A Neighborhood Analysis of the Consequences of Quercus suber Decline for Regeneration Dynamics in Mediterranean Forests

© 2015 Ibáñez et al. In forests, the vulnerable seedling stage is largely influenced by the canopy, which modifies the surrounding environment. Consequently, any alteration in the characteristics of the canopy, such as those promoted by forest dieback, might impact regeneration dynamics. Our work analyzes the interaction between canopy neighbors and seedlings in Mediterranean forests affected by the decline of their dominant species (Quercus suber ). Our objective was to understand how the impacts of neighbor trees and shrubs on recruitment could affect future dynamics of these declining forests. Seeds of the three dominant tree species (Quercus suber, Olea europaea and Quercus canariensis) were sown in six sites during two consecutive years. Using a spatially-explicit, neighborhood approach we developed models that explained the observed spatial variation in seedling emergence, survival, growth and photochemical efficiency as a function of the size, identity, health, abundance and distribution of adult trees and shrubs in the neighborhood. We found strong neighborhood effects for all the performance estimators, particularly seedling emergence and survival. Tree neighbors positively affected emergence, independently of species identity or health. Alternatively, seedling survival was much lower in neighborhoods dominated by defoliated and dead Q. suber trees than in neighborhoods dominated by healthy trees. For the two oak species, these negative effects were consistent over the three years of the experimental seedlings. These results indicate that ongoing changes in species' relative abundance and canopy trees' health might alter the successional trajectories of Mediterranean oak-forests through neighbor-specific impacts on seedlings. The recruitment failure of dominant late-successional oaks in the gaps opened after Q. suber death would indirectly favor the establishment of other coexisting woody species, such as drought-tolerant shrubs. This could lead current forests to shift into open systems with lower tree cover. Adult canopy decline would therefore represent an additional factor threatening the recruitment of Quercus forests worldwide.Was supported by a FPI (Formación de Personal Investigador) fellowship (MICINN-Ministerio de Ciencia e Innovación), JMA was supported by a FPU (Formación de Personal Universitario fellowship (MECD-Ministerio de Educación, Cultura y Deporte), IMPR was supported by a JAE doc-CSIC (Consejo Superior de Investigaciones Científicas) contract. This research was supported by INTERBOS-Interacciones ecológicas y Cambio Global en el bosque mediterráneo-CGL2008-04503-C03-03 (http://www.irnase.csic.es/users/interbos/ inicio.php), DIVERBOS-Diversidad funcional y resiliencia del bosque mediterráneo-CGL2011-30285-C02-01 (http://www.diverbos.com/es/), RETROBOSEl papel de los procesos de Retroalimentación planta-suelo en la dinámica de Bosques de Quercus con decaimiento-CGL2011-26877 and ANASINQUEAnálisis comparativo y síntesis de los patrones de regeneración, decaimiento y distribución de las especies de Quercus-PGC2010-RNM-5782 (http://www.anasinque.com/) projects. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscrip)Peer Reviewe