Reconstructing New England salt marsh losses using historical maps

Analyses of habitat loss are often restricted to the past 75 years by the relative youth of aerial photography and remote sensing technologies. Although photographic techniques are highly accurate, they are unable to provide measurements of habitat loss prior to the 1950s. In this study, historical maps from the late 1700s and early 1800s covering portions of Rhode Island, Massachusetts, New Hampshire, and Maine were used to approximate naturally occurring salt marsh cover in New England. Historical data was compared to current salt marsh coverage available in public geographic information system (GIS) data sets. The average loss in New England is estimated at 37% using this technique. Rhode Island has lost the largest proportion of salt marshes by state, a staggering 53% loss since 1832. Massachusetts has also experienced large losses, amounting to a 41% loss of salt marsh since 1777. The Boston area alone has lost 81% of its salt marshes. Salt marsh loss was highly correlated with urban growth. Restoration and preservation efforts have resulted in the retention of salt marsh in less populated areas of New England. Although historical maps are difficult to verify, they represent an extremely valuable and underused data repository. Using historical maps to trace land use practices is an effective way to overcome the short-term nature of many ecological studies. This technique could be applied to other habitats and other regions, wherever accurate historical maps are available. Analysis of historic conditions of habitats can help conservation managers determine appropriate goals for restoration and management.