Grass may always be greener on the other side, but when it comes to street trees it's the north side of Palo Alto that actually does have more than the south.

That is one of the findings -- and problems -- identified in the city's new Urban Forest Master Plan, a document that has been in the works for more than three years and that the City Council is slated to adopt on Monday night. Spearheaded by Urban Forester Walter Passmore, the master plan is at once an encyclopedia of local trees, a manual of best practices and a policy document with more than 90 suggestions for maintaining and enhancing the city's beloved canopy.

The master plan also lends credence to a perception that many residents have espoused in recent surveys: There's a difference between north and south. Two analyses conducted for the master plan led staff to identify what the plan refers to as a "disturbing trend."

"In 1982, the average canopy for the predominantly residential sections in the north was 11 percent greater than the average for those in the south -- and by 2010, that disparity had grown to 22 percent," the plan states. "To investigate and reverse this trend is a master plan priority."

The news is unlikely to shock residents in southern neighborhoods such as Fairmeadow, which according to aerial photos saw its canopy decrease by 6.3 percent between 1982 and 2010. Yet the reasons may come as a surprise. While redevelopment is often blamed for a loss of trees, in Fairmeadow's case the loss appears to have more to do with tree species.

When the post-war Eichler subdivision was created, there was a push to plant fast-growing trees, according to the master plan. These included short-lived species that now have reached the ends of their life spans and trees that were problematic for underground pipes installed for radiant heating and for other elements of Eichler developments. Other south Palo Alto neighborhoods also suffer from soil with a high clay content, according to the report, though that didn't seem to be the problem in Fairmeadow, where soil is mostly alluvial deposit.

The city's tree survey shows that while the neighborhood had a canopy cover of 41.5 percent in 1982, the number dropped to 38.9 percent in 2010.

The Greenmeadow and Charleston Meadows neighborhoods also saw slight decreases in canopy over the past three decades. Greenmeadow's tree coverage went down by 0.4 percent, with losses and gains effectively canceling each other out. A loss was caused by the replacement of stone pines with native oaks on San Antonio Road, a change that is expected to eventually increase the canopy. The maturation of some trees and new landscaping at the Rosewalk townhome complex on San Antonio also added trees.

Both the north and the south have seen an increase in canopy cover between 1982 and 2010, though the trend was much more pronounced in the north than in the south, according to the master plan. In 2010, the north's and south's canopy covers were 47.8 percent and 39.11 percent, respectively.

In the north, it is the city's oldest and most affluent neighborhoods that are also the most lush. Old Palo Alto and Crescent Park were 55.8 percent and 55.1 percent covered in foliage, respectively, while Professorville followed with 53.4 percent. Downtown North lagged behind its northern neighbors with 38.7 percent, though this is a significant jump from the 29 percent it had in 1982.

In south Palo Alto, Barron Park did comparatively well with 46.5 percent; out of seven southern neighborhoods surveyed it was the only one with more than 40 percent coverage. Green Acres had 39.9 percent, while Midtown had 38.6 percent.

The disparity hasn't been lost on residents, many of whom flagged it as a problem in a citizen survey that was undertaken as part of the plan. Even though no survey questions mentioned the issue specifically, it emerged as a "Hot Topic" and residents' opinions were consistent, the master plan notes. One respondent cited a "stark difference when you cross the Oregon Expressway from the north to the south side in atmosphere, as the south side has fewer trees and feels more barren and exposed to the harsh sun; the north side is absolutely gorgeous with its tree-lined shady streets."

Another respondent urged the city to "begin work in south Palo Alto, where the need for more trees is most urgent."

"Typically, programs like this start in north Palo Alto and run out of money before they ever get to Midtown or any other neighborhood south of Oregon Expressway," the response states.

"North Palo Alto looks beautiful because it has more established tree canopies on both sides of streets," reads another response. "I would like to see more trees in Midtown and South Palo Alto streets, to make the entire Palo Alto look uniform."

Deirdre Crommie, a south Palo Alto resident who sits on the Parks and Recreation Commission, commented on the disparity during the commission's April 22 review of the master plan, which it approved unanimously. One reason for the inadequate canopy growth is the "transformation of small homes into these humongous homes," Crommie said.

"That's particularly noticeable in the Fairmeadow neighborhood," Crommie said. "When I was on the market looking to buy a home in 2001, I looked in that neighborhood and I saw what I called a lot of monster homes being developed there. I really think that that went on in such a pronounced way in that neighborhood that it actually should be possibly acknowledged. When people increase the footprint of a home that large, you lose space for trees."

Much of the new plan is devoted to a comprehensive list of programs, some of which pertain to the next year or two while others look ahead to a decade from now. In the first two years, the plan proposes that the city "initiate the investigation of -- and resolution to -- disparity between the canopies of north and south Palo Alto." This includes assessing development-review procedures and creating new development-design standards that feature "innovative ways" to ensure that new development also enhances the natural environment.

Further in the future, the city should create a Comprehensive Conservation Plan for each of the city's major parks and open-space preserves and exploit the city's Geographic Information System for "exploring unprecedented ideas and partnerships," according to the plan.

The guiding document also includes numerous policies that intend to reconcile the city's canopy goals with other sustainability initiatives. In some cases, going green in one area may have the opposite effect in another. The community's hunger for solar power and for water-conservation initiatives could, for instance, conflict with its desire for a rich canopy, Passmore told the Parks and Recreation Commission in April.

"On the one hand, we want to conserve water. It's a very important sustainability aspect for our community in the future," Passmore said. "On the other hand, we also know that large-growing trees with dense canopy provide the greatest amount of benefits at the lowest cost. It's a balancing act there. There's some conflict, and we should expect that to occur as we have dialogue on these subjects."