Key Point 1—Physiology of Trees
- Sugars supplied by photosynthesis. Air and water are chemically recombined to form glucose, which stores energy captured from the sun. Oxygen is a byproduct.
- Water is required for most metabolic activities and serves as a vehicle to carry materials through a tree. A large tree may move as much as 50-100 gallons of water on a hot summer day
- Nutrients. It’s not how much of a particular nutrient exists in the environment, it’s a matter of how available the nutrient is to the tree. For example, the atmosphere is largely composed on nitrogen, but trees can only use nitrogen in forms that have been altered by soil bacteria and other organisms. The major chemical elements used by plants are: carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, calcium, iron, and magnesium. You might be able to remember this by a jingle formed using the abbreviations for these elements: C H O P K N S Ca Fe Mg . . . "see hopkins café, might good."
- Hormones and enzymes. These chemicals are critical in the controlling the timing and activity of physiological processes. They are usually produced in the roots or leaves. We don’t often think of plants having "hormone" deficiencies, but they are critical to the survival of any organism, including trees.
- Mycorrhizae. Pronounced "my-core-HI-zee", this a group of beneficial fungi associated with most tree roots. It represents an ecologically symbiotic relationship where the fungi receive food from the tree and the trees receive greatly enhanced nutrient and water absorption. Mycorrhizae will also protect tree roots from other invading fungi. There tends to be very specific species relationships between fungus and tree.
- Environmental factors. A tree needs an appropriate mix of precipitation, temperature, sunlight, and soils in order to thrive. These factors need to occur at the right time. Each tree species has a different set of environmental requirements. Changing climate will lead to changing environmental factors, which can lead to changes in forest ecosystems.
- First, a tree has all the characteristics of green plants. Beyond that, a tree is a tall plant with woody tissue. It has the capability to "push" its crown (the primary location for photosynthesis) above other vegetation competing for light. Also, most people don't readily connect trees with having flowers but they do, although our conifers (pines, spruces, firs, etc.) don't have true flowers with petals. The reproductive structures of each species are particularly unique and are used more than any other structure to categorize trees. This categorization is called taxonomy. The tree identification chapter talks more about taxonomy.
- A tree has a dilemma in terms of gathering its resources. It has a distinct light- gathering advantage of having its leaves high above other plants, but there is the problem of getting water and soil nutrients to the upper tissues. The microenvironment in the upper canopy is also rather hostile to sensitive tissues. At the other end of the tree, the roots are dependent upon materials produced way up in the crown. This problem, of course, is solved by the structure of the tree trunk, or bole, a most distinctive feature of trees.
- Most of a tree trunk is dead woody tissue and serves only to support the weight of the crown. The very outside layers of the tree consists of bark. Underneath the bark is a cork cambium layer that generates new bark. Under the cork cambium lies a thin band of phloem, which is living tissue that transports materials from the crown to the roots. Under the phloem is another vascular cambium zone that produces both new phloem cells and new xylem cells. The wider band of xylem, or sapwood, transports water to the crown, but is not necessarily living. The innermost portion of the trunk is non-living heartwood, which is a repository for many waste products of the tree's living tissue. Only a thin band around the trunk, roughly a centimeter wide, is living tissue.
Leaves: Broad-leaf or needles, the primary site of photosynthesis and the production of hormones and other chemicals
Twigs & Branches: Support structure for leaves, flowers, and fruits. Arrangement varies from species to species by growth strategy. Can sometimes have photosynthetic tissues. Two kinds of growth tissue, at the twig tips and cambium under the bark.
Crown: The upper region of the tree made up of leaves, twigs, branches, flowers, and fruits. Crowns of many trees are collectively called the "canopy."
Flowers: May have both female & male parts, or only or the other. Some trees are either all female or all male (i.e. aspen). Flowers may have a full complement of flower parts, or may be missing certain elements. Conifers do not have petals and associated structures.
Fruits & Seeds: All trees have seeds. Most trees have seeds inside fruits. Most fruits are NOT edible, but many are, such as apples, cherries, nuts, etc.
Trunk or Bole: Most definitions of trees include a "single bole" concept, but many of our tree species sometimes occur with multiple stems. The main functions of a trunk are transport and support. The trunk has growth tissue called cambium.
Bark: A highly variable tree part. The main function is to protect the sensitive living tissues from weather and predation (by animals, insects, fungi, etc.)
Roots: Roots serve two main functions; collection of nutrients and water, and anchoring the tree. Roots also have growth tissue, bark, and wood. Like twigs and branches, roots have two kinds of growth tissue, at the twig tips and cambium under the bark. Fine root hairs are where absorption occurs.
- So, photosynthesis produces all this glucose. . . what then? Essentially, the energy in glucose is used by trees (and most other living things) to drive metabolic processes that produce tissues and maintain life functions. Keep in mind that this whole thing called life is a big solar powered system!
- A tree will draw nutrients and minerals from the soil, break them down and put them back together to form compounds and chemicals that we recognize as a tree. The most common material made by a tree is "cellulose." Cellulose is a complex sugar that is the main component of wood and many other plant tissues. It’s also an extremely useful material for lots of human uses, such as food products, paper, strengthener in plastics and concrete, clothing, and other things.
- Wood is the answer to the tree challenge of pushing a crown as high as possible to obtain the best light-capturing position as possible, while maintaining a connection with water and nutrient supplies in the soil.
- Where does a tree grow? In three places, At the twig tips (meristem);At the root tips (meristem); Around the outside of the trunk, branches, and roots (cambium).
Sunlight and Tolerance of Shade:
- It’s commonly known that trees and plants need sunshine to live. However, not all trees need the same amounts of sunlight. Trees that require high amounts of sunlight are sensitive to shade. Foresters call this sensitivity "shade tolerance" or just "tolerance". The shade tolerance of some tree species will vary with age.
- Tree species such as aspen, cherry, paper birch, jack pine, and red pine require lots of sun and are not tolerant of shade. That’s part of the reason stands of these species tend to be all about the same age. Seeds of these species that germinate under a canopy of shade do not survive.
- Other tree species are more tolerant of shade, such as sugar maple, beech, balsam fir, hemlock, and cedar. They can survive as seedlings or saplings under a fairly heavy canopy of shade for many years. When exposed to light, the small trees (not always young trees!) can quickly grow to take advantage of the new light regime.
- There are a number of tree species There are a number of tree species that fall into the moderately tolerant category, such as red oak, red maple, yellow birch, white ash, white pine, and white spruce. The may be able to grow under the light canopy of an aspen or paper birch stand, but would not be very successful under the shade of a maple-beech-basswood stand.
- Shade tolerance is key component of forest management systems
Key Point 2—Forest Ecology
- Know the typical forest structure: canopy, understory and ground layers and crown classes.
- Understand forest ecology concepts and factors affecting them, including the relationship between soil and forest types, tree communities, regeneration, competition, and primary and secondary succession.
- Identify the abiotic and biotic factors in a forest ecosystem, and understand how these factors affect tree growth and forest development. Consider factors such as climate, insects, microorganisms, and wildlife.
- Identify and describe the life cycle of forest pests and invasive plants and describe their impact to a forest ecosystem. Research integrated pest management strategies for selected pests.
- Draw food webs of a mature deciduous forest and a mature coniferous forest. Explain how wildlife habitat relates to the forest community and describe the niches of various organisms that live in both of these forest ecosystems.
- Examine a “tree cookie” or core sample taken with an increment borer to determine the age, growing conditions, insect and disease damage, and past weather conditions.
- Understanding Fire: Explore patterns of change brought about by fires in a forest ecosystem.
Key Point 3—Sustainable Forest Management
- Understand the term silviculture, and be able to explain the uses of the following silviculture techniques: thinning, prescribed burning, single tree and group tree selection, shelterwood method, clear-cutting with and without seed trees, and coppice management.
- Explain the following silviculture systems: clear-cutting , seed tree method, evenaged management, unevenaged management, shelterwood and selection.
- Understand the methodology and uses of the following silviculture treatments: Planting, weeding, pre-commercial thinning (PCT), commercial thinning and harvesting.
- Know how to use forestry tools and equipment in order to measure tree diameter, height and basal area.
- Understand how the following issues are affected by forest health and management: biodiversity, forest fragmentation, forest health, air quality, aesthetics, fire, global warming and recreation.
- Understand how forestry management practices and policy affect sustainability.
- Understand how economic, social and ecological factors influence forest management decisions.
- Learn how science and technology are being utilized in all aspects of forest management.
- Use the following forestry tools and know how they are used in forest management. clinometer, increment borer, diameter tape, biltmore stick, abney level, and compass, prism and relescope.
- Use a variety of volume tables to calculate the volume of lumber for several different tree species.
- Project Learning Tree Activity 8, Fire Management: Learn the many interdependencies of forests and fire in healthy ecosystems.
- Compare two different forest types. For example: an eastern hardwood forest in PA to a conifer forest in Oregon. Identify economic, social and ecological factors that affect how both of these forests are managed.
- Explain the Information Technology used to monitor and productively manage
Key Point 4—Trees as an Important Renewable Resource
- Understand the importance and value of trees in urban and community settings, and know the factors affecting their health and survival.
- Understand the economic value of forests and know many of the products they provide to people and society.
- Explain the “Ecosystem Services” provided by trees, and understand why trees and forests are important to human health, recreation, wildlife, and watershed quality.
- Create a display showing the value of trees in both urban and suburban settings. Identify the factors that affect their health and survival, and explain how to properly care for trees in an urban environment.
- Make a list of products and by-products that come from your home and are made from trees. Describe the chemical and physical properties of trees used in making these products.
Urban Forestry and Human Benefits: College of Forest Resources, University of Washington
International Society of Arboriculture. 2001. Website
Marchand, Peter J. 1996. Life in the Cold. University Press of New England, Hanover and London. 304 pages.
Raven, Peter H., R.F. Evert, and H. Curtis. 1976. Biology of Plants. Worth Publishers, New York, NY. 685 pages.
Salisbury, Frank B. and C.W. Ross. 1978. Plant Physiology, second edition. Wadsworth Publishing Company, Belmont, CA. 422 pages.
Winchester, A.M. 1969. Biology and Its Relation to Mankind. Van Nostrand Reinhold, New York, NY. 717 pages.