Spatio-temporal variation of biotic and abiotic stress agents determines seedling survival in assisted oak regeneration

1. Mediterranean oak woodlands are currently undergoing considerable anthropogenic changes that globally threaten their long-term persistence. Restoration efforts via assisted regeneration depend on species traits and type of stress. However, how different sources of stress vary across space (microsites) and time (intra and inter-annual variation) for co-occurring oak species remains largely unknown. 2. We examined spatio-temporal variation of biotic (herbivory, seed predation) and abiotic (drought) stress agents to evaluate seedling survival across different regeneration microsites, and considering two climatically contrasting years. We used two co-occurring species of contrasting ecology and leaf traits in California oak woodlands: the deciduous Quercus lobata and the evergreen Q. agrifolia. 3. Most oak seedlings (98.8%) suffered from some type of stress. For both species, summer drought was the main cause of mortality, followed by rodent damage, ungulate browsing and insect damage. R...