|Title||Patterns of plant diversity in two salt marsh regions|
|Year of Publication||2006|
|Academic Department||M.S. Thesis|
|Number of Pages||70|
|University||University of Houston|
Although ecologists have been interested in explaining the diversity of ecological systems for many years, there is still no generally accepted theory to explain what determines diversity. Patterns of diversity are determined by which species are able to colonize a particular site and persist in a particular abiotic environment, and by biological interactions between species that may expand or contract their range across an abiotic gradient. By examining these patterns we can begin to understand which biotic and abiotic mechanisms are important for shaping the overall diversity of a system. I compared the salt marshes of Texas to those of Georgia to determine what differences in plant diversity patterns existed between these two systems with similar species pools and general abiotic environments. Both Gulf Coast and Atlantic Coast salt marshes are tidal systems and therefore plants must be tolerant to flooding, salinity, and anoxia. The major abiotic difference between the salt marshes of these two regions is the relatively irregular schedule and lower amplitude of tides in Texas. Tidal schedule and amplitude might affect plant distribution patterns by creating abiotic conditions that vary over time as much or more than over space, thereby altering competitive relationships between plant species.I quantified diversity patterns (richness and relative abundance) on transects across elevation at 59 salt marsh sites in Georgia and 49 sites in Texas. Diversity was measured at global, regional, site, and plot scales to consider processes occurring at all levels. Species pools were similar between regions. Texas had greater diversity at the site and plot scales, which was primarily due to processes occurring at the site level. The greater diversity of Texas was partially explained by the fact that Texas marshes had more middle marsh (a high diversity zone) and less low marsh (a low diversity zone) than Georgia marshes, and by the fact that most species were more widely distributed across the marsh landscape in Texas than in Georgia (i.e., zones were less discrete). Biomass data from a subset of plots and sites suggested that high diversity in Texas was not caused by lower productivity; instead, Texas marshes had greater standing biomass than Georgia marshes. Irregular flooding of Texas marshes might allow more species to exist in the marsh by making abiotic conditions more variable over time, thereby making the outcome of competitive interactions less predictable and rapid.This work suggests that Gulf Coast marshes may function differently in some ways than Atlantic Coast marshes. Managers of Gulf Coast marshes should not assume that paradigms based on the Atlantic Coast will automatically apply. In addition, because salt marsh diversity is determined by site-scale processes, protection efforts should focus on maintaining a range of different marsh types rather than simply maximizing the total marsh acreage protected in a region.