Millions of individuals all around the world are now familiar with the behaviour of social isolation, which has been utilised to stop the COVID-19 virus from spreading.
Several trees have also been avoiding one another, but they were already doing this before we arrived.
Gaps form when one or more trees fall in a forest. Yet, nearby trees typically encroach into these spaces quickly.
If you were to gaze up to the treetops in some forests, you may notice obvious spaces, resembling channels, between the trees’ outermost branches.
Crown shyness is the term for this distinctive border around trees. Since the 1920s, scientists have debated this phenomenon and offered numerous explanations as to why it might occur.
Not every tree exhibits crown shyness. It has been observed in various species, including Japanese larch (Larix kaempferi), lodgepole pine (Pinus contorta), black mangrove (Avicennia germinans), some eucalypt species, and lodgepole pine.
Although it typically occurs between trees of the same species, it can also happen between individuals of different species, as in the case of the spiny hackberry (Celtis spinosa) and amberoi (Pterocymbium beccarii).
According to some experts, the gaps may have been created as a result of wind shifting the canopy and producing abrasion between trees of similar heights. The branches, leaves, and buds of nearby trees rub against one another, breaking and causing harm.
Scientists were persuaded by a 1955 study of eucalypts in northeastern Australia, where strong winds frequently create contact between trees, that abrasion caused the loss of the trees’ delicate growth tips, leading to spacing.
A study on a region of Costa Rica characterised by black mangroves was later published in 1984. The distance between 22 trees of a comparable height that were randomly selected by scientists was measured, as well as their largest horizontal movement during wind gusts.
The branches intertwined “like loosely fitting pieces of a jigsaw puzzle” when the weather was quiet, they discovered. The branches frequently touched and entwined as the wind gusted. In comparison to more protected areas of the canopy, the branches along the borders of the crown shyness gaps were typically observed to have broken twigs and fewer leaves, indicating that interaction with other trees was a major cause of damage.
The crown shyness phenomenon can occur between branches of a single tree that are swinging independently as well as between trees next to one another.
Is wind the only cause of crown shyness?
If crown shyness is mostly brought on by abrasion, one may anticipate that trees growing in windy areas will exhibit it more noticeably than those in protected areas. Yet, a study of trees in Costa Rica’s Monteverde Cloud Forest Reserve revealed that this is not the case.
High winds regularly approach 100 kilometres per hour in some locations throughout the winter in this cloud forest. The crown shyness of trees in windy locations compared to more protected ones showed little variation.
The researchers saw that trees in windier regions had modifications that made them more wind-resistant, such as larger trunks and shorter, stouter twigs. These modifications would reduce the branches’ capacity to cut nearby trees.
Nonetheless, there was some evidence of dead twigs at the borders of trees, indicating that there is some abrasive contact caused by the wind.
Crown shyness can have several causes, not the least of which may not always be abrasion. There was no proof of direct abrasion in a study of crown shyness in the Malay camphor tree (Dryobalanops aromatica).
Direct abrasion doesn’t appear to be the cause of crown shyness in the Malay camphor tree.
The researchers who studied these trees hypothesised that crown shyness in this species of trees may instead be brought on by the ability of the trees’ developing tips to see light, which causes them to cease growing when they are close to the foliage of nearby trees.
According to research, plants are able to sense the far-red light frequency of visible light, which can inform them how far away from their neighbours they are. In order to prevent fading into the background, they can additionally utilise the blue portion of the spectrum.
Benefits of crown shyness
As with animals, plants also compete for resources – including nutrients, water, space and light – to survive.
There is fierce competition amongst plants for light in densely canopyed forests. It’s likely that crown shyness causes holes in the canopy, which enable trees to receive more light and maximise photosynthesis.
Trees and other plants benefit from the light that crown shyness allows to pass in areas with dense canopy for photosynthesis.
Crown shyness may have extra beneficial side effects, however the sources of it are still a subject of debate among experts.
Crown shyness may allow light to penetrate the forest floor, which may be advantageous for other plants and animals as well as the trees.
Moreover, trees may be able to inhibit the spread of dangerous leaf-eating insects and possibly also the transmission of dangerous diseases from tree to tree by having branches that do not directly touch those of their neighbours.
