Country: United States
Date: November 2006
What is the difference between tree density and tree cover?
Tree cover and tree density are different. You can have
trees with a large expanse of leaves at the top of the
trees, giving a large cover, but small density, such as
a forest of honey locust trees. On the other hand you
can have both a large tree density and cover, such as you
find in some coniferous forests (fir, pine, etc.).
Dense tree forests allow little light to reach the ground,
whereas some forests with a lot of cover can still allow
quite a bit of light to reach the surface (the light shines
in under the individual tree canopies).
We use a measurement called Leaf Area Index (LAI for short)
to determine canopy density (whether for trees, crops,
grass, etc.). The canopy includes the entire tree (or grass,
crops, etc.). The measurement compares the amount of sunlight
above the canopy with the amount near the surface. The
larger the LAI, the denser the canopy is. An LAI of 1 indicates
that, effectively, the leaves of the plants cover the same area
as the ground. An LAI of more than 1 indicates that there are
multiple leaf layers that each contribute to depleting the
amount of light under the canopy. As the growing season
progresses through the Spring and Summer, the LAI increases
as plant's and deciduous tree's leaves grow and fill out.
LAI is therefore a good measure of the mass and density
David R. Cook
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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