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Don’t Stand So Close to Me: The Phenomenon of Tree Crown Shyness

Most of the time, when you are walking in the woods and you look up, you will see a mass of intermingled tree branches that form a canopy above your head. But in some forests, you will see something strange. You may see a river of sky in a uniform width separating the crowns of each tree. This an odd, naturally occurring phenomenon call tree crown shyness, first documented in the 1920s, in which the upper branches of some varieties of trees avoid touching other trees. Scientists have been studying this phenomenon to determine how and why some trees need their personal space. And they have some interesting theories.

Tree crown shyness, also called canopy disengagement, has been observed around the world and occurs between of the same species and of different species. The trees create, in effect, a border around each individual tree, far enough away from the surrounding trees that the branches will not touch each other, even in high winds.

Researchers have discovered that tree crown shyness is not found in young, short trees, but seems to develop as the tree grows taller. They have also learned that trees with more slender trunks, that sway more in the breeze, develop smaller crowns as a way to further prevent tree top touching.

Early scientists who studied tree crown shyness theorized that the uppermost branches of the trees must have broke off from colliding with neighboring tree branches, thus creating the river of sky effect. Subsequent studies, however, have found that the shy trees showed no signs of damage or breakage. The branches simply stopped growing when they started to get close to a nearby tree.

This seems to indicate that the trees are spatially aware. An individual tree must have some knowledge of how far its crown spreads, how close its neighbors are, and how much space to leave empty around itself. But how is this possible?

The newest theory suggests that the leaves growing in the tree’s crown are particularly light-sensitive. When they detect shade from surrounding trees, they stop growing in that direction.

If the “how” is a difficult question to answer, perhaps the “why” is easier to crack. Two prevailing theories have been put forth by researchers. One suggests that the trees isolate themselves as a way in ensure that they will receive optimal sunlight for photosynthesis. The second theory proposes that the isolation is a way for individual trees to protect themselves from the spread of invasive insects or diseases.

Either theory sounds plausible, but the phenomenon of tree crown shyness forces us to expand our previously held ideas about intelligence in plant life. If trees can be spatially aware, cognizant of invasion threats, and can control its growth, we must appreciate both the intelligence of the trees and the beautiful patterns they create in the forest canopy.

Sources:

“Crown Shyness: A Peculiar Natural Phenomenon.” Amusing Planet, Sept. 2015. Web. 27 Aug. 2017.

Jobson, Christopher. “The Phenomenon of ‘Crown Shyness’ Where Trees Avoid Touching.” Colossal. 14 Aug. 2017. Web. 27 Aug. 2017.

Richman-Abdou, Kelly. “Trees with “Crown Shyness” Mysteriously Avoid Touching Each Other.” My Modern Met, 26 Aug. 2017. Web. 27 Aug. 2017.

Featured image from Meridianos