Crown shyness or canopy disengagement is a phenomenon observed in
some tree species in which the crowns of neighboring trees of similar
height do not touch each other, but are separated by a gap. This forms a
persistent and striking border around individual crowns that are visible
from the ground. The phenomenon is most prevalent among trees of same
species, but also occurs between trees of different species.
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he phenomenon of crown shyness has been discussed in scientific
literature since the 1920s, but what causes it is not fully understood.
One theory suggests that this empty space around the crown might be
caused by breakage of twigs and branches from violent collision that
happens during storms and high winds. Experiments show that if trees
with crown shyness are artificially prevented from swaying and colliding
in the wind, they gradually fill in the empty space in the canopy.
Researchers have also found that crown shyness is absent when the trees
are young and short, but develop later once the trees grow in height and
are able to sway in the wind. Trees with slender trunks have relatively
small crowns because of their lesser ability to resist deflection in
wind. They therefore sway widely in wind and are more likely to collide
with neighbors.
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One Malaysian scholar who studied Dryobalanops aromatica, however, found
no evidence of abrasions due to contact in that tree. He suggested that
the growing tips were sensitive to light levels and stopped growing when
nearing the adjacent foliage.
Some suggest that trees exhibit this phenomenon to prevent leaf-eating
insect larvae from spreading.
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One of the handful of places where you can see the crown shyness
phenomenon is the Forest Research Institute of Malaysia, in Kuala
Lumpur. All the pictures accompanying this article were taken there.
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