Abstract
Understanding community dynamics during early life stages of trees is critical for the prediction of future species composition. In Mediterranean forests drought is a major constraint for regeneration, but likely not the only factor determining the observed spatial patterns. We carried out a sowing experiment aimed at identifying main filters during seed-seedling transition. Specifically, we studied seed fate (predation, fungi infection, emergence) and subsequent seedling performance (mortality during the first summer and overall recruitment after 2 years) of four co-occurring Mediterranean tree species (Quercus ilex, Quercus faginea, Juniperus thurifera, Pinus nigra). We related these processes to the dominant species composition, microhabitat heterogeneity, herb cover and seed mass. The identity of the dominant species in the forest canopy was more important for recruitment than the forest canopy being dominated by conspecific vs. heterospecific species. The patterns we found suggest that biotic interactions such as facilitation (lower mortality under the canopies) and herb competition (during emergence of J. thurifera) are relevant during recruitment. Moreover, our results pointed to ontogenetic conflicts regarding the seed mass of Q. faginea and to density-dependent seed mortality for Q. ilex, rarely described in Mediterranean ecosystems. We propose that our study species experience population growth in forests dominated by heterospecifics where the recruitment success depends on habitat heterogeneity and on moderated biotic and abiotic stresses created by each species. Our results reveal patterns and mechanisms involved in recruitment constraints that add complexity to the well-known drought-related processes in Mediterranean ecosystems.
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Acknowledgments
We are very grateful to Mario Díaz for assistance in rodent sampling, Sasha Wright for comments on statistical methods and to all the people who helped in the field, especially David López and Gonzalo Caballé. We also thank the Junta de Castilla-La Mancha, the director and park rangers of the Alto Tajo Natural Park for permission and facilities provided. We thank the editor and the anonymous reviewers for their constructive comments, which helped us to improve the manuscript. The experiments comply with the current laws of the country (Spain) in which the experiments were performed. This work was supported by the Spanish Ministry for Innovation and Science with the grants FPI (CGL2007-66066-C04-02) to E. G., Consolider Montes (CSD2008 00040), VULGLO (CGL2010 22180 C03 03) and MOUNTAINS (CGL-2012-38427), and by the Community of Madrid grant REMEDINAL 2 (CM S2009 AMB 1783).
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Communicated by Ines Ibanez.
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Granda, E., Escudero, A. & Valladares, F. More than just drought: complexity of recruitment patterns in Mediterranean forests. Oecologia 176, 997–1007 (2014). https://doi.org/10.1007/s00442-014-3064-x
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DOI: https://doi.org/10.1007/s00442-014-3064-x