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

Abstract

Question: In the restoration of degraded arid environments, woody seedling survival is threatened by drought, extreme temperatures and radiance, and herbivory. Shelter may provide planted seedlings with suitable microsites; however, the effects of shelter provision under very dry conditions are not well known. Therefore a better understanding is needed to improve the success of restoration programs. Here we asked whether two types of tree shelters, solid-walled polyethylene tubes and mesh fabric tubes, improved 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, P. pinaster, Quercus coccifera, Q. 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 33 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, which strongly 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.