Trees grow slowly over time, adding new layers of wood each year that increase the height and width. Most trees are dormant during cooler, winter months. New growth begins in the spring when a series of processes begin to move food, water and minerals throughout the tree. These processes promote the tree's annual growth.
In the spring, growth areas on the tips of a tree's branches and stem become activated. These areas are called apical meristems. Meristems are regions on a plant where cell division occurs and growth is activated. Apical refers to the apex, or ends, of branches and stems. Apical meristems are where new foliage and buds will form. Apical meristems also activate a tree's vertical growth, as the top of a tree is considered the tip of the stem. Successive layers of wood are added to the stem each year, increasing a tree's height.
Growth in Diameter
Once the apical meristems are activated, growth hormones are released from them into the tree's vascular system. The vascular system in a tree transports food, water and minerals throughout the tree. These growth hormones activate lateral meristems, which are also called cambium. Cambium are living cells that exist between the tree's bark and its woody core. Once the cambium are activated the tree will begin to grow in diameter. Cambium are activated at the crown of the tree and then move downward through the stem. When new layers of wood are added near the core of the tree, older layers of wood are crushed and pushed outward. When you are looking at a tree, the visible bark is the oldest wood on the tree.
Tree crowns produce essential carbohydrates that are distributed to growth regions throughout the tree. Crowns are sometimes thought of as only the top of the tree, but in fact a tree crown includes all the foliage and plant parts above the ground. The size of a crown is important to a tree's growth because the crown of a tree is responsible for producing the carbohydrates that promote wood growth.
Each year a tree produces a new ring. This ring can be seen when a cross section of the tree is observed. Studying tree rings can tell you several things about long-term growth habits, including whether it received adequate water or experienced drought. Tree rings that are close together indicate shorter growing seasons, perhaps due to cooler temperatures or limits on the tree's access to sunlight.
The growth of trees, both in height and diameter, are also impacted by the level of crowding in a particular area. Trees crowded together may grow taller as they search for sunlight, but their growth in diameter will be slowed because lateral growth occurs only in relationship to successful vertical growth.