The main purpose of the bark on a tree is to protect the inner tissues from environmental factors. Bark acts as a barrier against physical damage, pests, and pathogens. It also helps to minimize water loss and insulates the tree against temperature extremes. The outermost layer, known as the cork, provides additional protection. Bark can also serve a role in nutrient transport through layers like the phloem, which carries the necessary nutrients produced by photosynthesis from leaves to other parts of the tree. Its protective qualities make it essential for a tree's survival and overall health.