How early do Cerrado grasses become fire-resilient? Insights from an ontogenetic experiment

Fire is a recurring ecological disturbance in tropical grassy biomes, exerting strong selective pressure. Although adult species have a high capacity for resprouting, little is known about the age at which young plants acquire resilience to fire. This knowledge has practical implications when considering fire management frequency and the introduction of prescribed burns in areas under restoration to ensure the survival of vegetation. Thus, our objective was to evaluate the time required for native Cerrado grasses to become resilient to fire, analyzing their survival and recovery capacities at different developmental stages.

We conducted a greenhouse experiment with three native species frequently used in restoration projects (Aristida riparia, Loudetiopsis chrysothrix, and Trachypogon spicatus). At 3, 6, 12, and 18 months of age, the plants were subjected to controlled burning (10 seedlings for each burning time). After each fire, we monitored plants' survival and traits related to regrowth (i.e., number of tillers, number of leaves, leaf length, and aerial biomass) for 120 days.

We found high survival rates as early as 3 months of age (above 50%), with increases to values above 70% in subsequent growth stages. Overall, the resilience to fire increases with plant age, reaching almost 100% in plants within 12 months. However, fire performed before the dry season reduces the rate of recovery. The biomass accumulation after fire was higher in plants within 18 months, likely due to the greater availability of stored reserves and buds for resprouting. Considering regrowth traits, we found positive values when compared to pre-fire values.

For fire management, it is recommended that burning be carried out when the grass seedlings are at least 12 to 18 months old. In addition, burning should be avoided before the start of the dry season to promote faster recovery and greater growth of grasses after the fire.