Nonadditive effects among threats on rare plant species

Holly L. Bernardo*, Rachel Goad, Pati Vitt, Tiffany M. Knight

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


The current loss of biodiversity has put 50,000 plant species at an elevated risk of extinction worldwide. Conserving at-risk species is often complicated by covariance or nonadditivity among threats, which makes it difficult to determine optimal management strategies. We sought to demographically quantify covariance and nonadditive effects of more threats on more rare plant species than ever attempted in a single analysis. We used 1082 population reports from 186 populations across 3 U.S. states of 27 rare, herbaceous plant species collected over 15 years by citizen scientists. We used a linear mixed-effects model with 4 threats and their interactions as fixed predictors, species as a random predictor, and annual growth rates as the response. We found a significant 3-way interaction on annual growth rates; rare plant population sizes were reduced by 46% during the time immediately after disturbance when populations were also browsed by deer (Odocoileus virginianus) and had high levels of encroachment by woody species. This nonadditive effect should be considered a major threat to the persistence of rare plant species. Our results highlight the need for comprehensive, multithreat assessments to determine optimal conservation actions.

Original languageEnglish (US)
Pages (from-to)1029-1034
Number of pages6
JournalConservation Biology
Issue number4
StatePublished - Aug 1 2020
Externally publishedYes


  • disturbance
  • especies leñosas
  • especies raras de plantas
  • evaluación de amenazas
  • habitat management
  • herbivoría de mamíferos
  • human intrusion
  • intrusión humana
  • invasión
  • mammalian herbivory
  • manejo de hábitat
  • perturbación
  • species’ viability
  • threat assessment
  • viabilidad de especies
  • woody species encroachment

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Ecology
  • Nature and Landscape Conservation


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