Abstract
Non-native plant pests and pathogens are increasing exponentially, causing extirpation of foundation species. The impact of large-scale declines in a single host on associated biodiversity is widely documented. However, the impact of multiple host loss on biodiversity and whether these impacts are multiplicative has not been assessed. Ecological theory suggests that systems with greater functional redundancy (alternative hosts) will be more resilient to the loss of sympatric hosts. We test this theory and show its importance in relation to pest/pathogen impact assessments. We assessed the potential impact on biodiversity of the loss of two widely occurring sympatric European tree species, Fraxinus excelsior and Quercus petraea/robur, both of which are currently threatened by a range of pests and pathogens. At the UK scale, the total number of associated species at risk of extirpation from plant diseases affecting these two sympatric hosts is greater than the sum of the associated species at risk from declines in either host alone. F. excelsior hosts 45 obligate species (species only found on that host) and Q. petraea/robur hosts 326. However, a decline in both these trees would impact 512 associated species, across multiple taxon groups, a 38% increase. Assessments at a local scale, 24 mixed F. excelsior–Q. petraea/robur woodlands revealed that these impacts may be even greater due to a lack of functional redundancy. Only 21% of sites were able to provide functional redundancy for F. excelsior and Q. petraea/robur associated species which can use other tree species. In most woodlands, the tree species required to provide functional redundancy were not present, although the site conditions were often suitable for them to grow. Synthesis. Understanding of functional redundancy should be applied to assessments of pests/pathogens impact on biodiversity. In risk assessments, higher impact scores should be given to pests/pathogens affecting hosts occurring with other host plant species already impacted by pests/pathogens. Current pest/pathogen risk assessment approaches that ignore the cumulative, cascading effects shown in this study may allow an insidious, mostly overlooked, driver of biodiversity loss to continue.
| Original language | English |
|---|---|
| Pages (from-to) | 221-231 |
| Number of pages | 11 |
| Journal | Journal of Ecology |
| Volume | 110 |
| Issue number | 1 |
| Early online date | 18 Nov 2021 |
| DOIs | |
| Publication status | Published - Jan 2022 |
Bibliographical note
Funding Information:This work was funded by BBSRC grant Protecting Oak Ecosystems (PuRpOsE): BB/N022831/1 with additional funding from the Scottish Government's Rural and Environment Research and Analysis Directorate 2016–2021 strategic research programme. The authors thank Nick Hodgetts for collating the lists of the bryophyte species associated with ash and oak, Ralph Harmer for conducting some of the site visits and the site owners for allowing us access to the sites. Katharine Preedy provided statistical advice. Steve Albon and Robin Pakeman kindly provided comments to improve earlier drafts.
Data Availability Statement
The peer review history for this article is available at https://publons.com/publon/10.1111/1365-2745.13798.DATA AVAILABILITY STATEMENT
All data are publicly available. The AshEcol database is available at http://publications.naturalengland.org.uk/publication/5273931279761408, the OakEcol database is available at https://doi.org/10.5285/22b3d41e-7c35-4c51-9e55-0f47bb845202 and species data from the sites were downloaded from National Biodiversity Network Gateway, https://nbn.org.uk/the-national-biodiversity-network/archive-information/nbn-gateway/. The species data from the sites together with information about their level of association with Fraxinus excelsior and Quercus petraea/robur are presented in Appendix S2.