<p>The Stress Gradient Hypothesis (SGH) predicts that the net effects of competition and facilitation among plants are determined by the interactions with environmental stressors. <i>Juniperus virginiana</i> is a stress-tolerant species that is native to the eastern United States but expanding into novel habitats, which may interact with changes in plant density as invasion proceeds to shape the course of species establishment. We tested this hypothesis by examining three sites along a complex latitudinal gradient shaped by historical glaciation and varying in snowfall, temperature, precipitation, and soil nutrients. We examined the impact of intraspecific competition (zero, one, two, and four competitors) on <i>J. virginiana</i> sapling growth metrics (relative growth rate, total biomass, and nitrogen concentration), physiological traits (midday water potential, assimilation rate, transpiration rate, and stomatal conductance), and water status. We found that abiotic conditions impacted plants in a non-linear fashion along a complex stress gradient, with the highest performance at high and low latitude sites. Intraspecific competition had limited effects overall, though some evidence suggests that negative impacts would develop over time at the highest density. Our study testing the expectations of SGH using this stress-tolerant species demonstrates how the theory can be applied to inform invasion management plans by showing that (1) intraspecific competition alone is unlikely to impact <i>J. virginiana</i> performance except at high plant densities, (2) environmental complexity, including the combined effect of temperature, precipitation, soil nutrient content, and competition, is a more likely driver of productivity and establishment, however (3) warmer, drier sites with higher soil nitrogen are expected to support higher growth rates, making them more vulnerable to <i>J. virginiana</i> invasion.</p>