Comparing ecosystem engineering efficiency of two plant species with contrasting growth strategies

Abstract

Abstract. Many ecosystems are greatly affected by ecosystem engineering, such as coastal salt marshes, where macrophytes trap sediment by reducing hydrodynamic energy. Nevertheless, little is known about the costs and benefits that are imposed on engineering species by the traits that underlie their ecosystem engineering capacity. We addressed this topic by comparing ecosystem engineering efficiency defined as the benefit-cost ratio per unit of biomass investment for two species from the intertidal habitat: the stiff grass Spartina anglica and the flexible grass Puccinellia maritima. These species were selected for their ability to modify their habitat by trapping large quantities of sediment despite their contrasting growth form. On a biomass basis, dissipation of hydrodynamic energy from waves (a proxy for benefits associated with ecosystem engineering capability as it relates to the sediment trapping capability) was strikingly similar for both salt marsh species, indicating that both species are equally effective in modifying their habitat. The drag forces per unit biomass (a proxy for costs associated with ecosystem engineering ability as it relates to the requirements on tissue construction and shoot anchoring to prevent breaking and/or washing away) were slightly higher in the species with flexible shoots. As a result, stiff Spartina vegetation had slightly higher ecosystem engineering efficiency, due to lower engineering costs rather than to a higher engineering effect. Thus, Spartina is a slightly more efficient rather than a more effective ecosystem engineer. Ecosystem engineering efficiency was found to be a species-specific characteristic, independent of vegetation density and relatively constant in space. Analyzing ecosystem engineering by quantifying trade-offs offers a useful way toward developing a better understanding of different engineering strategies.

Global urban signatures of phenotypic change in animal and plant populations

“…Seed dispersers have a significant impact on plant diversity and their functional roles in urban ecosystems. A great diversity of organisms modify the physical structure of estuarine and coastal environments, particularly dune and marsh plants, mangroves, seagrasses, kelps, and infauna (50). Evolution in ecosystem-engineering traits has potential functional impacts on maintaining the stability and resilience (e.g., flood control) of coastal cities and the capacity of cities to adapt to climate change.…”

Wave attenuation by submerged vegetation: combining the effect of organism traits and tidal current

“…This approach assumes linear wave dissipation along the patch. Previous studies have shown that the relationship between wave dissipation and distance into a vegetated area is non-linear (Möller et al 1999, Koch et al 2009, Bouma et al 2010. However, linearity is a valid simplification when studying flexible vegetation with relatively small wave-attenuating capacity over short distances (Fonseca & Cahalan 1992, Bouma et al 2005.…”

“…However, an effect of stiffness was not found when comparing a mimic showing cantilever motion to rigid structures (Augustin et al 2009). When comparing wave attenuation over stiff Spar tina anglica and flexible Puccinellia maritima marsh vegetation, Bouma et al (2010) observed that differences in wave attenuation between flexible and stiff vegetation disappear on a biomass basis, meaning that an increased shoot density can counteract the reduced wave-attenuating capacity of flexible plants. While previous studies have indicated that stiffness can play a role in wave attenuation by vegetation, most studies have been carried out on vegetation types other than seagrass (i.e.…”

“…ratio of water depth to vegetation height) as important factors in wave attenuation. However, a more systematic analysis of the effects that these traits have on wave attenuation is needed to understand how submerged vegetation like seagrass affects wave height (Bouma et al 2010) and to be able to ac count for seagrass in coastal design (Fonseca & Cahalan 1992). Within the existing studies on wave attenuation by vegetation, the effect of tidal currents is generally neglected, although a few studies have indicated that the presence of currents may be an important modifier on the wave-attenuating capacity of the plants.…”

Flume instrumentation for measurement of drag on flexible elements under waves

“…The bulk drag characterization requires the establishment of an obstruction field. This method can be cumbersome and the results cannot be translated over to other species easily (Bouma et al 2010), and needs to be performed on each species or plant morphology (USACE 2006). Even within a single species, the seasonal changes in plant foliage influence the bulk canopy drag (Schoneboom and Aberle 2009), so testing at several different stages of growth is needed to fully characterize some species (Paul and Amos 2011).…”