1. Vascular Cambium: This is a thin layer of cells located between the wood (xylem) and the bark (phloem) of the tree. The vascular cambium produces new xylem cells towards the inside of the tree and new phloem cells towards the outside. As a result, the girth (width) of the tree increases.
2. Cork Cambium: This is another thin layer of cells located just beneath the bark of the tree. The cork cambium produces cork cells, which form the protective outer layer of the bark. As the tree grows in diameter, the cork cambium also produces new cork cells to cover the expanding surface.
The annual growth rings that we see in cross-sections of tree trunks represent the layers of xylem produced by the vascular cambium each year. The width of the growth rings can vary depending on environmental factors such as rainfall, sunlight, and temperature.
In addition to secondary growth, trees can also increase their height through the growth of new shoots and branches. This process is known as primary growth and involves the division of cells at the tips of the shoots and branches.
The combination of secondary growth and primary growth allows trees to reach their impressive sizes and long lifespans, with some species living for thousands of years.
