Drivers of intraspecific variation in fecundity in rowan (Sorbus aucuparia)

Understanding the variation in fecundity, the reproductive capacity of individual trees, is crucial for predicting population dynamics and ecosystem functioning. However, estimating tree fecundity is challenging due to the large variation in seed production observed between trees and across years that necessitates logistically challenging long-term monitoring. This study aimed to investigate the factors influencing fecundity in rowan trees (Sorbus aucuparia) using a 22-year fruit-count dataset in 167 individual trees. We examined the relationship between fecundity and intrinsic (DBH, height, and leaf nutrient concentration) and extrinsic factors (soil nutrients, light availability, and neighborhood crowding). Our findings revealed that diameter at breast height (DBH) better explained variation in fecundity than height. After accounting for tree size using DBH, light availability had the strongest, positive effect on fecundity and was the major limiting factor for rowan’s fecundity. At the same time, neighborhood crowding index with conspecifics also showed significant, but negative correlation with fecundity, suggesting competition for pollinators among rowan trees. Our findings contribute to a better understanding of seed production ecology and can inform management and conservation efforts that aim for increased fruit supply, either for plant populations or fruit consumers.