Historic Fire Regimes of Florida Dry Prairies

Dry prairies were thought to have developed with a fire regime of every 1-4 years (Abrahamson and Harnett 1990), although some sources suggest an even higher fire return frequency (1-2 years) in regions devoid of major natural fire barriers (Orzell and Bridges 1999).  Frequent burning kept pines and oaks from invading dry prairie, turning them into pine flatwood or scrubby hardwood sites.  These burns would have been very intense due to the high flammability of saw palmetto and wiregrass, both of which are species that are tolerant of fire.  Dry prairie burns more intensely and completely compared to other Florida ecosystems such as scrub because scrub contains lower biomass litter and patches of bare sand (Abrahamson and Harnett 1990).

Historically, most of these burns likely occurred during the late spring and early summer months (fire season) and were caused by lightening.  Florida has a high frequency of lightening strikes, more than any other region in the United States (Abrahamson et al. 1984). When burned in the summer this ecosystem tended to burn completely, covering thousands of acres from a single ignition source.  Before construction of roads, power lines and canals, there were few firebreaks to slow down the speed of a fire in a dry prairie, so given the right conditions a single lightening strike could have burned large areas.

Although most lightning-ignited fires occurred during the late spring and early summer months, it is likely that under the right conditions dry prairies could have burned during any time of the year. Fires that burned at different times of the year would have likely been patchier because of moister conditions in the dry prairie.  Anthropogenic fires expanded the season of fires in dry prairies to all seasons of the year.  Along with flatwoods, ranchers typically burned dry prairies rangeland annually or biennially during the winter or early spring months to stimulate forage growth.