Trees and Forests
How a tree works, and how forests are built.
A tree is a perennial plant with an elongated woody stem supporting branches and leaves. A forest is not simply many trees — it is a layered system in which each level supports different life.
Inside the trunk
| Layer | Function |
|---|---|
| Bark | Protection against damage, water loss and pests |
| Phloem | Carries sugars from leaves to the rest of the tree |
| Cambium | The only growing layer; adds new phloem outward and xylem inward |
| Sapwood (xylem) | Carries water and minerals up from the roots |
| Heartwood | Dead xylem, now structural support |
Because growth happens only at the cambium, a nail driven into a trunk stays at the same height for the life of the tree. Trees grow taller at the tips, wider at the cambium.
Growth rings
In seasonal climates the cambium produces large thin-walled cells in spring and smaller denser ones later, giving one visible ring per year. Ring width records growing conditions, so dendrochronology reads climate history directly from wood — and cross-dating against known sequences can date timber to the year.
Forest layers
Emergent, canopy, understorey, shrub and forest floor. The canopy intercepts most light, so understorey species are adapted to shade or complete their cycle in early spring before the canopy closes.