Estimating Aboveground Biomass and Its Spatial Distribution in Coastal Wetlands Utilizing Planet Multispectral Imagery

Coastal salt marshes are biologically productive ecosystems that generate and sequester significant quantities of organic matter. Plant biomass varies spatially within a salt marsh and it is tedious and often logistically impractical to quantify biomass from field measurements across an entire landscape. Satellite data are useful for estimating aboveground biomass, however, high-resolution data are needed to resolve the spatial details within a salt marsh. This study used 3-m resolution multispectral data provided by Planet to estimate aboveground biomass within two salt marshes, North Inlet-Winyah Bay (North Inlet) National Estuary Research Reserve, and Plum Island Ecosystems (PIE) Long-Term Ecological Research site. The Akaike information criterion analysis was performed to test the fidelity of several alternative models. A combination of the modified soil vegetation index 2 (MSAVI2) and the visible difference vegetation index (VDVI) gave the best fit to the square root-normalized biomass data collected in the field at North Inlet (Willmott’s index of agreement d = 0.74, RMSE = 223.38 g/m2, AICw = 0.3848). An acceptable model was not found among all models tested for PIE data, possibly because the sample size at PIE was too small, samples were collected over a limited vertical range, in a different season, and from areas with variable canopy architecture. For North Inlet, a model-derived landscape scale biomass map showed differences in biomass density among sites, years, and showed a robust relationship between elevation and biomass. The growth curve established in this study is particularly useful as an input for biogeomorphic models of marsh development. This study showed that, used in an appropriate model with calibration, Planet data are suitable for computing and mapping aboveground biomass at high resolution on a landscape scale, which is needed to better understand spatial and temporal trends in salt marsh primary production.

The vascular flora of Coastal Indian clam shell middens in South Carolina, U.S.A.

The vascular plant species of Native American clam shell middens were sampled during the 2009–2013 growing seasons. The 15 middens selected in this study include Sewee midden north of Charleston, 6 at Hobcaw Barony in North Inlet-Winyah Bay Natural Research Preserve in North Inlet, and a cluster of 8 middens at Murrells Inlet, South Carolina. The vascular flora consists of 129 species within 114 genera in 48 families. The Poaceae (30 species), Asteraceae (12 species), and Fabaceae (12 species) are the largest families. Sporobolus (5 species) and Cyperus (3 species) are the largest genera in the flora. Species diversity was highest at the Sewee midden, and at the large Allston House midden on private property at Murrells Inlet. All middens in this study border on, or are islands within, salt marshes. Soil salinity and tidal flooding influence the distribution of salt marsh vascular plant species at South Carolina tidal marsh clam shell middens.

Perspectives on a 30-Year Career of Salt Marsh Research

A hallmark of my career has been the development of a model of the responses of salt marsh vascular plants to changes in sea level. This discovery would not have been possible without long-term support from the National Science Foundation (NSF) Long-Term Ecological Research (LTER) and Long-Term Research in Environmental Biology (LTREB) programs. The LTER and LTREB programs have provided platforms for student research that would have been difficult or impossible to duplicate. Most of my students have benefited from the background of data, which stimulate a never-ending source of thesis topics and from the logistical support. My communication skills have been improved by LTER-sponsored workshops with journalists. I also have had an opportunity to share my enthusiasm for fieldwork with primary school students and teachers. Many of my numerous collaborations are consequences of novel, long-term data that emerged from research supported by the LTER and LTREB programs. There are important environmental trends that develop slowly in response to climate or that reveal themselves infrequently, such as disturbance responses, thresholds, and tipping points. These require long-term, place-based observation of the kind that the LTER and LTREB programs are designed to facilitate. My history with the LTER program began in the late 1970s. As a Yale graduate student working at The Ecosystems Center, Marine Biological Laboratory (MBL) at Woods Hole, I participated in a workshop organized by Dan Botkin to develop a rationale for a longterm ecological monitoring program (Botkin 1978). After a 2-year postdoctoral fellowship, I moved in 1981 to the University of South Carolina (USC), which had sponsored one of the first LTER sites, North Inlet (NIN). North Inlet was the perfect place for starting a research program in salt marsh ecology, and my research there eventually was supported by the NSF LTREB program. I owe a great deal to NSF for that. My early career benefited enormously from infrastructure at USC’s field laboratory and support by the NIN LTER program, which I did not fully appreciate at the time.