Competitive abilities and ecological impacts of Tamarix aphylla in southern Nevada

Tamarix aphylla, an evergreen tree that hybridizes with the more widespread deciduous shrub T. ramosissima, has invaded the drawdown zone of Lake Mead in the southwestern U.S. To determine the ecological impacts and the invasive potential of T. aphylla, vegetative and soil characteristics of habitats dominated by either T. aphylla or T. ramosissima were measured, and competition experiments between T. aphylla and T. ramosissima , and between T. aphylla and the native Salix gooddingii were performed. Stands of both Tamarix species were similar in density and cover of vegetation, with each species tending to have higher density and cover values at one of the two sites measured. Tamarix aphylla plants were significantly taller than T. ramosissima, and tended to have larger basal diameters and canopies. Salinity was significantly higher in soils collected under the canopy of T. aphylla than in soils collected under T. ramosissima, whereas soil total Kjeldahl nitrogen, pH, and organic matter in soil varied between species by site. In the competition experiments, increases in T. aphylla density had a greater negative effect on relative growth rates of both T. aphylla and the native S. gooddingii when the two species were paired. However, T. ramosissima had a greater negative effect on the relative growth rate of both Tamarix species when the two species were paired. Because of the competitive abilities and ecological impacts of T. aphylla, action should be taken to ensure that this plant does not further invade riparian ecosystems in the southwestern U.S