Abstract
Mediterranean regions are projected to experience more frequent, prolonged and severe drought as a consequence of
climate change. We used a retractable rainfall shelter, to investigate the impact of extreme droughts on the
development of Quercus ilex leaves, flowers and fruit. In 2008, 97% of rainfall was excluded from a forest plot during
the autumn, representing 50% of the 1127mm of rain that fell during the year. In 2009, 87% of rainfall was excluded
during the spring, representing 58% of the 749mm that fell during the year. The rainfall shelter did not impact neither
incident radiation nor air temperature. Autumn rainfall exclusion did not significantly affect leaf, flowers or fruit
development. Spring rainfall exclusion resulted in larger and more sustained depression of leaf water potential during
the key phases of foliar and floral development. Consequently, only half of the sampled trees (6) reached the shoot
lengthening stage which leads to functionally mature leaves (phenophase 4), with one abandoning leaf development
at budburst (phenophase 3) and the other two at the bud swelling stage (phenophase 2). All trees of the control plot
passed phenophase 4, with most reaching complete leaf development. The impact of extreme droughts on flower
development differed between the sexes. The spring exclusion had no effect on male flower, but only one of six trees
completed female fruit maturation, compared with four in the control plot. The difference between the male and
female drought impacts is likely attributable to the occurrence of male floral development before the period of lowest
leaf water potential, and to the lower resource allocation requirements of male flowers. The information provided by
our experimental approach may constitute a crucial step to evaluate the impact of increasing drought due to climate
change on the most dominant Mediterranean tree species and to help drawing a full picture of the ecological
consequences of the decline in water resource on forest dynamics under changing conditions.
