This information is courtesy the Arbor Day Foundation
A: The outer bark is the tree’s protection from the outside world. Continually renewed from within, it helps keep out moisture in the rain, and prevents the tree from losing moisture when the air is dry. It insulates against cold and heat and wards off insect enemies.
B: The inner bark, or “phloem”, is pipeline through which food is passed to the rest of the tree. It lives for only a short time, then dies and turns to cork to become part of the protective outer bark.
C: The cambium cell layer is the growing part of the trunk. It annually produces new bark and new wood in response to hormones that pass down through the phloem with food from the leaves. These hormones, called “auxins”, stimulate growth in cells. Auxins are produced by leaf buds at the ends of branches as soon as they start growing in spring.
D: Sapwood is the tree’s pipeline for water moving up to the leaves. Sapwood is new wood. As newer rings of sapwood are laid down, inner cells lose their vitality and turn to heartwood.
E: Heartwood is the central, supporting pillar of the tree. Although dead, it will not decay or lose strength while the outer layers are intact. A composite of hollow, needlelike cellulose fibers bound together by a chemical glue called lignin, it is in many ways as strong as steel. A piece 12” long and 1” by 2” in cross section set vertically can support a weight of twenty tons!
Leaves make food for the tree, and this tells us much about their shapes. For example, the narrow needles of a Douglas fir can expose as much as three acres of chlorophyll surface to the sun. The lobes, leaflets and jagged edges of many broad leaves have their uses, too. They help evaporate the water used in food-building, reduce wind resistance— even provide “drip tips” to shed rain that, left standing, could decay the leaf.
Vertical Structure – Vegetation Layers
The vertical structure of the forest is divided into distinct layers, each adapted to increasingly filtered sunlight if going top down. The layers are: canopy, understory, groundlayer, and the forest floor. Not all forests have each layer. Generally; extreme environments such as deeply shaded woodlands, boreal forests, and frequently flooded woodlands have fewer layers.
The Canopy is the upper-most layer of a woodland. It is composed of dominant and associate tree species. These largest trees shield the layers below, shading them and influencing the microclimate. Under a dense, continuous canopy of sugar maple and basswood, the forest community below is generally cool and moist. Under an open canopy of oak or pine woodlands, the microclimate is warmer and dryer. Where light is allowed into the understory, shade intolerant canopy species may regenerate.
The understory is the next layer. It represents the middle layer and casts additional shade on the layers below. The understory may be subdivided into a subcanopy and shrub-seedling layers.
The subcanopy consists of a variety of small trees, some of which may be ironwood, chokecherry, serviceberry, mountain maple, hop-hornbeam, and younger individuals of canopy species.
The shrub and seedling layer consists of woody plants that usually have multiple stems such as dogwoods, viburnums, elderberry, blueberries, and raspberries. This layer also includes immature offspring of shade tolerant canopy species. These saplings and seedlings may take their place in the canopy with the death of the mature trees overhead. The understory is home to many woodland nesting birds and provides abundant food resources for wildlife.
The groundlayer is on the forest floor. Wildflowers, sedges, ferns, grasses, creeping shrubs, horsetails, liverworts, and mosses comprise this layer. Many woodland herbs are adapted to low light, sheltered conditions, and cannot tolerate direct light environments. Other woodland plants — ephemerals — adapted by grow rapidly and blooming in the early spring before the canopy leafs out and casts shade. Another adaptation is to develop large leaf surfaces to capture sunlight, and/or grow in colonies. Example of these plants include ferns, mayapple and wild ginger. When restoring a woodland, it may be years before the soil is favorable and light intensity is reduced enough for many of these plants to prosper.
Underfoot lies the forest floor. This lowest layer is composed of litter, humus and topsoil. On the forest floor lie fallen trees, leaves, and branches in various stages of decomposition. Here a diverse community of creatures live. Microscopic soil bacteria, fungi, and nematodes along with worms, insects, millipedes, and other small creatures break down the organic debris into humus and mix it with soil. Their nearly invisible action is critical for forest nutrient recycling and continued growth.
The composition and distribution of species can vary widely from one spot to the next. Environmental gradients, such as moisture, drainage, slope, slope aspect, soil type, and light intensity, influence these horizontal patterns within a forest. Ecologists call these species composition changes along an environmental gradient a vegetational continuum.
Other factors that influence the distribution and composition of species include: gaps in the canopy where individual trees die from old age; disease; lightening strikes; storms; seed availability; large clearings created from widespread insect and disease damage; or destruction from fire. New generations of trees and shrubs fill in these gaps and clearings. As a result the forest develops patches of different-aged vegetation, with trees varying in size and composition. Naturalists are able to read the history of the land through observing the mosaic of plants growing in a forest.
Different organisms exist within the forest layers. These organisms interact with each other and their surroundings. Each organism has a role or niche in sustaining the ecosystem.
Some provide food for other organisms; others provide shelter or control populations through predation:
All living organisms’ intake energy in order to survive. In a forest ecosystem, trees and other plants get their energy from sunlight. Plants produce their own food, in the form of carbohydrates. Plants are, therefore, called the primary producers, since they produce the basic foodstuffs for other organisms within food chains and food webs. Photosynthesis is the chemical reaction that allows plants to produce their own food.
Animals cannot produce their own food. They must consume food sources for die energy they need to survive. All animals, including mammals, insects, and birds, are called consumers. Consumers rely on plants and other animals as a food source. Details of these animals in a forest ecosystem have been given earlier.
Primary consumers only eat plants and are referred to as herbivores. Secondary consumers are referred to as carnivores and feed on herbivores. Tertiary consumers are carnivores that feed on other carnivores. Omnivores eat both plant and animal matter.
Leaves, needles, and old branches fall to the forest floor as trees grow. Eventually all plants and animals die. So what happens to all of this plant and animal material? Does it sit on the forest floor forever? Thankfully no. These materials are decomposed by worms, microbes, fungi, ants, and other bugs.
Decomposers break these items down into their smallest primary elements to be used again. Decomposers are important in that they sustain the nutrient cycle of ecosystems.
Location: The tropical rainforests contain the greatest diversity of species of all biomes on earth. They are found around the equator, between 23.5 degrees N latitude and 23.5 degrees S latitude.
Climate: Temperatures in tropical rainforests remain between 68 and 77 degrees Fahrenheit all year long. Winter is absent in these forests. Most tropical rainforests receive 100 inches of rain per year.
Soil: Because the temperature is warm and the air moist, decomposition happens at a very fast rate in tropical rainforests. High levels of rainfall often lead to leaching of nutrients from the soil, creating soils that are nutrient poor.
Plants: Trees in the tropical rainforests grow between 82 and 115 feet tall and are typically broad-leafed trees. Other plants include ferns, vines, mosses, palms and orchids.
Animals: Dense growing trees create a thick canopy layer in tropical rainforests that keep the sun from penetrating to the lower layers of the forest. This means that most animals that live here must be adapted to living in the trees. A variety of birds, bats, monkeys, snakes and other animals can be found in tropical rainforests.
Threats: The biggest threat to tropical rainforests is unsustainable forestry practices. Other threats include road construction, clearing land for agriculture and other development activities and climate change.
Temperate Deciduous Forest
Location: Eastern United States and Canada, Western Europe and parts of Russia, China and Japan.
Climate: There are four distinct seasons in temperate deciduous forests and precipitation falls throughout the year, as rain in the spring, summer and fall and snow in the winter. Temperate deciduous forests receive 30-60 inches of rain per year.
Soil: The soil in these forests is very fertile.
Plants: The forest floor in temperate deciduous forests supports mosses, ferns and wildflowers and the understory supports a variety of shrubs and ferns. Maple, oak and birch trees are some examples of the deciduous trees that dominate these forests. There are also small numbers of evergreen trees such as pines and fir.
Animals: Animals living in temperate deciduous forests must be adapted to cold winters. Common species found in temperate deciduous forests include, red fox, hawks, woodpecker and cardinals.
Threats: Acid rain caused by industrial and vehicular emissions poses the biggest threat to temperate deciduous forests. Over time, acid rain damages tree leaves, causes trees to produce fewer and smaller seeds and reduces resistance to disease. Other threats include unsustainable forestry, strip mining and the spread of invasive, non-native species that compete for space and food. Climate change is also a threat.
Temperate Coniferous Forest
Location: Temperate coniferous forests are typically found in coastal areas with mild winters and heavy rainfall or in in-land mountainous areas with mild climates. Examples of where these forests are found are Pacific Northwestern United States and Canada, southwestern South America, Southern Japan, New Zealand and small parts of northwestern Europe (Ireland, Scotland, Iceland and Norway).
Climate: Temperate climate with temperature that fluctuates little throughout the year. High levels of precipitation (50-200 inches per year) cause a moist climate and a long growing season.
Soil: Soils are generally rich with a thick layer of decaying material.
Plants: Evergreen conifers dominate these forests. Due to the high levels of precipitation and moderate temperatures, there is a long growing season, resulting in trees that grow very tall. Dominant tree species found in temperate coniferous forests include cedar, cypress, Douglas fir, pine, spruce and redwood. There are some deciduous trees such as maple, and mosses and ferns are common.
Animals: Examples of animals that live in temperate coniferous forests are, deer, marmot, elk, black bear, salmon, spotted owl, marbled murrelet
Threats: Unsustainable forestry, road construction and other development related activities are the biggest threat to temperate deciduous forests.
Boreal (taiga) Forest
Location: This is the northern most forest type and is found between 50 and 60 degrees N latitude. Boreal forests are found in Canada, northern Asia, Siberia and Scandinavia (Denmark, Norway, Sweden, Finland). About two-thirds of the world’s boreal forests are found in Scandinavia.
Climate: Boreal forests are characterized by long winters and short summers. Most precipitation is in the form of snow and these forests receive between 15 and 40 inches of precipitation per year.
Soil: Because of cold temperatures, decomposition takes a long time, resulting in thin soil.
Plants: Trees are mostly evergreen and include species such as spruce, fir and pine. The understory is limited because the canopy is so dense.
Animals: Animals found here must be adapted to long, cold winters and usually have thick fur. Deer, moose, elk, caribou, snowshoe hare, wolves, grizzly bears, lynxes and wolverines are some examples.