Trees, environment, and genes: in the evolutionary battle to survive and thrive, a species' parentage is just the beginning - Heartwood

American Forests, Summer, 2003 by Gary Moll

Think about a tree that in your mind is perfect. Now imagine creating more trees just like that one-trees that grow tall and straight, or low and spreading, trees that seem untouched by bugs or blight. How do you recreate a 'perfect tree?

It's a question that's been debated for decades. Some insist that a tree's genetic material is a recipe for superior trees, that harvesting genetic material and then producing offspring creates a "cloned tree, an exact replica of' the parent. Others insist a tree is as much a product of its environment as its parentage. Who's right? The answer begins with genetics.

The classification system devised for the plant kingdom gives each tree a unique name that provides a road map to its genetic structure. Within the genus or family of maple trees, for instance, a red maple is Acer rubrum and a sugar maple is Acer saccharum.

Knowing the difference between species is essential for environmental, as well as economic, decisionmaking. Sugar maple, for example, makes good syrup and hardwood flooring for basketball courts and bowling alleys; not so with red maple. Red maples boast a larger natural growing range and can more easily adapt to wet and dry sites. And the red maple produces a wide genetic diversity from its seed, which means a red maple in your backyard might produce very different-looking offspring. Those who think maples are basically all the same make a fundamental mistake about species with uniquely different genetic makeups.

Another fundamental mistake would be to assume that so-called "champion" trees--the largest known of their species in the U.S. and therefore on AMERICAN FORESTS' National Register of Big Trees- are somehow genetically superior to their counterparts. In some cases, in fact, just the opposite is true. While many of those trees are true beauties, some are downright ugly, bug-chewed, or dying. One--the national champion American elm, in Grand Traverse County, Michigan--has recently been declared dead from Dutch elm disease.

In the end, the trees that wind up on the national Register are a product of their environment. Although we wish there were some secret gene that made them supertrees, in fact they are no more likely to be genetically superior or longlived than any other tree in the forest or along a city street.

In fact, it's very possible that a tree growing old on one spot would not live to a ripe old age somewhere else. Tree selection is a science best left to experts with a detailed understanding of the process of selection and the production of improved plant material. The experts, too, know the best way to gather genetic material without causing damage to trees. Tree climbing spikes, for example, should be used only for tree removals or for climbing dead trees or telephone poles--never on living trees, especially national treasures.

THE NAMING OF TREES

Trees are grouped by their biological characteristics into order, family, genus, species, and variety. The process of naming plants and classifying them into those groupings is called nomenclature; the study of trees themselves is called dendrology. The "order" is the most easily recognized--a softwood, like pine, as compared to a hardwood. As you move toward "variety" the distinctions become more difficult. Understanding varieties, or differences within species, requires considerable expertise.

A tree geneticist trained in the science of tree breeding understands more than just the principles of population genetics established by Gregor Mendel 150 years ago (remember those peas from biology class). A tree geneticist has learned techniques for selecting desirable genetic material for tree breeding and conducting progeny tests (growing out trees in experimental plots) where the environmental conditions are kept the same and the plants genetic make-up is altered.

Scientists who work in tree genetics specialize. A forest geneticist working for a wood-products company might focus on genetic improvements to change the length of tree cells used for making paper or the volume of wood in a saw log. A tree geneticist working to improve urban trees might focus on the vigor of a tree for wound closure or disease-resistance.

NATURAL SELECTION

Of course, nature sorted trees (that survival of the fittest exercise) for millions of years before humans came along with their nomenclature classifications. Trees have been growing under natural conditions with flowers pollinated and new seeds formed for more than 200 million years.

When seeds germinate, if the conditions are right they grow into mature trees, although the vast majority of seeds cant make it in the environmental conditions in which they attempt to grow. As a result of this long evolutionary process, only the best survive. Over millions of years they've developed the unique characteristics we know today, allowing botanists Carolus Linnaeus to develop the nomenclature system and Andre Michaux to articulate the place in the nomenclature for North American trees. (The continental U.S. has 850 distinct species of trees and more than 10,000 tree varieties.)