Making a new tree:
reproduction and cloning

How are new sugar maple trees created for mature ones?
Here we discuss two ways: seed reproduction and cloning.

Reproduction
In school you may have learned that under normal conditions, trees reproduce naturally through seed reproduction. Here we discuss it only briefly, as an introduction to cloning.

Trees are naturally produced from seeds, which are created from mature trees. Most sugar maple trees need 30 years of healthy growing before they reach maturity. In sugar maples and many other trees, pollen from the male reproductive organs of a "father" tree fertilize the ovule, or female reproductive organ, of the "mother" tree.

This pollination results in the creation of a seed (click here to see a sugar maple seed) that eventually drops from the tree and lands on the ground - generally nearby, but often at quite a distance (think about how sugar maple seeds you may have seen can travel on the wind). If the environmental conditions are right, the seed will sprout roots, grow a shoot, and eventually become a small seedling. The seedling will have a genetic makeup that reflects both its parents.

Cloning
Do you remember "Dolly," the cloned sheep? Foresters have been cloning trees for years. This allows them to produce trees that are genetically identical to the parent tree, which is particularly useful in the Sugar Maple Tree Improvement Program. But how do you get clones of trees?

The first step in cloning a tree is taking a "cutting" or branch of the parent tree. The cuttings can then be "grafted" or allowed to grow onto roots ("root stock") of an existing tree. If you are familiar with grafting apple trees, you know that any genetic characteristics of the apple tree cutting will be expressed above the point where the cutting is grafted onto the rootstock. For example, if you take a cutting from an apple tree with crisp, green apples, and graft it onto rootstock from a tree with mushy, red apples, the new tree will produce crisp, green apples above the point where it is grafted. This same principle would hold for maple trees. If sap sweetness is genetically controlled, then a grafted tree should have similar sap sweetness to the parent cutting above the point where the tree is grafted.

Alternatively, cuttings can be "rooted." This involves treating the cuttings with hormones under special greenhouse conditions so that the cuttings form their own roots. It can be a tricky business as it involves growing the cuttings under just the right temperature, moisture, light, and nutrient conditions. Scientists from the U.S. Forest Service and Cornell University have pioneered new methods of developing roots on sugar maple cuttings.

 

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