Experiment 3: To Study Plant Population Frequency by the Quadrat Method

AIM

To study plant population frequency by quadrat method.

PRINCIPLE

Population is known as the aggregation of individuals of the same kind inhabiting a particular place or a particular geographical area at a particular time.

Frequency is concerned with the degree of uniformity of the occurrence of individuals of a species within a plant community. It is measured by noting the presence of a species in random sample areas (quadrats) which are widely distributed throughout the area of study.

Frequency can be determined by means of sample areas in order to check general impressions about relative values of species. Frequency is the number of sampling units (as %) in which a particular species occurs.

The frequency of each species (sps. A or sps. B or sps. X, etc.) is expressed in percentage and is calculated as follows:

REQUIREMENTS

• Cotton/nylon thread of 5 meters
• Nails
• Hammer
• Paper
• Pencil
• Magnifying lens

PROCEDURE

1. Select a field and lay a quadrat with the help of meter scale.
2. Measure area of about 1 m × 1 m with the meter scale. Hammer the nails firmly at corners and tie the thread on the nails.
3. Divide each quadrat into 16 small squares by tying thread at a distance of 25 cm each on either side, fix nails to the thread to mark these small squares.
4. List the names of the plant species seen in the quadrat (if the name is not known mark these as species A or B, etc. and if the same species is seen in other quadrats assign the same alphabet).
5. Similarly, lay ten more quadrats randomly in the field of study and record the number of individuals of each species.
6. Calculate the percentage frequency of occurrence of plants using the formula given below.

OBSERVATION

Record the total number of species seen in the ten quadrats. This will give an idea about the composition of the vegetation.

There will be a difference in the species composition in the quadrats made in shady areas, exposed areas with bright sunlight, dry or wet areas, etc.

Observe that the frequency of occurrence is not the same for all species.

RESULT

The frequency percentage of species X was found to be 70%, species Y 20% and species Z 10% using formula F = N/Q × 100. Species X occurred in maximum number of quadrats, indicating higher distribution.

CONCLUSION

Frequency determines the uniformity of distribution of a species in a plant community. Species with high frequency value are more uniformly distributed and widely present, while species with low frequency show restricted or rare occurrence in the study area.

PRECAUTIONS

• The measurement of quadrats should be accurate.
• The string or cord used should not be very thick.
• One individual of a species should be counted only once in the quadrat.
• Make sure that the vegetation is not damaged, while laying the quadrat.