The Trees of Governors Island: Surveying Our Diverse Canopy
Sep 23, 2022 1:41 pm
The young trees of Hammock Grove in the foreground, with the older trees of the North Island surrounding Liggett Hall in the background.
Guest post by Malcolm Gore, Arborist at the Trust for Governors Island
In the Winter and Spring of 2022, the Trust for Governors Island conducted a survey of all trees on Governors Island to better understand the diversity, health, and longevity of our unique urban forest. The Trust received a grant from the New York State Department of Environmental Conservation in 2021 to complete this survey, and contracted Davey Resource Group, a nationally respected tree company, to conduct the survey and create a Community Forest Management Plan for this crucial canopy resource situated in the middle of New York Harbor.
Why survey our trees? It’s critical that we have the full picture of the Island’s tree canopy to make sure we are the best stewards we can be, ensuring our trees survive — and thrive — for years to come. Governors Island is home to almost 3,500 trees (3,496 to be exact) comprising 123 different species. Of these trees, 97% are in either fair, good, or excellent condition — meaning they will continue to provide countless benefits to the many human and non-human visitors of Governors Island for years to come. Before diving into the specific benefits provided by our arboreal friends, let’s take a look at the diversity of this island forest.
London Plane Trees, with their distinctive white bark and arching branches, are the most plentiful tree on the Island as the 422 individuals represent 12% of the total tree population on Governors Island. They also account for a whopping 54% of the total leaf cover on the island, since most of them are mature trees that were planted when Robert Moses was NYC Parks Commissioner (while we aren’t sure the extent to which he had a say in the trees planted on Governors Island, London Plane Trees sprung up in huge numbers across the city during this time period— it seems they were his favorite tree). Having a single tree take up 12% of the canopy does come with some risk — if a new disease that affected London Plane Trees were to sweep through New York, Governors Island would lose a lot of its canopy. This disease risk is precisely why the Trust is actively planting many different native tree species that will make our urban forest more resilient.
Coming in second are Swamp White Oaks, with 202 individuals that comprise 6% of the total, followed by 150 of both Northern Red Oaks and River Birches. Rounding out the top five are the 120 Sweetgums that call the Island home. These native tree species are vitally important to bird and insect populations, as many types of caterpillars (AKA baby bird food) feed on their leaves in the spring and summer.
Additionally, the majority of these trees are young and, as they grow and mature, will provide more habitat and food for the plethora of fauna that visit the Island every year.
Photo by Sarma Ozols
Biodiversity isn’t the only important thing to consider when maintaining a healthy tree canopy; the age diversity of the Island’s tree population is also important. Mature trees provide more habitat and shade, but are also riskier given their greater bulk and surface area to catch windstorms. The below chart represents the relative age of Governors Island’s trees as compared to the ideal to sustain a healthy forest.
Age breakdown of Governors Island's trees as compared to the ideal, compiled by Davey Resource Group, Inc.
As you can see, Governors Island’s tree canopy contains nearly double the amount of recommended young trees — this is largely due to all of the trees planted within the last five years in the Island’s award-winning park space. With proper care and time, these young trees should develop into established ones as soon as 2024, and this new urban forest will become more robust and self-sufficient.
Currently, only about 91 acres of Governors Island’s 172 acres are considered shaded, and the vast majority of that is in the Island’s Historic District under those 422 London Plane Trees. As the young oaks, sweetgums, and birches grow and mature on the South Island, more of the Island will experience the cooling benefits of tree shade, thus ensuring that the island becomes a place to escape the city heat in upcoming summers.
Besides shade, what other benefits do these 3,500 trees provide for New Yorkers? For one, trees are experts at removing pollution from the air. The Island’s forest removes 1,160 pounds of air pollutants annually, improving the air quality and lung health of people in the surrounding area. The more trees in a given area, the better the air quality which translates to reduced rates of asthma and stress, and improved cognition.
Trees also benefit the health of the planet by storing carbon. The trees of Governors Island contain approximately 1,245 tons of stored carbon, and every year they capture and sequester an additional 22 tons. Mature trees store more carbon that younger ones, simply because they have more surface area and larger root systems. Every year, trees grow a dense network of small feeder roots, made of carbon, that will die and be turned into organic matter in the late fall. The larger the tree, the more feeder roots they grow each year, and the more carbon they sequester underground.
This is just one reason why the Trust is dedicated to maintaining the health and longevity of as many mature trees as possible, and is taking steps to reduce the upper canopy of at-risk trees so their roots systems can continue to capture and store carbon for many years to come.
In addition to storing carbon, trees can help mitigate the effects of climate change by reducing storm damage and runoff. Tree roots act as giant sponges, soaking up vast quantities of water that could quickly turn into toxic runoff, and the canopy intercepts deluges of rain that would otherwise hit the ground with force and cause compaction or flash floods. On Governors Island, the canopy prevents up to 378,000 gallons of runoff annually, improving the soil of our park space and preventing pollutants from contaminating New York Harbor.
All the data resulting from this survey is incredibly valuable to the Trust for Governors Island, as it will help inform decisions on tree planting, park maintenance, construction projects, and programming events. The 3,500 trees on Governors Island are a vital resource to the people of New York, and the Trust is committed to ensuring that this crucial urban forest remains healthy and resilient for many years to come. To learn more about urban forests and trees, come to Governors Island on October 15 for our City of Forest Day event — including a special volunteer activity and a tree walking tour around the Island. Click here to learn more and register.