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.)

Data from Many Sources

To make this happen, we collected data from many sources. We started with historical maps which described the original features of city. To those we added information from soil surveys, tree rings, descriptions of plant life and animal life, historical accounts, even field surveys from today. For Mannahatta, we “georeferenced” all this information to a single base map, 1782 British Headquarters map from The National Archives in the United Kingdom, and created a geographic information system (GIS) database, in this case, the most complete description of a landscape ever attempted. For the other boroughs, we will need to use a combination of maps from the 18th and 19th centuries to carefully reconstruct the forgotten landscape.

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

If the physical landscape sets the stage, and the ecological communities are the setting in which the play is acted, the ecological actors are the species. Through a long process of compiling historical and modern sources and consulting with scientists from many disciplines, we developed a species list for Manhattan. We can not be certain of exactly what species were once on the island, so we describe different species by their probability of occurance: likely, probable, possible and remotely possible. In total, our research leads us to conclude that just over 1000 species of plants and vertebrate animals (24 species of mammals, 233 birds, 32 reptiles and amphibians, 85 fish, and 627 species of plants, and unknown numbers of fungi, lichens, mosses, insects, shellfish and other invertebrates) once occurred on Mannahatta. These likely wildlife included wolves, black bears, mountain lions, beavers, passenger pigeons, heath hens, timber rattlesnakes, tree frogs, bog turtles and over 30 species of orchids and 70 species of trees.

We expect but don’t know yet that the biological abundance of Welikia Bronx, Queens, Brooklyn and Staten Island will be greater than Manhattan’s. We use similar techniques as for Mannahatta, but tailor them to these other four boroughs, producing borough specific species lists for the entire city.

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.