How Trees Grow Taller
Trees increase their height from their uppermost points. This vertical growth occurs through specialized tissues at the tips of shoots and roots, known as apical meristems. These regions contain actively dividing cells that produce new cells, leading to elongation. As new cells form at the growing tip, they expand and differentiate, pushing the stem or root further upwards or downwards into the soil.
This process ensures that the newest and most active growth happens at the very top of the tree, allowing it to reach for more sunlight. Similarly, root tips extend deeper into the ground, anchoring the tree and searching for water and nutrients. The continuous cell division and elongation at these meristematic zones enable a tree to gain height over its lifespan.
Why Markings Stay at the Same Height
A common observation that helps illustrate how trees grow taller is the fixed position of markings on their trunks. If you were to hammer a nail into a tree at a certain height, or carve initials into its bark, you would notice that these markings remain at the same distance from the ground year after year. This occurs because the trunk itself does not stretch or elongate from the bottom.
Existing wood and bark, once formed, do not move upwards. Instead, all new height growth happens at the tree’s top. Therefore, any point on the trunk that has already formed will stay at its original height above the ground, while the tree continues to add new growth above it. This phenomenon shows that trees extend upwards only from their tips.
How Trees Grow Wider
While a tree’s height increases at its tips, its girth, or width, expands through a distinct process involving a different growth tissue. This lateral growth occurs due to the activity of the vascular cambium, a thin layer of cells located just beneath the bark. The vascular cambium is responsible for producing new layers of wood towards the inside of the tree and new layers of phloem (part of the bark) towards the outside.
Each year, the cambium generates a new ring of wood, leading to the gradual thickening of the trunk and branches. This continuous addition of new cells increases the tree’s diameter, strengthening its structure and enhancing its capacity to transport water and nutrients. The outward expansion from the cambium gives trees their width over time.