Shoreline restoration including armor removal and log placement affect ecosystem recovery through time

Abstract

The impacts of individual restoration activities, such as the total area covered and specific actions taken, can be difficult to measure because they are typically not performed randomly or independently. In Puget Sound, Washington, United States, removal of hard armor is a primary shoreline restoration measure. The length of armor removed from a beach and additional restoration actions implemented can vary considerably. As such, it is challenging to attribute specific ecological responses to particular actions. We use an extensive collection of sites regularly monitored pre‐ and post‐restoration to explore the success of different extents of armor removal and three supplemental “living shoreline” restoration actions: native vegetation planting, log placement, and sediment supplementation (“nourishment”). We measured five ecological response variables: sediments (percent surface, subsurface gravel), beach logs (count, line width), beach wrack (percent cover, depth), riparian vegetation (percent cover of supratidal, backshore), and supratidal invertebrates (density, richness). Only beach logs were affected by the length of armor removed, whereas wrack increased regardless of length. Invertebrate abundance increased through time only when supplemental vegetation planting did not occur. Placement of logs post armor removal was an impactful supplemental restoration strategy, positively affecting not only the further accumulation of logs, but also the amount of wrack and gravel sediments. Sediment nourishment only affected the proportion of subsurface gravel, which decreased through time in nourished sites. We stress the importance of the thorough monitoring of the ecological effects of living shoreline restoration actions to better understand their role in ecosystem recovery through time.