Cover of Tamarix Covaries With Regional and Local Environmental Factors To Explain The Functional Composition Of Riparian Plant Communities
Annie Henry1*, Eduardo González2, Bérenger Bourgeois3, Anna Sher 1
1 University of Denver, Department of Biological Sciences, Denver, CO USA
2 Colorado State University, Department of Biology, Fort Collins, CO USA
3 Department of Plant Sciences, Université Laval, Quebec City, Quebec, Canada
In the southwestern U.S., Tamarix has become an inextricable part of the landscape. While removal has been a priority for decades and Diorhabda biocontrol agent continues to expand, studies reporting vegetation response to Tamarix control have focused on species-based approaches. Understanding the functional composition of plant communities sheds light on the mechanisms of change in response to species invasion as well as subsequent removal. This study employs functional diversity metrics as well as guilds - suites of species with similar traits - to assess the influence of Tamarix cover on the functional composition of riparian plant communities in the southwestern United States. We asked: 1) What traits define riparian plant guilds? 2) How do the abundances of each guild vary along a gradient of Tamarix cover and abiotic conditions? 3) How does the functional diversity of the plant community respond to the combined gradient of Tamarix cover and abiotic conditions? We found nine distinct clusters primarily defined by reproductive strategy, as well as 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 focused on sexual reproduction, i.e., producing many light seeds over a long period of time were more strongly associated with drier sites and higher Tamarix cover. Tamarix itself facilitated 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 in wetter, more flood prone, low Tamarix cover sites as well as in drier, more stable, high Tamarix cover sites. These guilds can be referred to when anticipating plant community response to restoration efforts and in selecting appropriate species for revegetation.