SAN JOSE -- For the first time, San Jose residents know exactly how much of their city has been paved over and how much is shaded by trees.

According to a new study that used lasers to map trees from the air, 58 percent of San Jose's urbanized area is covered with buildings, asphalt or concrete. And 15.4 percent is covered by trees.

Although leafier than San Francisco and Los Angeles, San Jose lagged behind Sacramento and Pasadena in terms of tree cover. And out of the six other California cities compared in the new report, San Jose's preponderance of pavement was topped only by Los Angeles.

Scientists from the U.S. Forest Service, UC Davis, Cal Fire and the University of Vermont used lasers and other imaging techniques to count and map out the city's trees. In a first-of-its-kind twist to the "urban canopy" study, the scientists then calculated the economic value the trees provide to the city's residents, both in terms of property value and ecological benefits such as cleaning the air and making hot summer days a bit cooler.

The city's arborist, Ralph Mize, welcomed the aerial intrusion. "We were very happy to be the guinea pigs in this type of study," Mize said. "Total canopy coverage was something we never really had a way of determining -- until now."

The study also found:


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  • City Council District 6, which includes Willow Glen and the Rose Garden, is the leafiest district, whereas populous District 7 in central San Jose is the least. District 6 is 21.3 percent covered by trees, District 7 only 12 percent.

  • The trees boost the city's economic value by $239 million annually -- $5.7 billion over the next century.

  • Planting 100,000 more trees -- the goal of Mayor Chuck Reed's Green Vision plan -- will increase tree cover by less than a percentage point -- to 16.3 percent.

  • There are 124,000 available spots for street trees -- and another 1.9 million spots for trees on private property.

    The 6-year-old Green Vision plan aims to plant 100,000 trees by 2022 as part of an effort to reduce the city's carbon footprint. But at the current rate of 2,000 trees per year, the city won't reach that goal for another half-century. The city, however, is now in the process of conducting an on-the-ground assessment of the city's street trees and has plans to ramp up tree planting when it's complete, arborist Mize said.

    To do the study, scientists used a technology called LiDAR, or Light Detection and Ranging, which uses a laser beam to measure the height of objects on the ground, allowing researchers to distinguish between trees, shrubs and grass. The scientists then used the resulting tree-canopy map to pinpoint the spots in each district that need more greening, said Forest Service researcher Greg McPherson, the study's leader.

    Each district's tree planting potential was affected by its proportion of "impervious surfaces" -- areas occupied by buildings or covered with pavement. The number varied widely between districts, but San Jose has fewer spots to plant trees than most other cities studied.

    "I was surprised with the amount of impervious surface that San Jose has -- and not a lot of plantable space," McPherson said. "The only city that has less is Los Angeles," with 61 percent.

    Even densely packed San Francisco, with 54 percent, had less impervious space than San Jose.

    Still, just because an area is paved shouldn't mean you can't carve out planting strips, said Rhonda Berry, the CEO of Our City Forest. The San Jose nonprofit has coordinated the planting of 65,000 trees along San Jose's streets and in schools and parks.

    Rather than labeling parking lots and other paved areas as "unplantable," Berry said, "it's about changing that paradigm to taking out as much cement as possible."

    For a few decades in the postwar period, San Jose earned a reputation as the poster city for higgledy-piggledy sprawl -- which could account for its large amount of impervious surface. But according to Joe Horwedel, San Jose's planning director, the city began requiring builders and property owners to plant a lot more trees beginning in the late 1980s.

    "We are focused on improving the number and quality of trees throughout the city," Horwedel said.

    The overwhelming majority of the 2 million potential planting sites exist on private land, out of reach from the city's street tree plan. This means that property owners have an extraordinary opportunity to boost the city's tree cover, Berry said.

    Our City Forest receives 20 percent of its funding from the city of San Jose, but it mostly relies on support from state and federal grants. Berry said that funding issues have forced the nonprofit to reduce its staff by 20 percent this year, adding that she hopes that Silicon Valley corporations will step up to provide some more funding.

    Despite the setbacks, Berry said she remains optimistic that local leaders will respond to the city's need for more greenery.

    "People recognize that trees bring character -- and make a neighborhood," said city Councilman Pierluigi Oliverio, who represents leafy District 6.

    The upscale district has the benefit of older, established neighborhoods with heritage trees. But the story is different in District 7, known for its tightly packed, working-class neighborhoods.

    Vice Mayor Madison Nguyen, who represents District 7, said her constituents hunger for more greenery.

    "I've been advocating for more trees in the district for several years," she said. "I hope that moving forward, we'll see more."

    Contact Jessica Shugart at 408-920-5782. Follow her at Twitter.com/jessicashugart.

    GROWING OUR
    URBAN FOREST
    Since acquiring a barren patch of land by Mineta San Jose International Airport four years ago, Our City Forest volunteers have transformed it into a thriving nursery that boasts a diverse collection of 5,000 native trees and shrubs.
    The trees are available for purchase. For details, go to www.ourcityforest.org.