Shoots of young cordgrass plants prefer some personal space

Clea N. van de Ven, Valérie C. Reijers, Carlijn Lammers, Jim van Belzen, Yeyeong Chung, Tjeerd J. Bouma, Tjisse van der Heide

This is a plain language summary of a Functional Ecology research article which can be found here.

Coastal vegetated landscapes such as dunes, seagrass meadows, and salt marshes are shaped by clonal grasses that improve their own growing conditions by capturing and stabilizing sediment particles with their dense canopies. However, especially in aquatic environments, their ability to stabilize their environment depends on the patch size of the clonally expanding grasses—the larger the patch, the more effective water flow attenuation and particle trapping becomes. Moreover, below a certain minimum patch size, young plants risk dislodgement as drag and turbulence around individual shoots results in sediment erosion rather than accumulation. Consequently, establishing plants need to surpass a size-threshold before their habitat engineering via particle trapping kicks in. This complicates the establishment of young plants.

Seaward edge of a salt marsh during low tide. Plant traits such as shoot organisation interact with sediment and flow velocity to build the landscape (credit: C. van de Ven)

Establishing common cordgrass plants across European marshes show a clustered shoot pattern. Shoot clustering minimizes erosion and helps young plants to reduce physical stress (credit: C. van de Ven)

To explore how clonally expanding salt marsh-building plants survive the first critical establishment phase, we investigated how common cordgrass (Spartina anglica) spatially organizes its shoots. Results from a survey across 18 different European salt marshes showed establishing plants always follow a clustered shoot organization, regardless of environmental conditions. Next, we showed with a follow-up experiment that this shoot organisation reduces erosion around the plant, compared to a strategy in which the plant would start to immediately form the dense aggregations observed in large, already established patches.

Our results highlighted that young plants initially follow a shoot organization that avoids physical stress by minimizing their engineering effect, instead of aiming to immediately try to modify the environment to their own benefit. This helps us understand how characteristics of landscape-forming plants interact with their environment to shape the landscape and may better inform restoration efforts on salt marshes.  

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