Species-specific drought effects on flower and fruit production in a Mediterranean holm oak forest

A holm oak forest was exposed to an experimental drought (reduction of 15 per cent soil moisture as predicted for this area for the next decades by General Circulation Models and ecophysiological models) during 7 years to elucidate the reproductive responses of the dominant species Quercus ilex L., Arbutus unedo L. and Phillyrea latifolia L. Soil moisture was partially reduced by plastic strips intercepting rainfall and by ditch exclusion of water runoff. During the period studied, meteorological conditions and soil moisture were continuously monitored, together with flower and fruit production in the three dominant species. In Q. ilex and A. unedo, flower and specially fruit production were strongly correlated with annual rainfall, but not in P. latifolia. The experimental drought reduced flower and fruit production in Q. ilex by 30 per cent and 45 per cent, respectively. Reductions in flower and fruit production were not significant in A. unedo and were not observed in P. latifolia. A decrease in production of reproductive structures and the different response of the species studied to a decrease in water availability could induce important changes in the competitive ability of the different species and in the long term in the community species composition and future distribution of these Mediterranean species.