Investigating Native and Invasive Riparian Species Under Varying Environmental Stressors in the Arid Southwestern United States

Investigating Native and Invasive Riparian Species Under Varying Environmental Stressors in the Arid Southwestern United States 

Amber Renee Archie1, Liza Holeski2, Rebecca Best3 

Affiliations: 

1Northern Arizona University, Flagstaff, Arizona, United States; aa3547@nau.edu 

2College of the Environment, Forestry, and Natural Sciences, Department of Biological Sciences, Northern Arizona University, Flagstaff, Arizona, United States; Liza.Holeski@nau.edu  

3College of the Environment, Forestry, and Natural Sciences, School of Earth and Sustainability, Northern Arizona University, Flagstaff, Arizona, United States; Rebecca.Best@nau.edu  

Abstract: 

Riparian ecosystems in the arid southwestern United States face increasing stress from climate change, altered hydrology, and invasive species expansion. Along the Little Colorado River (LCR), native species such as coyote willow (Salix exigua) must increasingly contend with rising salinity levels, prolonged drought, and competition from invasive tamarisk (Tamarix spp.). These conditions, exacerbated by reduced snowpack and evapotranspiration, threaten the resilience and biodiversity of riparian floodbanks that provide vital ecological services in a region where wetlands comprises less than 1% of the landscape. 

A critical element of this project is the integration of Traditional Ecological Knowledge (TEK) through collaboration with Navajo Nation liaisons and surrounding tribal communities. This partnership helps align restoration design with local cultural values, land stewardship traditions, and long-term sustainability goals. Although tribal community perceptions are not directly studied, restoration planning will be shaped by TEK-informed priorities gathered from chapter meetings and tribal consultations. 

This study contributes to understanding ecohydrological responses in scarce water environments by examining how salinity and invasive competition affect riparian plant survival and growth, with implications for restoration and ecosystem resilience in arid southwestern river systems. Through controlled experiments using coyote willow cuttings collected from multiple populations with variable salinity exposure histories, we evaluated survival, growth, and photosynthesis at three salinity levels and with a native vs. invasive competitor. 

We hypothesize that willow cuttings from lower elevation, high-salinity environments will demonstrate greater salt tolerance and competitive ability against tamarisk. Additionally, in competitive trials, we anticipate reduced growth and survival of willow in the presence of tamarisk, though original field collection site may influence the performance. Lastly, we predict that the combined effects of species competition with an invasive cutting along with the increased salinity treatments will result in the poorest willow growth. 

This research offers applied insights for riparian restoration in dryland regions, where abiotic stress and invasive species are key barriers to native vegetation recovery. By examining both ecological and cultural dimensions of restoration, this project aims to inform strategies that support biodiversity, ecosystem function, and tribal stewardship in Arizona’s vulnerable riparian zones.