Few studies have focused on forest research in plantations with Chilean native species midtolerant to shade. Such species may use resources that intolerant species cannot, increasing the total site productivity. This study aimed to define the factors that explain the growth of Euctyphia cordifolia Cav. and Laurelia sempervirens (Ruiz et Pavón) Tul., two midtolerant species of southern Chile. We sought to determine the effect on these species of competition in mixed-species plantations. At the time of this study, the plantations were 4 to 22 years old . Two competition indices were analyzed for each species: the Growing Space Polygon (GSP) and the Canopy Overlap (CO). The GSP proved to be very useful in predicting the growth in the older plantations where E. cordifolia and L. sempervirens had their crowns below the main canopy, suggesting strong competition for water and nutnents (also called symmetric competition). In contrast, in young plantations (around 10 years old ), growth was better explained by CO, suggesting that competition occurs mainly for light (also called asymmetric competition). Silvicultural techniques that could improve the growth of these species in mixed plantations were proposed, such as an earlier thinning entry to provide these species with more room for light, as dictated by their intermediate tolerance to shade.