A friend recently asked me: How does anybody figure out how much greenspace would be good for a city?
Whenever I’m asked a question, I usually start prattling away, and convincingly sound just as if I know what I’m talking about. I’ll be honest here, though, this question stumped me. It’s not surprising, either, that this turned out to have a complicated answer.
The first thing I thought of was asking around, as it were. For instance, what is Groundswell NW‘s goal for its service area? It wants to create open, public space in every arterial quadrant. That means a green space of some kind will be available to anyone with just a short walk, and without crossing a major street. This plan takes into account topography, bus lines, and so on. “Quadrant” in this case is a square or rectangle formed by four major streets. The quadrant Julie and I live in is four blocks east to west, but 10 blocks north-south. Groundswell is starting an open space survey this year which will count and look for opportunities for more greenspace, including curbside raingardens, greenways (streets modified to encourage bicycle and pedestrian traffic), intermittent use of roadways (Farmers Markets, festivals), and p-patches (public gardens).
The city, working at a different scale, considers its “open, usable space” (OUS) without regard to arterial roads or topography. The city first looks at “breathing room or total open space.” That’s parks, greenspaces, trails, playfields, community centers, and boulevards. Over the entire city, the desirable goal is 1 acre per 100 residents. The acceptable goal is 1/3 acre per 100 residents. This is split up into different types of neighborhoods. For a residential neighborhood, the desirable goal is 1/2 acre within 1/2 mile of all residents; the acceptable goal is 1/2 acre within 1 mile (there are offsets for school playgrounds, among other things). In an urban village, an area zoned for greater density (we live in the Ballard HUV, “hub urban village”), the requirements are slightly more complex: One acre of open space per 1,000 households, and 1/4 acre within 1/8 of all locations in urban village. In the downtown urban core, 1/4 acre of open space per 10,000 jobs. Sheesh. The answer quickly gets pretty arcane and wonky.
Another important consideration is canopy coverage. In fact, as we better understand the value of the urban forest, percent canopy coverage (which includes trees on public and private land) is increasingly important. Seattle’s canopy was measured a couple years ago at 23%. This is done by using software to analyze aerial photographs.
Seattle reLeaf has a goal of 30% canopy cover. Why 30%? It’s a realistic stretch goal, considering our urban density. It also brings us on par with Portland and Vancouver BC, to which we’re always comparing ourselves. Increasing open space will help the city get to 30% tree canopy, but most of this increase is going to come from adding trees to front and back yards and parking strips. That’s why “Trees for Neighborhoods” gives away 1,000 trees a year. There are six or seven different kinds of trees, a few of which are suitable for planting under power lines. Most are deciduous, and usually only one or two are native to the PNW. Native trees, particularly the conifers, are too large for most urban spaces.
Seattle has had a few bold plans for urban greenspace. The Olmsted Brothers firm had a great proposal, but it didn’t get very far, despite their having designed the Alaska-Yukon Exhibition and the University of Washington Campus. The Municipal Plans Commission had another one that was rejected by the voters in the early 20th century. Either one would have made Seattle a much greener city than it is now (but probably also correspondingly more expensive). In the 1990s, Paul Allen (Microsoft co-founder) had a big plan for a park in South Lake Union that was soundly rejected by voters as a billionaire’s park. Alas, I was one of the people who voted against it.
Currently, there is a committee working on a “Parks Legacy Plan” which would, among other things, create a metropolitan parks district with taxing authority. It’s probably the only way to get the funding the parks department needs (lots of deferred maintenance, which doesn’t even include the restoration work people like me do).
This answer only touches the surface of how to figure out what is enough greenspace in a city. I’d hoped to look at it in more detail, but even this little glance is a little intimidating.
I’d like to thank Jana Dilley (Seattle Trees for Neighborhoods) and David Folweiler (Groundswell NW) for information they provided for this post. Any errors are mine, of course.