SUMMARY OF
CITY PRUNING GUIDELINES FOR STREET TREES, MATURE SIGNIFICANT TREES AND SPECIMEN
(HERITAGE) TREES
Experts
from the city of Pomona Street Tree Policy Manual
1.
All tree trimming by the city of
2. Tree trimming shall be done in a manner that maintains the following minimum clearances
· Clearance over residential streets shall be a minimum of eleven feet (11')
· Clearance over major thoroughfares shall be a minimum height of fourteen feet (14').
· Clearance over sidewalks shall be a minimum of nine feet (9').
Summary
of Professionally Accepted Pruning Techniques
1) Standard Pruning Techniques. Thinning cuts, sometimes called drop-crotching in mature trees, shall be the standard pruning technique for pruning city street trees, mature significant trees, and specimen (heritage) trees on historic sites. A thinning cut is the removal of a branch at its point of origin, or the shortening of a branch to a lateral that is large enough to assume the terminal role.
a) When removing a dead branch, the final cut should be made just outside the branch bark ridge and collar of live callus or woundwood tissue. If the collar has grown out along the branch stub, only the dead stub should be removed. The live collar should remain intact.
b) If it is necessary to reduce the length of a branch, the final cut should be made just beyond (without violating) the branch bark ride of the branch being cut to. The remaining branch should be not less than one third (1/3) the diameter of the branch being removed, and with enough foliage to assume the terminal role.
c) Pruning cuts should be clean and smooth, leaving the bark at the edge of the cut firmly attached to the wood. A three-cut process, sometimes referred to as “jump-cutting,” should be used to remove larger limbs in order to avoid stripping or tearing of the bark, and to minimize unnecessary wounding.
2) Training Young Trees. Properly trained trees will develop into structurally strong trees well-suited for their surroundings. These trees should require little corrective pruning as they mature. However, they should be trained so that when the young trees a large mature size, they have a sturdy, tapered trunk with well-spaced branches that are smaller in diameter than the trunk.
3) Pruning Mature Trees. As trees mature, their need for structural pruning should decrease. Pruning should then focus on maintaining tree structure, form, health and appearance. This shall be accomplished through one of the three methods described below.
a) Crown cleaning, or cleaning out, is the removal of dead, dying, broken, diseased, crossing, weakly attached, and low-vigor branches from a tree’s crown; as well as the elimination of water sprouts, sucker growth and foreign materials from the entire tree.
b) Crown restoration is intended to improve structure and appearance of trees that have sprouted vigorously after being broken, topped or severely pruned using heading cuts. One to three sprouts, on main branch stubs, should be selected to form a natural appearing crown. The vigorous sprouts may need to be thinned or cut to a lateral to control length growth or ensure adequate attachment for the size of the sprout. Crown restoration may require several prunings over a number of years.
c) Crown thinning, is the selective removal of branches to increase light penetration and air movement through the crown.
· When thinning the crown of mature tress, no more than twenty percent (20%) of the tree’s live growth should be removed.
· When thinning the crown of slower growing, or particularly sensitive species (such as Native Oaks), no more than ten percent 10%) of the live growth should be removed.
· Trees shall always be thinned to their natural form, and should retain well-spaced inner lateral branches with foliage.