Zonation of Salt-Marsh Plant Species in Mediterranean Climate: does salinity play a greater?


The predominant abiotic factor in salt marshes may vary with climate in mid-latitude temperate salt-marshes impacting varying species sustainability and overall zonation pattern based on tolerance adaption. The question being what are the driving forces behind species zonation in salt-marshes, are they limited to abiotic factors such as salinity or flooding and if so is there one that is more predominant than another? Or do biotic factors such as competition and facilitation play a predominant or supportive role in generating these observed patterns. Flooding is known as a major factor to influence distribution of plant species within salt-marsh communities. Salinity and competition however, may play the same if not more of role in distribution than just flooding.  In past studies, most of which were in salt-marshes of New England, the emergence of flooding to be a major factor on species distribution became the prevalent findings. Because the majority of these studies were within a single climactic habitat, the question is whether or not this is an overall occurrence in all salt-marshes. In a study conducted in a low-latitude habitat, salinity played a more major role (Penning et al. 2005). Can then latitude and or climate play another role in the mid latitude regions of salt marshes inhabiting Mediterranean climate where there is a lack of fresh water fluctuation? Therefore, is the paradigm scope insufficient due to the majority of studies being conducted in similar habitats not taking into account salt-marsh climate variety based on their location. Investigation of different habitats might provide a better picture of each mechanism involved in species distribution. Overall, this project is seeking to understand the role of climate variation as it impacts plant performance and interactions in plant community diversity and distribution patterns. My first objective is to determine if salinity is the predominant abiotic force in Mediterranean salt-marshes. My second being do biotic factors facilitate species establishment under these higher salinity conditions. Understanding if the roles of both salinity and biotic facilitation being a more prevalent mechanism in species zonation for salt-marshes in different climates may provide more insight thus shifting the current paradigm to be climate specific. The Mediterranean climate regions of California have a strong impact on habitats and the species found within them. The characteristics being warm wet winters, which very in rain intensity, and dry hot summers providing a limiting factor on what species can be successful in establishing themselves in these types of habitats. Salt-marshes located in the San Francisco Bay region experience this type of climate. Environmental pressures such as high evaporation rates, salinity, and the typical flooding of these marshes play a crucial role in what type of species can be successful and also provide a gradient of distribution. Lack of overall rainfall within this region also provides another pressure to salt-marsh species by exposing them to environments with higher concentration of salinity from lack of exposure to fresh water provided by rain…

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