How can oils in leaves, wood, and roots help protect plants?

Essential oils found in leaves, wood, and roots serve as a natural defense system for plants, primarily by protecting them against plant parasites or depredations by animals.1

These substances function in several ways:

• Chemical Defense: Many essential oils possess insecticidal, antibacterial, and antifungal properties, which help the plant resist infection and herbivory.2
• Protective Barriers: When a tree trunk is injured, it may release oleoresinous exudations—resinous oils—that act as a protective seal. This prevents the loss of vital sap and shields the plant from disease organisms and parasites.1
• Signaling: Plants can release volatile organic compounds (VOCs) in response to stress, such as drought, microbial infection, or insect attacks. These chemicals can warn neighboring plants of impending threats, prompting them to increase their own production of toxic compounds or release chemicals that attract the natural predators of the attacking pests.3

While the exact function of all essential oils remains a subject of study, they are widely considered a critical component of a plant's broader strategy to survive environmental pressures and herbivory.14