Although it has been demonstrated that environmental changes within a year can affect the reproduction, survival, and growth of invasive species, these factors have rarely been incorporated into demographic analyses. Therefore, we applied multistate demographic models (based on capture–recapture animal methods accounting for imperfect detectability of individuals in natural conditions) to evaluate the effects of reproductive phenology and rainy season on the survival and transition/retrogression rates among stage categories of black elderberry (Sambucus nigra L.)—an invasive tree species widely distributed in temperate forests of Europe and America. In the Abies religiosa temperate forest, Mexico City, a multistate demographic model of S. nigra was built using bimonthly censuses during a year. We selected the best-fitting model according to Akaike's information criterion adjusted for small sample sizes (AICc). We determined the response of reproductive phenology of S. nigra to the rainy season for 2 yr through repeatability and phenotypic plasticity indexes. Our results showed that the reproductive phenology of S. nigra has a low repeatability index and a high phenotypic plasticity index. We demonstrated that additive and interactive effects of reproductive phenology and rainy season promote changes in survival and transition/retrogression rates among stage categories. During the rainy season, the survival probability of seedlings and transition probability toward the adult category increased. Therefore, our study represents a significant contribution to the knowledge of the demographic dynamics of invasive species on an intra-annual scale.