F2 - sampling techniques

Why sampling is used:

• Habitats are too large to study completely

• Saves time and resources

• Allows data to be collected and analysed

How sampling helps plant studies:

• Estimates population size

• Measures species distribution

• Shows how abiotic factors affect plants

Random Sampling

What is random sampling?

Random sampling means every location has an equal chance of being chosen.

Examples:

• Using random number generators

• Throwing a quadrat without choosing the location

Why is random sampling important?Reliability

• Results can be repeated

• Reduces chance variation

Validity

• Data truly represents the habitat

• Reduces bias (personal choice)

Overall importance

• Data is more accurate

• Conclusions are more trustworth

Investigating Abiotic Factors

Abiotic factors include:

• Light intensity

• Moisture

• Temperature

• Soil pH

Sampling techniques allow scientists to:

• Measure abiotic factors

• Compare plant populations across conditions

Sampling Techniques

What is a quadrat?

A quadrat is a square frame placed on the ground to sample plants.

Open Quadrat

What it is:

• A square frame with no internal divisions

Used for:

• Counting plants

• Estimating percentage cover

Advantages:

• Quick and simple

• Useful for large plants

Limitations:

• Less accurate for dense vegetation

Gridded Quadrat

What it is:

• Quadrat divided into smaller squares

Used for:

• Estimating percentage cover more accurately

• Sampling dense vegetation

Advantages:

• More accurate

• Easier to estimate cover

Limitations:

• Takes longer to use

How quadrats investigate abiotic factors

• Place quadrats in areas with different conditions

• Measure abiotic factors at each quadrat

• Compare plant abundance or percentage cover

Transects

What is a transect?

A transect is a line laid across a habitat to show changes over distance.

Line Transect

What it is:

• Plants touching the line are recorded

Used for:

• Showing distribution patterns

• Identifying zonation

Belt Transect

What it is:

• Series of quadrats placed along a line

Used for:

• Measuring changes in abundance across an abiotic gradient

How transects investigate abiotic factors

• Used where conditions change (e.g. light, moisture)

• Shows how plant distribution changes with the factor

Point Frames

What is a point frame?

A point frame is a frame with pins lowered vertically to touch vegetation.

Used for:

• Estimating percentage cover

• Dense or layered vegetation

Advantages

• Reduces observer bias

• More precise than visual estimates

Limitations

• Time-consuming

• Requires specialised equipment

Choosing the Correct Sampling Technique

Situation	Best Technique

Large habitat

Random quadrats

Change across distance

Transect

Dense vegetation

Gridded quadrat or point frame

Investigating abiotic gradient

Belt transect