Question
Hi Jim,
Hoping you can settle a discussion question........do tree branches grow with the tree? In other words, if a branch is two feet from the ground today, will the same branch be at that height ten years from now? I have 3.6 million dollars bet on the answer!

Answer
The tree grows from the top. Branches that are two feet up the trunk will be two feet when the tree is mature unless the branch dies. You may have seen fences attached to trees these will be the same height years later. The growth will be outward --the diameter of the trunk will increase but the height growth will be only at the top of the tree.

To set the stage for our discussion of tree growth we must review some terminology.
Trees have six organs. These are: leaves, stems and roots (known as vegetative structures) and flowers, fruits, and seeds (known as reproductive structures). We will discuss vegetative growth--that is the growth of leaves, stems and roots. Tree growth is the increase in size and numbers of leaves, stems, and roots.

Growth occurs in meristems. A meristem is a tissue that contains cells which have the capacity to divide to make new cells. In general, during growth cells divide, cells elongate, and cells differentiate into structures such as roots and shoots.

Tree growth above ground includes shoot elongation (height growth), leaf growth, and diameter growth.
Shoots elongate or grow in height at the tips of the branches.  What happens is--cells at the apical meristem divide, elongate and differentiate. The steps that we can see are: (1) The bud at the tip of the branch opens, (2) Leaves emerge and enlarge, and (3) The area between the leaves expands (i.e., the stem grows). This is what you generally see in the spring.

Diameter growth
Between the wood and bark is a thin layer of dividing cells called the vascular cambium. This vascular cambium is a meristem which is only a few cells thick. This meristem divides, creating wood on the inside and bark on the outside.  Layer by layer these new cells increase the diameter of the trunk and branches. The wood cells are called "xylem" which means wood in Greek; they carry water and minerals up from the roots. The bark cells are called "phloem", meaning bark in Greek. These cells carry sugars and other materials produced by the plant.


Annual rings
New layers of wood are added each year between the bark and the previous year's wood. These are called growth or annual rings and may be used to age a tree. Cells that are produced in the spring are larger with thinner cell walls. These are the light-colored rings, and the wood is called "early" or "spring" wood. Cells produced in the summer are smaller, and this "late" or "summer" wood has a higher density and darker color.

Roots can grow in length (root elongation) and diameter, and new lateral roots can form. At the tip of a root is the root cap.  This cap protects the root and it must be constantly replaced as it pushes through the soil. Behind the root cap is a meristem which produces new cells for the root cap and for root elongation. These new cells elongate, divide and differentiate into root parts. The root grows in length and pushes through the soil. The majority of the root growth is in the summer and fall months.