Relationship of Salt Marsh Vegetation Zonation to Spatial Patterns in Soil Moisture, Salinity, and Topography |
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Authors: | Kevan B Moffett David A Robinson Steven M Gorelick |
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Institution: | 1. Department of Environmental Earth System Science, Stanford University, Stanford, California, 94305, USA 2. Centre for Ecology and Hydrology, Environment Centre Wales, Bangor, Gwynedd, LL57 2UW, UK
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Abstract: | An intertidal San Francisco Bay salt marsh was used to study the spatial relationships between vegetation patterns and hydrologic
and edaphic variables. Multiple abiotic variables were represented by six metrics: elevation, distance to major tidal channels
and to the nearest channel of any size, edaphic conditions during dry and wet circumstances, and the magnitude of tidally
induced changes in soil saturation and salinity. A new approach, quantitative differential electromagnetic induction (Q-DEMI),
was developed to obtain the last metric. The approach converts the difference in soil electrical conductivity (ECa) between
dry and wet conditions to quantitative maps of tidally induced changes in root zone soil water content and salinity. The result
is a spatially exhaustive map of edaphic changes throughout the mapped area of the ecosystem. Spatially distributed data on
the six metrics were used to explore two hypotheses: (1) multiple abiotic variables relevant to vegetation zonation each exhibit
different, uncorrelated, spatial patterns throughout an intertidal salt marsh; (2) vegetation zones and habitats of individual
plant species are uniquely characterized by different combinations of key metrics. The first hypothesis was supported by observed,
uncorrelated spatial variability in the metrics. The second hypothesis was supported by binary logistic regression models
that identified key vegetation zone and species habitat characteristics from among the six metrics. Based on results from
108 models, the Q-DEMI map of saturation and salinity change was the most useful metric of those tested for distinguishing
different vegetation zones and plant species habitats in the salt marsh. |
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