PBS will broadcast a new documentary, 10 Parks That Changed America, on April 12th. Produced by WTTW in Chicago and featuring Geoffrey Baer, the show identifies the 10 most influential urban parks in the country, from the era of America's early settlers to the present day. In a preview at the National Press Club in Washington, D.C., Baer and show producer and writer Dan Protess announced the 10 parks selected by WTTW and its expert advisors, including Thaisa Way, ASLA, professor of landscape architecture at University of Washington; Walter Hood, ASLA, professor of landscape architecture at University of California, Berkeley; and Peter Harnik, Hon. ASLA, director of city park excellence at the Trust for Public Land and author of Urban Green: Innovative Parks for Resurgent Cities.

Here are the parks they settled on:

1) The Squares of Savannah, Georgia
2) Fairmount Park, Philadelphia, Pennsylvania
3) Mt. Auburn Cemetery, Cambridge, Massachusetts
4) Central Park, New York City, New York
5) Chicago's Neighborhood Parks, Chicago, Illinois
6) The Riverwalk, San Antonio, Texas
7) Overton Park, Memphis, Tennessee
8) Freeway Park, Seattle, Washington
9) Gas Works Park, Seattle, Washington
10) The High Line, New York City, New York

At the preview, Nancy Somerville, Hon. ASLA, executive vice president and CEO, American Society of Landscape Architects (ASLA), and Harnik discussed the list. Somerville said the parks were all created to solve complex environmental, social, or economic problems, and those problems are still here today. "Savannah's squares were created with the belief that everyone should have access to a park. Today, we see the same ideas underlying the environmental justice movement and the quest for clean air and clean water for everyone."

She argued the one important park left out of the list was the National Mall in Washington, D.C. because it's a symbol of the "accessibility of our democracy." The National Mall shows the "power of places to bring people together. It was hugely influential in setting the public park or plaza as the place where people get together to express themselves. It's the epitome of that."

Protess said it was challenging to select just 10 parks that changed America and admitted many good candidates for the list had to be left on the cutting room floor. "Parks were selected for their influence, but we also needed to represent diverse geographies and include a diversity of forms, so it wasn't all trees and grass."

Somerville and Harnik were largely positive about the state of American urban parks. Somerville said "most urban park bonds pass. While Americans seem to be anti-government and hate spending these days, they are happy to put money into parks because they know how much they do for communities." Harnik argued that "with the further densification of cities, every city now knows they need good parks to compete." He said young people moving into the cities are looking for "places to play" and "empty nesters," or retirees, moving back into cities from the suburbs, are looking for "some of the green space they had in suburbia."

They also argued that showcase parks like the High Line in New York City and Millennium Park in Chicago aren't being built at the expense of neighborhood parks either. Somerville said "the momentum for more parks is greater than that." And Harnik, who ranks urban parks with his ParkScore tool, said "there is now a political movement for parks. There is a whole group of people who think parks are cool and important and they are bringing their voices." In particular, dog owners are revitalizing the parks movement by pushing for investment in dog parks, which is having positive ripple effects for the rest of parks.

Somerville pointed to the slew of new research on the health benefits of nature, arguing the science shows "humans are hard-wired for nature, and so urban communities are putting in green spaces wherever they can." The research shows that spending time in nature "reduces blood pressure, releases all these good hormones, decreases stress levels, and these effects last a while." The opportunity to spend time in an urban park is "precious." In the future, she sees only "more opportunities to bring in nature" in underused urban edges, like damaged waterfronts, and even in underpass parks, which are being developed in a number of cities. The key will be making these places resilient to climate change, storm-proof respites that can also mitigate flooding and the urban heat island effect.

Park access must become more equitable, and Somerville and Harnik identified some communities showing the way forward. Somerville said "under-served areas are now turning post-industrial landscapes into resilient public spaces that people want to be in." She pointed to Hunts Point Landing, a park that sprung up amid a damaged waterfront in the South Bronx, which has some of the highest asthma and obesity rates in New York City. And Harnik explained how New York City's new Mayor Bill de Blasio has shifted away from previous Mayor Michael Bloomberg's focus on the showcase parks like the High Line to invest in small parks in poorer neighborhoods. But Harnik also cautioned that the rise of park conservancies and "friends of" groups, which privately finance the upkeep of many public parks, may also be exacerbating park inequality, given so many communities don't have the local wealth to channel into these groups and must therefore rely on minimal public support.