Topic 12.3: Pruning

In some markets and for some species, timber values are increased by the presence of knot-free or “clear” wood.  The number and size of knots is a direct function of the number of branches, their sizes, and the length of time they remain attached to the trunk.  By pruning branches while they are still small relative to the trunk diameter, the extent of knot-free wood can be increased.  Pruning is not a common practice in managed natural forests in the tropics and is labor intensive, but should be considered where timber values are high and where profits from timber sales need to be maximized on a per unit area basis.  Where prescribed, pruning requires some training and close monitoring so that it is done properly and inadvertent damage to the bole is avoided.

One common mistake is pruning too close to the trunk and cutting off the branch collar.  The branch collar helps protect the bole from the entry of fungi and other pathogens from the branch stub.  A branch collar is analogous to an abscission zone on a leaf.  Xylem vessels in the collar zone are narrower, and parenchyma cells react quickly by secreting protective compounds (e.g., tannins) that seal-off the trunk from the branch wound, thereby reducing the incidence of stem rot.