Contrasted impacts of yellow flag iris (Iris pseudacorus) on plant diversity in tidal wetlands within its native and invaded distribution ranges

Authors: GALLEGO-TEVAR, BLANCA - University Of Seville; Grewell, Brenda; WHITCRAFT, CHRISTINE - California State University; Futrell, Caryn; BARCENAS-MORENO, GAEL - University Of Seville; CASTILLO, JESUS - University Of Seville

Submitted to: Diversity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2022
Publication Date: 4/22/2022
Citation: Gallego-Tevar, B., Grewell, B.J., Whitcraft, C.R., Futrell, C.J., Barcenas-Moreno, G., Castillo, J.M. 2022. Contrasted impacts of yellow flag iris (Iris pseudacorus) on plant diversity in tidal wetlands within its native and invaded distribution ranges. Diversity. 14(5). Article 326. https://doi.org/10.3390/d14050326.
DOI: https://doi.org/10.3390/d14050326

Interpretive Summary: Intertidal vegetation in coastal wetland ecosystems is increasingly vulnerable to unprecedented rates of climate change, sea level rise, and biological invasions that compromise diversity and critical ecosystem services provided by wetlands. Intertidal plant species diversity, often including many endemic taxa, exists along pronounced environmental gradients of salinity and inundation and contributes to biological diversity on a landscape scale. This vegetation also prevents shoreline erosion, decreases flood risks, and sequesters carbon at high rates. These ecologically important plant communities have been invaded by alien species, including yellow flag iris. It is important to improve understanding of the performance and ecological outcomes of these species in both their native and naturalized ranges to improve understanding of their ability to thrive under a broad spectrum of conditions. From a conservation perspective, improved knowledge of the impacts of invasive plant species on diversity and distribution thresholds of intertidal vegetation is needed to maintain essential ecosystem services and restore wetlands for climate change resilience. Yellow flag iris (Iris pseudacorus L.; Iridaceae) is a perennial macrophyte native to Europe, North Africa and western Asia, which is often used as an ornamental aquatic plant in garden and ponds worldwide and has escaped cultivation and invaded natural wetlands. We conducted an intercontinental biogeographic survey to analyze the effects of an invasive plant species in its native and invaded ranges. Our study system included tidal wetlands colonized by Iris pseudacorus L. (yellow flag iris, Iridaceae) along salinity gradients in two estuaries in its native European and invaded North American ranges. This aquatic macrophyte has been introduced as an ornamental aquatic plant worldwide and has escaped cultivation and naturalized, becoming invasive. We investigated the impacts of Iris pseudacorus (yellow flag iris) on the diversity of intertidal vegetation in the Guadalquivir Estuary (Andalusia, Spain), and in the invaded San Francisco Bay-Delta Estuary (California, USA). We hypothesized I. pseudacorus would impart more negative community-level impacts on plant species diversity in the invaded range compared to the native range. We also postulated impacts on plant community diversity would vary along a salinity gradient that corresponds to more diverse freshwater tidal areas to less diverse brackish wetlands. Our results show that the colonization of Iris pseudacorus has very different effects on the diversity of tidal plant communities in its native and invaded range. In the native range, I. pseudacorus promoted plant diversity by increasing evenness and species richness. On the contrary, I. pseudacorus greatly reduced plant diversity in the invasive range, being more resistant to invasion impacts those communities with lower species richness and diversity levels. In view of these results, urgent management practices are needed to control and eradicate I. pseudacorus from the inland Sacramento-San Joaquin Delta Estuary since this invasive macrophyte is reducing plant diversity at local and landscape scales. In view of these results, urgent management practices are needed to control and eradicate I. pseudacorus from the inland Sacramento-San Joaquin Delta Estuary since this invasive macrophyte is reducing plant diversity at local and landscape scales.

Technical Abstract: We conducted an intercontinental biogeographic survey to analyze the effects of an invasive plant species in its native and invaded ranges. Our study system included tidal wetlands colonized by Iris pseudacorus L. (yellow flag iris, Iridaceae) along salinity gradients in two estuaries in its native European and invaded North American ranges. This aquatic macrophyte has been introduced as an ornamental aquatic plant worldwide and has escaped cultivation and naturalized, becoming invasive. We investigated the impacts of Iris pseudacorus (yellow flag iris) on the diversity of intertidal vegetation in the Guadalquivir Estuary (Andalusia, Spain), and in the invaded San Francisco Bay-Delta Estuary (California, USA). We hypothesized I. pseudacorus would impart more negative community-level impacts on plant species diversity in the invaded range compared to the native range. We also postulated impacts on plant community diversity would vary along a salinity gradient that corresponds to more diverse freshwater tidal areas to less diverse brackish wetlands. Our results show that the colonization of Iris pseudacorus has very different effects on the diversity of tidal plant communities in its native and invaded range. In the native range, I. pseudacorus promoted plant diversity by increasing evenness and species richness. On the contrary, I. pseudacorus greatly reduced plant diversity in the invasive range, being more resistant to invasion impacts those communities with lower species richness and diversity levels. In view of these results, urgent management practices are needed to control and eradicate I. pseudacorus from the inland Sacramento-San Joaquin Delta Estuary since this invasive macrophyte is reducing plant diversity at local and landscape scales.