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Crown Shyness

By Adnan Yousef, KwF Intern - Pakistan

Just under 100 years ago, in 1920, an ecological marvel, crown shyness, was first observed and photographed. In 1955, the botanist Maxwell R. Jacobs coined the term "crown shyness" after studying various populations of eucalyptus. Crown shyness is also known as canopy disengagement, canopy shyness, or inter-crown spacing.

Crown shyness is a phenomenon observed in some tree species, in which the crowns of fully stocked trees do not touch each other, forming a canopy with channel-like gaps. The wonder is most pervasive among trees of similar species, yet additionally happens between trees of various species. Numerous speculations exist about why crown shyness occurs, and research recommends that it may inhibit the spread of leaf-eating insect larvae.

Some hypotheses contend that the inter-digitation of canopy branches leads to the “reciprocal pruning” of adjacent trees. Trees in breezy regions endure physical harm as they crash into one another amid winds. As the aftereffect of scraped areas and impact damage, there is an induced crown shyness response.

Why does crown shyness occur? Mainstream researchers have not yet achieved accord regarding what causes this wonder. A sum of three speculations have attempted to clarify the crown shyness:

The underlying speculation of Maxwell R. Jacobs (scarcely acknowledged by established researchers) clarifies that the grating of certain branches with others, when the breeze hits them, would restrain the development of the branches from contacting the neighboring trees, to avoid scraping and other damage (Friction hypothesis).

The most supported hypothesis currently indicates that crown shyness has an allelopathic origin. In botany, allelopathy is any impact that one plant transmits to another through the creation of various concoction mixes, either causing a positive or negative impact on the other plant. These mixes are the purported allelochemicals. At the end of the day, plants and trees speak with one another by substance signals. This relationship happens more much of the time among trees and plants of similar species, even though it likewise happens between various species (Allelopathy hypothesis).

In addition to chemical signals, another theory contends that phytochrome photo-receptors (sensors of lightly equipped for identifying the territory of removed red light) controlled by trees and plants enable them to see the nearness of people. Another kind of photo-receptor recognizes blue light, which creates in plants and trees the shirking of shadows delivered by different people (Photo-receptors hypothesis).

Are all trees “Shy”?

Crown shyness has been seen in certain European oak and pine species, as well as tropical and subtropical species. For example, some eucalyptus, types of the Dryobalanops genus, Pinus contorta, Avicennia germinans, Didymopanax pittieri, Clusia alata, Celtis spinosa, Pterocymbium beccarii, Picea sitchensis and Larix kaempferi.

In different species, the highest points of the trees come to contact and even cross their branches, although the canopy (territory that incorporates the highest points of the trees) does not usually mix completely.

Hypotheses on the advantages of the canopy shyness

  1. A few more speculations propelled by organic science include: It permits a more noteworthy infiltration of light in the woods which enables plants to perform photosynthesis more effectively.

  2. It protects the branches and leaves from hitting against one another if there should arise an occurrence of tempest or whirlwinds.

  3. It inhibits illnesses, larvae, and insects that feed on leaves from spreading effectively; starting with one tree then onto the next.

  4. For the time being, it appears that crown shyness is because of a relationship of a coordinated effort between species for survival, instead of a challenge (prominently known as the "survival of the fittest"). We should trust that future examination will reveal somewhat more insight into this still obscure marvel.


H Fish, VJ Lieffers, U Silins, RJ Hall (2006). "Crown shyness in lodgepole pine stands of varying stand height, density and site index in the upper foothills of Alberta". Canadian Journal of Forest Research. 36 (9): 2104–2111. doi:10.1139/x06-107.

Franco, M (14 August 1986). ". The influences of neighbours on the growth of modular organisms with an example from trees". Biol. Sci. 313 (1159): 313, 209–225. doi:10.1098/rstb.1986.0034. Retrieved 10 June 2016

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