Natural Regeneration in Agroforestry : the Case of Sierra de Grazalema ; Régénération naturelle des systèmes agroforestiers : le cas des dehesas de la Sierra de Grazalema, Andalousie, Espagne

The regeneration of Holm oak (Quercus ilex) populations remains problematic in most dehesa agroforestry systems, allegedly due to the absence of a shrub layer protecting seedlings from grazing and heat. This thesis explores the latter claim using the regressive method. Our study focuses on the Sierra de Grazalema Natural Park, a site located at the periphery of dehesa regions in Andalusia, Spain and not previously analyzed in this manner. Regeneration was interpreted as a naturalized technique that evolves over time and within disciplinary fields. Our study features an analysis of historical documents, from 1765 to the present day, as well as fieldwork including 71 transects measuring shrub and tree layers on five public lands and three private lands. The tree layer was examined using a distribution into diameter classes and variograms analyzed seeding patterns on several scales. The reverse J-shaped diameter distribution indicates successful regeneration, but with a strong heterogeneity both among transects and due to land status. A significant number of young trees were found: 4516.65 seedlings / ha, 986 thickets / ha and 543 saplings / ha. Variograms indicate regeneration patterns present at several scales; at about ten meters, at 45 to 90 meters, at 100 to 200 meters and near one kilometer. These results, very different from previous studies, complement historical trajectories, and indicate that there is not one form of regeneration but several, related to both historical eras and environments. Patterns of regeneration include cases without a matorral shrublands and woodlands stage, cases belonging to a regressive or progressive series, and finally, cases of regeneration sensu stricto. ; La régénération naturelle des peuplements de chênes verts (Quercus ilex) des systèmes agroforestiers de « dehesas » pose problème dans leur aire de distribution principale. La cause invoquée est l’absence de strate arbustive protégeant les semis de l’abroutissement et de la chaleur. La thèse, à travers la méthode régressive, ...