Escape of spring frost and disease through phenological variations in oak populations along elevation gradients

1. The timing of tree flushing follows strong phenotypic and genetic clines across environmental gradients. It may be seen as an adaptive response to abiotic (escape of spring frost and maximizing growing season length) and biotic (escape of pest and disease) hazards. However, few studies have investigated jointly both types of hazards. 2. We assessed exposure to both abiotic (spring frost) and biotic (powdery mildew) hazards within and between sessile oak populations along elevation gradients, during the flushing period in several years. For each population and phenological phenotype (early- vs. late-flushing trees), we estimated safety margins, defined as the time period separating budburst from the hazard occurrence (spore emission, spring frost). 3. We observed that powdery mildew phenology (initiation of spore release in spring) was less responsive to the elevation gradient than oak phenology (budburst) and that it was not correlated with tree phenology within populations. The spri...