Indirect climate risks for tree fecundity that come through variation in size and growth (climate-conditions interactions; CCI) are not currently part of models used to anticipate forest regeneration. Yet CCI may be among the most-important mechanisms needed to accurately predict forest responses to climate change. Meta-analyses of trends and species distribution models to predict them will be misleading if responses depend on the condition of individual trees. A synthesis of tree species in North America shows that CCI dominate through two pathways, i) effects of growth on fecundity that depend on climate, and ii) effects of climate that depend on tree size. Because fecundity declines in large trees, climate changes that stimulate growth move small trees into more fecund and large trees into less fecund size classes. There is a biogeographic divide to this CCI, reducing fecundity in the West and increasing it in the East. Continental-scale responses to climate change are thus dominated by interactions at the individual scale, highlighting the importance of ecosystem management that considers multiple demographic rates.