In general, old growth ecosystems are characterized by the presence of old trees and their associated plants, animals and ecological processes. Ultimately, these forests show minimal evidence of human disturbance. The tree species found in these old forests can often live for a time length of three to five hundred years.
No forest is ever static, as they represent ever changing ecosystems. The process of change in a forest is called forest succession. A forest is "born" (or reborn) after any major distubance. These can include fire, windstorms, logging and even floods. The first tree species to grow back after these events are called "pioneer" species. Each of these tree kinds have an evolutionary strategy for arriving early to the new real estate. An example of this is how Poplar trees have very light seeds that can be blown far distances in the wind.
A new forest is a very competitive place, thus, the pioneer species must grow quick to stay in the sunshine above other trees. At first, these young forests are very dense. As they grow and mature, the smaller trees are shaded from the sun and die. When a forest then reaches adolescence, the trees continue to grow quickly and are all roughly the same age.
As a forest reaches maturity (typically over 150 years of age), many openings begin to form in the canopy as trees die. These openings allow light to penetrate to the forest floor and encourages new plant growth. These multi-age stands are characteristic of old growth forests, as they represent the highest diversity. After a very long time, a forest can reach a point where the trees are constantly growing and constantly dying without changing the average age of the forest. This is often referred to as a "climax forest" and is made up primarily of trees that are shade tolerant.
Now that we have briefly covered what an old growth forest actually is. Here, we are going to discuss some things to pay attention to when hiking to help you locate and identify older forests.
Forest origins can be narrowed by looking for shade-intolerant pioneer species. These include trees like Birch and Aspen. Remember that old growth forests have a great deal of diversity. Thus, presence of these pioneer species can indicate that the forest was cleared in the past.
Stumps left behind after logging can be found up to a century after they were cut. Large conifer stumps can last in a forest for well past a hundred years, especially in dry conditions. By intuition, all stumps should have a tree next to them on the ground. Look for a down tree or even just a moss trail, which could be all that is left of the log. With no signs of a remaining log, one can be quite certain that the area was cleared and had it's timber hauld off.
There aren't many better signs of old growth than an abundance of large logs in different stages of decay. This also includes trees that are dead but still standing. This simply shows a long history of being left alone.
Observing the width and height of forest trees is a great way to wrap your head around the history of the forest. For instance, a forest with a very tall canopy and wide trees is typically very old. The height of these trees often signifies the extent to which they have had to compete to get there. This typically means less availibility of light and nutrients, slowing the growth of the trees. Thus, most old growth forests will have exceedingly tall canopies.
Edited by John Borg last on 07/20/2019