Swamp White Oaks at the 911 Memorial in New York

In October 2016 I was in New York on business and one morning before work I took the subway down to the Financial District to visit the 911 Memorial. I had avoided the site on previous trips, as it was a place that brought back bleak memories. My family and I were living in New York on Sep 11, 2001, and I was only a few miles away in Midtown Manhattan when the attack occurred. I spent the rest of the day walking north for over four hours to our home in Riverdale in the Bronx, with the appalling column of dun smoke at my back. But what enticed me now to visit the Memorial was the fact that one of the main features of the monument is a plantation of over 400 swamp white oak trees (Quercus bicolor).

At the Memorial’s structural and emotional center are two huge square black pits, seemingly bottomless, marking the footprints of the Twin Towers. A constant flow of water cascades down the sides of the pits and disappears into a square well in the middle. The rows of oak trees that surround these dark depressions provide a welcome contrast, drawing one’s gaze up into their canopies, through which one can glimpse the sheer sides of One World Trade Center (formerly known as Freedom Tower).  

Quercus bicolor was chosen as the species to be used in the Memorial for two principal reasons: it is native to all three spots affected by the attacks (New York City, Arlington County in Virginia, and Shanksville, Pennsylvania)

A view of one of the black pools in the heart of the Memorial. Water cascades down the sides and flows into the void in the center. A line of swamp white oaks frames the pool from this angle, some just beginning to turn color. (Click on the images to enlarge.)

and also to the regions of the US where most of the victims came from; furthermore, it adapts well to the challenges of an urban environment, tolerating dry, moist, or wet soils as well as salt and soil compaction. The original design included a number of sweet gums (Liquidambar styraciflua), but these were eventually omitted as their fall coloring was considered to be too harsh.

The trees have been described as “the world’s most cared for trees.” They were sourced from several nurseries across swamp white oak’s range and then grown for over four years in an above-ground nursery in New Jersey, under the supervision of Bartlett Tree Experts. Growing them in large wooden boxes sitting on the ground meant that transplanting stress was minimized, as none of the trees’ roots were lost when they were moved and planted in the Memorial. They grew under constant human supervision, and electronic probes also monitored soil conditions in a large sample of the trees. In order to create a uniform effect, the oaks were pruned to obtain a similar structure throughout the plantation.

The results are impressive: the trees are growing with remarkable vigor and homogeneity, and are on track to create the desired effect of a single canopy that will cover the whole area around the black pools. It was interesting to note some variation in leaf shape, with some lobes being more pointed than the rest; also, some

The original design by Michael Arad and Peter Walker called for 412 swamp white oaks. I have not been able to determine the actual number at the Memorial: most articles I have read give an approximate figure (e.g. over 400, about 450, etc), and I did not have time to count them during my short visit!

trees had turned color, or even lost their leaves, while others were still green.

I assume that a plantation of this size and uniformity is unique, but I would be keen to learn of any anything similar that readers may know of. You can learn more about the whole project, including the remarkable care taken of the young trees, following the links to articles, websites, and videos listed below.

Having experienced it first hand, I would recommend a visit to the 911 Memorial if you are in New York: brace yourself for the emotional impact, but you will not be disappointed by the legion of swamp white oaks standing guard and whispering in the breeze their message of life and rebirth.  

Articles

9-11 Memorial Trees (Horticulture Magazine) – a good account of the whole project
Not Your Average Trees (Lawn & Landscape) – focuses on the work of Bartlett Tree Experts caring for the trees
Trees for 9/11 Memorial at Ground Zero grown at Millstone nursery (nj.com) – features Halka Nurseries, where the trees were grown

Websites

PWP Landscape Architecture – website of the designer, includes details about how the trees were procured
9/11 Memorial and Museum – includes a Design Overview and a 360-Degree view of the Memorial

Videos

Caring for the Trees of the 9/11 Memorial  - a video by Bartlett Tree Experts
Trees from Millstone nursery bring life to Ground Zero site – includes great footage of the transplanting process
9/11 Memorial Trees – an two-part interview with Wayne Dubin of Bartlett Tree Experts, a detailed account of the tree-growing process
Oak Trees Breathe New Life into Ground Zero  – an overview by Bartlett Tree Experts, images and titles
Official 9/11 Memorial Museum Tribute In Time-Lapse 2004-2014 – a fascinating time lapse of the construction of the Memorial, watch for the appearance of the oaks at 1:02

The "Survivor Tree", the only other tree aside from the swamp white oaks at the Memorial. This Callery pear (Pyrus calleryana) was found still alive after the attacks and taken care of off site before being replanted at the Memorial.  Water cascades down the sides of the black voids at the Memorial. Tears? Washing away of grief?
Variation in leaf shape: pointed and rounded lobes. The "Oculus", the World Trade Center Transportation Hub designed by Spanish architect Santiago Calatrava to resemble wings spread in flight.
Same species, different behavior: some trees had lost almost all their leaves, while others hardly any.
In a few years' time, the trees' canopies will join and fuse into one. The oaks at the Memorial are dwarfed by surrounding skyscrapers
The rugged bark of swamp white oak One World Trade Center framed by Quercus bicolor