It is a beauty in the way trees tend to respect one another’s space and maximize each other access to light. The practice of crown shyness helps them grow in perfect harmony with each other and refers to the tendency of trees to avoid touching one another in their uppermost reaches.
This tendency was first observed a century ago and there have been several hypotheses surrounding the intriguing behavior of threes. While some believe that it is a way to protect branches of one tree from coming in contact with and harming the other, others think that this is a way to protect them from pests.
Another plausible theory for crown shyness is that it helps to maximize the process of photosynthesis through the equal distribution of sunlight. This helps the trees share their resources and stay healthy.
The mesmerizing kaleidoscope-like patterns are created by a practice of ‘reciprocal pruning’ whereby neighboring trees brush past and snap of bits of the outermost leaves and branches. This causes crown shyness, or tracks of space ringed around the canopy of the trees when they are close to one another.
This phenomenon has been documented around the world from the forests of Malaysia to the mangroves of Costa Rica. But scientists are still to fully understand the occurrence of crown shyness.
Scientists wonder if trees need their personal space but then this marvel is not observed in all trees. Crown shyness has been observed in lodgepole pine (Pinus contorta), black mangrove (Avicennia germinans), and the Japanese larch (Larix kaempferi). It has been seen both in trees of identical species though it can also occur between individual trees of dissimilar species, such as the amberoid (Pterocymbium beccarii) and the spiny hackberry (Celtis spinose).
It has been observed that crown shyness occurs more in trees of similar age, more so if they belong to the same species. But this is not consistent and can occur in any forest. The reasons most closely associated with it by scientists are resource sharing and the rubbing of canopies.
Resource Sharing May Cause Crown Shyness
Resource sharing is believed to be the main reason for crown shyness. By this trees ensure they get the maximum sunlight to aid in the process of photosynthesis. As trees are ‘sessile’ or stationery, they need to make sure that they can access all that is required to sustain and defend themselves despite their immobility.
The process of photosynthesis helps them create their food and gain nourishment. And for that to happen, then need access to plenty of sunlight. Trees are acutely sensitive to sunlight that is more than merely inching towards the source.
Trees have photoreceptors that are sensitive to both levels of red and far-red light (R and FR). They both are present in sunlight in equal quantity but when it beams on the leaves, more of R light gets absorbed.
Trees are thus able to sense if something comes in the way and turn away from any form of obstruction. Individual trees thus turn away from each other and thus create intricate patterns.
This method of sharing sunlight without resorting to competition is the optimum method to derive the maximum sunlight and causes the tree canopies to keep a certain gap which is called crown shyness.
Rubbing Of Branches And Leaves In The Uppermost Reaches Causes Crown Shyness
A second reason espoused by scientists is that the uppermost branches of the trees brush against one another during winds and storms which causes the branches and leaves to fall off. This leads to a small opening between the trees at their outermost edges.
This explanation is also strengthened as broken branches were observed at the edge of the canopy of each tree. Trees sense that grown close could only cause the branches to break up and thus form a safe distance from the next tree.
This observation was based on a 12955 study in north-eastern Australia of eucalyptus trees. Strong windy conditions cause high contact between trees and cause the tips to break away at the edges to create crown shyness.
But one argument that goes against this theory is that crown shyness thus should be more common in a windy area, though it doesn’t appear to be the case.
A more detailed study on black mangroves in Costa Rica was done, comparing their state in both windy and still conditions. It was observed that the branches of the black mangrove trees during calm conditions caused them to loosely interlock like matching pieces of a jigsaw puzzle.
But when the conditions were windy, the outer edge of the branches of neighboring trees interlocked and it was observed that areas, where crown shyness was observed, had lesser leaves and more broken twigs. This reinforced the idea that interaction during windy conditions causes the gaps to form between neighboring trees causing the crown shyness.
Whatever the reasons, scientists have found additional benefits of this phenomenon. Crown shyness allows sunlight to penetrate the floor of the forest. Moreover, the distance between the trees prevents the transmission of diseases, insects, and pests.