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Trees Count! Methodology

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To achieve our management, education, research, and planning goals, Parks carefully identified the relevant information to collect for each tree. Parks collected three times the amount of data during the 2005-2006 effort than it did in the 1995-1996 census, tracking over 15 million pieces of information.

Location. So Parks could find its way back to a tree that was surveyed, fully one-third of the volunteer training session focused on how to use an address to assign trees to the nearest building.

image of locations and species

Species. We developed a Leaf Key to identify trees. Volunteers were trained to identify both genus and species, given a photo guide of 54 species and an additional choice of 72 species online. Download the Leaf Key [PDF, 1MB]

Size. Using a measuring tape specifically designed to calculate tree diameter from a circumference measurement, census workers measured the tree at a standard 4.5 feet from the ground (or breast height).

Condition. Staff developed a simple assessment system using leaf health, branch structure, and trunk condition geared toward an amateur workforce. Condition ratings were broad—excellent, good, poor, and dead—and comparable to those used in the 1995-1996 census.

Site Type. We recorded whether a tree was growing in a lawn area, an individual sidewalk pit, or a shared sidewalk cutout (see below).

images of trees

images of infrstructure and tree pit

Soil Level. We asked if the soil level is at least one inch below the sidewalk grade, if the soil is piled around the base of the trunk, or if the soil is level with the sidewalk.

Sidewalk Condition. Assessing the sidewalk directly adjacent to the tree opening, surveyers noted cracks and raised paving.

Vertical Treatment. Census takers noted fencing around the perimeter of a tree pit, those close to the tree, and solid walls built around the trees.

Horizontal Treatment. We looked for granite, concrete, or other blocks installed in tree pits at sidewalk grade and identified metal grating as well as decorative planting.

Overhead Wires. Beyond redcording their existence, volunteers identified the type of overhead utility wires—primary, secondary, or house tap—to help guide our pruning and planting work.

Infrastructure Conflicts. We documented anything harming or restricting the growth of the tree including canopy debris, choking wires, close paving, choking tree guards and grates, tightly wrapped tree lights, electric outlets, and sneakers.

Trunk Damage. Census takers recorded the presence of torn bark, trunk wounds, and cavities.

Tree Pit Status. The census looked at more than just living trees. We included dead trees, shafts (standing dead trees with branches removed), stumps (trees cut to the ground) and empty tree pits.

Did you know?

  • Over 15 million pieces of data were collected, entered, and analyzed as a result of the census effort.
  • Parks divided the city into 1,649 zones, and used these units to track our progress in recruiting volunteers, and collecting and entering data.

Then & Now

The 1995-1996 census used over eight fields of data while the latest effort included 27 pieces of data. Many new fields were required to do the environmental benefits analysis (STRATUM), and inform management decisions.