How to Build a Forgotten Landscape from the Ground Up

The science behind the Welikia (and Mannahatta) Project is landscape ecology. Landscape ecology is the study of how different ecosystems (e.g. forests, wetlands, streams, etc.) combine together to create habitat for plants and animals. The Wildlife Conservation Society uses landscape ecology to understand how to conserve wildlife and wild places, especially as many of the changes people make to the landscape (e.g. building roads, clearing land for agriculture, constructing cities) affect wildlife species. Our goal in the Welikia Project is to build a digital version of New York City’s original ecological landscape, layer by layer, literally “from the ground up,” starting with geology, soils, topography, then streams, springs, ponds, wetlands, etc., eventually working up to species of plants and animals (including people.)

To recreate Mannahatta, we used GIS software to layer spatial datasets (i.e. maps), to derive maps of topography, streams, and eventually species and ecological community types, the original ecology of Mannahatta.

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 result of five years of historical map research, fieldwork, and GIS analysis, the Digital Elevation Model, or DEM, of 1609 was a vital step in the process of recreating Mannahatta. ©WCS

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.

This image illustrates the differences in the island's elevation between 1609 and today. Grays and blacks indicate increases in elevation, mainly waterways that have been filled in, while browns indicate decreases in elevation, such as leveling hills for construction.©WCS

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 had 55 different ecological communities, including terrestrial communities (like forests and grasslands), wetland, pond and stream communities, and estuarine communities in the surrounding waters.©WCS

Mannahatta’s Abundant Wildlife

Mannahatta was home to a large population of beavers. These "ecosystem architects" build dams to create beaver ponds -- a unique ecological feature that would not otherwise exist. This particular beaver is named Jose; he re-colonized New York City in 2008 after a near 200 year absence of his kind from the city. Photo by Julie Larsen Maher ©WCS.

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.

The 1735 portrait of Lenape Chief Tishcohan by Gustavus Hesselius. Courtesy of The Historical Society of Pennsylvania Collection, Atwater Kent Museum of Philadelphia.

Muir Webs

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.

This Muir Web shows all the habitat relationships for all the species on Mannahatta. Visualization by Chris Harrison of Carnegie-Mellon University. ©WCS