Sources: Temperate Forest Foundation Ecolink: for Forest, Soil; Various for forest stratification.
Forest Stucture schmied©2009 Go to SCI METHOD The Basics all rights reserved Background: Forest Stratification refers to the different layers of plants in a forest. In older, mature forests there are typically several distinct layers of vegetation spread out from the forest floor to the tree canopy. Young forests may not show clear separations between layers. Once the forest ages and trees grow to create a tall canopy, layering becomes visible.
1. The Canopy Layer - Primary Vegetation:
Mature Trees (ex Conifers: Douglas Fir, Western Hemlock, Red Cedar, Deciduous Trees: Big Leaf Maple, Red Alder, Black Cottonwood)
The canopy, sometimes called the "overstory", is the highest vegetative layer in the forest. The canopy is filled by leaves from large mature trees. During the growing season, canopy leaves intercept much of the sunlight available to a forest. Typically less than 50% of the total amount of sunlight can pass through the canopy to plants in the forest layers below.
In a deciduous forest, the canopy is typically the last layer to show green in the spring. Since the canopy trees receive sunlight throughout the growing season, they can wait longer to sprout their leaves. This reduces the risk of the young tender leaves being destroyed by a late freeze.
Some trees grow especially tall. Sometimes these tall growing trees can actually grow through the canopy. Giant trees that poke through the canopy are called "emergents." Emergents are able to harness immense amounts of direct sunlight above the canopy. However, the leafy crowns of emergent trees are exposed to the fierce winds above the canopy. Therefore, emergents are often able to be blown down during gusty storms.
2. The Understory Layer - Primary Vegetation:
Tree Saplings,
Small Shade -Tolerant Trees (ex. Cascara, Crabapple, Pacific Dogwood, Pacific Yew, Madrone, Black Hawthorn, Oregon Ash, Pacific Vine Maple )
Tall Shrubs (Mock Orange, Beaked Hazelnut, Elderberry, Pacific Rhododendron, Indian Plum etc)
Just beneath the Canopy and above the Shrub layer lies the Understory. This is home for many native small trees and tall shrubs that can tolerate lower amounts of sunlight. In fact, many small to mid sized shade tolerant trees (ex: Pacific Yew) and tall shrubs (ex: Pacific Rhododendron) grow and thrive in the Understory region.
The understory is also a waiting area future canopy trees, called tree saplings. In a mature forest, many tree saplings can claim enough nutrients and sunlight to grow into the understory. However, further growth is not possible as the saplings are not left enough nutrients from established canopy trees to grow any higher. So many saplings slow their growth and wait in the understory until a mature canopy tree dies. How well a sapling can grow in full shade and how long a sapling can survive in the understory are two principle measures of a tree's shade tolerance.
When a mature tree dies and opens a gap in the canopy, the tree saplings waiting in the understory grow upward. The race to reach grow into the canopy is a race for survival. There is often only room for one new tree in the canopy. The tree that reaches the canopy grows and expands, reducing the flow of sunlight and nutrients to the trees below, which either stop growing and wait for another chance, or die off.
3. Shrub Layer - Primary Vegetation:
Young Tree Saplings,
Mature Shrubs and Bushes (ex Red & Evergreen Huckleberry, Douglas Spiraea, Gooseberry, Pacific Ninebark, Oceanspray, Oregon Grape, Nootka Rose, Red Flowering Current, Salal, Salmonberry, Snowberry, Black Cap etc)
Between the Understory and Litter Layers is the Shrub Layer. This low lying layer of vegetation is around 3' and 7' from the ground surface. Mostly bushy shrubs occupy this position in the forest.
An abundance of food for animals such as deer and bears is found on shrub layer vegetation. In fact, many of these shrubs depend on wildlife to distribute their seeds. The animals ingest the plants' fleshy fruits and distribute the seeds in their feces.
4. Herb/Fern Layer - Primary Vegetation:
Tree Seedlings,
Herbs (Trillium, Camas, Trailing Blackberry, Stinging Nettle, Foxglove etc)
Ferns (Sword fern, Bracken fern, Deer Fern, Lady Fern),
Grasses and Weeds ( Sedges, Rushes, Bull Thistle etc)
The Herb/Fern layer ranges from the ground surface to about 3' and is considered the lowest forest layer with leafy living vegetation. This layer is typically the first forest layer to turn green in the spring. Plants on the forest floor have to grow out their leaves early in the growing season to capture direct sunlight and start their growth cycle right away! That's because once the understory and canopy trees have leaves, very little sunlight remains for the plants in the Herb/Fern Layer. As a result, most of the plants in the Herb/Fern layer have short life cycles
5. Litter Layer - Primary Vegetation:
Decaying plant and animal matter,
Fungi, Mosses & Lichens
Lying directly on the forest floor is the final forest layer, the Litter Layer. The litter layer is the repository of all of the dead matter in the forest. Leaves, trees and other plants die, then fall and land onto the forest floor. A host of bacteria, fungi, worms, insects and other waste consumers in the leaf layer eat the litter. Once digested, vital nutrients are released into the soil, eventually creating nutrient rich topsoil. Nutrients are taken in from the soil by forest plant roots. Then, the plants use the nutrients to create new leaves and other organic matter. Later cycle continues and this matter is eventually discarded and returned to the Litter Layer. This recycling of matter is an on-going balanced cycle, ensuring the long term sustainability of the forest.
6. Soil: - Primary Layers (or horizons) Topsoil (Humus or A layer), B layer & C layer
The Soil is included because the interaction between forest and soil is so strong it's unclear which is more important. Soil helps secure the roots of the forest plants and provides valuable nutrients, including water to the forest. The top two feet of the soil, including the litter layer, provides raw materials for the forest. The soil decomposes plant material and dead animals. These nutrients are used by the forest. The soil filters and holds water, providing the forest with moisture. Also some soil organisms, fungi in particular, form partnerships with forest plants to help extract nutrients and moisture from the soil.
On the other hand, the forests keep the soil in place, slowing wind and water erosion. The forest keeps the soil cool; its roots help make the soil porous, and forest waste provides food and nutrients for the billions of organisms living in the soil.
Answer all the questions below in complete, quality, and correct sentences that reflect the question. Please follow all writing standards.
1. Explain three ways that your team's observations in the Center were the same or different than the description of the Forest Structure given in the article.
2. What does the term Forest Stratification refer to?
3. Tell where the canopy is located and what type of trees will be found there.
4. Describe how much of the sunlight is captured by the canopy.
5. Explain which types of plants are present in the Understory layer.
6. Tell how the shrub layer plants and animals depend on each other.
7. Describe two adaptations plants in the Herb / Fern layer need to make so these plants can survive near the forest floor. Be sure to explain why
8. Explain why the Forest depends on having a properly functioning Litter layer.
9. Tell three ways the soil helps the forest to be healthy.
10. Describe three ways the forest helps the soil remain healthy
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