Manhattan's Future Greenery: Embracing Optimal Trees

Have you ever been to Manhattan and noticed the abundance of trees that line its streets? While it may seem that there are many different types of trees, it turns out that certain species are more common than others. These trees provide much-needed shade on scorching hot summer days while also helping to clean the air by filtering pollutants from cars and other sources of air pollution. Furthermore, these urban trees are relatively low maintenance compared to other species meaning they require less effort from caretakers while still offering numerous benefits for both people and wildlife alike.

Let’s take a look at the tree species in Manhattan, their characteristics, benefits, health indicators and location, both with respect to the curb and the neighborhoods. The urban design team believes tree size (using trunk diameter as a proxy for size) and health are the most desirable characteristics of city trees. The city would like to learn more about which tree species are the best choice to plant on the streets of Manhattan.

The aim of this exploration is to:

• characterise the dataset;
• identify most common tree species in Manhattan;
• select neighborhoods with the most trees;
• visualize trees' location in Manhattan's neighborhood; and
• pinpoint 10 most suitable tree species suitable for future planting based on health parameters.

Data

The team has provided access to the 2015 tree census and geographical information on New York City neighborhoods (trees, neighborhoods):

Tree Census

• "tree_id" - Unique id of each tree.
• "tree_dbh" - The diameter of the tree in inches measured at 54 inches above the ground.
• "curb_loc" - Location of the tree bed in relation to the curb. Either along the curb (OnCurb) or offset from the curb (OffsetFromCurb).
• "spc_common" - Common name for the species.
• "status" - Indicates whether the tree is alive or standing dead.
• "health" - Indication of the tree's health (Good, Fair, and Poor).
• "root_stone" - Indicates the presence of a root problem caused by paving stones in the tree bed.
• "root_grate" - Indicates the presence of a root problem caused by metal grates in the tree bed.
• "root_other" - Indicates the presence of other root problems.
• "trunk_wire" - Indicates the presence of a trunk problem caused by wires or rope wrapped around the trunk.
• "trnk_light" - Indicates the presence of a trunk problem caused by lighting installed on the tree.
• "trnk_other" - Indicates the presence of other trunk problems.
• "brch_light" - Indicates the presence of a branch problem caused by lights or wires in the branches.
• "brch_shoe" - Indicates the presence of a branch problem caused by shoes in the branches.
• "brch_other" - Indicates the presence of other branch problems.
• "postcode" - Five-digit zip code where the tree is located.
• "nta" - Neighborhood Tabulation Area (NTA) code from the 2010 US Census for the tree.
• "nta_name" - Neighborhood name.
• "latitude" - Latitude of the tree, in decimal degrees.
• "longitude" - Longitude of the tree, in decimal degrees.

Neighborhoods' Geographical Information

• "ntacode" - NTA code (matches Tree Census information).
• "ntaname" - Neighborhood name (matches Tree Census information).
• "geometry" - Polygon that defines the neighborhood.

Tree census and neighborhood information from the City of New York NYC Open Data.

Descriptive Analysis

In the dataset with total count of 64,229 trees in Manhattan, 1,802 are dead, as evidenced in Fig. 1. Those dead trees do not have any assigned tree species (except 1 that is honeylocust) nor do they have an indicator of health status. These trees can be excluded from the basic analysis for now. However, they can provide us with clues on what causes trees to die later.

Tree Species

Fig. 2 shows a wordloud illustration of the living tree species present in the sample. It seems that honeylocust, pin oak, callery pear, sophora, ginkgo, japanese zelkova, littleleaf linden and london planetree are amongst the most common.

For example, london planetree has a rounded canopy which provides plenty of shade during summer months while still allowing light through during winter months when its leaves drop off. The Callery pear is another popular species often seen in Manhattan's streetscape due to its ability to thrive in urban settings with minimal maintenance required. Ginkgo biloba trees thrive in sunny conditions with adequate water drainage—making them ideal candidates for planting along sidewalks or other locations throughout the city.

Fig. 2: Wordcloud of Individual Tree Species of Manhattan

Indeed, the absolute count of living tree species in Fig. 3 shows that, by far, honeylocust is the most common tree species with 13,175 examples. Callery pear and ginkgo occupy the second and third place, respectively, with approximately half of the honeylocust count. From pin oak to littleleaf linden, the number of trees hovers around 4,ooo. American elm and American linden come last at 2,000 plants per species.