Differences in the facilitative ability of two Mediterranean shrubs on holm-oak seedling recruitment in Mediterranean savanna-forest ecosystems

Abstract

This paper analyses the nurse effect of Cistus salvifolius and Myrtus communis on holm-oak seedling recruitment in Mediterranean savanna-like ecosystems. Changes in microenvironmental conditions beneath the shrubs canopies, leaf phenology and nurse effect of the two shrubs on holm-oak seedlings emergence and survival in the field were studied. C. salvifolious exhibited a null effect on holm-oak seedlings recruitment in the field, showed a high seasonal variability in leaf area (52% decrease during summer), and high variability in photosynthetic photon flux density (PPF) beneath the understory. By contrast, M. communis exhibited the opposite characteristics: had a positive effect on holm-oak seedlings recruitment in the field and showed big changes on air temperature and PPF beneath the understory (94% reduction), small seasonal variability in leaf area, and small variability in PPF beneath the understory. It is discussed that grazing abandonment that leads to the expansion of C. salvifolus and other early succesional chamephites does not guarantee sexual self-regeneration of holm-oaks in dehesas. Strategies to enhance late-successional evergreen and some different potentially occurring, pioneer shrub species that facilitate holm-oak seedling recruitment should be taken into account.