Elymus athericus encroachment in Wadden Sea salt marshes is driven by surface elevation change

Abstract

Questions What are the main drivers of vegetation succession and the encroachment of Elymus athericus (Link) Kerguélen in ungrazed Wadden Sea salt marshes? Is (a) elevation, a proxy for tidal inundation and thus abiotic conditions, limiting the expanse of Elymus. Does sedimentation increase the spread of Elymus by (b) leading to surface elevation change or does it (c) add nitrogen and thereby allows Elymus to grow in lower elevation? Location Salt marsh at Sönke‐Nissen‐Koog, Wadden Sea National Park Schleswig‐Holstein, Germany. Methods The experiment was established in 2007 in the high marsh and consisted of four blocks of 12 m × 8 m. The blocks differed in surface elevation change during the experiment. Each block was subdivided into 24 plots of 1 m × 1 m. The original elevation of all plots in relation to the German ordnance datum (NHN) was assessed at the start of the experiment. Plots within the blocks were randomly assigned to one of the three N fertilization treatments. Within each plot we planted five randomly chosen individuals of Elymus. After four years of treatment, the vegetation composition and cover were recorded in all plots and aboveground biomass was collected. Results Original elevation was found to be a main driver of succession favouring Elymus and other late‐successional plants. There was no effect of N fertilization, but a positive effect of surface elevation change on Elymus cover was detected. Conclusions We can conclude that the positive effect of surface elevation change on Elymus is based on the resulting higher elevation and more favourable abiotic conditions caused by sedimentation, but not by the addition of nitrogen with the freshly deposited sediment. This case, therefore, is an example for an ecosystem in which encroachment is driven by a natural factor, rather than anthropogenic eutrophication.

Salt Marsh Elevation Drives Root Microbial Composition of the Native Invasive Grass Elytrigia atherica

“…For instance, nitrogen is often the limiting soil nutrients restraining plant growth in saline environments [ 74 ], as plants also use nitrogen to increase salt tolerance by synthetizing nitrogen compounds [ 14 ]. In this context, interaction with microbes could contribute to nitrogen acquisition, as demonstrated by the higher abundance of taxa with the potential ability to fix atmospheric nitrogen in the endosphere of ecotypes from HE, which showed lower soil nitrogen content, especially in 53-year-old sites [ 75 ].…”

New tools for old problems — comparing drone- and field-based assessments of a problematic plant species

“…It is a typical species of the high saltmarsh. Its establishment is facilitated by natural sedimentation processes (Nolte et al 2019 ). It was observed that E .…”

“…athericus is able to partially invade the low marsh overgrowing smaller species (Bakker et al 2009 ). When grazing is abandoned or reduced, the species becomes dominant (Nolte et al 2019 , Bakker et al 2020 ) and then negatively affects species diversity of plants (Wanner et al 2014 ) or halophilic spiders (Pétillon et al 2005 ) and reduces the habitat suitability for certain breeding birds (Mandema et al 2015 ). Nevertheless, long-term abandoned saltmarshes with high dominance of E .…”

Phragmites australis meets Suaeda salsa on the “red beach”: Effects of an ecosystem engineer on salt-marsh litter decomposition

“…Encroachments of new species into ecosystems, which lead to dramatic changes in vegetation composition, might have significant consequences for ecosystem functions (Hibbard et al, 2001;Archer et al, 2017;Nolte et al, 2019). In particular, new species encroachments might affect the quality and quantity of primary and secondary production, decomposition and nutrient cycling, and the pools and flows of materials (Eldridge et al, 2011;Friedrich et al, 2011;Zhou et al, 2018).…”

“…nitrogen fixation by Myrica faya changing the nutrient status of entire islands on Hawaii (Vitousek, 1990). The consequences of new species encroachments have been widely described in many kinds of terrestrial ecosystems (Schlesinger et al, 1990;McLaren et al, 2017;Zhou et al, 2018), mainly focusing on woody plant species (Hibbard et al, 2001), but the consequences of non-woody-plant species encroachments have seldom been tested especially in coastal wetlands (but see Nolte et al, 2019).…”