Trees can’t run away from threats, so they rely on chemical warfare to defend themselves. Their primary defence compounds include resins, tannins, and secondary metabolites, which serve to repel, poison, or trap attackers such as insects, fungi, and bacteria.
🔹 What Are They? – Sticky, aromatic substances secreted by conifers (pines, spruces, firs) and some broadleaf trees.
🔹 How They Work:
- Physically trap insects (like bark beetles) before they can burrow into the tree.
- Flush out pathogens by creating a flowing, antiseptic barrier.
- Seal wounds, preventing fungal or bacterial entry.
🔹 Example:
- Pines use resin to “pitch out” bark beetles – the beetles get stuck and suffocate before they can infest the tree.
🔹 What Are They? – Bitter, toxic compounds found in leaves, bark, and acorns.
🔹 How They Work:
- Make leaves taste bad → discourages herbivores like insects and deer.
- Bind to proteins in insect guts, making digestion impossible → slows down or kills leaf-eating pests.
- Inhibit microbial growth, reducing fungal and bacterial infections.
🔹 Example:
- Oaks & chestnuts produce high tannin levels to stop deer from eating their young saplings.
🔹 What Are They? – Chemicals that trees don’t need for growth but use as weapons against pests.
🔹 Types & How They Work:
- Alkaloids (e.g., Nicotine, Caffeine, Morphine) → Poisonous to insects & fungi.
- Terpenoids (e.g., Camphor, Limonene, Pyrethrin) → Repel herbivores & pests.
- Phenolics (e.g., Salicylic Acid – related to aspirin) → Act as antifungals & antibacterials.
🔹 Example:
- Aspens release salicylic acid to warn nearby trees of insect attacks, triggering a collective defence response.
- Eucalyptus produces toxic terpenoids that repel pests and make its leaves inedible to most animals.
- Drought & Carbon Starvation Weaken Defence Production
- Trees need carbon from photosynthesis to make these compounds.
- If they close their stomata (to save water), they can’t produce enough resins, tannins, or secondary metabolites.
- This makes them easy targets for bark beetles, fungi, and disease.
Trees defend themselves using a combination of sticky barriers (resins), bitter digestibility reducers (tannins), and toxic chemicals (secondary metabolites) to fend off pests, pathogens, and herbivores. However, if they are stressed (drought, heat, competition), they can’t make enough defences, making them vulnerable to attack.
💡 A well-fed, hydrated tree is a fortress. A starved, thirsty tree is a feast. 🍽️🌳