Tree Defence Mechanisms
Tree Defence Mechanisms
Trees possess many features and behaviours to help protect themselves against pests, pathogens and environmental stress.
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Research has found that some trees can “smell” danger and can alert other trees. When an oak tree is under attack by insects, it releases chemicals into the air as a signal to nearby trees. In response, the neighbouring tree rapidly increases tannin production in their leaves to discourage insects from feeding. (Mehra and Mazumdar-Leighton, 2024)
Tonka bean trees and some other tall trees are remarkably resistant to lightning strikes, and actually appear to thrive on lightning, using the energy to kill off surrounding competitors and parasitic vines, providing a significant competitive advantage in dense rainforests! According to research, the patterns observed suggest that lightning plays an underappreciated role in tree competition and the coexistence of different tree species. (Gora et al., 2025)
Some trees have exceedingly thick bark due to evolution in areas where there are frequent forest fires or volcanic eruptions. This has been observed in Douglas Firs and Monkey Puzzle trees.
Tonka bean trees can conduct electrical current internally with minimal damage, therefore they are remarkably resistant to lightning strikes, often surviving unscathed while neighbouring trees are devastated. In fact, these trees appear to thrive on lightning, using the energy to kill off surrounding competitors and parasitic vines, providing a significant competitive advantage in dense rainforests!
When leaves begin to change colour in the autumn, the tree releases hormones designed to take the last sugars out of the tree to protect themselves against the harsh cold weather, which helps it to survive through the winter.
Most trees grow with a slight spiral twist in the trunk to defend themselves against strong wind, preventing bending.
Trees can be shy
Trees can be shy
Crown shyness is a natural phenomenon where the uppermost branches of trees, often of the same species, refuse to touch, leaving gaps in the canopy, only a few cm wide.
A leading explanation for the behaviour is that it prevents abrasion of branches during wind. Trees that avoid contact suffer less breakage and grow more successfully.
It may also help to get the best amount of light. Trees may detect reduced light via photoreceptors, and adjust its growth to avoid the shaded or crowded areas!
Crown shyness can reduce the spread of insects, fungi, and disease by limiting direct contact between trees.
Commonly seen in species like Eucalyptus, mangroves, and pines.
Individual trees grown in isolation do not show crown shyness – the effect only emerges when trees grow close to others. Moreover, different species growing side-by-side may not exhibit crown shyness with each other, suggesting the behaviour is species-specific rather than universal.
Crown shyness is an amazing phenomenon to observe, and an example of trees' intelligence! It is considered a physical or physiological process rather than an act of intentional “communication” between trees.
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