3. Canopy cover

While land cover is about what type of plants are on the land, canopy cover is about how much of the land is actually covered by them, i.e. how big is the area covered with trees, grass, vegetable plants, or mulch?
This can give you more specific information about important aspects affecting plant growth, such as how much light your plants get, how humid the soil might be, what relative temperature you can expect, or how quickly wet soil surface will dry up.

Observing and estimating canopy cover

Imagine taking a bird’s eye view for estimating how much the different layers of land cover actually cover up your sensor parcel. You’ll be making a guess of the total area that is covered by each layer during the growing season. This estimate can only be an approximation. If you plant vegetables, you know that actual canopy cover – the amount of ground covered by a plant – can change significantly over the course of a year.
Canopy cover is estimated for each land cover class (layer) separately. If the land cover is complex, so there are two or more land cover elements, they can also overlap in covering the ground. E.g. shrubs under trees overlap in covering the ground, or mulch under vegetables – seen from a bird’s eye view – also overlap in covering the ground.
To familiarise yourself with the concept of canopy cover, you can, for example, go outside and look straight up through a paper roll (standing, kneeling, lying down). Do you see leaves and branches? If yes, your spot would be under canopy cover. You can also do this the other way around and look to the ground to determine which ground plants cover a single spot. If you looked at enough spots on a piece of land (a “representative sample”), you could consider all single observations together and from that get an estimate of canopy cover. This is how scientists do it, with more sophisticated tools and a clear sampling design, but the general idea is the same.

A person looking at the ground and then the sky through a rolled up paper tube
Estimating canopy cover   © Gerid Hager

You can also try to estimate canopy cover for smaller parcels from sight on the ground using visual aids such as these diagrams. Each image represents cover in percent, imagined from a bird’s eye view, similar to photos taken from space onto a piece of land. Or the other way around, as if you’d look up from the ground in an exact vertical direction.

Scale for assessing canopy cover © University of Dundee/GROW

A human viewpoint, however, always has a specific angle, so without using special tools, we need to use some tricks to get a good enough estimate.

  • You can use online services with satellite images (online maps which provide a photo layer) on your computer or smartphone to help you take a bird’s eye view. Find your location on a map and explore your parcel and its cover. This is especially suitable for very large parcels with trees or shrubs (e.g. a vineyard or an orchard).
  • You can also look at the shade on the ground to get a better idea about canopy cover of trees and shrubs. However, this only works if the sun is high up (steep angle), ideally directly above the plants. Shadow can be misleading if the sun falls in from a lower angle, so this really only works well during the summer months around midday. For places close to the equator, this works well around midday all year long.
  • You can move around to a few different spots on the piece of land you are observing and consider canopy cover from different viewpoints. Do your estimates change depending on where you stand? Do your estimates change depending on what time of the day you make your observations? If you have a friend with you, do you get the same estimates?
  • You may also consider, that people have shown a tendency to underestimate canopy cover when they are trying to make exact estimates by eyesight and for a larger area. We do not ask you for an exact estimate, but for estimating which range your canopy cover falls into. This should already help buffer human error in the estimates. Nevertheless, you may weigh your estimate and try to be aware of this potential human bias.

How to use the diagrams

To arrive at a final percentage range, first, eliminate the options that seem the least likely. Then, weigh the other options and close in on your final approximate estimate. Look at the examples below to get a feel for how to estimate canopy cover.

Olive Grove

Spruce forest

Pasture

Vineyard

In the case of vineyards, you can see a recurring and very regular pattern: a row of vines, grass, a row of vines, grass, a row of vines, grass etc. In this case, you can try to estimate canopy cover for one element of the pattern (a row of vines, grass) and extend for the whole vineyard. If you look at one row plus the grass area, it becomes relatively clear, that the vines cover less than a quarter of the area, but likely more than 10%. And the cover estimate for grass would be > 91%. This example also shows how shade can be misleading as a visual aid. It is autumn and the sun comes in at a low angle, producing a shade area that is larger than the vertical cover above ground.

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Updated on 14th November 2018

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