the mature elms, the floodplain forests degenerate into weedy meadows after the shade-intolerant floodplain pioneer trees like silver maple die off.”
As a personal note I must comment that the Silver Maple/Sycamore dominated system found in many islands on the Allegheny River in PA seems to be a pretty stable system. The silver Maples are not dieing off. It doesn't make sense that the shade intolerant silver maples are dieing off - if there are not other species growing that are somehow shading them out, then what does it matter that they do not grow well in the shade? There certainly is enough open areas within these island systems to provide open areas for the silver maples to replace themselves. The big problem really seems to be invasive reed canary grass crowding out regeneration, rather than ther ebeing a problem with shade.