If you’ve ever walked among a cluster of trees or in a forest and looked up towards the sky, you may have noticed a phenomenon where the outstretched branches of one tree don’t touch neighboring tree branches.
This condition is known as “crown shyness”. With crown shyness, the upper branches that form the crowns full-grown trees don’t touch the upper branches of neighboring trees, creating river-like gaps of light in the canopy where the sun shines through.
Where is crown shyness found?
Crown shyness is most commonly found among trees of the same species and age but it can also occur in heterogenous forests. Crown shyness is also known as canopy disengagement. Canopy disengagement is a natural phenomenon where the canopies of individual trees avoid overlapping leaves and branches with those of adjacent trees. This phenomenon can be found in forests globally.
What is canopy closure?
The opposite of crown shyness in a forest is known as canopy closure.
Why does crown shyness happen in trees?
Crown shyness has been studied extensively, but researchers still don’t understand why it happens (MacDonald, 2018).
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There have been various theories put forward over the decades as to why crown shy exists in some forests.
Mechanical Damage Theory
One theory is that mechanical abrasion from neighboring trees causes the gaps. As trees growing, colliding branches abrade and more fragile branches are trimmed off (Hastings et al., 2020). As growth continues, the cycle of abrasion and branch removal maintains the gaps.
Light Optimization Theory
A different hypothesis proposed that the buds of trees have light receptors to sense when nearing adjacent vegetation and stop growing to avoid getting too close.
The avoidance of growing into neighboring trees is believed to be an adaptive response to maximize access to sunlight while minimizing the harmful effects of competition (Franco, 1988). This theory suggests that crown shyness is a phototropic response, where trees grow towards the most abundant light source to maximize photosynthesis. The phenomenon is seen as a strategy for individual trees to capture and utilize light most efficiently.
Insect and Disease Avoidance
The third prevailing theory argues that crown shyness serves as a defense mechanism against the spread of disease and pests. By avoiding physical contact, trees minimize the risk of having pathogens or parasites transfer to that tree fromadjacent trees.
Benefits of crown shyness in forests
The gaps created by crown shyness allows better sunlight penetration down tot the forest floor. The greater amount of sunlight enhances the forest understory’s ability to support various plant species through photosynthesis, the process by which plants convert sunlight to sugars. This can lead to higher levels of biodiversity within the forest, creating a more resilient ecosystem.
Watch: Crown Shyness – When Trees Need Personal Space
References
Franco, M. (1986). The influence of neighbours on the growth of modular organisms with an example from trees. Philosophical Transactions of the Royal Society of London. B, Biological Sciences, 313(1159), 209-225. https://www.jstor.org/stable/2396899
Hastings, J. H., Ollinger, S. V., Ouimette, A. P., Sanders-DeMott, R., Palace, M. W., Ducey, M. J., … & Orwig, D. A. (2020). Tree Species Traits Determine the Success of LiDAR-Based Crown Mapping in a Mixed Temperate Forest. Remote Sensing, 12(2), 309. https://doi.org/10.3390/rs12020309
MacDonald, J. (2018, August 25). The Mysteries of Crown Shyness. JStor Daily. https://daily.jstor.org/the-mysteries-of-crown-shyness/
