PARENT SESSION
Oral Session # 8: Plant Ecology I: Physiology and Function I.
Presiding: E Hamerlynck
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.
Linking shoot stiffness to capacity for ecosystem-engineering and facilitation: Effects on wave attenuation and drag.
Bouma, Tjeerd*,1, De Vries, Mindert2, Low, Elinor1, Herman, Peter1, Tanczos, Ilka2, Peralta, Gloria1, 1 Netherlands Institute of Ecology (NIOO), Yerseke, The Netherlands2 Delft Hydraulics, Delft, The Netherlands
ABSTRACT- Wave attenuation by salt marsh vegetation plays an important role in coastal protection. Wave attenuation is also important for ecosystem engineering by sediment trapping and facilitation by offering shelter from hydrodynamic forces, which are both important structuring mechanisms in the stressful environment of salt marshes. The pioneer zone of salt marshes in the SW Netherlands is dominated by Spartina anglica and Zostera noltii. The remarkable contrast in shoot stiffness between these species suggests that this plant trait is an important factor in coping with hydrodynamic stresses. The objective of our study was to identify how shoot stiffness affects (1) the capacity of a plant species to act as ecosystem engineer and facilitator by attenuating wave energy and (2) the demands on plant structures in withstanding drag. In a flume, we mimicked the hydrodynamic conditions typical for estuarine marshes in the Schelde estuary. Wave attenuation and drag was quantified for different densities of Spartina plants, Zostera plants, and plant mimics with variable stiffness but identical morphology. Our results show that wave energy decreases linearly with a logarithmic increase of the number of plant structures. The dissipation of wave energy was a magnitude higher in vegetations with stiff shoots than those with flexible shoots, making stiff plants superior ecosystem engineers and facilitators. However, the costs associated to having such stiff shoots is related to withstanding drag, as drag increases strongly with increasing shoot stiffness. Present results clearly demonstrate how the physical properties of stiff Spartina plants and flexible Zostera plants fit well to their differences in physiology and habitat requirements. The general relationships that were obtained from these experiments are subsequently used to indicate the effectiveness of different vegetation types for coastal protection against waves.
Key words: facilitation, ecosystem-engineer, waves, drag