Tree Canopy

The following information is provided courtesy of David Dockter, Environmental Planner/Landscape Advisor, ASCA, ISA, APA.

Solar Access Needs—more than windows

Various properties may be occupied by mature oaks or other evergreen or deciduous specimens dependent on full sun exposure (especially those facing the west with longer/lower exposure) and constitute a significant value in one way or another. Shading of leaf area could have minor to significant negative impact on canopy, disease susceptibility, tree health and mortality.

Environmental View

Smart Environmental Impact Assessments/Reports will evaluate the shading effects on significant trees when subjected to a potential new structure or objects. A shading study is now common practice for architects evaluating solar panels and must be interpreted by a Registered Consulting Arborist or other ASCA qualified arborist. This should be prepared in any above ground alternative where permanent shade may subject existing trees to solar access restrictions. For example, in Palo Alto, trees on the east and west of the RoW may be affected. The California Historic Landmark #2 tree, El Palo Alto Redwood, would not tolerate any above ground shading to its lower foliage and ground environment.

Project Sponsor Accountability

In any event, if a tree died it would need to be assessed as to project cause (shade, damage to roots, trunk, canopy, other) and loss, whether public loss (located on city park lands) or private loss (commercial residential, etc.) asset value loss must be assessed for closure. For this reason, an essential and fundamental mitigation measure would be to require the project to provide for each potentially affected property (owner) a Tree Inventory Survey accompanied by a contemporary Tree Appraisal to document value prior to project implementation (or beforehand if needed to assess property condemnation domain value, or other). The overall EIR would need to have this quantified beforehand rather than ‘as needed’ for several reasons. The aggregate appraisal value needs to be assessed by the sponsor to weight the total potential impact, in addition to the

Transferable Information Available to all Communities

These assessment and mitigation measures are standard requirements in the Palo Alto Tree Technical Manual, Standards and Specifications. The above tree survey (§6.20), tree appraisal (§ 6.40); construction impact assessment standards (§ 6.40 & 2.00) and other information would be useful for any community representative, HSR technical assessment, environmental firm or consulting arborist addressing tree resources. Many communities across the nation have adopted parts or entire components of the Manual because of its transferability and usefulness in a variety of land use situations. The best news, is it can be utilized copyright free and adapted to fit the local need. The document is the only North American reference cited for use by the New South Wales Attorney General’s Office 2006 Tree Regulations Standards that apply to the entire territory. A hardcopy of Palo Alto Tree Technical Manual can be purchased from the City of Palo Alto by contacting Diana Tamale.


Californians Advocating Responsible Rail Design (CARRD)