Abstract: Niche and fitness concepts are applied in this study of the dynamics of water availability and growth characteristics under five separate restoration planting regimes on stable sand dunes in the Shapotou area. Field soil water data was used to parameterize a mathematical model that calculates the relative water fitness of two species—Artemisia ordosica Krasch. and Caragana korshinskii Kom—along a gradient of water availability. This model indicates that A. ordosica had the lowest water deficit in July and that its water fitness was higher in mono-species plantings than in mixture. The water fitness of C. korshinskii was lower in mono-specific stands than when mixed. These trends occurred despite two-fold variation in growth season precipitation. Of three single-species planting patterns the 2 × 2 gave the best results in terms of plant growth. Of the two mixed planting patterns, 2 lines of A. ordosica × 2 lines of C. korshinskii with one line blank after every four lines was best.