Fire intensity effects on flowering and post-fire bud activity in the endemic savanna bunchgrass Aristida beyrichiana.

The bud bank of perennial grasses is a key aspect of their reproduction and longevity in frequently burned ecosystems. We investigated how fire intensity and time since fire affected fire-stimulated flowering and bud activity of wiregrass (Aristida beyrichiana), a foundational bunchgrass in south-eastern US pine savannas. We manipulated fuels and monitored fire temperatures in plants during an experimental fire. We tested effects of plant size and fire intensity on flowering stem production and proportions of active and dead buds. We compared active, dead and total buds from plants in the experimental burn with those in stands burned one and 2 years ago, and described the species' bud morphology and anatomy. The duration above 60 °C had a marginally significant negative effect on the number of flowering stems per plant. This effect was less than the significant positive correlation of flowering stem number with plant size. Fire intensity did not affect the proportions of dead and active buds 5 months after fire. There were significant differences in proportions of active, dead and dormant buds 1 year after fire, and the total number of buds decreased with time since fire. Plants had an average of one bud per tiller, and mean bud depth was 3 cm. Perennial bud banks are a substantial source of regenerative biomass for plants in fire-prone savannas. For fire-stimulated flowering species, frequent fires are likely important for maintaining large bud banks that supply both vegetative and flowering structures. A focus on belowground structures should shed light on long-term ecosystem dynamics in fire-prone ecosystems.