What is the outermost layer of a tree trunk called?

The outermost layer of a tree trunk is called the outer bark. This layer serves several crucial functions for the tree. It acts as a protective barrier, safeguarding the inner layers from physical damage, pathogens, and pests. The outer bark is often rough and can vary in texture and thickness depending on the tree species. Unlike the inner bark, which transports nutrients and water, the outer bark primarily serves a defensive purpose, helping to prevent moisture loss and protect against environmental stressors. Understanding the role of the outer bark is important in studying tree biology and ecology, as it directly impacts the tree's health and longevity.