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Title Serious declines in a large area of Georgia Salt marsh plant biomass are linked to climate variables
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In initial work, we studied aboveground biomass dynamics and spatial patterns of Spartina alterniflora, the keystone species of Central Georgia's salt marshes. Geospatial techniques were used to scale up in situ biomass measurements to landscape scale and applied to 290 Landsat 5 TM scenes from 1984 to 2011. We documented biomass declines of 31.6 %, 33.4 %, and 38.7% for tall, medium, and short Spartina classes. The declines strongly correlated with increased drought frequency and severity and coincided with marsh die-back events and increased snail grazing. To explain temporal patterns, we compared biomass estimates with a suite of abiotic drivers. River discharge, total precipitation, Palmer Drought Severity Index, and mean sea level best explained biomass variations. We then extended our analysis to a much larger area (620 km2; St. Simons Sound to the Savannah River) and found the same inter and intra-annual biomass patterns. Moreover, higher biomass was associated with proximity to larger rivers (Altamaha, Ogeechee, and Savannah) and greater precipitation. In 2001, after an extended and severe drought, there was little net growth between late winter and fall and many marsh areas had net biomass loss. We're now using Landsat 7 and 8 imagery to update our analysis to the present time. Collectively, these approaches address a key question: Are the serious declines we documented in Spartina alterniflora biomass and marsh health cyclical, or are they longer-term, directional trends related to climate change?

Contributors J.P. O'Donnell, John F. Schalles and Christine M. Hladik

O'Donnell, J., Schalles, J.F. and Hladik, C.M. 2017. Presentation: Serious declines in a large area of Georgia Salt marsh plant biomass are linked to climate variables. Collaborating across geographic scales: integrating estuarine and coastal ocean information. Coastal and Estuarine Research Federation Biennial Meeting, November 9, 2017, Providence, Rhode Island.

Key Words climate drivers, plant biomass, remote sensing, Spartina alterniflora, Student Publication
File Date 2017
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This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959, OCE-1237140 and OCE-1832178. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.