Abstract
There is a growing interest in understanding and forecasting the responses of plant communities
to projected changes of environmental conditions. Multi-stage demographic approaches, where plant
recruitment is explored across multiple and consecutive stages, are essential to obtain a whole overview
of the consequences of increasing aridity on tree recruitment and forest dynamics, but they are still rarely
used. In this study, we present the results of an experimental rainfall exclusion aimed to evaluate the
impact of projected increasing drought on multiple stage-specific probabilities of recruitment in a key
tree species typical of late-successional Mediterranean woodlands (Quercus ilex L.). We calibrated linear
and nonlinear likelihood models for the different demographic processes and calculated overall probabilities
of recruitment along a wide range of microhabitat conditions. Rainfall exclusion altered Q. ilex
recruitment throughout ontogeny. Seed maturation, seedling emergence and survival and, to a lesser
extent, post-dispersal seed survival were the most sensitive demographic processes to decreased rainfall.
Interestingly, both the identity of the most critical stages for recruitment and their specific sensitivity to
rainfall manipulation depended largely on the yearly pattern of precipitation. The microhabitat heterogeneity
strongly determined the success of recruitment in the study species. The experimental increase
in drought displaced the peak of maximum overall recruitment towards the low end of the light gradient,
suggesting that the dependence on shrubs for an effective recruitment in Q. ilex could be intensified
under future environmental scenarios. In terms of phenotypic plasticity, Q. ilex seedlings responded
more strongly to light availability than to experimentally increased drought, which could reduce its ability
to persist under on-going environmental conditions due to climate change. Results from this study
provide a full picture of the ecological and functional consequences of the projected rainfall reduction on tree recruitment and forest dynamics in two years of contrasting precipitation.
