Abstract
Invasive species are a major cause of biodiversity loss worldwide, but their impact on communities and the mechanisms driving those impacts are varied and not well understood. This study employs functional diversity metrics and guilds—suites of species with similar traits—to assess the influence of an invasive tree (Tamarix spp.) on riparian plant communities in the southwestern United States. We asked: (1) What traits define riparian plant guilds in this system? (2) How do the abundances of guilds vary along gradients of Tamarix cover and abiotic conditions? (3) How does the functional diversity of the plant community respond to the gradients of Tamarix cover and abiotic conditions? We found nine distinct guilds primarily defined by reproductive strategy, as well as growth form, height, seed weight, specific leaf area, drought and anaerobic tolerance. Guild abundance varied along a covarying gradient of local and regional environmental factors and Tamarix cover. Guilds relying on sexual reproduction, in particular, those producing many light seeds over a long period of time were more strongly associated with drier sites and higher Tamarix cover. Tamarix itself appeared to facilitate more shade-tolerant species with higher specific leaf areas than would be expected in resource-poor environments. Additionally, we found a high degree of specialization (low functional diversity) in the wettest, most flood-prone, lowest Tamarix cover sites as well as in the driest, most stable, highest Tamarix cover sites. These guilds can be used to anticipate plant community response to restoration efforts and in selecting appropriate species for revegetation.
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Data are available in the Zenodo Digital Repository; https://doi.org/10.5281/zenodo.5047316
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Acknowledgements
We acknowledge the National Science Foundation Dynamics of Coupled Natural and Human Systems award (project number 1617463) and the University of Denver for providing A.L.H. with salary funding, and the U.S. Geological Survey Invasive Species Program that partially funded E.G. collaboration. We thank Emily Palmquist for advising on trait data collection, Lindsay Reynolds for contributing some trait data and Pat Shafroth for advising on plant traits and guild definitions. Thanks also to the authors of González et al. 2017, Ecological Applications and González et al. 2017, Biological Conservation for providing plant species and environmental data, as well as to Alex Goetz, Kayleigh Kearnan, Kyla Reiner and James Sheinbaum for assistance in trait data collection. This study complies with the current laws of the country in which it was performed.
Funding
We acknowledge the National Science Foundation Dynamics of Coupled Natural and Human Systems award (project number 1617463) and the University of Denver for providing A.L.H. with salary funding, and the U.S. Geological Survey Invasive Species Program that partially funded E.G. collaboration.
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ALH, EG and AAS conceived the ideas. ALH collected and analyzed the data with the advice of all authors. BB contributed to scripts for analysis. All authors discussed and interpreted the results. ALH led the writing and all authors contributed to the manuscripts revisions and intellectual content and gave approval for publication.
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Communicated by Edith B. Allen.
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Henry, A.L., González, E., Bourgeois, B. et al. Invasive tree cover covaries with environmental factors to explain the functional composition of riparian plant communities. Oecologia 196, 1139–1152 (2021). https://doi.org/10.1007/s00442-021-04990-z
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DOI: https://doi.org/10.1007/s00442-021-04990-z