Increasing tree survival to facilitate the conversion of conventional systems to agroforestry systems using plant growing aids and plant-plant facilitation under climate change

Several global commitments have established a compromise to greatly increase the presence of trees in agricultural lands, fostering therefore the adoption of agroforestry systems and the destination of some areas for reforestation. Such tasks are challenging, particularly under the current climate change scenarios, and several studies have demonstrated a high risk of seedling mortality under harsh and extremely variable environmental conditions, calling for solutions that must increase the success and reduce the costs of growing a tree. In this study, inside the project LIFE Desert Adapt, we tested the effects of different types of growing aids such as shelters, mulching and innovative methods such as biodegradable paper devices (Cocoon™) as well as plant-plant facilitation using nurse species to try to enhance survival and growth of planted seedlings in agricultural and forest areas at high desertification risk in Sicily, Italy. The growing aids were used on three species, two native (wild olive Olea europaea var. sylvestris and broom Spartium junceum) and one crop (almond Prunus dulcis) in three different sites, while plant-plant facilitation was evaluated assessing the effects of prickly pear (Opuntia ficus-indica) and wild olives on richness and density of recruitment at community level in four sites. Growing aids greatly enhanced seedling growth and survival in all cases, with a high mortality found on the control seedlings, mostly due to drought. Both prickly pear and wild olives facilitated the recruitment of 8 native species, in some cases boosting tree growth very quickly. We found relevant species-specific responses, a crucial data to define whether invest on more costly methods, such as the cocoon. However, in all cases emergency irrigations during summer were needed. Our results indicate that with current variations in climate, the use of growing aids to promote tree growth is highly recommended, or in some cases obligatory. Additionally, our results indicate a very good potential in the use of prickly pear and wild olives as facilitators to promote natural regeneration and to speed up the formation of agroforestry systems.