Fire and bunchgrass dynamics in pine savannas

Ecological disturbance regimes affect plants, and plants can in turn affect the disturbance regime. For example, plant fuels can play an important role in determining natural fire regimes in potential feedback loops. Fire is a powerful evolutionary filter that can radically influence plant populations and communities in a matter of minutes. Changing fire regimes are expected to accompany climate change, with unknown implications for plant populations and communities.

  • Recently burned longleaf pine savanna showing resprouting bunchgrasses in understory
  • Burned longleaf saplings (on the right) - despite how they look, these survived the fire
  • Bunchgrass plot in early April, pre-fire
  • Same plot in May, immediately after fire
  • Three weeks post-fire
  • In September, same year

To explore interactions between fire regimes and plants, I have investigated the relative importance of different fire characteristics on species-rich pine savanna understory vegetation. Results demonstrate how fire severity can drive large-statured bunchgrass dynamics (Gagnon et al. 2012), with important implications for community assembly in this species-rich ecosystem. Fire residence time has proven to be a more important driver of plant dynamics than other metrics of fire intensity like measured temperature (Gagnon et al. 2015). These empirical results have led me to develop a new evolutionary hypothesis to explain why so many plants in fire-prone ecosystems produce highly flammable fuels and burn with great intensity (Gagnon et al. 2010). This hypothesis also informs burning prescriptions by managers of natural areas. Along with colleagues, I am now exploring the influence of dominant, large-stature bunchgrasses on alpha and beta diversity in longleaf pine savannas at Camp Whispering Pines in SE Louisiana and at Eglin Air Force Base in NW Florida. I next plan to experimentally test different facets of this hypothesis of plant flammability by manipulating composition and architecture of plant fuels at one or both of these research sites.