Tree Tips--Forest Canopies and Structural Diversity--3/16/01
Printed in the Mendocino County Observer, 3/16/01.
Forest Canopies and Structural Diversity
March 16, 2001
A few weeks ago while on a walk with a friend through an old-growth grove, he commented that in college he had worked as a research assistant for a redwood canopy study. "It's a totally different thing going on up there compared to what you see on the ground," he commented. "There are times when the canopy is so thick that you can't even see the ground."
We know that canopies are important "structures" in the forest. My friend was struck by the canopy's "thickness", or canopy cover. Equally important is the concept of structural diversity. Ideally, the forest should have variation in terms of vertical (from the ground up) and horizontal (moving around from place to place, either on the ground or in the air) structure. This is called vertical and horizontal structural diversity.
What are some examples of components of structural diversity? Gaps are one-they occur when, for example, a tree is blown over in a windstorm. Through the gap, sunlight can reach the forest floor, which might change what plants grow there or how fast they grow. The physical gap as well as the changes in vegetation may in turn change how wildlife uses the space. Other examples include having trees of different ages, different sizes, and different species. Or having snags of varying size classes and stages of decay. Each of these forest "structures" provides its own niche for wildlife.
We understand many of these niches, but others are difficult for us to predict. This underscores the importance of maintaining good diversity within a forest. My friend, for example, described seeing plants growing on tree branches where enough "soil" had formed over the years for the plants to take root. Who (wildlife biologists and botanists aside) would have predicted that?
Clare Nunamaker is a Registered Professional Forester and member of NorCal SAF, CLFA, and the Forest Stewards Guild.
