Cork oak seedling establishment following an exceptionally dry winter: effects of container type in a Mediterranean forest restoration initiative

Changing climatic conditions pose significant obstacles for reforestation and restoration, increasing the risk of planting failure. Following outplanting, seedlings face a critical stage where the root system is not yet fully developed to ensure adequate water uptake. In this context, container type influences nursery seedling traits and may affect establishment in Mediterranean forest restoration, where erratic drought events are becoming increasingly frequent. We evaluated the effects of four container types (Tray, Single pot, Small Air-pot and Big Air-pot) on nursery morphology and outplanting performance of Quercus suber 1-yr-old seedlings planted in December 2022 in a post-fire restoration site in central Italy, across two slopes with different aspects, which were characterised in terms of soil and spontaneous vegetation. Shortly after planting, an unusually dry winter led to complete defoliation of all seedlings, providing a rare opportunity to assess their response to unexpected postplanting drought in terms of resprouting, physiology, and stable isotope signatures. Container type strongly influenced nursery seedling morphology and post-planting performance under the unexpected winter drought conditions. Seedlings grown in the Big Air-pot, the largest container tested, exhibited greater nursery size, higher survival, faster early growth, and enhanced resprouting capacity after outplanting. Physiological traits of the dominant resprouting shoot did not reveal signs of stress during the growing season. In contrast, south-facing slopes imposed harsher environmental conditions, resulting in more constrained seedling responses, in agreement with plant ecological requirements observed across sites. These findings identify container design as a key determinant of seedling quality and early establishment success, highlighting its importance for Mediterranean forest restoration under increasing climatic stress.