Experiment 2: To Study Plant Population Density by the Quadrat Method

AIM

To study the plant population density by quadrat method.

PRINCIPLE

Population Density: It represents the numerical strength of a particular plant species in the community per unit area at a specific time. The unit area may be small or large, depending on the size and nature of the plant community being studied.

Population density of an organism in an ecosystem varies from place to place and depends on various factors such as food and water availability, predation, weather conditions, birth rate, death rate and migration rates.

The value thus obtained is then expressed as number of individuals per unit area.

Quadrat Method: Quadrats are the sampling units of a known area. These sampling units must be distinct and must not overlap each other. The quadrats having a rectangular frame and dimensions of 1 m × 1 m are most commonly used for herbaceous plants.

Quadrat method is considered as the most preferable method to calculate population density and percentage frequency of different plant species.

REQUIREMENTS

• Cotton/nylon thread (five meters)
• Nails
• Hammer or wooden quadrat of size 1 m × 1 m
• Paper
• Pencil
• Hand lens
• etc.

PROCEDURE

1. Select an area having varied vegetation for study.
2. Fix four nails with the help of hammer in the selected area such that the area enclosed by them is a square of 1 m × 1 m dimension. Make the boundaries of the square by tying thread over the nails. Or You can also use a commercially available ready-made quadrat of size 1 m × 1 m. Keep it over the area under study.
3. Note down the names of all the plant species seen in the quadrat. If the names of the plants are not known, assign alphabets such as A, B, C, D, etc. to them.
4. Count the number of individuals of a plant species present in the quadrat and note down the number in front of the species name.
5. Repeat the same step (4) for every plant species present in the quadrat. Record the data as shown in the observation table ahead.
6. Now, repeat the steps 1 to 5 to obtain data of nine more quadrats placed randomly at the site of study. Take care that all the regions taken as sample areas should be distinct and non-overlapping.

OBSERVATION

Write down the total number of species seen in ten quadrats. This will give an idea about the composition of the vegetation. There will be difference in the species composition in the quadrats made in shady areas, exposed areas with bright sunlight, dry or wet areas, etc.

RESULT AND CONCLUSION

The population density of a plant species in a given field can be calculated by the formula given below. The density is expressed as number of individuals per unit area.

PRECAUTIONS

• The measurement of the quadrat should be accurate.
• Count the individuals of one plant species at a time.
• Squares should be marked from one field only and they should not be very far from each other.
• Make sure that the vegetation is not damaged while laying the quadrat.