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. 2016 Feb 12;6(6):1579-89.
doi: 10.1002/ece3.1904. eCollection 2016 Mar.

Vegetation as self-adaptive coastal protection: Reduction of current velocity and morphologic plasticity of a brackish marsh pioneer

Jana Carus  1 , Maike Paul  2 , Boris Schröder  3
Affiliations

Vegetation as self-adaptive coastal protection: Reduction of current velocity and morphologic plasticity of a brackish marsh pioneer

Jana Carus et al. Ecol Evol. .

Abstract

By reducing current velocity, tidal marsh vegetation can diminish storm surges and storm waves. Conversely, currents often exert high mechanical stresses onto the plants and hence affect vegetation structure and plant characteristics. In our study, we aim at analysing this interaction from both angles. On the one hand, we quantify the reduction of current velocity by Bolboschoenus maritimus, and on the other hand, we identify functional traits of B. maritimus' ramets along environmental gradients. Our results show that tidal marsh vegetation is able to buffer a large proportion of the flow velocity at currents under normal conditions. Cross-shore current velocity decreased with distance from the marsh edge and was reduced by more than 50% after 15 m of vegetation. We were furthermore able to show that plants growing at the marsh edge had a significantly larger diameter than plants from inside the vegetation. We found a positive correlation between plant thickness and cross-shore current which could provide an adaptive value in habitats with high mechanical stress. With the adapted morphology of plants growing at the highly exposed marsh edge, the entire vegetation belt is able to better resist the mechanical stress of high current velocities. This self-adaptive effect thus increases the ability of B. maritimus to grow and persist in the pioneer zone and may hence better contribute to ecosystem-based coastal protection by reducing current velocity.

Keywords: Adaptive value; Bolboschoenus maritimus; brackish marsh; flow velocity; mechanical pressure; morphological adaptation; phenotypic plasticity; pioneer zone.

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Figures

Figure 1
Figure 1
Location of the two study areas and position of the 16 transects in the Elbe estuary.
Figure 2
Figure 2
Scheme of the measurement locations. (A) Positioning of current measurements along the transect. (B) Top view of the installation design of ADV devices (black dot represents the measuring volume). (C) Side view of the installation design of ADV devices. Gray colouring indicates vegetated areas.
Figure 3
Figure 3
Normalized mean flow velocity at four distances from the marsh edge (d). The dashed line symbolizes the marsh edge. (A) and (B) Mean of measurements in April (white) and August (black) at the respective location. (C) and (D) Quantification of the effect of the vegetation on flow velocity (normalized flow velocity in August/normalized flow velocity in April). Continuous lines are the functions fitted to the data.
Figure 4
Figure 4
Running means of long‐shore flow velocity during one flood (30 min before until 30 min after high tide) in April (A) and August (B). Bin width for running mean: 1 min. Positive flow velocities represent downstream flow; negative velocities represent upstream flow respectively. Flow velocity in front of the vegetation is illustrated with a continuous black line. Vegetated plots are displayed in different shades of gray.
Figure 5
Figure 5
Running means of cross‐shore flow velocities during one flood (30 min before until 30 min after high tide) in April (A) and August (B). Bin width for running mean: 1 min. Positive flow velocities represent on‐shore flow; negative velocities represent off‐shore flow respectively. Flow velocity in front of the vegetation is illustrated with a continuous black line. Vegetated plots are displayed in different shades of gray.
Figure 6
Figure 6
(A) Comparison of ramet diameters at two different distances from the marsh edge (B) Prominent examples of ramets (above) and cross sections (below) from the marsh edge (left) and from inside the vegetation belt (right).
Figure 7
Figure 7
Correlation of mean cross‐shore flow velocity and stem diameter. Black dots represent the mean of measured values of stem diameter and flow velocity time series at each transect and the continuous line is the result of a linear regression. Dashed lines define the 95% confidence interval.
Figure 8
Figure 8
Correlation of stem diameter and breaking force and bending stiffness. Black and grey dots represent measured values and the respective lines are derived from linear regressions of the log‐transformed data.
Figure 9
Figure 9
Bending stiffness and breaking force of ramets in relation to distance from marsh edge. Ramets from the marsh edge and from inside the vegetation differ significantly in bending stiffness and breaking force.
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