Extreme Precipitation and Flooding Contribute to Sudden Vegetation Dieback in a Coastal Salt Marsh.

Tiffany C Lane,Jena A Moon,Camille Lafosse Stagg,Claudia Laurenzano,Stephen B Hartley,Michael J Osland,William R Jones,Laura C Feher

doi:10.3390/plants10091841

Abstract

Climate extremes are becoming more frequent with global climate change and have the potential to cause major ecological regime shifts. Along the northern Gulf of Mexico, a coastal wetland in Texas suffered sudden vegetation dieback following an extreme precipitation and flooding event associated with Hurricane Harvey in 2017. Historical salt marsh dieback events have been linked to climate extremes, such as extreme drought. However, to our knowledge, this is the first example of extreme precipitation and flooding leading to mass mortality of the salt marsh foundation species, Spartina alterniflora. Here, we investigated the relationships between baseline climate conditions, extreme climate conditions, and large-scale plant mortality to provide an indicator of ecosystem vulnerability to extreme precipitation events. We identified plant zonal boundaries along an elevation gradient with plant species tolerant of hypersaline conditions, including succulents and graminoids, at higher elevations, and flood-tolerant species, including S. alterniflora, at lower elevations. We quantified a flooding threshold for wetland collapse under baseline conditions characterized by incremental increases in flooding (i.e., sea level rise). We proposed that the sudden widespread dieback of S. alterniflora following Hurricane Harvey was the result of extreme precipitation and flooding that exceeded this threshold for S. alterniflora survival. Indeed, S. alterniflora dieback occurred at elevations above the wetland collapse threshold, illustrating a heightened vulnerability to flooding that could not be predicted from baseline climate conditions. Moreover, the spatial pattern of vegetation dieback indicated that underlying stressors may have also increased susceptibility to dieback in some S. alterniflora marshes.Collectively, our results highlight a new mechanism of sudden vegetation dieback in S. alterniflora marshes that is triggered by extreme precipitation and flooding. Furthermore, this work emphasizes the importance of considering interactions between multiple abiotic and biotic stressors that can lead to shifts in tolerance thresholds and incorporating climate extremes into climate vulnerability assessments to accurately characterize future climate threats.

Highlights

As Earth’s climate continues to change, life on our planet will be determined by higher temperatures [1] and rising sea levels [2], and by changes in the frequency and intensity of climatic events [3]
To provide an indicator of ecosystem vulnerability to climate extremes, we investigated the relationship between extreme abiotic conditions and large-scale plant mortality of a coastal wetland foundation species
The study was conducted in the San Bernard National Wildlife Refuge (NWR), which is located along the northern Gulf of Mexico, in the mid-coast region of Texas (Figure 1)

Summary

Introduction

As Earth’s climate continues to change, life on our planet will be determined by higher temperatures [1] and rising sea levels [2], and by changes in the frequency and intensity of climatic events [3]. Hurricanes are expected to become more extreme [5,6], moving more slowly, with faster winds [7] and heavier precipitation [8] These climate extremes threaten ecological communities [9,10] by lowering the resilience of foundation species [11], which, in the most extreme cases, can lead to ecological regime shifts or ecosystem collapse [12]. Extreme ecological responses, such as large-scale die-off of foundation species, have been linked to climate extremes around the world. Extreme climatic events, triggered by extreme hurricanes and drought, have led to the massive die-off of foundation species in coastal wetlands, including mangrove trees [14] and salt marsh grasses [15]

Methods

Results

Conclusion