Declining fruit production before death in a widely distributed tree species, Sorbus aucuparia L.

Abstract

Key message: Trees are commonly thought to increase their seed production before death. We tested this terminal investment hypothesis using long-term data on rowan trees (Sorbus aucuparia) and found no support. Rather, seed production declined significantly before death, which points to the potential detrimental effects of reproductive senescence on regeneration in stands of old trees. Context: Aging poses a fundamental challenge for long-lived organisms. As mortality changes with with age due to actuarial senescence, reproductive senescence may also lead to declines in fertility. However, life history theory predicts that reproductive investment should increase before mortality to maximize lifetime reproductive success, a phenomenon termed terminal investment. Aims: To date, it is unclear whether long-lived, indeterminantly growing trees experience reproductive senescence or display terminal investment. Methods: We investigated fruit production of rowan (Sorbus aucuparia L.), widely distributed trees that live up to 150 years, as they approached death. Results: In our study population in Poland’s Carpathian Mountains, 79 trees that died produced up to 20% fewer fruits in the years before their demise compared to 199 surviving trees of the same population. Conclusion: The pattern of reproductive investment in S. aucuparia is suggestive of age-independent reproductive senescence rather than terminal investment. These findings highlight that the understanding of the generality of life history strategies across diverse taxa of perennial plants is still in its infancy.