I’d like to introduce a topic: street trees! At the perennially amusing data.seattle.gov, under the “Transportation” category, lies a dataset titled ‘Trees in the Public Right of Way Diameter >= 40″‘. As an admitted tree enthusiast this sounded tremendously exciting (treemendously exciting?). Let’s take a look at where the large street trees supposedly reside, with a little help from the Google Maps API.

A few things immediately jump out. First, it looks like Capitol Hill (the neighborhood just above and to the right of the ‘Seattle’ label) and Queen Anne (the neighborhood just above and to the left of the label) hold the highest concentration of grand old street trees. This probably isn’t surprising given the age of these neighborhoods. It also looks as though large street trees scatter throughout north Seattle with a concentration in Ravenna, cluster in the north point of West Seattle, and remain almost absent in south Seattle.

The last point immediately trips the social justice alarm. It’s a bit of a pisser, but not surprising, that lower Socio-Economic Status neighborhoods seem to lack stately trees in the same quantity as more traditionally prosperous neighborhoods. South Seattle at least historically has been home to non-white communities and people of modest income. It seems a bit frustrating that such an area would lack elderly and elegant street trees.

Let’s look a bit closer at the two high-density street tree areas of Queen Anne and Capitol Hill. The map below zooms in on the two neighborhoods.

Queen Anne is the neighborhood in the upper left. The neighborhood is somewhat comprised of two distinct segments, so-called “Lower Queen Anne” at the bottom of the hill, closer to downtown and containing the Seattle Center, and “Upper Queen Anne”, which includes the hill itself. Much of the upper part of the hill is ringed by view boulevards, often with stone railings and stately trees, so it’s no surprise that the map roughly shows a ring of large diameter street trees. In addition a cluster exists in Lower Queen Anne, in and near the Seattle Center. Even if you’ve never been to Seattle, you probably know the view from Queen Anne, as the following iconic view of the city comes from the neighborhood’s tiny Kerry Park.

In contrast to the apparent view boulevard pattern of Queen Anne, Capitol Hill seems to hold a fairly uniform distribution of street trees. In fact, the heart of Cap Hill — Broadway, Pike/Pine, the perpetual party zone — has very few large trees at all. Mostly they seem scattered about north Capitol Hill and the Central District, as well as a smattering near Lake Washington.

In addition to a macro view of tree location, we can also look at species. The bar plot below shows the counts of trees greater than 40″ diameter by species.

It looks as though many of Seattle’s large street trees are fairly unique: looking at listed species with at least four individuals shows “Other” as the most popular category, although we also see such illustrious categories as “Stump” and “Unknown”. Also not surprisingly we see that Bigleaf Maple (or Oregon Maple) is the most popular large-diameter street tree of Seattle. As a fairly oblivious arborist more likely to appreciate the energy and aesthetics of an impressive tree more so than its genus and species, even I notice the abundance of Bigleaf Maple around these parts. The number two entry was a bit surprising, as I had not even heard of a London Plane tree (again, the oblivious arborist). According to Wikipedia “it is a popular urban roadside tree,” so there you have it.

Looking through the rest of the abundant species I find myself surprised at the specific associations I hold with many of those species. Growing up I recall visiting extended family — eastern Washington orchardists — where rows of tall, skinny Lombardy Poplars acted as wind breaks for the acres of fruit trees, and I awoke frightened in the middle of the night to the sound of horse chestnuts falling, bouncing, and rolling down the roof over the guest room in the spooky chalet. At the University of Idaho I walked daily below Black Locusts; visiting family in Klickitat County I fondly remember fall among the pin oaks; growing up in Alaska the cottonwoods grew like weeds by my parents’ house, and I killed many a woodstove fire with a soggy log of papery cottonwood.

Enough nostalgia. As with other data.seattle.gov datasets, this one appears to have its problems. For example, the most obvious thing I can think to do here — for entertainment purposes — is to look at the several largest street trees in the city. The alleged largest street tree is obviously a data error, unless you believe that a 25′ diameter Littleleaf Linden grows near Swedish in Ballard. In addition, looking up the other largest trees on Google Earth at their alleged locations — including a supposed 10′ Austrian Black Pine and Honey Locust — revealed locations with few, if any trees, much less ten foot diameter trees.

This post is meant to serve as an introduction to an ongoing project. I plan on following up with photos, field trips, and further commentary. Hopefully some of these impressive trees turn out to be real and not data errors!