Tree treks

Published 5:51 pm Thursday, November 10, 2011

Photo by Terri Gordon / Trees are not the only plants to show their colors in the fall. These blueberry bushes have turned deep red with the changing season.

Forests are like civilizations or like the fall of Rome — only quieter. As generations come and go, the forest reaches a climax.
Recently touring Sarett Nature Center, director Chuck Nelson and naturalist Mindy Walker were able to identify signs of a new succession among the native trees there.
Currently, there is a solid generation of oak and hickory.
“The young trees coming in, the saplings we see,” he said, “are largely beech and sugar maple.”

Photo by Terri Gordon / As days shorten in fall, trees slow their production of chlorophyll (which makes leaves green), revealing leaves’ true colors — plants rich in carotenoids become yellows, oranges and browns, while trees that produce anthocyanins turn red.

Nelson and Walker demonstrated how to “key” trees, using botanical features — whether leaves are singular or composite, toothed or lobed, whether they grow in alternate or opposite patterns and whether tree branches are alternates, opposites or whorls.
“But the best way to learn your trees,” Nelson said, “is to go along with someone who knows trees and learn from them,” Nelson said.
At Sarett, 2300 Benton Center Rd., just outside of Benton Harbor, the maples are fairly easily identified — think Canadian flag. Telling the various maples apart is a bit trickier, and there are five or six varieties. To identify a sugar maple, for instance, one needs to examine a leaf.
“Look at the middle lobe,” Nelson said. “There are no teeth on the middle lobe.  It’s clear.”
Oaks? Oaks fall into two categories: the black-red oak family and the white oak family. The white oak family has rounded edges, while members of the black-red family have points.
“”White oaks have a little anthocyanin and can turn a nice rosy color in the fall,” Nelson said.
Elms are double-toothed and feel like sandpaper, populus trees — like cottonwoods and aspens — have flat leaves that “tremble” in the wind.   To tell a quaking aspen from a big-toothed aspen, hold it out at arm’s length. If you can see the teeth, it is a big-toothed variety; if not, it is quaking aspen.
Deer like white cedar, but will only eat the prickly red cedar, if desperate.
Beavers like the bark of the big-toothed aspen. And, when choosing a stick to roast marshmallows or hot dogs, it is best to avoid black cherry, which contains cyanide. Heat activates the poison, distributing it into the food and making the person eating it sick.
Of course, one of the spectacles of autumn is the changing leaf colors.  Contrary to legend, this has nothing to do with Jack Frost or cooler temperatures. It is the shortening of the days.  As sunlight diminishes, photosynthesis slows, and chlorophyll lessens.
Leaves made green by chlorophyll now reveal their natural pigments, carotenoids that produce yellows, oranges and browns and anthocyanins that create reds. As the tree seals off its branches in order to survive the coming winter, the leaves die and drop to the ground. Leaves undergoing this transformation are called deciduous.
Evergreens, on the other hand — firs and spruces being the two most common trees on earth — have developed a sort of antifreeze, allowing them to keep their leaves throughout the year, though they do shed old growth.
Of course, there’s the exception: The tamarack, a deciduous pine tree whose leaves turn golden in fall and drop.