Single fire events impose lasting reproductive costs in savanna trees

Fire acts as a primary ecological filter, influencing the structure, composition, and evolutionary pathways of savanna ecosystems globally. While numerous savanna tree species exhibit resprouting, the impact of fire on seed quality remains poorly understood. Using Caryocar brasiliense, a keystone tree species in the Cerrado, as a model, this study examines whether post-fire trees prioritize vegetative recovery to restore canopy function, potentially limiting resources allocated to reproduction and, consequently, reducing both reproductive output and seed reserve concentrations.

Structural responses, reproductive phenology, and seed traits were assessed in two 3-ha Cerrado sensu stricto areas: one burned and one unburned. Forty adult trees were monitored for structural responses, and 20 individuals for phenological over a 30-month period. Seeds from the first post-fire reproductive cycle were collected; 120 were analyzed for mass, viability, and germination, and 50 were used for biochemical-reserve quantification. We applied GLM/GLMM models and complementary tests.

Although the survival rate was 95%, the fire caused significant structural damage. Fifty-two percent of individuals experienced topkill. Branch number and crown area decreased by 28% and 56%, respectively, with minimal recovery observed over 30 months. Reproductive activity was suppressed for two cycles and resumed only after 25 to 27 months at a reduced level. Seeds from burned trees exhibited lower mass, approximately 20% lower viability, and diminished lipid and carbon reserves. However, germination rates remained similar between treatments.

Fire-induced structural damage and diminished seed quality demonstrate that a single burn event can restrict the short-term reproductive capacity of Cerrado trees. Such limitations may impede population recovery, highlighting the importance of extended fire-free intervals to facilitate canopy restoration and high-quality seeds. The findings indicate that the structural and physiological impacts of a single fire may endure for considerable periods before the ecosystem restores its pre-fire ecological functions.