How to Calculate Shade Factor of Trees
Trees are an important natural source of UV protection and energy efficiency. Not only do their leaves block the sun, but they actually convert the energy into clean air for the surrounding environment. Shade factor is a technical term that refers to the overall amount of sunlight blocked by an object---both natural and man-made. Calculating the shade factor of a tree just takes a few measurements. Does this Spark an idea?
Instructions
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Determine the crown spread of your tree. Crown spread simply refers to the average area of your tree's branches. Measure at the widest and most narrow points of the tree's spread and average them. The resulting number is your tree's crown spread.
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Get as accurate an estimate of the tree's height as possible. This is best done with a clinometer, a common forestry tool used to calculate angles and distances to determine heights. You can also compare to nearby objects whose height is known (houses, basketball goals, etc.). On June 21, which represents the peak of the sun's intensity in the northern hemisphere, most trees in the region will cast a shadow half as long as their actual height. Therefore, an 80-foot tree will cast a shadow roughly 40 feet long.
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Add the estimated shade length of the tree to the crown spread to determine the overall shade factor of the tree. This measurement will give you an idea of how valuable a tree's shade is in your yard, and will also provide useful information for future tree planting and spacing, not to mention determining suitable locations for other landscaping plants.
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Factor in variables to help make your measurements more specific. Such variables include tree health and variety (which can affect how much sunlight is able to filter through the tree), as well as seasons and distance from the equator. Trees in Minnesota will have longer shadows (even on June 21) than those in Florida because of the angle of the sun. Also, shadows will be longer in spring, fall and winter. Since shade factor is usually calculated when planning a landscape, all of these variables can help provide insight as to the ideal placement of other plants in the yard.
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