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Variable effects of forest diversity on invasions by non-native insects and pathogens


The geographical distributions of non-native forest insects and pathogens (pests) result from a multitude of interacting abiotic and biotic factors. Following arrival, the presence of suitable host trees and environmental conditions are required for pests to establish and spread, but the role of forest biodiversity in this process is not well-understood. We analyzed county-level data for 22 non-native forest pests in the conterminous United States, developing species-specific models to investigate the effects of spatial contagion, human activities, and host and non-host tree biomass or richness on the occurrence of pest species. Species-specific models indicated that (i) the spatial contagion of invasions was the most common driver of invasion incidence, (ii) facilitation effects from host biomass and richness were present in approximately half of the invasions and almost entirely observed in invasions by sap-feeding insects or pathogens, and (iii) there was substantial variation in the direction and magnitude of the effects of non-host tree biomass and richness on invasion. Our analyses highlighted the prominent role of spatially derived propagule pressure in driving intracontinental invasions whereas effects of forest biodiversity were variable and precluded broad generalizations about facilitation and dilution effects as drivers of forest pest invasions at large spatial scales.

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The data supporting findings of this study are available in the supplementary material (Online Appendix 2).


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We thank survey crews, technicians, and scientists from the USDA FIA program for collecting and managing forest inventory data. We also thank the handling editor and an anonymous reviewer for insightful comments that improved the manuscript.


This research was supported by National Science Foundation Macrosystems Biology Grant 1638702, the USDA Forest Service, and grant EVA4.0, No. CZ.02.1.01/0.0/0.0/16_019/0000803 financed by Czech Operational Programme "Science, Research, and Education.” This publication is a contribution of the Mississippi Agricultural and Forestry Experiment Station and based upon work supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, Hatch project under accession number 1025843.

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All authors contributed to the study conception, data curation, and analyses. The first draft of the manuscript was written by SFW and all authors provided substantial input on subsequent versions. All authors read and approved the final manuscript.

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Correspondence to Samuel F. Ward.

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The authors have no relevant financial or non-financial interests to disclose.

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Communicated by B. D. Hoffmann.

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This article belongs to the Topical Collection: Forest and plantation biodiversity.

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Supplementary file2 (CSV 11033 kb)

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Ward, S.F., Liebhold, A.M. & Fei, S. Variable effects of forest diversity on invasions by non-native insects and pathogens. Biodivers Conserv (2022).

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  • Biodiversity
  • Forest insect
  • Habitat invasibility
  • Invasion
  • Pathogen
  • Species richness
  • Spread