Fire Effects in Dry Prairies

Different burning seasons tend to favor different groups of species in Florida dry prairies.  In dry prairies, dormant season burns favor graminoids over forb species, while burns during the growing season tend to favor forbs.  Calopogon mutiflorus has been shown to flower after dormant season burns, but rarely flowers in years that have not burned, or burned during the summer (Goldman and Orzell 2000).  Cutthroat, beard grasses (Andropogon spp.), and wiregrass are more likely to flower when burned in the early growing season (Abrahamson 1984).  Burning during the growing season also delays the flowering of certain species and synchronizes flowering peaks of groundcover species (Platt et al. 1988).

Fires play an important role in nutrient cycling of dry prairie ecosystems.  Frequent, low-intensity fires increase the rate of nutrient turnover, raise pH and stimulate nitrogen fixation (Abrahamson and Hartnett 1990).  Phosphorus and cations in biomass are mineralized in these conditions as well (Abrahamson and Hartnett 1990).

Effects of Fire Suppression

Deviation in fire intensity, fire return interval, and seasonality from the natural fire regime of frequent growing-season burns have modified vegetation structure and composition of dry prairie communities (Perry 1997, Dye 1997, Bridges 1997). Loss of ground cover species, changes in pine density and recruitment, invasion of non-constituent oaks, and excessive shrub growth has been documented from dry prairies with long periods (ca. 35 years) of fire exclusion (Dye 1997, Perry 1997). When dry prairie is frequently burned, saw palmetto is typically of small stature and sparsely distributed, but it tends to increase in stature and density when fire is absent or infrequent (Cole et al. 1994a).

Parts of Myakka River State Park, located in the southwestern peninsula of Florida in Sarasota and Manatee Counties, have not burned for 35 years.  With fire suppression, more woody shrubs and oaks have invaded dry prairies.  In the Wilderness Preserve Series at Myakka State Park, areas of dry prairie that were adjacent to oaks saw open areas decrease from 66 percent to 26 percent in 37 years (Huffman and Blanchard 1991).  Saw palmettos that are small and sparse in frequently burned dry prairies become larger and tend to overtake wiregrass if the area is fire suppressed (Orzell and Bridges 1999).  If there is an available seed source pines will creep into dry prairies, it is thought that a burning frequency of 1-5 years will keep pines from invading dry prairies and turning them into pine flatwoods (Orzell and Bridges 1999).

After years of fire suppression, recovery to a state that was present pre-suppression is not likely after one burn.  After years of fire suppression, woody shrubs that invade prairie develop extensive root systems that will send up many sprouts if burned.  Herbicides and roller chopping are two methods that are used often in combination with burning in the restoration of dry prairies to a pre fire-suppressed state.