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Climate change can have important effects on plant performance by altering the relationship between spring temperature and other abiotic factors, such as light availability. Higher temperatures can advance plant phenology so that seedling germination takes place when days are shorter, and affect light availability for understory plants by altering the relative timing of seedling germination and canopy closure. To predict the effects of climate-induced changes in phenology and light availability on plant performance and species interactions during the growing season, we need to determine i) how effects of plant phenology on plant performance and the plant-associated community depend on light availability, and ii) to what extent effects of phenology and light availability on plant performance are direct vs. mediated by changes in the plant-associated community. We conducted a multifactorial field experiment to test for the effect of germination timing and light availability on Quercus robur seedling traits and performance, as well as attack by specialist plant pathogens, insects, and small mammals. Germination timing strongly affected seedling performance whereas light availability’s effects were limited. Likewise, germination timing strongly affected herbivore and pathogen attack, whereas light availability and its interaction with germination timing explained a minor part of the variation. Small mammals preferentially attacked later germinating seedlings, which strongly affected plant survival, while insect herbivores and pathogens did not mediate the effect of germination timing and light availability on plant performance. The results showed that the effect of germination timing can have greater influence than light availability on plant performance and plant attack, and that small mammal herbivores can play a larger role than diseases and insect herbivores in mediating the effect of spring phenology on plant performance. Together, these findings advance our unders