(4) Surveying Method 3: Estimating the percentage cover (distribution) of a species from a quadrat

Usually a plant species e.g. wild flower or lichen (NOT animals)

Another way to do a survey is to photograph the area or habitat of an organism you are interested in.

This is done on a large scale to survey farmland and monitor the distribution and growth of crops.

Above is a photograph of a section of a stone wall on which two species of lichen are growing.

In order to help estimate the % cover of the orange lichen and grey lichen a 10 x 10 grid (the quadrat) has been drawn over the photograph - making 100 squares (or mini-quadrats).

If a mini-square is filled with half or over half of the species it counts as 1/100 of the area.

If the mini-square is less than half-full a species does not count.

 

My estimates of the distribution as measured by the % cover (do you agree?)

You can think of the percentage cover as a measure of the distribution or abundance.

Orange lichen: Only 3 squares present (all in top left).

Therefore the orange lichen cover estimate is 3%.

Grey lichen: I found it easier to count the squares where it was absent, which I found to be 17.

Therefore the grey lichen cover estimate is 83%

The estimate of total lichen cover is 3 + 83 = 86%

If you surveyed another part of the stone wall in e.g. different light or moisture conditions, you would find the % cover might be different.

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Key points - Estimation of percentage cover (distribution) of a species from a quadrat

Based on the syllabus-specifications for students taking the UK AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10 biology).

Revision notes on Estimating Percentage Cover Using Quadrats - a key method in Biology fieldwork to study the distribution of plant species.

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What Is Percentage Cover?

Percentage cover is a way of estimating how much of the quadrat area is covered by a particular species. It’s especially useful for studying plants, mosses, and lichens, which often overlap or grow densely.

This method avoids having to count every individual and gives a good indication of abundance and dominance.

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When Is Percentage Cover Used?

• When it’s difficult to count individuals (e.g. grass, moss).

• To compare distribution across habitats.

• To identify dominant species in an ecosystem.

• Along transects to observe how cover changes with environmental factors (light, moisture, trampling etc.).

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How to Estimate Percentage Cover – Step by Step

1. Place your quadrat (usually 1 m²) on the ground at a randomly or systematically chosen location.

2. Look at the species you're surveying (e.g. clover).

3. Visually estimate how much of the quadrat is covered by the species:

   • This can be done roughly by eye.

   • Or use a grid quadrat (100 small squares = each square is 1%).

4. Count the number of squares that the species occupies (even partially).

5. Calculate the percentage cover:

6. Percentage cover} = (Number of squares covered) x 100 / (Total squares)

6. Repeat in different areas to get a more accurate average.

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Exam Tips

• You don’t need to identify every individual plant — just estimate coverage.

• Practice estimating with diagrams or in the school field — accuracy improves with experience.

• If overlapping species: it’s fine if total cover goes over 100%, since multiple species may share the same space.

• Always justify: "Percentage cover was used to estimate abundance because counting individuals was impractical."

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Keywords, phrases and learning objectives for this part on ecological surveying and biodiversity

Using quadrat data analysis in ecology surveying, be able to estimate the percentage cover (distribution) of a species from quadrat measurements.

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