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

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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