How does a forest grow and change over time? How does it respond to changes in the environment, both intense and short-term, like a fire, and chronic and long-term, like global warming?

In a forest, trees compete for resources: light, water, and nutrients. Smaller trees are greatly affected by surrounding taller trees. For example, taller trees can block the sun, take up more soil with their larger roots or take the water from the soil before the smaller trees can get it. The same may be true for chemicals in the soil that a tree needs, especially nitrogen, phosphorus and potassium.

Some trees do best right after a clearing, where there is plenty of light, and the rain falls directly on the ground. Often these trees have seeds that travel readily - either light seeds that blow easily in the wind, as do aspen seeds; or fruits that birds and small mammals eat and carry from one place to another,
as do oaks, cherries and red cedar.

Other trees do best in the shade. They can grow when the light is low.
These trees often have heavy seeds that do not move readily in the wind, but provide a large supply of food for the seedling, so that it can grow until it gets big enough to have leaves that can capture light in the shady forest. Beech has such large seeds which are rich in oil. Sugar maple grows well in the
shade, as do spruce and fir.

Trees can be quite different in adapting to climate and to physical properties
of soils. Some trees grow well where it is cold - some even require frost to complete their life cycle. Others grow best where it is warm.

What is an "old-growth" forest?
Natural forests that have developed over a long period of time — generally
at least 120 years — without going through severe disturbances such as windstorm, fire or logging are considered old-growth. Technically, an
old-growth forest is more than a stand containing old trees — it is a living ecosystem that supports numerous species of plants, wildlife and insects that are dependent upon ecological conditions that cannot be found outside of mature forests.

Old-growth forests provide a unique habitat for species that do better in old forests than young, helping to continue a genetic line that would be lost with the forest's demise.

How Species Benefit from Old-growth Forests

• There are specific types of hawks, such as the northern goshawk, a large forest raptor and owls, like the Barred Owl, that prefer older forests.
• Many species of songbirds, such as warblers and tanagers are found in these old-growth areas.
• Organisms that provide critical nutrients such as lichens and fungi appear in old-growth forests in greater number and diverse species than in younger forests.
• Old pines provide bald eagle nesting sites.
• Fallen trees provide shelter for insects and small mammals.

Old-growth forest research points to the importance of genetic diversity for forest conservation, restoration and general health. Thousands of years of genetic conditioning are found in old-growth forests. They could contain
genes that would enable them to survive global warming along with other threats that may appear in the future. Younger forests do not have the
same genetic reservoirs and therefore may have a more difficult time transitioning to old-growth forests.

Old-growth wood is desirable due to its fine grain and natural beauty. The lumber industry defines trees by lumber grades, not age. As old-growth wood provides the highest quality lumber, it accounts for much of the "upper" or "architectural" grade wood. Because of these qualities it is usually the first to be harvested. As consumer demand controls the market for wood, public pressure can make all the difference in saving this irreplaceable world treasure. To preserve our last unprotected ancient forests while ensuring a supply of lumber for future generations, we have to support sustainable harvesting methods and use sustainable alternatives.