Qiu, Tong; Aravena, Marie-Claire; Andrus, Robert; Ascoli, Davide; Bergeron, Yves; Berretti, Roberta; Bogdziewicz, Michal; Boivin, Thomas; Bonal, Raul; Caignard, Thomas; Calama, Rafael; Julio Camarero, J.; Clark, Connie J.; Courbaud, Benoit; Delzon, Sylvain; Donoso Calderon, Sergio; Farfan-Rios, William; Gehring, Catherine A.; Gilbert, Gregory S.; Greenberg, Cathryn H.; Guo, Qinfeng; Hille Ris Lambers, Janneke; Hoshizaki, Kazuhiko; Ibanez, Ines; Journé, Valentin; Kilner, Christopher L.; Kobe, Richard K.; Koenig, Walter D.; Kunstler, Georges; LaMontagne, Jalene M.; Ledwon, Mateusz; Lutz, James A.; Motta, Renzo; Myers, Jonathan A.; Nagel, Thomas A.; Nuñez, Chase L.; Pearse, Ian S.; Piechnik, Lukasz; Poulsen, John R.; Poulton-Kamakura, Renata; Redmond, Miranda D.; Reid, Chantal D.; Rodman, Kyle C.; Scher, C. Lane; Schmidt Van Marle, Harald; Seget, Barbara; Sharma, Shubhi; Silman, Miles; Swenson, Jennifer J.; Swift, Margaret; Uriarte, Maria; Vacchiano, Giorgio; Veblen, Thomas T.; Whipple, Amy V.; Whitham, Thomas G.; Wion, Andreas P.; Wright, S. Joseph; Zhu, Kai; Zimmerman, Jess K.; Zywiec, Magdalena; Clark, James S. 2021. Is there tree senescence? The fecundity evidence. Proceedings of the National Academy of Sciences. 118(34): e2106130118. doi:https://doi.org/10.1073/pnas.2106130118
Physiological decline in large, old trees could involve diminished reproductive effort, but evidence is lacking. A global analysis finds that fecundity decline in large trees is pervasive, consistent with physiological decline, thus providing new evidence for tree senescence. For the 20% of species not showing fecundity declines, this lack of evidence was linked not to specific species groups, but rather to lack of large trees in the data. Large trees remain important for their structural attributes, but results highlight the critical role of intermediate trees for their contribution to reproduction. Despite its importance for forest regeneration, food webs, and human economies, changes in tree fecundity with tree size and age remain largely unknown. The allometric increase with tree diameter assumed in ecological models would substantially overestimate seed contributions from large trees if fecundity eventually declines with size. Current estimates are dominated by overrepresentation of small trees in regression models. We combined global fecundity data, including a substantial representation of large trees. We compared size?fecundity relationships against traditional allometric scaling with diameter and two models based on crown architecture. All allometric models fail to describe the declining rate of increase in fecundity with diameter found for 80% of 597 species in our analysis. The strong evidence of declining fecundity, beyond what can be explained by crown architectural change, is consistent with physiological decline. A downward revision of projected fecundity of large trees can improve the next generation of forest dynamic models.