Fire and bunchgrass dynamics in pine savannas

It is well known that ecological disturbance regimes affect plants; it is less commonly appreciated how plants, in turn, affect those disturbance regimes. For example, plant fuels often play an important role in determining natural fire regimes. Fire is a powerful evolutionary filter with the potential to radically change plant populations and communities in a matter of minutes or hours. Changing fire regimes are expected under climate change theory, 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 the interactions between fire regime and plants, I have investigated the relative importance of different fire characteristics on diverse pine savanna understory vegetation. Results from this study have demonstrated how fire severity drives large-statured bunchgrass dynamics (Gagnon et al. 2012), with important implications for community assembly in this species-rich ecosystem. This same work has 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; the hypothesis also informs burning prescriptions by managers of natural areas (Gagnon et al. 2010). I next plan to experimentally test different facets of this new hypothesis of plant flammability by manipulating composition and architecture of plant fuels.

A related avenue involves global change phenomena viewed through the lens of disturbance ecology. Rising sea and CO2 levels, altered rainfall-, drought-, fire- and hurricane-regimes all have the potential to disrupt ecosystems and therefore, conservation plans. The perspective that plant populations and communities are dynamic assemblages provides a natural fit for global change-related investigations, and I am planning to establish a research program that explores how intensifying disturbance regimes are likely to affect plant populations.

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