Interspecific variation in mortality and growth and changes in their relationship with size class in an old‐growth temperate forest

1. Understanding trade‐offs between demographic parameters is crucial when investigating community assembly rules in high‐diversity forests. To this end, we estimated mortality and growth parameters, and correlations among them, across entire size classes for 17 tree species (Betula, Carpinus, Fagus, Quercus, Castanea, Acer, Cerasus, Swida, Kalopanax, and Styrax) using a dataset over 18 years obtained from an old‐growth forest in Japan. 2. Size classes were represented by 12 categories determined by age, height, and diameter at breast height (DBH) from new seedlings to stems of DBH >85 cm. We derived the annual mortality and growth for each species and class using estimates of transition probabilities between classes. Trade‐offs or synergies in growth and survival among species per size class were analyzed with and without the inclusion of phylogenetic relationships. 3. Annual mortality showed U‐shaped patterns across size classes for species that could potentially reach a DBH ≥55 cm: 0.2–0.98 for seedlings, 0.002–0.01 at DBH 35–45 cm, and ca. 0.01 at DBH ≥55 cm. Other species demonstrated monotonically decreasing mortality toward specific maximum size classes. When phylogenetic information was included in analyses, the correlations between survival and growth changed across size classes were significant for some classes: As an overall tendency, synergy was observed in growth and survival for seedling to sapling classes, trade‐offs for juvenile to DBH 15–25 cm classes, and synergy again for larger classes. When phylogenetic information was not included, a significant trade‐off was observed only at DBH 5–15 cm. 4. Synthesis. Trade‐offs at intermediate classes imply differentiation in demographic characteristics related to life history strategies. However, evolutionarily obtained demographic characteristics are not substantial drivers of niche differentiation in the study area. The polylemma of mortality, growth, and other parameters such as the onset of reproduction may also be important factors driving species‐specific demographic traits.