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xternal stresses on plants have the ability to change the structure and composition of forest ecosystems. Common external stress that Pinaceae experience are herbivore and pathogen attack which often leads to tree death. In order to combat these stresses, trees need to adapt or evolve defenses against these stresses. Pinaceae have evolved a myriad of mechanical and chemical defenses, or a combination of the two, in order to protect themselves against antagonists. Pinaceae have the ability to up-regulate a combination of constitutive mechanical and chemical strategies to further their defenses. Pinaceae defenses are prevalent in the bark of the trees. This part of the tree contributes a complex defensive boundary against external antagonists. Constitutive and induced defenses are both found in the bark. Constitutive defenses Constitutive defenses are typically the first line of defenses used against antagonists and can include sclerified cell
s, lignified periderm cells, and secondary compounds such as phenolics and resins. Constitutive defenses are always expressed and offer immediate protection from invaders but could also be defeated by antagonists that have evolved adaptations to these defense mechanisms. One of the common secondary compounds used by Pinaceae are phenolics or polyphenols. These secondary compounds are preserved in vacuoles of polyphenolic parenchyma cells (PP) in the secondary phloem. Induced defenses Induced defense responses need to be activated by certain cues, such as herbivore damage or other biotic signals. A common induced defense mechanism used by Pinaceae is resins. Resins are also one of the primary defenses used against attack. Resins are short term defenses that are composed of a complex combination of volatile mono- (C10) and sesquiterpenes (C15) and nonvolatile diterpene resin acids (C20). They are produced and stored in specialized secretory areas known as resin ducts, resin blisters,
or resin cavities. Res
