Tidal wetlands after Hurricane Sandy: Baseline restoration assessment and future conservation planning

Elphick, Chris; Olsen, Brian; Shriver, W; Cohen, Jonathan; Correll, Maureen; Hantson, Wouter; Klingbeil, Brian; Tymkiw, Elizabeth

From the executive summary: "Hurricane Sandy has fundamentally altered the way in which society thinks about coastal resilience in the mid-Atlantic and New England states. Considerable funds are being invested in restoring coastal resources and the need to systematically plan how we invest is increasingly apparent. A thorough understanding of the effectiveness of Hurricane Sandy restoration projects on tidal marshes and the wildlife they support is thus needed to direct conservation actions where they will have the greatest benefits toward increasing the resilience of green infrastructure. Many species of conservation concern use tidal marshes and face additional threats from sea-level rise. The Saltmarsh Habitat and Avian Research Program (SHARP) has assembled a large collection of historical and contemporary measures of plant and bird communities in tidal marshes from Virginia to Maine. In the current project, we used this platform to begin to assess the efficacy of restoration activities and to provide planning guidance to enhance the future resiliency of natural coastal assets. Our primary focus was to collected elevation, vegetation, and bird data to quantify baseline conditions at National Fish and Wildlife Foundation (NFWF) funded Hurricane Sandy resiliency sites throughout the Northeast and mid-Atlantic states and at paired control sites. These data have been combined with similar data collected at Department of the Interior-funded resiliency sites across the same region into a common database, and will form the basis for long-term investigations into the efficacy of coastal restoration and management work. In addition to baseline data collection at resiliency sites, our work has had three specific research goals. First, we investigated whether elevation data collected in the field via real-time kinetic (RTK) GPS methods can be accurately replicated using remote sensing data products. Collection of RTK elevation data is both time consuming and expensive, and thus difficult to obtain for large areas with high spatial resolution. Remote sensing data, by contrast, are available across vast areas and are often publically available for free. We tested a variety of remote sensing data at both local and regional scales and found that the 1/9 arc-second (~1 m resolution) data layer from the National Elevation Dataset (NED) produced high quality predictions of the RTK measurements. These predictions were especially good for high elevation marsh, a habitat of particular interest to land managers. Other resolution NED data, and data collected used an unmanned aircraft system, were far less satisfactory and were poor substitutes for field-collected data in our tests. Second, we compared several remote sensing techniques to develop a tool that accurately maps high- and low-marsh zonation for use in management and conservation planning. We found that random forests outperformed other classifier tools when applied to the most recent National Agricultural Imagery Program (NAIP) imagery, NAIP derivatives, and elevation data between coastal Maine and Virginia, USA. We then used these methods to classify plant zonation within a 500-m buffer around coastal marsh delineated in the National Wetland Inventory. We found mean classification accuracies of 94% for high elevation marsh, 76% for low marsh zones, and 90% overall map accuracy. The detailed output is a 3-m resolution continuous map of tidal marsh vegetation communities and cover classes that can be used in habitat modeling of marsh-obligate species or to monitor changes in marsh plant communities over time..."