Extreme salinity fluctuations and invasion by <i>Phragmites australis</i> in wetland ecosystems
Creators: name: Waryszak, Pawel
name: Birnbaum, Christina
name: Farrer, Emily
Publisher: name: F1000 Research Limited
Year: 2018

description: Background/Question/Methods<br><br>Ongoing climate change is producing extreme weather events that are likely to modify local ecosystems. For example, increased hurricane intensity combined with sea level rise is expected to have a deleterious effect on coastal plant communities, which in turn causes an increase in wave energy and land loss. Coastal land loss rate equates to about 56km<sup>2</sup> per year in Louisiana alone. Plants play pivotal role in stabilizing wetlands ecosystems and yet understanding of what specific environmental and biological factors are facilitating invasion of alien plants species and support native wetland plant communities is often missing. We focus on the model invasive plant, <i>Phragmites australis</i>, to understand what drives plant invasion in Gulf Coast and what its long-term effect on native plant communities is. Using long-term environmental data (314 sites, over 2009–2016 period) from Coastal Protection and Restoration Authority (CRMS) in Louisiana, we sought to answer the following questions: 1) What is the interannual variability in water salinity and water table level on Louisiana coast? 2) How does the variability in water salinity and water table affect local plant communities and occurrence of <i>P. australis</i>? 3) How does the presence of <i>P. australis</i> affect local plant communities?<br><br><br> Results/Conclusions*<br><br>Mean surface water salinity in Louisiana coastal communities showed a slight decline and water table increased over 2009–2016. Variability in salinity in research sites ranged from a 94.2% decrease to a 113% increase compared to the previous year, while variability in water table ranged from 4458% decrease to 2657% increase. Despite negative association with mean salinity, invasive <i>P. australis</i> was most likely to occur in intermediate wetland communities that recorded the broadest oscillations in mean water salinity (0.171–30.7 PPT) and mean water table (-37.2–35.2 cm). Similarly, presence of <i>P. australis</i> showed the highest impact on plant composition in intermediate communities explaining 7.6 % of variation (P &lt; 0.01). The observed extreme fluctuations in salinity and water table may destabilize local plant communities and open an invasion window for non-native plants such as <i>P. australis</i>. <i>P australis</i> likely performs well in areas of variable, especially high, water levels because of its adaptive traits for inundation and anaerobic conditions (<i>e.g.</i>, aerenchyma). Looking to the future, if variability in water tables and salinity continues to rise, this invasive plant may be well-suited to these anthropogenic conditions and may actually help to stabilize marshes and prevent land loss.<br><br><br><sub>  *<i>The above abstract describes the results of the initial study that focused on Phragmites australis. This study was broadened to encompass all alien and native plant communities in Louisiana wetland ecosystems (see also here). The results of the broader analysis were presented at the 103<sup>rd</sup> Ecological Society of America (ESA) Annual Meeting 2018 under modified title: “Direct and indirect effects of climate change on plant communities (alien &amp; native).</i></sub>