How to Build a Forgotten Landscape from the Ground Up
Data from Many Sources
Starting from Scratch
The process of layering and analyzing spatial data is not, in and of itself, new. Many different fields use geographic information to answer questions in business, government and science. The challenge in recreating Mannahatta, or Welikia writ large, is that none of the data layers existed prior to our work. No one alive today knows where the streams flowed in 1609 or where the bears lived or where the oak-hickory forest grew, and the native Lenape people who would have known these things left no maps behind. In other words, we had to start “from scratch.”
Our starting point to reconstruct Mannahatta was geolocating the 18th century British Headquarters Map to the modern street grid of New York. We found over 200 control points where we could locate features on the map (e.g. streams, hills, ponds) to their current locations. The final rectification was accomplished with an error of approximately 40 meters, or about half an uptown block in midtown. Georeferencing the British Headquarters Map with this level of accuracy means that all data layers derived from it will also be that spatially accurate, allowing us to estimate the distribution of ecological features block by block across the city. The result is a testament to the workmanship of the British military cartographers who created the map.
For the rest of the city, it won’t be so easy, because we won’t have only one map to work with. Rather we will need to work even harder to synthesize information from many different sources into one composite base map to work with. Fortunately though because development of the rest of the city (Brooklyn partly excepted) proceeded later in time than Manhattan, we can use maps through most of the 19th century to detect old streams, hills and shorelines that have since been erased by development.
The Physical Landscape
The complex topography of the “Island of Many Hills” created the basis for over 55 different ecological communities for plants and animals and is an important factor behind Mannahatta’s original biodiversity.
The non-living, physical environment (the soils, waters, hills, and climate) can be thought of as the stage on which the ecological play is acted. Our next objective was to reconstruct these factors; an interesting exercise in itself, especially as these physical factors have been so transformed in the intervening centuries. Mannahatta once had 570+ hills, more than 60 miles of streams, over 20 ponds, and over 300 springs. The rest of the city had many more. Sandy beaches stretched from the tip of Manhattan to past 42nd Street on the Hudson River shore. And beyond the shore was the vibrant, dynamic tidal estuary, with complex currents, sedimentary pattterns, and the influence of the Hudson River. Together these physical factors made for a stage as interesting as anything on Broadway today.
The Biological Landscape: Ecological Neighborhoods
Over the physical landscape, we mapped the biological landscape of ecological communities. Ecological communities are regularly occurring collections of plants and animals, like forests or wetlands; they can be thought of as “ecological neighborhoods.” Where Manhattan has the Upper West Side and Tribeca today, Mannahatta once had “coastal oak-pine forest” and “red maple swamps.” We used a system of ecological communities for New York State developed by the New York State Natural Heritage Program. Why an ecological community occurs where it does is a matter of the physical conditions of the site plus the interaction of disturbance processes like fire, windthrows, freezing, and habitat change caused by people or other animals (e.g. beavers). Taken together, we estimate the Mannahatta once had 55 different ecological community types. This wealth of different communities in such a narrow space in large part explains the extraordinary biodiversity of the island. We expect that similar patterns enabled the biodiversity characteristic of the other boroughs as well, with important differences in the different parts of the city.
Mannahatta’s Abundant Wildlife
The Lenape – The Original New Yorkers
The abundance of wildlife, the island’s location near the estuarine waters, and the hilly topography made “Welikia” a great home for the Native American Lenape people, who lived on the island when Hudson arrived. The Lenape and their ancestors lived in this area for thousands years before European contact, obtaining all the food, water and materials they needed from the surrounding forests, wetlands and waters. In Northeast Algonquin culture, the Lenape were considered the “Ancient Ones;” they told legends of North America as “Turtle Island;” and their folklore suggests a close connection to the land and appreciation of their role, one among many, given the plentiful other species which shared the landscape with them.
We studied the effect of the Lenape on the landscape through computer models, based on the reconstructions described above. We used a wildfire model created by the U.S. Forest Service to estimate the effect of Native American fire on the landscape, showing that through repeated burning as little as once every 10 years, places like the Harlem Plains could be transformed from forest to grasslands. We also created a geographic model of shifting horticulture and estimated how much crops like corn, beans and squash (the traditional “three sisters” garden) contributed to their diet. Today after a long diaspora, Lenape people live in Oklahoma, Kansas, Wisconsin, New Jersey and Ontario, Canada.
Once we had the species lists, an understanding of the physical and biological landscapes, and a sense of how Native Americans affected the ecology of the island, we wanted to know where different species lived on Mannahatta. In scientific terms, we wanted to map the habitats for all the species. This led to the invention of a new way of understanding and visualizing ecosystem relationships called the Muir Web.
Habitat is defined as the place where an plant or an animal can be meet its basic ecological needs, that is, needs for food, water, shelter, and reproductive resources (e.g. materials for building nests, or a den where an animal can give birth). We began compiling habitat descriptions for the 1001 likely species of Mannahatta into a database, using habitat information found in field guides. A tree species might grow best in “dry sandy soils” or a warbler may eat “tree insects, especially in open deciduous woods.” As we developed these lists, we added entries to include the definition of “openness” or of “woods” and eventually even “dry sandy soils.” We reconstructed the habitat relationships until eventually they reached the physical and ecological variables we had mapped, and then even further. At the base of the “Muir Web” of habitat relationships are fundamentals like space, time, geology and climate. We named these webs of habitat relationships (inclusive of food webs, but adding additional relationships) after John Muir, the famous naturalist. John Muir once wrote “When we try to pick out anything by itself we find that it is bound fast by a thousand invisible cords that cannot be broken, to everything in the universe.” The Muir Web for Mannahatta makes these cords visible for all to see.
To learn more about Muir webs, watch a presentation made at Columbia University on September 18, 2009. For Welikia we will create a Muir web separately for each borough of city, reflecting the differences in species and ecological community composition. Also based on a study conducted in 2009-2010 by Dr. Eric Sanderson and Dr. John Waldman (Queens College), we believe we now have a way of incorporating seasonality into the Muir webs, and thus express different data views of the pre-European natural landscape in different seasons.
Cities as Habitat
Thinking of Welikia’s Muir webs can lead one to wonder: what are the webs that sustain us today? In New York City we can trace connections to our friends and family, to our workplaces, to public institutions like the police and the fire department, and to our causes, whether we support music, arts or nature conservation. Just as Mannahatta nurtured so many plants and animals, so Manhattan today nurtures so many kinds of people. Diversity, density and interdependence are still alive and well on Manhattan, though the players have changed; and surprisingly, more of nature persists in New York that one might think. An important part of the Mannahatta Project is not leaving ecology in the past, but to appreciate it in our current times, to see how we can live in ways that are compatible with wildlife and wild places and that will sustain people and planet Earth for the next 400 years.
Through the Welikia Project we aim to quantify the changes to the landscape that have happened over the last 400 years, so that we can help the city create a plan to re-invigorate the nature of the city over the next 400 years. Our plan is to compare our historical species lists and ecological community maps to existing information about the biodiversity and ecosystem composition of the city today. Some species will still be here (perhaps some even in greater abundance, like the peregrine falcon); others may be entirely and irretrievably gone (like wolves or black bears); while others perhaps could come back through conservation efforts. We wish to push the boundaries of what is possible for the future by looking to the past, and therefore contribute to New York City’s greatness, not only for its people, but for all of nature.
To learn more about the science of Mannahatta, read Eric Sanderson’s Mannahatta: A Natural History of New York City (Abrams, 2009).
To find out more about Welikia, become a “Landscape Ecology Insider” by supporting one or more boroughs through the Welikia Map. Click on any borough to begin. For Manhattan you can support any block to gain insider access to our work.