By: Steve Roark
Volunteer, Cumberland Gap National Park

It is often assumed that small trees are young and large ones old. But I've seen large trees that were only 50 years old, and others the size of fence posts over 100. Individual trees grow at different rates based on their genetics and growing conditions.

Some trees are bred for speed. Yellow poplar, most pines, and red maple will grow rapidly under good conditions. Other species like beech, hickory, and white oak grow at slower rates. What also determines how fast a tree grows are the growing conditions of its immediate surroundings. Foresters call this Site Quality.

Here are some site factors that affect tree growth speed: Soil (deep moist fast, shallow slow); Location on a hill (dry upper slopes slow, moist lower slopes fast); Aspect (direction the hill faces); north and east facing slopes are moist and fast, west and southern slopes dryer and slower; Competition from neighboring trees for sunlight is a big growth factor, with crowded trees growing slower than trees with more elbow room

It's important to look at these site factors for several reasons. When investing money in forest management, you want to put your money on the best sites, as they'll have a greater return. When planting trees, you want to pick a species that will tolerate the growing conditions. Pine can take it being dry, while black walnut prefers it moist.

When a tree is cut, it is well known that you can age it by counting the tree rings on the stump. When you look at tree rings, you are actually seeing two different growth rates in a given year. Each individual ring is made during the spring of the year when the tree is growing fast, and the rings are actually large pores. The space between each ring was grown during the summer when conditions are usually dryer and growth slows down. The pores here are much smaller, but you can see them with a magnifying lens.

The wider the tree rings are apart, the faster the tree was growing, so by looking at a stump you can read the history of the tree. The first few years maybe the rings are wide where the tree had lots of room and could grow fast and free. Later the rings may gradually get closer, indicating the tree had to compete with other trees for light. There may be one ring extra wide compared to other rings, indicating a long, moist growing season. Very close rings may also indicate drought years.