Review of the ecosystem service implications of mangrove encroachment into salt marshes

• Published in: Global change biology 2017-10, Vol.23 (10), p.3967-3983
• Main Authors: Kelleway, Jeffrey J., Cavanaugh, Kyle, Rogers, Kerrylee, Feller, Ilka C., Ens, Emilie, Doughty, Cheryl, Saintilan, Neil
• Format: Article
• Language: English
• Subjects: Bats; Bird watching; Birds; blue carbon; Capacity; Carbon capture and storage; Carbon sequestration; Climate; Climate Change; Coastal ecosystems; Coastal environments; Coastal management; coastal protection; cultural values; Ecosystem; Ecosystem services; Ecosystem structure; Ecosystems; Encroachment; Fauna; Fisheries; Foraging; Foraging habitats; Habitat availability; habitat function; Humans; Hunting; Livelihoods; mangrove expansion; Mangroves; Migratory birds; Migratory species; Mineral nutrients; Nutrient availability; nutrient cycling; Protection; Salinity; salt marsh; Salt marshes; Saltmarshes; Sea level; Sea level rise; Shrubs; Storms; Structure-function relationships; threatened species; Vegetation; Wetlands
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.13727

Salt marsh and mangrove have been recognized as being among the most valuable ecosystem types globally in terms of their supply of ecosystem services and support for human livelihoods. These coastal ecosystems are also susceptible to the impacts of climate change and rising sea levels, with evidence of global shifts in the distribution of mangroves, including encroachment into salt marshes. The encroachment of woody mangrove shrubs and trees into herbaceous salt marshes may represent a substantial change in ecosystem structure, although resulting impacts on ecosystem functions and service provisions are largely unknown. In this review, we assess changes in ecosystem services associated with mangrove encroachment. While there is quantitative evidence to suggest that mangrove encroachment may enhance carbon storage and the capacity of a wetland to increase surface elevation in response to sea‐level rise, for most services there has been no direct assessment of encroachment impact. On the basis of current understanding of ecosystem structure and function, we theorize that mangrove encroachment may increase nutrient storage and improve storm protection, but cause declines in habitat availability for fauna requiring open vegetation structure (such as migratory birds and foraging bats) as well as the recreational and cultural activities associated with this fauna (e.g., birdwatching and/or hunting). Changes to provisional services such as fisheries productivity and cultural services are likely to be site specific and dependent on the species involved. We discuss the need for explicit experimental testing of the effects of encroachment on ecosystem services in order to address key knowledge gaps, and present an overview of the options available to coastal resource managers during a time of environmental change. Mangrove encroachment alters the ecosystem structure of coastal wetlands, with ramifications for ecosystem service delivery. The low vegetation structure of salt marsh provides roosting and feeding birds with a longer line of sight to any ambush predators, while insectivorous bats prefer to feed over open salt marsh or at the marsh–forest edge, avoiding the acoustic clutter of closed forest. The higher biomass and structural rigidity of mangrove may also increase storm wave attenuation.