What provides strength and support in tree trunks?

In tree trunks, strength and support are primarily provided by the xylem tissue, particularly the secondary xylem, which is formed during secondary growth. This tissue is composed of lignin, a complex organic polymer that reinforces the cell walls and contributes to the trunk's rigidity and structural integrity. Additionally, the cambium layer plays a crucial role by facilitating the growth of new xylem and phloem, allowing the tree to increase in diameter and maintain stability over time.