SAMPLING METHODS
There are following two types of sampling methods:
(a) Transect method
A transect is a long rectangular sample plot. It is used to study variations in vegetation. Vegetation varies with the changing environments. These variations are caused by slope, exposure, edaphic and topographical irregularities. It also shows how one plant community is replaced by the other. Two types of transects are commonly used:
- Line Transect: It is also called as line intercept method. In this case, plant species are recorded along a line. It is useful for dense. Vegetation. This method is rapid. It gives accurate information about the vegetation.
- Strip MethOd: It was introduced by Canfield (1941). It is very good method for sampling of forest shrubs or trees with crown cover. It is actually an improvement…of:44u; transect method. This sampling method requires measuring tapes, nails and a rod of ten feet and nine inches in length.200 feet long line is drawn with the help of a measuring–tape from the starting point. An area of 10 – 9– is marked from all side of this line strip with the help of a rod. It makes the transect of 200′ x 21 ‘–6–, All species intercepted in this transect are recorded. The crown cover is taken by. long stick. The stick is kept in perpendicular position. The upper end of the stick faces the periphery of the crown. The other end is pointing to the ground. Now the stick is moved downwards, so that it may touch the ground. Distance of this point to the trunk of the tree is taken. It gives us the radius of the circle. Then circumference is calculated. It is converted into cover with the help of conversion table. Frequency of the species is determined by the following formula:Frequency = Number of times a species is intercepted/Total number of interceptions
3. Bisects method: It shows the vertical distribution of plants or profile of the vegetation. This distribution includes all the strata or layers of the community, from dominant trees, shrubs, herbs, climbers and ground flora. It is also used to study relative position of underground parts like rhizome, bulb, tuber and roots of each plant. Their relative positions are carefully measured. It is done by digging a trench in the community.
- (b) Quadrat Method
A quadrat is a sampling unit used for the quantitative study of plant communities. It may be a square, rectangular or circular in shape. But rectangular plots are more useful. A quadrat can have any size. But generally, large quadrat is used for richer and heterogenous plant community. A number of quadrat should be taken during sampling. These quadrates should include all the possible variation. It should represent the data of all the vegetation.
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- Naib cords and measuring tapes are required for making quadrat. Its size is fixed. Then the quadrat is laid down. It is fixed at four points with top of nails. Cord is tightly tied to the four nails. At least 15-20 quadrat are taken. There are intervals of twelve steps between each quadrat
- The size, shape and number of quadrats have been determined. The quadrats are distributed in random, uniform, or stratified manner.
- All the plant species inside the quadrats are recorded. Then number of individuals of each species is counted.
- Their cover (circumference) is measured with the help of measuring tapes. The measured cover is then converted into square feet.
- The community attributes are density. cover, and frequency and importance value. These attributes are calculated separately for each species by different formulae of density, cover and frequency.
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