Facilitation shifts paradigms and can amplify coastal restoration efforts

Abstract

Restoration has been elevated as an important strategy to reverse the decline of coastal wetlands worldwide. Current practice in restoration science emphasizes minimizing competition between outplanted propagules to maximize planting success. This paradigm persists despite the fact that foundational theory in ecology demonstrates that positive species interactions are key to organism success under high physical stress, such as recolonization of bare substrate. As evidence of how entrenched this restoration paradigm is, our survey of 25 restoration organizations in 14 states in the United States revealed that >95% of these agencies assume minimizing negative interactions (i.e., competition) between outplants will maximize propagule growth. Restoration experiments in both Western and Eastern Atlantic salt marshes demonstrate, however, that a simple change in planting configuration (placing propagules next to, rather than at a distance from, each other) results in harnessing facilitation and increased yields by 107% on average. Thus, small adjustments in restoration design may catalyze untapped positive species interactions, resulting in significantly higher restoration success with no added cost. As positive interactions between organisms commonly occur in coastal ecosystems (especially in more physically stressful areas like uncolonized substrate) and conservation resources are limited, transformation of the coastal restoration paradigm to incorporate facilitation theory may enhance conservation efforts, shoreline defense, and provisioning of ecosystem services such as fisheries production.shoreline defense | facilitation | coastal wetlands | wetland restoration D egradation of coastal ecosystems is occurring worldwide (1).Human-generated threats such as overharvesting, eutrophication, climate change, habitat destruction, and pollution have threatened these valuable ecosystems at local, regional and global scales (2-6). As these threats have intensified and combined, substantial declines in overall habitat coverage have occurred in almost all major coastal ecosystems, including those generated by key habitat-forming foundation species. For example, oyster reefs have declined by at least ∼85% (7), coral reefs by ∼19% (8), seagrasses by ∼29% (9), North American salt marshes by ∼42% (10), and mangroves by ∼35% (1). Because these ecosystems generate some of the richest biodiversity hotspots on Earth (11, 12), and provide critical services for human populations, including storm protection (13), fisheries production (2, 14, 15), and carbon storage (16, 17), conservation resources totaling over 1 billion US dollars have been spent globally in an attempt to halt and reverse the decline of foundation species in the coastal realm (18,19).A number of strategies have been used to conserve coastal ecosystems, including threat reduction, marine protected areas, buffer establishment, and international treaties. Habitat restoration, although in existence for many decades, has only recently been elevated as a global strategy for ...

Fertilizer legacies meet saltwater incursion: challenges and constraints for coastal plain wetland restoration

“…Wetland restoration is becoming an important tool to counteract coastal degradation and enhance the provision of ecosystem services (Silliman et al, 2015). Restored wetlands can ameliorate nutrient runoff to sensitive coastal ecosystems (Zedler, 2003), and wetland restoration efforts are increasingly being used to mitigate or adapt to sealevel rise and increased frequency of severe storms (Jones et al, 2012;Temmerman et al, 2013).…”

Phylogenetic relatedness, ecological strategy, and stress determine interspecific interactions within a salt marsh community

“…For example, the interactions between C. chinense and S. salsa support the SGH at medium and high salinities but not at the low salinity treatment. Therefore, future experiments incorporating more salinity increments over a more narrow salinity range, as suggested by Silliman et al (2015), may be more informative when testing the SGH. Previous studies have classified the ecological strategies of species as either competitive or stress-tolerant because of the general belief that there is a trade-off between competitive ability and stress tolerance (Crain et al 2004;Liancourt et al 2005).…”

“…The stress gradient hypothesis (SGH) states that the frequency or intensity of facilitative and competitive interactions between species is inversely related to abiotic or biotic stress levels (Bertness and Callaway 1994;He et al 2013;Lortie and Callaway 2006;Silliman et al 2015). This influence of stress on interspecific interactions is thought to be due to mitigation of the stress effects by stress-tolerant species within the community, which enhances the fitness of neighboring species.…”

Phylogenetic Relatedness Influences Plant Interspecific Interactions Across Stress Levels in Coastal Ecosystems: a Meta-Analysis

“…Planting distantly related species can promote growth of the protected species, following the theory of using facilitation in restoration (Halpern et al 2007;Silliman et al 2015;Zhang and Shao 2013). Therefore, regardless of stress levels within the managed ecosystem, the positive effects of neighboring distantly related species on target species should be considered.…”