Green beach vegetation dynamics explained by embryo dune development

Marinka E.B Van Puijenbroek,Robbert T Van Den Dool,Elske C Koppenaal,Christian Smit,Frank Berendse,Juul Limpens,Jan P Bakker

doi:10.1016/j.baae.2021.06.003

Marinka E.B Van Puijenbroek, Robbert T Van Den Dool + Show 5 more

Open Access

https://doi.org/10.1016/j.baae.2021.06.003

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Abstract

Sandy coastlines are dynamic environments with potential for biodiverse habitats, such as green beaches. Green beach vegetation can develop on nutrient-poor beaches landward from embryo dunes. It is characterised by low-dynamic coastal wetland habitat such as salt marshes and dune slacks. It has been hypothesised that the establishment of green beach vegetation is facilitated by the shelter provided by embryo dunes, however evidence is lacking.We explored the importance of geomorphology and soil conditions on the species richness and turnover of green beach vegetation over a time period of 10 years. We recorded 107 plots along 11 transects over a gradient from beach to dune on the island of Schiermonnikoog, the Netherlands. We characterised transect geomorphology at transect level and soil conditions and vegetation at plot level in 2006 and 2016.We found that the green beach vegetation was highly dynamic, total plant cover increased by 62% within 10 years. In 2006 beach width was an important factor in explaining species richness, with the highest number of species occurring on narrow beaches with a large volume of embryo dunes. In 2016, species richness was positively associated with the build-up of organic matter. Overall species richness declined relative to 2006 and was accompanied by an increase in elevation due to sand burial and the expansion of embryo dune volume.Our data suggests that geomorphology influenced the vegetation indirectly by affecting sand burial rate. Plant species richness declined less at sheltered conditions where sand burial was limited, allowing the build-up of organic matter. This indicates a time-dependent relationship between the development of embryo dunes and plant species richness: embryo dunes can be a source of shelter, thus increasing species richness, but can compete for space over time, lowering species richness again. Our results are relevant for engineering and management of biodiverse sandy shores.

Highlights

Sandy coastlines are dynamic environments with potential for rich biodiverse pioneer habitats, such as green beaches
We addressed the following questions: 1) how does beach geomorphology affect the abiotic soil conditions in the rooting zone, and can this relationship change over time? 2) Which abiotic soil conditions drive species composition and turn-over of biodiverse pioneer vegetation along a beach-dune gradient? We hypothesised that green beach vegetation would be positively associated with the presence and development of embryo dunes
The changes in beach morphology did not hamper embryo dune development, as embryo dune volume increased by 40.2§3.6 m3/m between 2006 and 2016

Summary

Introduction

Sandy coastlines are dynamic environments with potential for rich biodiverse pioneer habitats, such as green beaches. Green beaches form a transitional habitat between the beach, the dune system including dune slacks and salt marshes, containing a varying mix of species from all three habitats. Green beaches support more biodiversity than other coastal habitats (Speybroeck et al, 2008) and represent a high conservation value (Acosta, Carranza, & Izzi, 2009; de Groot, Janssen, et al, 2017; European Commission, 2007). Sandy coastlines are increasingly under pressure from recreation and measures aimed at improving flood safety. Safeguarding green beach habitats in the face of these competing demands requires in-depth knowledge about the spatial-temporal dynamics and environmental drivers necessary for their development and maintenance

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