Named for a tree, the city of Palo Alto is challenged to sustain its urban forest in the midst of development and a changing arboreal canopy.
The plan envisions a future forest that can meet the challenges of a changing environment and a rapidly developing city. Trees, so much the character of Palo Alto's past small-town look and feel, will play an important future role in maintaining the city's quality of life while making economic contributions in the hundreds of thousands of dollars, Passmore said.
But disparities between the north and south residential areas, increasing use of reclaimed, more salinated water, increased conflict between trees and solar installations and development will need consideration for the tree canopy to maintain its present and future continuity, according to Passmore.
"We need to be very innovative," he said.
Only seven of 96 species planted in the city are good street trees. The rest are fast-growing forest giants that are raising sidewalks and interfering with utilities. As the city replaces the trees over time, the master plan will use more adaptable species and techniques that avoid costly damage to infrastructure such as sidewalks and building foundations. When considering new plantings, the city would choose species that have a lower "thirst rating" for street trees to reduce water usage and cost, according to the plan.
The master plan analyzed tree benefits to the city in real dollars. The urban forest has a net benefit of more than $4.5 million -- $156.93 per tree -- for right-of-way trees alone when considering energy, carbon dioxide, air quality, stormwater and aesthetics, according to analysis.
The findings will shape the types of trees planted in the urban forest in the years to come. Some are better at reducing energy needs and sequestering carbon dioxide, the plan showed. Palo Alto's trees reduce carbon dioxide by a net 3,437.5 tons per year, at a saving of $1.77 per tree annually, according to the document.
Street trees alone also intercept 42,600,000 gallons of stormwater per year. As the trees mature, that number will increase, according to the plan.
Planning commissioners praised the document. But they suggested ways to strengthen its clout. Policy integration with the Comprehensive Plan and other city planning documents, enforcement and expansion of the city's tree-protection ordinance and developer requirements to maintain or replace trees should be clearly defined in the plan, they said.
"What is the greatest threat to our urban forest? As a public policy, it's urban development. I didn't see anywhere where we addressed a reaction or policy or program that addressed downtown development or development in neighborhoods," Commissioner Eduardo Martinez said.
A policy for urban development should include some responsibility of developers for the urban forest, he said.
Commissioner Michael Alcheck added concerns about conflicts between trees and the expansion of solar energy. The panels require direct sunlight.
Passmore is working with the city Utilities Department to figure out ways to have both, he said.
Commissioner Arthur Keller wanted a more refined analysis in neighborhoods, since the plan did not count neighborhoods that are part of commercial/residential areas.
Defining the city's canopy percentage and how it can be retained is also a goal.
Currently, thresholds for tree cover in the city are only recommended as guidelines for the city's Tree Technical Manual. They are not requirements in the zoning ordinance, Passmore said.
The plan should advise the City Council to consider changing the municipal code's tree ordinance regarding tree-cover requirements -- particularly for preserving or replacing trees when putting in new developments, commissioners said. The current tree ordinance protects certain species, including redwoods and two native oaks, heritage trees, trees of a certain diameter and so-called "designated" trees that are part of a development landscape plan.
The forest master plan will also rectify a disparity between north and south Palo Alto, where there is a 10 to 20 percent deficit in the tree canopy in southern neighborhoods. The difference emerged as a hot topic among 600 respondents to a community survey, the plan noted.
Original street trees throughout the city, and especially in south Palo Alto, were fast-growing, short-lived species planted to accommodate rapid residential growth. A post-World War II Federal Housing Authority requirement mandated a tree on every lot.
But while adding more than 2,000 trees per year to Palo Alto streets, those choices mean a decline and die-out of trees that has caused a void. Where street trees were replaced, they are too young to contribute to the canopy, the report noted.
Keller said he wanted to see a more refined analysis that includes commercial/residential neighborhoods so that no neighborhoods are excluded. Currently the analysis does not include commercial areas.
Ironically, development has increased the number of trees in the city, according to the plan. A 2011 analysis found the urban canopy cover was 32.8 percent in 1982, but 37.6 percent in 2010. Neighborhoods averaged 36.6 percent in 1982 and 41.1 percent in 2010. But where land is redeveloped, there was a net loss, the report noted.
City staff are developing a citywide "sustainability plan," which Passmore said provides an unprecedented opportunity to develop compatibility between the trees and other programs. He will incorporate the suggestions he has received from the Parks and Recreation and Planning and Transportation commissions. He expects to return to the planning and transportation commission in February for an endorsement of the master plan.
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