Alameda County Department of Public Works

Specifications for Utility Line Clearance Pruning
San Lorenzo Londonplane Sycamore Trees

The following standards were prepared by the Alameda County arborist, Jim Browne, January 11, 2002, in response to controversy in San Lorenzo Village over the manner of pruning street trees by contractors of Pacific Gas & Electric Co. These standards are part of a permit issued to Davey Co. on Jan. 15, 2002 for pruning street trees in San Lorenzo. See the drawing following the text. See also Trees in San Lorenzo.


The purpose of these utility line-clearance pruning standards is as follows:

1. To promote and engage in proper pruning practices that will not compromise the health, structural integrity, and longevity of the trees,

2. To promote and engage in pruning practices that consider and promote the safety and welfare of the community and its residents,

3. To consider aesthetics and appearance in the implementation of pruning operations, and

4. To promote and engage in pruning practices that will eliminate excessive pruning as defined in the County's Pilot Tree Policy, as it has been determined that there is no need for such pruning.


Critical Pruning Zone: an area that is 5 (five) feet from the high voltage wires in the vertical direction (above or below) and 5 (five) feet in the horizontal direction (at either side).

Height Reduction: A pruning technique that uses "natural" or "drop-crotch" techniques (i.e., thinning cuts) in the correct way to reduce the height of a tree.

Pollard Head: An enlarged branch-end from which branch sprouts emerge, created over a period of several to many years by pruning the sprouts back to the pollard head annually (Note: the removal of branches from a pollard head is not the same as a topping cut: topping is the heading back of branches back to a stub).

Rounding-Over: The practice of pruning trees back to a pre-determined height on a regular basis. The form is the result of a combination of thinning cuts using "drop-crotch" techniques (see height reduction), and pollarded heads.

Topping Cut: The heading back of branches back to a fresh stub.

Thinning Cut: The removal of a branch back to a lateral limb. The remaining lateral should be at least 1/3 the diameter of the stem removed.


Standards. All pruning performed by Contractor shall conform to the ANSI A300 Pruning Standards as set forth in the County's Pilot Tree Policy, this Specification, and accompanying diagrams. No other guidelines shall take precedence, or be used unless mutually agreed upon by Contractor and the Public Works Director.

Review. Each tree shall be reviewed by a certified arborist or utility forester provided by Contractor before the tree is pruned. This review shall take into consideration the range of options presented in these Specifications and accompanying diagrams, and the best option(s) for implementing the intent of these Specifications shall be carried-out in good faith.

Limits of Pruning. Pruning is not allowed beyond an area that is greater than 5 (five) feet from the secondary high voltage wires (critical pruning zone) vertically and 5 (five) feet in the horizontal direction (except an additional vertical clearance of 3 (three) feet shall be allowed in order to establish the directional prune). This will allow for a clearance of 18 inches within a reasonable amount of time after pruning takes place, considering line sag, sway, wind, and the growth rate of the trees.

Preservation of Form. Contractor shall preserve the rounded-over structural elements and features wherever possible using a combination of:

1. Thinning cuts,
2. Selective removal of pollard heads as shown on the accompanying diagram, limited to those within the critical pruning zone, and
3. Small V-branch removals (Dr. John Ball, 1996) directly beneath critical areas (centered) that are within the limits of pruning.
The resulting form shall be a "modified" version of the V-Pruning technique -- which is less severe and does not allow for excessive pruning. Directional pruning shall commence from a point that is considerably higher in the canopy (approx. 20 feet distance from the ground). Size of branches removed. No branch greater than 4 inches in diameter shall be removed that is 3 feet beyond the critical pruning zone (unless there is no acceptable lateral branch within this zone to be used in order to establish the directional prune). This allowance is provided in order to achieve acceptable (proper) thinning cuts to a lateral as specified in ANSI A300.