Pests and diseases

Longevity in trees varies greatly by individual as well as species, driven by numerous variables – especially the stability of heat, light and moisture levels. When these misalign, there’s always a combo of insects, fungi, bacteria and viruses ready to strike.

Trees maintain energy reserves to fight these threats but suffer when the growth-defence balance is thrown out. For example, a fallen tree enables its neighbours to harvest lots of new sunlight, which they use to grow new branches as quickly as possible. However…

When a tree puts all its energy into new growth, it’s less able to fight pests and diseases. Some trees will get away with this but an attacker realising a tree has no defensive response means trouble.

Fungi, insects and arachnids can cross oceans in imported timber or parcels. Similarly, migrating birds transport small animals, seeds and fungal spores across huge distances and multiple borders.

Ash dieback is a great (if unfortunate) example of a fungus that has spread virulently and established itself far from its origin.

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Phytoncides from trees, especially conifers like this Scots pine, disinfect the air and have a distinctive ‘forest’ scent that’s more acute in hot, sunny conditions.

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Walnut leaves contain effective insect-repellent compounds, making the shade of its tree a good spot to for mosquito avoidance.

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A tree is likelier to survive another tree falling on it in winter because the bark is drier and tighter-fitting. In summer it’s full of water and more easily removed, making it vulnerable to invaders.

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When fungi reach dry heartwood through a wound, they hollow out the tree, only penetrating the sapwood if the air dries it enough before the tree seals the wound (heart rot).

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The Asian long-horned beetle lays its eggs in the split bark of deciduous trees. Larvae hatch and feed while adults drill large exit holes which are attacked by fungi, leading to the trunk breaking.

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The ash dieback fungus proliferated throughout Europe (including Jersey), causing a vast proportion of ash trees to die or be destroyed, changing the landscape forever.

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