Does shelter enhance early seedling survival in dry environments? A test with eight Mediterranean species

Question: Do solid-walled polyethylene tubes and mesh fabric tubes improve the short-term survival of eight Mediterranean tree and shrub species often used in the restoration of arid environments? Location: We conducted two experimental plantations in degraded field sites in the province of Almería (SE Spain), under arid Mediterranean conditions. Methods: One-year-old seedlings of Ceratonia siliqua, Juniperus phoenicea, Olea europaea, Pinus halepensis, Pinus pinaster, Quercus coccifera, Quercus ilex and Tetraclinis articulata were planted either sheltered by one of the above shelter tubes, or by being left unsheltered. Survival was recorded the first growing season after planting, which was a very dry season. Results: Overall, seedling survival ranged from as little as 0% to 24%, and tree shelters consistently enhanced survival in Quercus species only, ranging from 16% in walled shelters to 8% in mesh shelters. Shelters failed to boost survival in the six remaining species. Conclusion: The results of this study suggest that both walled and mesh shelters were mostly ineffective at increasing seedling survival for the Mediterranean species used in this experiment; these species coincide with those used in restoration programs. The use of shelters in restoration programs conducted in arid environments should be reconsidered, while walled shelters might be advisable for Mediterranean Quercus species only. Further research is necessary to develop and assess improved types of shelters for arid environments.