شنبه 10 تیر 1391 05:24 ب.ظ
Scientific classification or taxonomy is the ordering and ranking of organisms into groups having common characteristics. Scientists classify organisms to bring order and efficiency to data storage and information.
- Phylum or Division
Nomenclature is the assignment of names to organisms. In distinguishing between tree species we use common or vernacular names and scientific names - genus and species. The word vernacular means “native to a region”. Vernacular names are used in common everyday speech, but not by scientists. Because there are many common names listed for every tree, it is necessary to have a universal system for distinguishing organisms. Latin is the language used for scientific names, so that scientists world-wide can speak the same language when it comes to identifying organisms.
The first word in a scientific name is always the genus. The second word is the species name and is usually a Latin description of an important characteristic of the organism. When writing the genus and species, the first letter of the genus is always capitalized and the species is always in lowercase. Both words should be either underlined or italicized.
While examining tree form, note the size, shape and branching patterns of the tree. Also, observe its location in relation to other trees that might affect its form. Is the tree found in the upper, middle, or lower part of the canopy? A shade intolerant tree that is found in the lower canopy of a forest will be greatly affected by the lack of sunlight and will display different form than if it received the sunlight it requires. Understanding a tree's adaptations and living requirements helps when identifying trees.
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Understanding that trees require water, sunlight, nutrients and space is just the beginning in comprehending a species habitat. Every species is best adapted to a particular combination of environmental factors or conditions. The natural environment of a plant or animal containing all the necessary resources for the plant or animal to live, grow and reproduce is known as the habitat.
The mountain forests of West Texas add other factors in understanding tree habitat: aspect and elevation. The temperature change at higher elevations and amount of sunlight a tree receives directly influence the species found in an area. Rainfall and soil structure also change at higher elevations.
More information can be found about habitats for different tree species on the Texas Eco-Regions page.
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Bark can vary greatly from species to species. How to identify tree by their bark is particularly important during winter months when deciduous trees have lost their leaves. While examining the bark observe the thickness, texture, type and color.
Examining the leaves is probably the most common way to identify trees, because leaves can be very distinctive from species to species.
While investigating a leaf, determine if the leaf is simple or compound. This is determined by looking for the bud. Compound leaves can be tricky; are you looking at a leaf or a leaflet? Only by finding the bud, will you know for certain.
Study the size, shape and variations on the same tree. In distinguishing conifer species, identifying the number of needles per fascicle is useful. Some species like mulberry and sassafras display different leaf shapes on the same tree. Also, note the leaf arrangement on the twig – opposite, alternate or whorled. Observe the blade, stalk, margin, venation(veins), base , and upper and lower surfaces of each leaf. The texture and color of the leaf will also help in identification.
Leaf Shape Descriptions
Parts of a Leaf
Twig identification is useful during winter months when deciduous trees have lost their leaves. Note lateral arrangement on branches. Are branches opposite or alternate or whorled? Observe if the twig is flexible or stocky, rough or smooth. Differences will occur between new growth and old. Many twigs have a distinctive color, smell, and taste. By cutting a thin slice along a twig down into the central core of the twig, you can identify the pith. The pith is the central portion of the twig. Most native species have a solid pith. Some species have diaphragmed pith, which displays regularly spaced disks of horizontally elongated cells. The third type of pith you may find is called chambered, which is divided into empty chambers by cross partitions. Note the size, shape and color of the pith.
Determine the presence or absence of lenticels. Lenticels are small dots found on some twigs that provide aeration to the tissues beneath them.
Like bark and twigs, the buds are helpful in winter identification. Identifying the bud is important in determining if a leaf is simple or compound. Often, people confuse a leaflet of a compound leaf for a simple leaf.
There are usually two types of buds, the terminal and lateral. Terminal buds are found at the apex or end of each shoot. Lateral buds, which are most commonly used to identify tree species, are found along the twig. Terminal buds are usually larger than lateral buds. Not all tree species have a true terminal bud.
Note the size, scale coverings and shape. Buds are either scaly or naked. Bud scales that are numerous and overlap one another are called imbricate. Buds that have two scales which do not overlap are calledvalvate. Observe the arrangement and position of the buds on the twigs; compare terminal and lateral buds.
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Flowers are modified short shoots consisting of a stem, sterile leaves and reproductive leaves. Trees will vary widely in flowering habits, so studying flowers during the proper season can be very helpful in identification. Observe the size, form, shape of parts, color and arrangement. Discover whether the tree has one or two kinds of flowers – if two, whether male and female flowers are on the same tree. This is referred as monecious or dioecious. Monecious are plants that have both male and female flowers or cones per plant and dioecious are plants having either male or female flowers or cones per plant.
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A fruit is a ripened ovary, usually with seeds. During the proper season and when available, fruits provide another distinguishing characteristic for identifying trees. Observe the type, form, structure and method of distribution.
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Common Types of Fruits and Seeds
Studying cones is an excellent way to identify conifer species. The size, shape, color, and texture are all distinguishing characteristics of cones. Some cones are armed with spines on the end of the scales. For example, loblolly pine cones have armed scales, whereas slash pine cones do not; otherwise the cones can be difficult to distinguish. In East Texas the most commonly found pine species are longleaf, slash, loblolly and shortleaf pine. Pinyon pine is commonly found in the mountain forests of West Texas.
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آخرین ویرایش: سه شنبه 13 تیر 1391 05:44 ب.ظ