If you look at old pictures of NYC, you might notice something missing.   Trees.  We sort of take them for granted now.  And when I think of tree-lined neighborhoods, my mind quickly goes to the West Village or Brooklyn Heights.  What do those neighborhoods have in common?  Wealth.  

This got me thinking… are there more trees in higher income neighborhoods than there are in lower-income ones? 

Amazingly enough, open data can help here.  It turns out the city did a “Tree Census” in 2005, where they literally counted every single street tree and mapped it. 

So, with that data in hand, we can start to explore the question.  First, I created a “Tree Heat Map” of the city, showing the neighborhoods with the highest tree density.  Red on the maps indicate the highest tree density:

Brooklyn:

Bronx:

Manhattan:

Queens

Staten Island

As expected, neighborhoods like Brooklyn Heights and The West Village pop in these charts.  But so do lots of others neighborhoods. At the very least, I noticed a bit of a wealth/tree correlation.  Note the border of 96th Street on the Upper East Side and 110th Street on the Upper West. These boundaries are in-line with what I understand anecdotally to be some wealth boundaries.  On the other hand, Lower Manhattan and Battery Park have very few trees due to the large buildings and narrow streets.

While the heat maps above show us densities, it does not account for the density of streets themselves.  One reason that the West Village has so many trees is that is has so many streets; the blocks are quite short.  So in order to control for this, I don’t just want to measure the number of trees in an area.  I want to measure the number of trees per unit length of road.  

With this in mind, I built a tree index for each Neighborhood ( or Neighborhood Tabulation Area more technically).    For each neighborhood, I calculated the number of trees and divided by the miles of street.  I then made an index with Mean 0.  (Negative is below average, positive is above.  Similar to a Z-scores for all you stats people).  With this new tree index, I am able to find the top 10 most and least “treeful” neighborhoods in the city and across all 5 boroughs: 

The lists are quite interesting.  Sunset Park West is the least treeful Brooklyn neighborhood, and the second lowest in the entire city.  East New York is also at the bottom of the Brooklyn list. The neighborhood with the highest street-to-tree ratio? Prospect Park South.  

One of the things that surprised me most was that the West Village did not make it on any of these lists.   The reason?  It turns out that there are lots of trees but also lots of streets.  (The blocks are very small).   So the number of trees per mile of street in the neighborhood is actually not particularly high.  It might be more the short blocks and narrow streets that give it the tree-feel. 

The MillionTreesNYC program has targeted certain neighborhoods to place trees.  These six neighborhoods—referred to as Trees for Public Health neighborhoods (TPH)—were selected because they have fewer than average street trees and higher than average rates of asthma among young people. 

5 out of the 6 neighborhoods are on my bottom 10 lists above.  (Morrisania is not.)  

So what about equal access to street trees across income levels?  

To determine that, I ran a correlation between median income in each neighborhood and the street tree density. It turns out that there is in-fact a slight correlation between median income in a neighborhood and that neighborhoods street-tree density:

The chart shows a positive correlation ® in all 5 boroughs, but the correlation in Staten Island is the highest at 0.39, which is a moderate correlation. Overall in NYC, the correlation stands at around 0.19.

In conclusion, the correlation is present but fairly weak.  (I am not making any claims as to causation here, bur rather I am just exploring the numbers.)   Note that this census was taken in 2005-2006, and the income data was from 2012.  Also, this does not account for trees in parks or other land.  So the results have to be taken with a grain of salt. Nevertheless, I hope that data like this is used by the Parks Department and other program administrators as they finish off MillionTrees NYC.  The TPH is a good start, but there are many more neighborhoods that are lagging behind.

I would also  like the city to release the locations of all planted trees in the MillionTrees NYC program. Might higher income neighborhoods be requesting more trees than poorer ones? And if so, could this correlation be strengthening?  We won’t know until we see that data.  But we should make sure that the trees end up in a diverse set of neighborhoods.

Side note: Speaking of diversity, Pratt’s Diversity Initiatives Group is hosting an event bringing together residents, community-based organizations, students, and public officials all across the city for a grassroots style conference to discuss diversity and urban planning in our communities: Saturday, March 29,2014, 9:30 AM to 4:30 PM, Register at: diverCityNYC.eventbrite.com.

Results calculated using QGIS, The Tree Census and DCPLION. 

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