Below-ground biomass of plants, with a key contribution of buried shoots, increases foredune resistance to wave swash

Abstract

Background and aims Sand dunes reduce the impact of storms on shorelines and human infrastructure. The ability of these ecosystems to provide sustained coastal protection under persistent wave attack depends on their resistance to erosion. Although flume experiments show that roots of perennial plants contribute to foredune stabilization, the role of other plant organs, and of annual species, remains poorly studied. Furthermore, it remains unknown if restored foredunes provide the same level of erosion resistance as natural foredunes. We investigated the capacity of three widespread pioneer foredune species (the perennial Ammophila arenaria and the annuals Cakile maritima and Salsola kali) to resist dune erosion, and compared the erosion resistance of Ammophila at natural and restored sites. Methods Cores collected in the field were tested in a flume that simulated a wave swash. A multi-model inference approach was used to disentangle the contributions of different below-ground compartments (i.e. roots, rhizomes, buried shoots) to erosion resistance. Key Results All three species reduced erosion, with Ammophila having the strongest effect (36 % erosion reduction versus unvegetated cores). Total below-ground biomass (roots, rhizomes and shoots), rather than any single compartment, most parsimoniously explained erosion resistance. Further analysis revealed that buried shoots had the clearest individual contribution. Despite similar levels of total below-ground biomass, coarser sediment reduced erosion resistance of Ammophila cores from the restored site relative to the natural site. Conclusions The total below-ground biomass of both annual and perennial plants, including roots, rhizomes and buried shoots, reduced dune erosion under a swash regime. Notably, we show that (1) annual pioneer species offer erosion protection, (2) buried shoots are an important plant component in driving sediment stabilization, and (3) management must consider both biological (plants and their traits) and physical (grain size) factors when integrating dunes into schemes for coastal protection.

Sediment availability provokes a shift from Brownian to Lévy‐like clonal expansion in a dune building grass

“…Previous studies have demonstrated that the engineering ability of species can be related to its species‐specific expansion strategy (Hacker et al ., 2012; Bouma et al ., 2013; Schwarz et al ., 2018; Mullins et al ., 2019; Reijers et al ., 2019b). However, so far in the field of ecosystem‐engineering and biogeomorphology, engineering traits have been mostly considered as invariant properties of species, even though intraspecific variability and environment‐dependent trait expression can have far‐reaching consequences for ecosystem dynamics and functioning (Hughes & Stachowicz 2004, de Battisti et al 2020). Here we investigated how environmental conditions impact the expansion strategy of a dune building grass.…”

“…We expect different clonal expansion strategies to be advantageous in different environmental settings. In physically challenging environments a tight shoot clumping – indicative of Brownian‐like expansion (Reijers et al ., 2019b) – may enhance engineering strength and protect plants against hydrodynamic forcing or alleviate local anoxia stress (Silliman et al ., 2015; Maximiliano‐Cordova et al ., 2019; Reijers et al ., 2019c; de Battisti and Griffin, 2020). However, in more benign environments a Brownian‐like pattern may hamper plant expansion and local nutrient limitations may restrict growth potential (Fischman et al ., 2019).…”

Spatial Variation in Coastal Dune Evolution in a High Tidal Range Environment

“…Equally, dependent on dune morphology, offshore winds can move sediment from the dune to the backshore and intertidal [13,14], renourishing the intertidal beach. Dune vegetation helps to trap dune directed aeolian sediment supply [15,16] and also stabilizes the dune from erosion by wind [17] and waves [18]. Waves are typically considered from an erosive perspective in relation to dune systems e.g., [19][20][21][22][23][24][25]; however, there is a recognition that wave-driven onshore transport can provide sediment reservoirs that subsequently can nourish dunes through aeolian transport [26][27][28].…”

The resilience of coastal ecosystems: A functional trait‐based perspective

“…For instance, field observations showed that mangrove forests can reduce shore erosion up to 15 times in comparison with unvegetated shores (Sánchez‐Núñez et al, 2019), while seagrass meadows can reduce the wave height reaching the shore up to 50% (Infantes et al, 2012). Similarly, flume studies (a flume is a laboratory facility that allows to generate waves and/or water currents of desired intensity) in salt marshes and sand dunes demonstrated that vegetation can reduce erosion rate up to 80% (Lo et al., 2017) and 36% (De Battisti & Griffin, 2019) respectively. Therefore, understanding the mechanisms by which vegetation ensures sediment stability is crucial for gaining insights on the resilience of coastal ecosystems.…”

“…Regarding sediment stability, studies have found that two main factors drive sediment erosion and they act antagonistically: sediment grain size and vegetation root biomass (De Battisti et al., 2019; Lo et al., 2017). Sand content can strongly influence erosion rates (De Battisti et al., 2019; De Battisti & Griffin, 2019; Feagin, 2009) because sand (i.e. big grain size) erodes much easier than clay (i.e.…”