Question: Does the influence of plant canopy on seedling establishment interact with climate conditions, and particularly, do intensified drought conditions, enhance a positive effect of the vegetation canopy on seedlings in Mediterranean-type ecosystems.

Location: Mediterranean shrubland near Barcelona, Spain at 210 m a.s.l.

Methods: Over the course of four years we recorded seedling emergence and survival in open areas and below vegetation under control, drier and warmer experimental climatic conditions.

Results: Seedling emergence is more sensitive to climate conditions than later stages of growth. When considering the whole set of species, the total number of established seedlings at the end of the experiment was lower in the drought and warming stands than in control ones, and vegetation canopy increased the number of these seedlings in the drought stands. Drought reduced seedling emergence but not warming, while the interaction between climate treatments and vegetation canopy was not significant. Seedling survival was lower in the warming treatment than in the control. Under drought conditions, vegetation canopy increased seedling emergence of the dominant Globularia alypum. In control stands, vegetation canopy reduced their survival. Vegetation canopy increased the survival of the dominant Erica multiflora in warming stands, and it reduced the survival of G. alypum in drought stands. No significant effects of drought and warming were observed in the seed rain of these two species.

Conclusions: The balance of the facilitation-competition interactions between vegetation canopy and seedling establishment in Mediterranean-type ecosystems determined by water availability, and drought conditions enhance the positive effect of vegetation canopy. This interaction is species-specific and shows important between-year variability.

Nomenclature: Bolós et al. (1990).