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Review article - Peer-reviewed, 2016

Dieback of riparian alder caused by the Phytophthora alni complex: projected consequences for stream ecosystems

Bjelke, Ulf; Boberg, Johanna; Tattersdill, Kristina; Mckie, Brendan; Oliva Palau, Jonàs

Abstract

1. Alder trees (Alnus spp.) are key nitrogen-fixing riparian species in the northern hemisphere. Inputs of nitrogen-rich leaf litter from alder into stream food webs can contribute significantly to nitrogen dynamics at local and landscape scales. Alder trees also provide habitats for terrestrial and aquatic organisms, and help stabilize river banks. 
2. Recently, substantial declines in alder stands have occurred along streams in Europe, with damages observed in some parts of North America also. A major driver has been the invasive oomycete pathogen Phytophthora alni species complex, which can spread rapidly along stream networks. 
3. This review synthesises information on the pathogen, processes of spread and infection, and its impacts on alder. We further address the potential ecosystem-level and management consequences of the decline of alder, and highlight research needs. 
4. The alder dieback caused by P. alni is associated with reductions in shade and quality and quantity of leaf litter. A decline in the structural integrity of branches and roots further threatens bank stability. Stream banks dominated by other tree species or no trees at all will result in ecosystem-level changes both above and below the waterline. 
5. The P. alni taxonomic complex includes different species with varying phenotypes. An improved understanding of their environmental tolerances, virulence and evolution, along with the processes regulating the spread and impacts of the pathogen, would assist in identification of the riparian and stream systems most vulnerable not only to invasion but also to the heaviest disease outbreaks and ecosystem-level impacts. 
6. Within the P. alni complex, the highly pathogenic hybrid species P. x alni is favoured by mild winters and warm, but not excessively hot summer temperatures suggesting possible changes in distribution and level of impact under future global climate change.

Keywords

ecosystem change; invasive species; pathogens; riparian communities; running waters

Published in

Freshwater Biology
2016, volume: 61, number: 5, pages: 565-579

Authors' information

Swedish University of Agricultural Sciences, Swedish Species Information Centre
Swedish University of Agricultural Sciences, Department of Forest Mycology and Pathology
Tattersdill, Kristina
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment
Oliva Palau, Jonàs
Swedish University of Agricultural Sciences, Department of Forest Mycology and Plant Pathology

Associated SLU-program

SLU Future Forests
SLU Network Plant Protection

Sustainable Development Goals

SDG15 Life on land

UKÄ Subject classification

Microbiology
Fish and Aquacultural Science
Ecology

Publication Identifiers

DOI: https://doi.org/10.1111/fwb.12729

URI (permanent link to this page)

https://res.slu.se/id/publ/73773