Layers of a forest

I spend a lot of time drawing during some of my classroom programs.  I draw to illustrate key concepts such as food chains and trophic levels.  I draw to show the parts of plants and animals.  I draw to show students what they are expected to do on activity sheets.   I draw to explain things in a way that I cannot with words alone.

I especially draw during my program on forest habitats.  During this program I usually end up drawing an entire forest from the tops of the trees on down to the soil beneath our feet.  Sometimes these drawings are done on whiteboards with dry-erase markers.  Other times those drawings are done on paper and projected via a document camera to an interactive whiteboard.  I never take these drawings with me.

Last Wednesday (13 DEC) I didn't have any school programs;  I decided to draw the layers of a forest and scan the drawings so I can access them any time I want.  Here are the drawings.

First up is the canopy.  The canopy is made up of the tallest mature trees in the forest.  Here in Mid-Michigan the canopy begins 20 to 30 feet off the ground and extends upwards to a height of 50 - 100 feet (or more) above the ground.  Some canopy trees include Red, Silver and Sugar Maples; Red and White Oaks; Green, White, and Black Ash; some Willows; Basswood; White and Red Pines;  Balsam Fir; Paper Birch; Hickories; etc..

Forest Canopy

Beneath the canopy is a second layer of trees known as the understory.  The understory is composed of two groups of trees.  Some trees in the understory are immature canopy trees - these trees are waiting for a space to open up in the canopy when a mature tree dies or falls over.  Other understory trees will never take a place in the canopy.  Instead, they have evolved to live in the shade provided by the canopy - making due with less sunlight.  Some trees in this category include Nannyberry, Hornbeams, Striped Maple, Speckled Alder, Redbud, etc..  Most of these trees top out at a maximum height of 15 to 30 feet.

Forest Canopy and Understory

Below the understory is a third layer of woody plants known as shrubs.  Unlike trees that have a single dominant trunk, shrubs typically branch out right at ground level.  Sometimes these branches droop enough to make contact with the ground and develop new roots.  Shrubs are often wider than they are tall.  Shrubs range in height from a few inches to about 15 feet.  Native shrubs in Mid-Michigan include Dogwoods, American Fly Honeysuckle, Witch Hazel, Winterberry, Spicebush, and more.

Forest Canopy, Understory, and Shrubs

Beneath the shrub layer we come to a layer of herbaceous plants.  Herbaceous plants are those plants that lack a woody stem such as ferns, grasses, wildflowers, and moss.  These plants range in height from less than an inch in height to about 10 feet - without a woody stem, it is very difficult for these plants to support their own weight above a certain height.  The majority of these species are below our eye-level.  Some of the more well-known herbaceous plants include Trilliums, Lilies, Sunflowers, Asters, and many more.  There are hundreds of species that fit in this category.

Lack of sunlight is a major challenger for herbaceous plants in a forest ecosystem.  The trees and shrubs above them my block as much as ninety-five percent of available light during the growing season.  To overcome this shortage, many herbaceous plants have developed strategies to ensure that they receive adequate sunlight to meet their energy needs.  Some species have evolved to make due with less sunlight.  A few species have developed into parasites that meet their energy needs by stealing sugars from other plants.  Many species have evolved to complete their annual cycle of growth and reproduction in early spring before the canopy leaves have fully developed, ensuring that their own energy needs are met while sunlight is readily available.

Forest Canopy, Understory, Shrubs, and Herbaceous Plants

We have finally come to the forest floor.  In a healthy forest, the forest floor is covered with a layer of organic debris including leaves, small branches (fine woody debris), and large branches and logs (coarse woody debris).  This layer of debris is filled with trillions of organisms working to break down all of this organic matter.  This includes invertebrate animals feeding on the debris and fungi and bacteria decomposing everything that is left.  Without the work of these decomposers the nutrients trapped in the organic debris would be unavailable for uptake by the layers of plants.

Forest Canopy, Understory, Shrubs, Herbaceous Plants, and Floor

Finally we come to a layer that we think very little of and know even less about - the subterranean layer.  This layer is composed of organic (the decomposed remains of living organisms) and mineral soils (rock that has broken down to the size of sand particles or smaller) with larger pieces of rock included in the mix.  This layer of soil may be only a few centimeters deep or may extend hundreds of feet deep before reaching the underlying bedrock.  The top couple of feet of soil are usually criss-crossed with an interlocking web of roots from trees, shrubs, and herbaceous plants.  The mycelium of fungi add their own root-like structures.  In addition to roots, this hidden world is home to untold numbers of invertebrate animals and bacteria.

Forest Canopy, Understory, Shrubs, Herbaceous Plants, Floor, and Subterranean Layers

The old saying "can't see the forest for the trees" is used to describe someone who gets so involved in details that they cannot see the big picture.  In a forest it is easy to look at the trees and fail to see that they are part of a much larger complex system.  Hopefully this article has helped you learn to "see the forest".