How do trees develop and grow?

When a tree trunk is cut horizontally, it can be observed that the outer layer is the bark, followed by layers of cells forming the annual rings, and finally the innermost part is the heartwood. The only truly living part of the tree is a thin layer of cells on the surface of the wood beneath the bark, known as the cambial layer. This layer is responsible for the development and growth of the tree, with growth occurring from the inside out, from the core to the bark. The wood contains structures called ray cells, which extend either from the bark towards the core (primary ray cells) or from one annual ring to another (secondary ray cells). Once the cambial layer forms a new ring, this ring becomes woody by transforming into non-living tissues with the deposition of lignin substance on the cell walls over time. Subsequently, growth stops completely when the wood tubes in the stem are primarily blocked by chemicals like resin. Growth ceases entirely during winter. In spring, the cambial layer forms a thin layer filled with gaps between the walls. In summer, cell walls thicken, forming a second layer with fewer gaps. A certain portion around the core begins to darken due to physiological changes, and trees with this characteristic are known as "heartwood trees."

The thin layer composed of cells living between the inner bark (phloem) and wood (xylem) is known as the cambial zone. Cell division and radial growth (secondary growth) of the tree occur in this zone.

Like all living organisms, trees have a continuous circulation of fluids between their tissues. To ensure this fluid circulation, trees need a constant and sufficient supply of water. Trees produce their own food directly from soil and air through sunlight, a highly complex process that no animal can accomplish.