Tree forks

A tree fork is a bifurcation in the trunk of a tree giving rise to two roughly equal diameter branches. These forks are a common feature of tree crowns. The wood grain orientation at the top of a tree fork is such that wood cells interlock to provide sufficient mechanical support. A common "malformation" of a tree fork is where bark has formed within the join, often caused by natural bracing occurring higher up in the crown of the tree, and these bark-included junctions often have a heightened risk of failure, especially when bracing branches are pruned out or are shaded out from the tree's crown.

In arboriculture, junctions in the crown structure of trees are frequently categorised as either branch-to-stem attachments or co-dominant stems. Co-dominant stems are where the two or more arising branches emerging from the junction are of near equal diameter and this type of junction in a tree is often referred to in layman's terms as 'a tree fork'.

There is actually no hard botanical division between these two forms of tree junction: they are topologically equivalent, and from their external appearance it is only a matter of the diameter ratio between the branches that are conjoined that separates a tree fork from being a branch-to-stem junction. However, when a small branch joins to a tree trunk there is a knot that can be found to be embedded into the trunk of the tree, which was the initial base of the smaller branch. This is not the case in tree forks, as each branch is roughly equal in size and no substantial tissues from either branch is embedded into the other, so there is no reinforcing knot to supply the mechanical strength to the junction that will be needed to hold the branches aloft.

Research has shown that a unique wood grain pattern at the apex of forks in hazel trees (Corylus avellana L.) acts to hold together the branches in this species, and this is probably the case in most other woody plants and trees. This is an example of 'trade-off' in xylem, where mechanical strength to the tree's junction is gained at the expense of efficiency in tree sap conductance The complex interlocking wood grain patterns developed within tree forks present a great opportunity for biomimicry (the mimicking of natural biological structures in man-made materials) in fibrous materials, where the production of a Y-shaped or T-shaped component is needed: particularly in such components that may need to act as a conduit for liquids as well as being mechanically strong.

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Wikipedia