Differences in water-acquisition strategies of tree root systems can determine the capacity to survive under severe drought. We evaluate the effects of field water shortage on early survival, growth and root morphological variables of two South American Mediterranean tree species with different rooting strategies during two growing seasons. One year-old Quillaja saponaria (deep-rooted) and Cryptocarya alba (shallow-rooted) seedlings were established under two watering treatments (2 L·week⁻¹·plant⁻¹ and no water) in a complete randomized design. Watering improved the final survival of both species, but the increase was only significantly higher for the shallow-rooted species. The survival rates of deep- and shallow-rooted species was 100% and 71% with watering treatment, and 96% and 10% for the unwatered treatment, respectively. Root morphological variables of deep-rooted species such as surface area, volume, and diameter were higher under unwatered treatment. On the other hand, shallow-rooted species had a higher total root dry mass, length, surface area with watering treatments. Our findings suggest that deep-rooted species are highly recommended for reforestation in dry conditions, even under low soil water availability. Water supplements during the summer season can attenuate the differences between deep- and shallow-rooted species in their ability to survive drought during the early stage.