Can community structure track sea‐level rise? Stress and competitive controls in tidal wetlands

Abstract

Climate change impacts, such as accelerated sea‐level rise, will affect stress gradients, yet impacts on competition/stress tolerance trade‐offs and shifts in distributions are unclear. Ecosystems with strong stress gradients, such as estuaries, allow for space‐for‐time substitutions of stress factors and can give insight into future climate‐related shifts in both resource and nonresource stresses. We tested the stress gradient hypothesis and examined the effect of increased inundation stress and biotic interactions on growth and survival of two congeneric wetland sedges, Schoenoplectus acutus and Schoenoplectus americanus. We simulated sea‐level rise across existing marsh elevations and those not currently found to reflect potential future sea‐level rise conditions in two tidal wetlands differing in salinity. Plants were grown individually and together at five tidal elevations, the lowest simulating an 80‐cm increase in sea level, and harvested to assess differences in biomass after one growing season. Inundation time, salinity, sulfides, and redox potential were measured concurrently. As predicted, increasing inundation reduced biomass of the species commonly found at higher marsh elevations, with little effect on the species found along channel margins. The presence of neighbors reduced total biomass of both species, particularly at the highest elevation; facilitation did not occur at any elevation. Contrary to predictions, we documented the competitive superiority of the stress tolerator under increased inundation, which was not predicted by the stress gradient hypothesis. Multifactor manipulation experiments addressing plant response to accelerated climate change are integral to creating a more realistic, valuable, and needed assessment of potential ecosystem response. Our results point to the important and unpredicted synergies between physical stressors, which are predicted to increase in intensity with climate change, and competitive forces on biomass as stresses increase.

Environmental Controls, Emergent Scaling, and Predictions of Greenhouse Gas (GHG) Fluxes in Coastal Salt Marshes

“…Based on the IPCC scenarios for sea level rise (SLR), salinity was anticipated to increase from the 2013 baseline by 10% in 2050 and 21% in 2080. This assumption of increasing salinity with SLR in estuarine ecosystems is supported by previous studies (Cloern et al, ; Hilton et al, ; Morris, ; Schile et al, ). Although sediment accretion and increased belowground biomass may significantly compensate the rising level (Cherry et al, ; Morris et al, ; Schile et al, ), tidal wetlands are expected to experience a net loss in relative elevation (Schile et al, ).…”

El Niño Increases High‐Tide Flooding in Tidal Wetlands Along the U.S. Pacific Coast

“…The additional flooding we documented throughout the 2015–2016 El Niño relative to ENSO‐neutral conditions could have a range of potential ecological impacts to tidal wetland function and services but has largely been understudied. In general, the productivity of tidal marsh vegetation is strongly affected by differences in inundation duration (Janousek et al, ; Langley et al, ; Schile et al, ), with some common high marsh species such as perennial pickleweed ( Salicornia pacifica ) showing declines in productivity with even modest increases in flooding levels (Janousek et al, ) or changes in soil saturation (Schile et al, ). Other west coast plant species that are generally restricted to high marshes with infrequent flooding could be heavily impacted by the increased inundation associated with El Niño (Kuhn & Zedler, ).…”

Towards Salt Marsh Harvest Mouse Recovery: A Review

“…Understanding of SMHM habitat use is continuously evolving, and will likely continue to do so, especially if relationships among salinity, inundation, and vegetation change. The combined effect of increased inundation and salinity, as projected under most climate scenarios, can reduce plant height and the structure of the salt marsh-dominant pickleweed (Woo and Takekawa 2012), compromise the competitive ability of stress-sensitive plant species and communities (Schile et al 2017), and lead to shifts in plant communities where salt-tolerant plants replace salt-intolerant plants at low elevations (Watson and Byrne 2012). Earlier research found that shorter vegetation and more extreme tidal ranges of marshes in the south bay may make these less suitable for SMHM (Schaub 1971;Cummings 1975;Gilroy and Shellhammer 1980;Figure 4).…”

“…Beyond these limited observations, essentially nothing is known of SMHM diet in the wild, and diet is not addressed in depth in the 2013 Recovery Plan or status review, although it is presumed to be dominated by pickleweed (USFWS 2010(USFWS , 2013. Impacts associated with climate change, such as sea-level rise and increased salinity, could alter vegetative assemblages throughout the range of the species (Watson and Byrne 2012;Schile et al 2017) and result in substantial habitat loss (Thorne et al 2018). Without a baseline understanding of SMHM diet, managers lack the information needed to protect habitat that provides a rich food base, or to design habitat enhancements and restorations for food production that are resilient to these sorts of impacts.…”