Autumnal Foliage Can Be Pretty Tree-Killers

Oct. 19, 2005 — -- That maple tree in your front yard may be magnificent this time of year, cloaked in the colorful robes of splendor that herald the transition from one season to the next, but you might want to give it even more respect. It could be a killer.

Researchers at New York's Colgate University have found evidence that the brilliant red hues of autumn aren't just there for our personal enjoyment. They're engaged in a kind of chemical warfare, releasing poisons that could kill off the competition.

Thus maple trees, and probably some other species that turn crimson in the fall, join a growing list of plants that don't just beat around the bush when other plants start intruding into their space. They kill them off. Scientists call it "allelopathy."

For years scientists have known that black walnut trees are lethal when it comes to protecting their turf. And more recently, the mighty chestnut tree that once blanketed the Appalachians has come under suspicion. But the maple tree adds a surprising twist. How could anything that lovely be deadly?

It all began when Colgate biology professor Frank Frey and a former student, Maggie Eldridge, started looking into a peculiarity involving plants that turn red in the fall. The predominant colors of autumn break out when chlorophyll in the leaves breaks down and exposes remaining pigments, which are often yellow or orange.

But it takes a different process to produce red. That isn't a pigment that is left over when everything else is gone. Instead, it's produced in the fall, at the very time when the tree is struggling to cope with the energy demands of a changing and challenging season.

Why, Frey and Eldridge wondered, did the maple go to all that trouble at a time when it needed its metabolic energy for other purposes, like stimulating the growth of its root system?

So they collected chemical extracts from red and green maple leaves and yellow and green beech leaves and poured it over lettuce seeds. Some previous research had shown that wood extracts from red maple and red cedar inhibited the growth of lettuce.