Nursery fertilization and tree shelters affect long-term field response of Acacia salicina Lindl. planted in Mediterranean semiarid conditions

Transplant stress limits establishment of newly planted seedlings in semiarid Mediterranean regions, which are characterized by very low precipitation and poor fertility soils. Nursery cultural regimes which influence stock quality, as well as silvicultural treatments applied at outplanting may affect the capacity of seedlings to establish successfully. We examined the influence of nursery mineral nutrition and application of individual tree shelters on 9-year seedling performance of the leguminous species, Acacia salicina Lindl., planted on a degraded site in southeastern Spain. Survival was significantly greater throughout the duration of the study for seedlings fertilized at high rates, while initial benefits to field growth associated with nursery fertilization diminished after 4 years. A significant relationship was established between P supplied in the nursery and both seedling survival and root dry weight after the first growing season (R2 = 0.68 and 0.77, respectively), though no relationship was detected for N. The capacity of this species to fix N through root nodulation apparently dictates that P fertility is relatively more important to initial establishment on low fertility sites characteristic of this region. Survival of protected seedlings became significantly greater than that of non-protected seedlings following an extended drought after the sixth year. Stem diameter was significantly greater for non-protected seedlings as of the fourth year but height was greater for protected seedlings throughout the study, reflecting differential carbon allocation within the sheltered environment. Our results suggest that mineral nutrient status of nursery stock (especially high P content) and tree shelters may positively affect long-term plantation establishment of A. salicina seedlings in semiarid Mediterranean climates.