Article #50, August 2001
By Bill Cook
Most of our tree species regenerate best without people having to plant them. If you take a moment to think about that, it’s common sense. Trees have been reproducing a lot longer than people have been harvesting them.
Of course, tree planting is still an important part of forestry. About 30 million trees are planted in Michigan each year. But many millions more are established through forest management and natural regeneration.
Natural regeneration comes in four flavors, seeds, sprouts, suckers, and something called “layering”. How a tree regenerates is an important factor in prescribing a management system to a forest.
All trees produce flowers and fruits.
Tree flowers are usually inconspicuous, but some can be rather showy. Not all flowers have both male and female parts. Many times the separate male and female flowers mature at different times to help avoid self-pollination. Some species even have separate male and female trees. Watch a ruffed grouse during the winter and you’ll learn where the male aspen trees are.
The fruits have many names, such as acorns, pods, nuts, catkins, helicopters, cherries, cones, and many others. Fruits and seeds are not the same thing. The fruit is the part of the tree that contains the seed. The seed contains the tissue from which a new tree might grow. For example, an apple is a fruit with seeds inside. A pine cone is also a fruit, with the seeds inside.
The variety of tree fruits and seeds is amazing. Some float on the air. Others must pass through the digestive tract of birds. Fruits ripen at different times. Red oak acorns take two years to mature. Spring seeds take advantage of the current growing season. Fall seeds often require a period of cold weather in order to germinate in the spring. Sugar maple germinates at a temperature of 34 degrees, even under the snow.
However, some tree species have alternative forms of regeneration.
Sprouts and suckers begin from dormant buds. Normally, these buds are suppressed by chemicals travelling down the tree. For a variety of reasons, including top death or illness, the dormant buds will grow. Sprouts come from buds around the base of the trunk and suckers shoot up from buds on root systems.
Oaks, basswood, red maple, and white birch are common examples of trees that have sprouts. Whenever you see clumps of trees in the forest, it usually means the tree has compensated for either a stressed or dead top. In Europe, certain hardwood forests are managed and regenerated using this biological characteristic. The presence of tree clumps in a stand sends a message about its past history.
Aspen species (quaking, bigtooth, balm, and cottonwood) are noted for their ability to send up thousands of suckers per acre from root systems. This ability, coupled with the strong affinity for full sunlight, is why aspen responds well to clearcutting. A tree can’t tell if the top is killed by chainsaw or wildfire. The root system will respond the same way, and it’s what they’re designed to do.
The most unusual form of regeneration is called layering. When a branch or trunk comes in direct contact with soil, certain species will grow roots at that point from the branch. This can result in some strange sights in the woods. The U.P. species that layers is white cedar, and even that is not common. Layering is more a feature in humid tropical forests.
Tree reproduction employs a wide range of strategies and requirements. It is one of several critical biological characteristics that foresters must be aware of as they match forest types to management systems. Knowing these sort of things is part of what makes forestry such a rewarding profession.
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Bill Cook is an MSU Extension forester providing educational programming for the entire Upper Peninsula. His office is located at the MSU Upper Peninsula Tree Improvement Center near Escanaba. The Center is the headquarters for three MSU Forestry properties in the U.P., with a combined area of about 8,000 acres. He can be reached at firstname.lastname@example.org or 906-786-1575.
by Bill Cook, Forester/Biologist, Michigan State University Extension, 6005
J Road, Escanaba, MI 49829
906-786-1575 (voice), 906-786-9370 (fax), e-mail: email@example.com
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