2005 – 2006 Trees Count! Street Tree Census

The results of the 2005-2006 census allow us to characterize the street tree population according to species, size, condition, and a host of other factors. In all, surveyors counted 592,130 trees–93,660 more than in 1995-1996, a 19% increase.

Species. The most common street tree in New York City is the London planetree. This venerable urban tree, platanus x acerifolia, has been a mainstay of the urban environment for almost a century. Although the London planetree just edges out the second most numerous street tree, the Norway maple, its canopy covers more than double the land area than its closest rival.

Importance Value. Importance value is a measure of a species' dominance within a population. It is an average of overall size, leaf area, and canopy cover. London planetree is twice as significant as Norway maple in our current street tree population. Pin oak, which has fewer trees than callery pear, has a higher importance value due to its larger stature and leaf size. An importance value greater than 25 indicates too much reliance on a species, which can subject a population to sudden catastrophe in the face of insects and disease.

Top Five Species

	Total Trees	Canopy Cover	Importance Value
Planetree, London	15.3%	29.1%	24.49%
Maple, Norway	14.1%	13.9%	13.44%
Pear, Callery	10.9%	4.9%	6.87%
Honeylocust	8.9%	8.2%	8.24%
Oak, pin	7.5%	10.9%	9.89%

Condition. Just over 90% of the trees were rated in good to excellent condition.

Size. Census takers measured the girth of each tree at chest height. Onequarter of all street trees citywide are small, with Manhattan having the highest percentage of small trees (35%). Five percent of trees are extra large (over 30 inches wide), with Queens having the highest percentage of extra large trees (6.3%). Most (70%) of the City's largest street trees are comprised of just three species: London planetree, pin oak, and silver maple. By contrast, there is much greater species diversity in the small tree population (14 species in the first 70%).

Damage. Street trees are located on the busy interface between humans and nature, and as such are vulnerable to environmental and physical damage. Signs of damage include torn bark, wounds or cavities on the trunk and branches. Causes of such damage can include vehicles, vandals, or animals. Over 15% of our street trees have trunk wounds (89,211), with 6.6% having torn bark (39,524) and 5.3% with cavities of some type (31,103).

Conflicts. Overhead wires are the predominant urban infrastructure that conflict with trees in all neighborhoods in New York City with the exception of Manhattan. More than 35% of the City's street trees are growing under wires. Other urban conflicts common to street trees are listed below.

Preliminary Management Observations. With the data from the census, there are a few key insights that have begun to emerge that will help us as we go forward:

• London planetree is our most important species and should always have some representation in our tree population;
• Almost 31% of our street tree species are susceptible to the Asian Longhorned beetle and our planting practices need to continue to strive for increased diversity, and reduced susceptibility to pests and diseases;
• Large, canopy trees confer the most benefits and we need to continue to focus on planting large tree species that will successfully mature.

The 2005-2006 census effort mobilized an unprecedented number of volunteers. Over 1,100 volunteers participated, logging 30,000 volunteer hours.

Recruitment. Parks cast a wide net to recruit census volunteers in all five boroughs. Most of the volunteers found the tree census through newspapers, the internet, word-of-mouth, and Parks-affiliated groups. The typical volunteer was female, aged 41-60, employed full time, with a college or advanced degree, and has lived in New York City for at least twenty years. *

Training.All volunteers were required to attend one 3-hour indoor training session and had an option to attend an outdoor session as well. We offered 111 training classes in all five boroughs on evenings and weekends. Volunteers received a 123-page training manual, clipboard, data collection forms, diameter measuring tape, a zone map, and a Trees Count t-shirt (see example below).

Support. After the mandatory training session, volunteers received ongoing support and encouragement. Parks sent weekly email or snail mail updates. We established a dedicated email account and telephone number, along with a website where volunteers could download training information and participate in an on-line bulletin board (see example below) that received 521 postings. One volunteer posted the following observation: “Lots of people ask me what I am doing. I tell them I'm counting the trees, and they look at me very strangely and walk away quickly!” One volunteer, dubbed “Treewright”, helped to answer many of the questions posted by others. All volunteers who submitted data were automatically entered into monthly raffles offering free tickets and entry to events and gardens throughout the city. Parks feted volunteers at a series of thank you parties held in each borough.

Beyond Volunteers. While volunteers provided the core of the census workforce, Parks turned to its Americorps initiative (the Green Apple Corps), an urban forestry consulting group, and Parks own staff to complete the effort. Volunteers completed 42% of the census.

Technology was a hallmark of the 2005-2006 street tree census. Parks used computer mapping, email, the internet, and handheld computers to recruit volunteers, report our progress and anaylze results, while only ten years ago we relied 100% on paper, copy machines and highlighters.

Computer Mapping. In 1998, Parks used Geographic Information Systems (GIS) to map the 1995-1996 census results. We used that information to organize the 2005-2006 effort, creating zones of approximately 300 trees each. These zones served as the organizing unit for the census. Each volunteer was asked to commit to one zone, we customized our recruitment efforts by mapping assigned zones and we provided a custom designed GIS zone map for each volunteer.

Using the most up to date New York City Department of Planning's GeoSupport application, the census data was mapped providing a basis for borough and neighborhood scale spatial analysis in ArcGIS. For example, the mapped census data will allow us to estimate how many additional trees could be planted on every block in all five boroughs.

Email. While email is a vital part of any business transaction or public program today, it was still in its infancy during the last census effort. Staff used email extensively to recruit volunteers and communicate with them through weekly updates and other notices.

Trees Count Website

FoRMS Sample Web Interface

Website. Parks designed a completely interactive census website where volunteers could:

• View a training calendar and register for classes;
• Access resources including the training manual, data collection, forms, and the leaf key;
• View weekly census updates;
• Communicate with other volunteers through a facilitated bulletin board;
• Enter tree census data into an online form;
• Participate in a volunteer survey.

Handheld computers. Hewlett Packard donated 40 handheld computers. The Davey Resource Group’s professional staff designed a customized database to put on the handhelds that matched the paper data forms so their data could be easily imported into Parks’ online database. This bypassed the data-entry phase and saved paper and trees.

Forestry Management System (FoRMS). This fall, Parks will roll out a GIS-based application for tracking our tree inventory and work orders. Using a map-based application for everyday operations will revolutionize how Parks manages our urban forest. By tracking our inventory and work orders within a map of our city, Parks will be able to manage every tree in relation to other trees and infrastructure such as roads, highways and buildings. FoRMS will also allow people to submit and track requests on the Parks website.

Our street trees work for us every day, providing benefits that directly improve our quality of life. Trees purify and cool the air, reduce stormwater runoff, and conserve energy. They increase property values, beautify neighborhoods, and improve human health and well-being. Until recently, it was very difficult to put a dollar value on these benefits. But now scientists with the U. S. Forest Service have developed a way to assess the bottom line impact of many–but not all–benefits of urban trees.

Benefits are directly linked to tree size. The environmental benefits of trees arise from respiration and transpiration – the biological processes by which trees breathe and absorb water from the environment. Because these processes involve interactions between a tree’s leaves, the environment, and the atmosphere, the benefits increase as trees grow in size. In general, the larger a tree, the more canopy cover and leaf surface area (the total area of the leaf spread) it has.

How do we take tree measurements? Measuring the canopy size, leaf surface area and total organic matter (biomass) for every tree would be impossible. Instead, scientists designed a method to sample a small number of trees that would provide data that could be extrapolated to the entire tree population.

Modeling tree growth to predict benefits. The U.S. Forest Service can model tree growth by individual species according to different climate regions. When information about tree size and species is fed into the growth model, it yields an estimate of canopy size, leaf area and biomass for every street tree in that region. Tree benefits can then be calculated using local data including hourly climate and air pollution concentrations, local energy costs, power plant fuel types and emissions, and building construction information. The benefits are detailed below.

• Air Quality Improvement. Leaves absorb gaseous pollutants (carbon dioxide, nitrogen dioxide, and sulfur dioxide), and capture air-borne particles including dirt, dust and soot. Trees also prevent the release of many airborne pollutants by reducing energy generation. Ground level ozone, a contributor to greenhouse gas formation, is reduced through the tree’s ability to lower air temperatures.
  ANNUAL BENEFIT VALUE: TO NYC: $5.3 MILLION
• Energy Savings. Trees provide shade, reducing the demand for electricity for cooling in the summer. Trees also reduce wind speeds, slowing the loss of heat from interior spaces during the winter. Trees cool the air through the process of transpiration, where moisture is converted to water vapor. An estimate for energy usage for every building in NYC was derived from data on building age, tree shading effects, and local climate. This estimate was drawn with two scenarios–with and without street trees–in order to show the difference in the resulting energy use. Local energy prices were then used to calculate the value of the impact of trees on building energy use.
  ANNUAL BENEFIT VALUE TO NYC: $27.8 MILLION
• Carbon Dioxide (CO2). Trees indirectly reduce emissions of CO2 from power plants by reducing building energy use. Also as trees grow, they remove CO2 from the atmosphere and store it in woody plant tissue. At the same time, trees release CO2 as they decompose. These releases are subtracted from the total amount of CO2 avoided from power generation and absorbed by tree growth to calculate the net CO2 benefit.
  ANNUAL BENEFIT VALUE TO NYC: $754,947
• Reducing Stormwater Runoff. Trees help reduce flooding and improve water quality, as runoff flowing over impervious surfaces picks up contaminants including oil and metals. Trees intercept rain on their leaf, branch and stem surfaces and by absorbing water through their roots. The water that trees intercept in NYC each year was calculated using local rainfall data.
  ANNUAL BENEFIT VALUE TO NYC: $36 MILLION
• Property Value and Other Benefits. Research has shown that homes with a tree in front sell for almost 1 percent more than similar homes without trees. The difference in sale price indirectly reflects the value buyers place on trees and their more intangible benefits, such as aesthetics. This difference was applied to the median New York City home resale price ($537,300) to calculate the total value.
  ANNUAL BENEFIT VALUE TO NYC: $52 MILLION

TOTAL ANNUAL BENEFIT VALUE TO NYC: $122 MILLION

Citywide, the 2005-2006 census showed that our tree population grew by almost 19% since the last count. A breakdown by borough gives greater detail on the distribution, composition, and condition of our street trees.

The borough with the largest increase in trees counted between the two census efforts is Staten Island (32.5%), followed by Brooklyn (27%) and the Bronx (25%).

Borough	1995-1996	2005-2006	% Increase
Bronx	47,995	60,004	25%
Brooklyn	112,400	142,747	27%
Manhattan	45,793	49,858	9%
Queens	217,111	239,882	10%
Staten Island	75,171	99,639	33%

Species. London planetree may be the most common species citywide, but it is number one only in Brooklyn (23.6%). In the Bronx and Manhattan, honeylocust is the most plentiful street tree (12.9% and 23.3% respectively), while in Queens the honor still goes to the Norway maple (18.3%). The top five street tree species in each borough are shown in the charts to the left.

Diversity. The more species comprise a population, the less impact pests and diseases can have on the health and vitality of the whole population. A population that lacks species diversity is termed a monoculture. A general rule of thumb when measuring diversity is to assemble a population with no greater than 10% of any species. Another measure of diversity is the extent to which a single species dominates a population. In general, no one species should exceed 25% of a population. By this measure, Brooklyn (London planetree), Manhattan (honeylocust), and Staten Island (Callery pear) show significant dominance by the most plentiful species.

Condition. Just over 90% of the trees were rated in good to excellent condition, with the remaining trees judged to be in poor condition (8.3%) or dead (1.4%). Staten Island has the highest number of trees in good and excellent condition (94%), with Brooklyn (91%) and Queens (90%) close behind. The Bronx had the highest number of trees in poor and dead categories (12%), followed by Manhattan (11.3%) and Queens (10%).

Conflicts. Overhead wires are the predominant urban infrastructure that conflict with trees in all neighborhoods in New York City with the exception of Manhattan. More than 35% of the City’s street trees are growing under wires. Other urban conflicts common to street trees are listed below.

Preliminary Management Observations. With the data from the census, there are a few key insights that have begun to emerge that will help us as we go forward:

• London planetree is our most important species and should always have some representation in our tree population;
• Almost 31% of our street tree species are susceptible to the Asian Longhorned beetle and our planting practices need to continue to strive for increased diversity, and reduced susceptibility to pests and diseases;
• Large, canopy trees confer the most benefits and we need to continue to focus on planting large tree species that will successfully mature.

Borough	Damaged Sidewalks	Canopy Debirs	Choking Wires	Close Paving	Choking Grate	Tree Lights	Electric Outlet
Bronx	8,867	879	1,858	2,232	270	203	353
Brooklyn	28,424	2,625	3,632	17,436	1,070	554	172
Manhattan	2,984	1,451	772	1,373	1,193	771	929
Queens	49,245	2,034	6,161	18,258	813	702	324
Staten Island	11,309	352	1,442	4,110	572	296	97
Citywide Total	100,829	7,341	13,865	43,409	3,918	2,526	1,875

Tree Benefits. The value of the street trees in each borough can be quantified in terms of the amount of air pollution removed, emissions avoided, stormwater runoff intercepted, and energy saved. In addition, street trees increase property values. The dollar value of the trees in each borough are shown below (in 000s).

Tree Benefits Details (in 000s)

Borough	Energy<	CO2	Air Quality	Stormwater	Property Values	Total
Bronx	$2,699	$73	$505	$3,300	$5,339	$11,916
Brooklyn	$7,352	$195	$1,378	$9,409	$12,697	$31,031
Manhattan	$1,646	$42	$293	$1,804	$4,411	$8,196
Queens	$12,308	$342	$2,375	$16,238	$21,567	$52,830
Staten Island	$3,814	$103	$719	$4,877	$8,478	$17,991
Total	$27,818	$755	$5,270	$35,628	$52,492	$121,964

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.

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.

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).

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.

 

• Arbor Day Finds 100,000 More Street Trees And More


• Full Tree Count Report


• Municipal Forest Resource Analysis provided by the USDA Forest Service (STRATUM)