Tree
A tree is a perennial woody plant. It most often has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance.[1] A minimum height specification at maturity is cited by some authors, varying from 3 m[2] to 6 m;[3] some authors set a minimum of 10 cm trunk diameter (30 cm girth).[4] Woody plants that do not meet these definitions by having multiple stems and/or small size are usually called shrubs, although many trees such as Mallee do not meet such definitions. Compared with most other plants, trees are long-lived, some reaching several thousand years old and growing to up to 115 m (379 ft) high.[5]
Trees are an important component of the natural landscape because of their prevention of erosion and the provision of a weather-sheltered ecosystem in and under their foliage. They also play an important role in producing oxygen and reducing carbon dioxide in the atmosphere, as well as moderating ground temperatures. They are also elements in landscaping and agriculture, both for their aesthetic appeal and their orchard crops (such as apples). Wood from trees is a building material, as well as a primary energy source in many developing countries. Trees also play a role in many of the world's mythologies (see trees in mythology).[6]
Classification
A tree is a plant form that occurs in many different orders and families of plants. Most species of trees today are flowering plants (angiosperms) and conifers. Trees show a variety of growth forms, leaf type and shape, bark characteristics and reproductive organs. For the listing of examples of well-known trees and how they are classified, see List of tree genera.
The tree form has evolved separately in unrelated classes of plants, in response to similar environmental challenges, making it a classic example of parallel evolution. With an estimate of 100,000 tree species, the number of tree species worldwide might total 25 percent of all living plant species.[7] The majority of tree species grow in tropical regions of the world and many of these areas have not been surveyed yet by botanists, making species diversity and ranges poorly understood.[8] The earliest tree-like organisms were tree ferns, horsetails and lycophytes, which grew in forests in the Carboniferous period, however these plants were not trees[citation needed], since they lacked woody tissue. Trees evolved in the Triassic period, when conifers, ginkgos, cycads and other gymnosperms appeared producing woody tissue, and were subsequently followed by tree-form flowering plants in the Cretaceous period.
A small group of trees growing together is called a grove or copse, and a landscape covered by a dense growth of trees is called a forest. Several biotopes are defined largely by the trees that inhabit them; examples are rainforest and taiga (see ecozones). A landscape of trees scattered or spaced across grassland (usually grazed or burned over periodically) is called a savanna. A forest of great age is called old growth forest or ancient woodland (in the UK). A young tree is called a sapling.
Morphology
The parts of a tree are the roots, trunk(s), branches, twigs and leaves. Tree stems consist mainly of support and transport tissues (xylem and phloem). Wood consists of xylem cells, and bark is made of phloem and other tissues external to the vascular cambium. Trees may be grouped into exogenous and endogenous trees according to the way in which their stem diameter increases. Exogenous trees, which comprise the great majority of trees (all conifers, and almost all broadleaf trees), grow by the addition of new wood outwards, immediately under the bark. Endogenous trees, mainly in the monocotyledons (e.g., aloes and dragon trees), grow by addition of new material as discrete bundles within the existing trunk tissue.
Trees can be identified to genus or species by a combination of the tree's shape, and the characteristics of its bark, leaves, flowers, and fruit. The leaves may be either deciduous or evergreen.[2][3]
As an exogenous tree grows, it creates growth rings as new wood is laid down concentrically over the old wood. In species growing in areas with seasonal climate changes, wood growth produced at different times of the year may be visible as alternating light and dark, or soft and hard, rings of wood.[3] In temperate climates, and tropical climates with a single wet-dry season alternation, the growth rings are annual, each pair of light and dark rings being one year of growth; these are known as annual rings. In areas with two wet and dry seasons each year, there may be two pairs of light and dark rings each year; and in some (mainly semi-desert regions with irregular rainfall), there may be a new growth ring with each rainfall.[9] In tropical rainforest regions, with constant year-round climate, growth is continuous and the growth rings are not visible nor is there a change in the wood texture. In species with annual rings, these rings can be counted to determine the age of the tree, and used to date cores or even wood taken from trees in the past, a practice known as the science of dendrochronology. Very few tropical trees can be accurately dated in this manner. Age determination in this manner is also impossible in endogenous trees.
The roots of a tree are generally embedded in earth, providing anchorage for the above-ground biomass and absorbing water and nutrients from the soil. However, while ground nutrients are essential to a tree's growth the majority of its biomass – over 90 percent – comes from carbon dioxide absorbed from the atmosphere (see photosynthesis).[10] Above ground, the trunk gives height to the leaf-bearing branches, aiding in competition with other plant species for sunlight. In many trees, the arrangement of the branches optimizes exposure of the leaves to sunlight.
Not all trees have all the plant organs or parts mentioned above. For example, the saguaro cactus of North America has no functional leaves. A plant form that is similar to a tree, but generally having smaller, multiple trunks and/or branches that arise near the ground, is called a shrub. However, no precise differentiation between shrubs and trees is possible. Given their small size, bonsai plants would not technically be "trees", but one should not confuse reference to the form of a species with the size or shape of individual specimens. A spruce seedling does not fit the definition of a tree, but all spruces are trees.
Damage
The two sources of tree damage are either biotic (from living sources) or abiotic (from non-living sources). Biotic sources include insects that bore into the tree, deer that rub bark off, and fungi.[11]
Abiotic sources include lightning, vehicles impacts, and construction activities. Construction activities can involve a number of damage sources, including grade changes that prevent aeration to roots, spills involving toxic chemicals such as cement or petroleum products, or severing of branches or roots.
Both damage sources can result in trees becoming dangerous, and the term "hazard trees" is commonly used by arborists, and industry groups such as power line operators. Hazard trees are trees that, due to disease or other factors, are more susceptible to falling in windstorms, or having parts of the tree fall.
Evaluating the danger a tree presents is based on a process called the Quantified Tree Risk Assessment.[12]
Assessment as to labeling a tree a hazard tree can be based on a field examination. Assessment as a result of construction activities that will damage a tree is based on three factors: severity, extent and duration. Severity relates usually to the degree of intrusion into the TPZ and resultant root loss. Extent is frequently a percentage of a factor such as canopy, roots or bark, and duration is normally based on time. Root severing is considered permanent in time.
Trees are similar to people. Both can withstand massive amounts of some types of damage and survive, but even small amounts of certain types of trauma can result in death. Arborists are very aware that established trees will not tolerate any appreciable disturbance of the root system.[13] However, lay people and construction professionals seldom recognise how easily a tree can be killed.
One reason for confusion about tree damage from construction involves the dormancy of trees during winter. Another factor is that trees may not show symptoms of damage until two years or longer after damage has occurred. For that reason, persons uneducated in arboricultural science may not correlate the actual cause and resultant effect.
Various organisations, such as the International Society of Arboriculture, the British Standards Institute and the Tree Industry Association (formerly the National Arborist Association), have long recognised the importance of construction activities that impact tree health. The impacts are important because they can result in monetary losses due to tree damage and resultant remediation or replacement costs, as well as violation of government ordinances or community or subdivision restrictions.
As a result, protocols for tree management prior to, during and after construction activities are well established, tested and refined. These basic steps are involved:
- Review of the construction plans
- Development of the related tree inventory
- Application of standard construction tree management protocols
- Assessment of potential for expected tree damages
- Development of a tree protection plan (providing for pre-, concurrent, and post construction damage prevention and remediation steps)
- Development of a tree protection plan
- Development of a remediation plan
- Implementation of tree protection zones (TPZ)
- Assessment of construction tree damage, post-construction
- Implementation of the remediation plan
Trees in culture
The tree has always been a cultural symbol. Common icons are the World tree, for instance Yggdrasil,[14] and the tree of life. The tree is often used to represent nature or the environment itself.
The tree is also a symbol and mascot for Stanford University and Currier House (Harvard College).
Tree value approximation (USA)
Studies have shown that trees contribute as much as 27% of the appraised land value in certain markets and cite the following[15] which can be extrapolated with care.
| diameter (inches) |
value (1985 US$) |
|---|---|
| 10 | $1,729 |
| 14 | $3,388 |
| 18 | $5,588 |
| 26 | $11,682 |
| 30 | $15,554 |
These most likely use diameter measured at breast height, 4.5 feet (140 cm) above ground, not the larger base diameter. A general model for any year and diameter is Value = 17.27939*(diameter^2)*1.022^(year-1985) assuming 2.2% inflation per year.[17] The right side of this equation is written to paste into Excel or Google to perform the calculation. Extrapolations from any model can vary widely, so value estimates for diameters larger than 30 inches (760 mm) may have to be capped so trees do not exceed 27% of total appraised land value.
See also
References
Notes
- ^ Huxley, A., ed. (1992). New RHS Dictionary of Gardening. Macmillan ISBN 0-333-47494-5.
- ^ a b Rushforth, K. (1999). Trees of Britain and Europe. Collins ISBN 0-00-220013-9.
- ^ a b c Mitchell, A. F. (1974). A Field Guide to the Trees of Britain and Northern Europe. Collins ISBN 0-00-212035-6
- ^ Utkarsh Ghate. "Field Guide to Indian Trees, introductory chapter: Introduction to Common Indian Trees" (RTF). Retrieved 2007-07-25.
- ^ Gymnosperm Database: Sequoia sempervirens
- ^ Going Out On A Limb With A Tree-Person Ratio, Morning Edition, National Public Radio. 12 Nov 2008.
- ^ "TreeBOL project". Retrieved 2008-07-11.
- ^ Friis, Ib, and Henrik Balslev. 2005. Plant diversity and complexity patterns: local, regional, and global dimensions : proceedings of an international symposium held at the Royal Danish Academy of Sciences and Letters in Copenhagen, Denmark, 25–28 May 2003. Biologiske skrifter, 55. Copenhagen: Royal Danish Academy of Sciences and Letters. pp 57-59.
- ^ Mirov, N. T. (1967). The Genus Pinus. Ronald Press.
- ^ "Jonathan Drori on what we think we know | Video on". Ted.com. Retrieved 2010-10-18.
- ^ Wiseman, P. Eric, Integrated Pest Management Tactics, Continuing Education Unit, International Arboricultural Society Vol 17, Unit 1, February 2008
- ^ Ellison, M. J. Quantified Tree Risk Assessment Used in the Management of Amenity Trees. Journal Arboric. International Society of Arboriculture, Savoy, Illinois. 31:2 57-65, 2005
- ^ Schoeneweiss, D. F., Prevention and treatment of construction damage. Journal of Arborculture 8: 169
- ^ Mountfort, Paul Rhys (2003). Nordic runes: understanding, casting, and interpreting the ancient Viking oracle. Inner Traditions / Bear & Company. p. 279. ISBN 978-0-89281-093-2.
{{cite book}}: Cite has empty unknown parameter:|coauthors=(help) - ^ "Protecting Existing Trees on Building Sites" p.4 published by the City of Raleigh, North Carolina, March 1989, Reprinted February 2000
- ^ "How Valuable Are Your Trees" by Gary Moll, April, 1985, American Forests Magazine
- ^ based on 1985 to 2009, using NASA inflation calculator
Bibliography
- Pakenham, T. (2002). Remarkable Trees of the World. ISBN 0-297-84300-1
- Pakenham, T. (1996). Meetings with Remarkable Trees. ISBN 0-297-83255-7
- Tudge, C. (2005). The Secret Life of Trees. How They Live and Why They Matter. Allen Lane. London. ISBN 0-7139-9698-6
External links
- Gymnosperm database
- Silvics of North America
- University of Florida's Landscape Plants website
- Global Trees Campaign (campaigning to save the world's most threatened trees)
- International Society of Arboriculture
- Eastern Native Tree Society
- Western Native Tree Society
- Trees The Arbor Day Foundation
- Tree Encyclopedia Extensive collection of diagnostic photos, Morton Arboretum Specimens
- Wondermondo - Trees Largest and most unusual trees of the world
- Venerable Trees Venerable trees of the planet