"Changes in biotic interactions are one of the key drivers of biodiversity loss. In order to preserve biodiversity, it is essential to achieve a deep understanding on all aspects of biotic interactions. Plants benefit from positive interactions but, at the same time, they have to cope with detrimental agents that cause plants to become stressed. Most studies have examined biotic and abiotic stressors separately. However, biotic interactions may also influence plant performance under abiotic stress and, simultaneously, abiotic stress may affect the net outcome of biotic interactions. This IOF proposal is aimed to understand the mechanisms underlying plant interactions at increasing levels of both biotic and abiotic stress and would serve to improve our knowledge of how plants can respond to current global change. Thus, we will use two main consequences of the current global change as stressful agents: 1) The increase of water deficit (abiotic stress) and 2) The increase of herbivore pressure (biotic stress). The general objective of this proposal is to combine both sources of stress to analyse whether they may alter the sign and strength of different plant interactions. This will be performed in Mediterranean oak woodlands (California and Spain) where both sources of stress (drought and overpopulation of herbivores) are considered important drivers of biodiversity loss. We will use field and lab data in seedling performance (survival and growth) and spatial explicit models to analyse plant interactions at different levels: intraspecific (above vs. below ground), interspecific (shrub-tree) and plant-animal interactions (seed dispersal). The multidisciplinary character of this proposal, combining global change biology, applied ecology (restoration and forest management) and computer science (complex model implementation) represents a novel and ambitious approach that will produce scientific advances and new directions within this challenging topic"