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CROWN SHYNESS: A Process of Physical Distancing Among Plants

The phenomenon of crown shyness is known to us for a long time. In 19205 descriptions of crown shyness have appeared in some of the scientific literatures. But, the first scientific research on this topic started only in 1982. Eminent Biologist Francis "Jack"

By Jayveer ValaPublished 3 months ago 6 min read

For the last few years the term physical distance or social distancing has gained considerable usage, thanks to the pandemic! It is advised to stay at least 6 feet (roughly about 2 arms' length) away from other persons both in indoor and outdoor spaces to slow the spread of the COVID-19 virus. You will be amazed to know that the plant world has been following the norms for ages!

In forests, when you look up you will see a network of imaginary cracks formed by gaps between the outermost edges of certain tree branches. It looks like a precisely engineered jigsaw puzzle, each branch growing just perfectly so that it almost-but not quite--touches the neighbouring tree. It is really interesting to see how some trees maintain distance from others. This beautiful phenomenon is known as crown shyness or canopy shyness. Scientists still don't fully understand why few species of trees so often refuse to touch each other.

The phenomenon of crown shyness is known to us for a long time. In 19205 descriptions of crown shyness have appeared in some of the scientific literatures. But, the first scientific research on this topic started only in 1982. Eminent Biologist Francis "Jack"

Putz one day strayed into a knot of black mangrove trees while conducting a fieldwork with his team members on March 1982. As he gazed skyward, he observed when the wind stirred the tops of the mangroves above him, it caused the limbs of neighbouring trees to claw at each other and snap off some of their outermost leaves and branches. Putz also noticed that this reciprocal pruning had left tracks of empty space running through the canopy. Putz concluded that trees need personal space and from then he started to work for unravelling the causes of this behaviour. Since then this phenomenon draw attention of the scientists and they are still working on it.

Species showing Crown shyness

Crown Shyness has been documented in forests around the world. From the mangroves of Costa Rica to the towering Borneo camphor trees of Malaysia, gaps can be seen in the canopies. There's a special structure for a forest called a cathedral forest, where the forest has lost its understory (underlying layer of vegetation) and the big, giant canopy trees kind of over-arch, and those are the most favourable places for crown shyness. However, there are plenty of forests where crown shyness is not found.

The interesting thing is the younger the forest the rare it is, whereas in old forest there is maximum probability of crown shyness.

Some of tree species that usually display crown shyness are Black Mangrove, Eucalyptus, Camphor, Sitka Spruce, Japanese Larch, etc.

Probable causes of crown shyness

Trees might be tall and strong, but few of those are still a bit sheepish. There are a few hypotheses for their growth patterns that cause crown shyness.

a. Relation of Wind and Abrasion Australian

forester M.R. Jacobs, who studied the crown shyness patterns in eucalyptus in 1955, believed that the growing tips of the tree were sensitive to abrasion, resulting in canopy gaps. We know about Pruning in plants and often do it in our garden. In this process we artificially remove certain parts of trees and plants, such as branches, leaves and buds. It affects the lateral growth of the trees. In nature it can happen due to winds. Blowing wind causes flexible branches of trees to move randomlv which hit their adjacent trees. It gives rise to unnecessary pruning.

So, pruning with the help of winds may lead to damage of important parts of the tree like foliage, which plays a vital role for performing photosynthesis. As a result, trees limit growth at these locations to avoid further damage. This reflects that for preventing unnecessary abrasion with neighbouring trees, trees may show crown shyness.

This theory makes sense, given that crown shyness is exhibited between trees of different and same species, and sometimes even between branches of the same tree. When researchers were able to prevent wind-induced collisions between trees, they filled in the canopy.

b. The Relation of the Blue-Green Pigment 'Phytochrome'

There is another theory for timid tree branches based on their ability to sense nearby plants. We know that Phytochrome is one type of photoreceptor in trees and plants which helps to detect light. They are sensitive to far-red and red region of the visible spectrum. Based on light sensitivity we may classify them as type I (activated by far-red light) and type II (activated by red light). Neighbouring plant detection is thought to be a function of several unique photoreceptors. Few plants are able to sense the proximity of any neighbour by sensing backscattered far-red (FR) light with the help of phytochrome photoreceptors.

Phytochrome is responsible for expansion of lateral branches. When they receive the light directly from the Sun, both kinds of lights are received. But when the light falls indirectly on the leaves, much of the red light is already absorbed making greater far-red light reach the shaded leaves. The leaves can thus sense that the light coming on the top branches is not direct sunlight. This forces the branches and leaves to stop growing and avoid obstruction. Physical distancing on both ends ensures that neighbouring trees do not cover their crowns and minimize harmful competition for resources.

This theory could also explain why some trees do not exhibit crown shyness when interacting with trees of their own species. Studies have shown that some plants that sense nearby relatives wil position their leaves to avoid casting shade on their kin, even at the cost of shading themselves. On the other hand, in dense forest the natural resources. especially sunlight, is limited. Hence this behaviour also helps other species to survive.

c. The Camphor Connection

Camphor (CoHO) is a solid compound. Eucalypt and Dryobalanops are two most popular tree species, which show crown shyness. It is interesting to note that both of these plants have camphor. The essential oil extracted from their leaves have some amount of camphor. Studies are going on to find the role of camphor for crown shyness.

A recent study has suggested that 'Arabidopsis' shows different leaf placement strategies when they are grown amongst kin and unrelated conspecifics, shading dissimilar avoiding kin.

This response was shown to be contingent on the proper functioning of multiple photosensory modalities. However, a strong link between photoreceptors and a crown asymmetry is yet to be proven experimentally.

d. Competition and Adaptation

Some species have gradually adapted to take advantage of crown shyness. They choose to grow into shapes that complement the nearby trees, so that they don't have to compete for canopy room. Thus, it helps both the species to survive; it is one kind of mutual relationship.

Benefits of crown shyness

As the natural resources are limited, plants, like any other living beings, compete for nutrients, water, space, and light in order to survive. In forested areas with dense canopies there is intense competition between plants for light. If there is a gap in the canopy resulting from crown shyness it will allow trees to increase their exposure to light and optimize the process of photosynthesis. Scientists are still debating on the potential causes of crown shyness, but they have agreed with the positive side effects of crown shyness.

In dense forest it is very rare that sunlight could reach the soil. But for any soil to become fertile sunlight is required. It is also essential for the survival of microbes and decomposers.

Crown shyness allows the light to reach the forest floor, which could benefit other plants and animals that may in turn be beneficial to the trees.Additionally, by having branches that do not physically touch those of their neighbours, trees may be able to limit the spread of harmful insects. Sometimes diseases spread from one plant to other when those are in contact.

Through crown shyness plants avoid the transmission of harmful diseases. Crown shyness teaches us a lot. Contrary to the concept of survival of the fittest, recent ecological development indicates sustainable coexistence and collaboration rather than competition.


About the Creator

Jayveer Vala

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  • Julie Shetler3 months ago

    Thank you for sharing. I’vr never heard of crown shyness before.

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