What is the outer layer of a tree that protects against various environmental factors?

The outer layer of a tree that provides protection against environmental factors is bark. Bark serves as a protective covering for the tree, helping to guard against physical damage, pathogens, and adverse weather conditions. It is composed of two main parts: the outer bark, which is made up of dead cells and serves primarily as a barrier, and the inner bark, or phloem, which transports nutrients throughout the tree. The structural integrity of the bark plays a crucial role in safeguarding the tree from insects, disease, and water loss, making it essential for the overall health and survival of the tree.

By contrast, heartwood is the dense inner part of a tree, primarily responsible for providing structural support, while the wood core refers to the central region of the trunk that is primarily composed of xylem and is not directly involved in protection. The pith, on the other hand, is the innermost part of the tree, contributing to storage but not acting as a protective layer. Thus, bark is specifically designed to offer the protective functions necessary for a tree's survival in diverse environments.