Are All the Parts of a Tree Alive?
Actually, most of the wood in the trunk and branches (the heartwood) of a tree is dead. The outer layer of bark is also dead. The root tips, leaves, and a growing layer of soft tissue just under the outer covering (bark), called cambium, are the living parts of the tree.
The cambium adds bark to the tree and builds a new layer of wood around the trunk and branches each year. This makes the rings you see in the trunk when the tree is cut down. As the tree grows, the older wood stiffens and becomes solid heartwood, which gives strength to the tree.
Interestingly enough, trees start out in life as a germinating seed with every living cell in hyper drive. As a tree seed becomes a seedling, and then a sapling, and then a mature tree, its living contents become less and less as a percentage of total volume.
So trees increasingly lose their living cytoplasm cells and metabolism ceases in that cell. They are no longer alive but now provide protective, transport and physical support.
The large, non-living part of a tree does the heavy lifting and is very important structurally to the tree. Also, a tree’s bark cover is essential in protecting thin living cell layers underneath.
This supporting and protective wood is created by cambial-hardened wood cells produced on the inner and outer cambial layer. Sandwiched between the outer cambial layer and the bark is the ongoing process of creating sieve tubes which transport water and nutrient food both from leaves to roots and back.
The sound, non-living cells of a tree are very important to helping a tree protected from attacking pests like insects and disease. Compromising these bark and structural cells will introduce pathogens and other pests and environmental damage into the vulnerable living tissues that maintain life.
To be more precise, future dead tree cells have the responsibility of transporting nutrients both to the leaves and sugars made by the photosynthetic leaf and then back to the growth of parts that determine a tree’s healthy future.