The Magnificence of Old Growth

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Published on: Sep. 2, 2000

Last revision: Nov. 5, 2010

in Missouri.)

We often envision old-growth forests being chock-full of giant trees. That’s not the case, though. There are typically fewer than five large, old trees on a given acre of Missouri old-growth forest, but due to their size they are some of the most memorable.

For every large, old tree in an old-growth forest there are hundreds of smaller, young trees. In fact, on dry, rocky, south-facing slopes even the oldest trees may remain small in diameter and short in stature due to the harsh growing conditions. The best opportunities to find any remaining undiscovered patches of old forest are on dry, south-facing slopes that are too steep to log and too dry to produce large timber.

Compared to the bustle of our daily lives, a forest - especially an old-growth forest - seems like a place where things never change much from year to year. However, old-growth forests are surprisingly dynamic. One characteristic always associated with old forests is the presence of scattered large gaps in the treetops. These openings can be 50 feet or more in diameter. The gaps are created when large trees fall over.

Trees can be weakened by old age, insects, disease and competition with other trees, but wind, ice or snow typically bring them down. Often a falling tree knocks down neighboring trees on its way to the ground. Nothing in the forest commands your attention as quickly and completely as the sound of a large tree crashing down on a wet, windy day. It immediately alters your perspective about how rapidly these forests can change and the physical forces that are involved.

The light that reaches the forest floor through gaps in the canopy promotes the growth of new trees. Initially there may be hundreds of small trees in a gap, but most will eventually be crowded out as they get bigger. Only a few trees will grow fast enough to reach the top levels of the forest canopy. It may take 50 years or more for the new trees to fill a large gap and reach the height of the surrounding trees. This is the process that allows old-growth forests to continuously regenerate themselves. It is also the reason that old-growth forests have many more small, young trees than large, old ones.

One thing that old-growth forests have in abundance is dead wood. It is easiest to see this in the winter when the leaves are off

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