Download Forest Exploration – Student Data Sheet

Forest Structure Basics
Forest Layers:
healy/schmied2012
Emergent --The tallest trees that rise above the canopy.
Exposed to stronger sunlight and winds.
1. Canopy – Made of large mature trees. Forms roof of the
forest, absorbs over 50% of incoming sunlight. Sometimes
called the overstory.
2. Understory - Smaller trees and tall shrubs that tolerate
shade. Also area for future canopy trees awaiting the
opportunity to grow into the canopy.
3. Shrub Layer – Medium to low lying vegetation (3-7”).
Bushes and saplings provide food for many forest
animals. In return the animals spread the shrub’s seeds.
4. Herb - Fern Layer – Ground to about 3’. Lowest forest
layer with leafy vegetation. Typically the first layer to
turn green in spring. Often plants with short life cycles.
O
A
B
C
5. Litter or Organic (O) Layer -Dead material from all layers
are decomposed here into topsoil. Especially by fungi, also
bacteria, and soil invertebrates (worms, insects, &
nematodes). Decomposition releases nutrients like NPK for
reuse by the forest plants…. Decomposed organic material
makes soil spongy, able to filter and hold water better!
6. Topsoil or A Layer - Uppermost soil layer. Dark and rich with organic material. Provides valuable
nutrients, including water to forest.
7 & 8. B and C layers. Deeper layers… have more and larger rocks & less organic matter than layers above.
Key forest terms
Coniferous: Cone-bearing trees, usually with evergreen needle- or scale-like leaves
Deciduous: Trees or shrubs that lose their leaves seasonally.
Snag: A dead standing tree. Most people consider dead trees as a sign of an unhealthy forest, but snags are
actually extremely important for many forest species, from tiny insects to large winged predators (eagles & hawks).
Healthy forests have an abundance of snags.
Log: A tree that has fallen to the ground. Often called “downed woody debris” and can last over a hundred
years on the ground. This debris is home to wildlife and returns nutrients to the soil. Large amounts of
downed woody debris are a sign of a healthy forest.
There is a regular cycle to the life of a downed tree.
First, insects such as beetles invade the tree. Bark beetles chew into the sapwood and carpenter ants carve
tunnels for their colonies.
The insect pioneers pave the way for the next wave of immigrants: especially fungi, also bacteria, and
nematodes. Nematodes are microscopic roundworms that feed on rotting logs.
Then predators higher up the food chain such as woodpeckers and salamanders feed upon life in the log.
Mushrooms, mosses and lichens feed on the moist, decaying log. The moist environment acts as an oasis
for organisms, which feed on the log, accelerating the log’s decomposition.