Site description and phylogenetic isolation estimation
Our study was conducted in the Forest of Rennes (surface area: 2000 ha), Brittany (France). The forest and selection of trees was detailed in Yguel et al . 2011 (Supplementary Methodology S1). Overall 11 pair of oaks with contrasting phylogenetic distance of neighbours were chosen, with neighbours belonging to 10 different species. For each focal oak, phylogenetic isolation was quantified as its mean phylogenetic distance to all neighboring trees with which its crown was in contact, and phylogenetic distances were extracted from published phylogenies following procedures applied previously (Vialatteet al . 2010; Yguel et al . 2011; Supplementary Methodology S1).