How to Calculate Shade From Trees

Written by marlene affeld
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Both deciduous and evergreen trees provide natural beauty and visual appeal to urban landscapes and country gardens. An important benefit of tree planting is to provide shade for UV protection and energy efficiency. Trees planted to provide shade near home patios, driveways or sidewalks, or in parks or along city streets and car parks, help reduce the amount of heat absorbed by stone and concrete. A tree's shade factor refers to the total amount of sunlight blocked by the tree. A basic understanding of how to calculate the shade any given tree will provide will enable you to determine tree spacing and planting locations.

Skill level:
Moderate

• Tape measure
• Clinometer

Instructions

1. 1

Calculate the area or amount of shade provided by a tree with trigonometry. First determine the sun's altitude (for a specific hour, day, month and latitude). Next, you measure the size of the crown or canopy and then the approximate height of the tree. (Determine the species of trees in your landscape, measure their current height and crown size and make note of their likely size at maturity.) Using these measurements, a triangle formed by the trees height, crown size and altitude will reflect the length or the tree's shadow.

2. 2

Measure the widest and narrowest points of the tree spread, then average out these measurements to calculate the tree's crown spread. The crown spread of a given tree simply means the area the branches cover. (The size of the crown spread will change and increase as the tree matures.) The size of the crown spread is a factor in determining the amount of shadow a tree provides.

3. 3

Determine the height of your tree with a clinometer. This is a handy tool used in the forest industry. You can purchase the tool from hardware stores or home and garden centres. The tool calculates the distance and angles to estimate height. Follow package instructions for figuring out height. By combining the estimated height of the tree with the crown spread, you will achieve a fairly accurate estimate of the tree's overall shade factor.

Tips and warnings

• Plan before you plant. Trees are the longest living plant we add to our landscapes and require a bit of forethought. When planning the location of shade trees to grace your landscape, consider the impact of the tree shadow on the proposed planting location. Include the crown width at maturity, habitat, height and leaf density of the tree you are planting. There are literally hundreds of different tree species, each providing a different amount of shade. Deciduous trees will provide shade only while in leaf; evergreen trees cast their shadows year-round.
• The shadow cast by a tree growing on level ground will be longer than a tree planted on a slope or hillside.

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