Shade Tolerance of Trees

Wayne K. Clatterbuck Associate Professor Forestry, Wildlife & Fisheries University of Tennessee

2.4_1Most trees have very specific requirements for how much sunlight or shade that they are able to endure. Some trees do well in full sunlight, while other trees do not perform as well. Recognizing the light requirements of different species of trees will assist in proper tree selection in the landscape and will promote healthy trees. This fact sheet discusses and lists the comparative tolerance of trees to shade or sunlight.

Shade tolerance is a comparative term used to describe a tree species’ ability to become established, grow and persist under shade or low light intensity, quality and duration. Tolerant species can grow comparatively well when little light is available. Intolerant species cannot grow well in low light levels, but grow very well at light levels approaching full sunlight.

Knowledge of tolerance is necessary in establishing and managing trees in urban landscapes. Unfortunately, many shade-tolerant trees are planted in full sunlight conditions, increasing the stress and affecting their physiological processes. These trees usually do not adapt readily to increased light levels, usually decline and may eventually die. Shade-tolerant trees grow best in partial shade beneath larger trees or nearby structures or buildings that provide some shade during the day.

Sunlight is the key to successful flowering of trees. Enough sunlight must reach the tree for flowers and fruit to develop.. As the amount of sunlight decreases, so will the number of flowers. Thus, management of the amount of sunlight received by more shade-tolerant trees should be balanced to provide enough sunlight for flowering, but not so much that it affects the health of the tree.

Age affects tolerance, as trees usually become more intolerant with age. Most maples and oaks are more shade-tolerant when young, but become more intolerant as they mature. Tolerant species are usually photosynthetically more efficient because they are able to utilize light at lower levels than shade-intolerant trees.

The morphology and physiology of leaves and trees that are tolerant and intolerant of shade are quite different. These attributes of trees can provide different species with different shade tolerances.

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