The City adheres to two tree care industry pruning standards — American
National Standards Institute (ANSI) A-300 Pruning Standards and International
Society of Arboriculture (ISA) Best Management Practices for Pruning.
Some people have stated that their tree is too tall and needs to be cut.
Physiologically, trees do not grow “too tall.” Trees can grow
too lengthy for their structure, too heavy for the branch attachment, and/or
can be allowed to grow for too many years without maintenance pruning. Trees
also can develop structural defects that may predispose a trunk or limb
Normal maintenance pruning will remove dead wood and weakly attached branches,
thin-out any overly-thick foliage, shorten long limbs, and remove or mitigate
most branch defects. In some instances, the pruning can lower the overall
height of a tree through “crown reduction.” The typical percentage
of live foliage removed during pruning should not exceed 33%, depending
on the existing condition of the tree. Following these pruning guidelines,
when pruning is completed, the natural structure of the tree is not compromised.
Topping, or severe heading cuts, is not a recognized pruning standard or
maintenance technique. “Topping” is the indiscriminate cutting
of branches and trunk to a predetermined height without regard to tree structure.
Topping normally removes an unacceptably high percentage of the foliage
from the tree. A tree’s natural response to topping is to quickly
grow a flush of new leaves to achieve the same balance in the number of
leaves as it had prior to the cutting. These new small sprouts grow from
buds usually around the cut area and become overcrowded and weakly attached.
If left unattended, the sprouts enlarge, grow into each other and will be
prone to failure. Additionally, the cut limb is exposed to greater opportunity
for decay and can eventually cause wood failure. Even if the sprouts are
attended to by follow-up pruning, the limbs are weakly attached, growing
from the point where decay has weakened the structure.
Thank you in advance for your cooperation towards keeping Redwood City's
privately owned urban forest safe and healthy.