Prescribed Fire in Florida Scrub

Ecosystem Maintenance and Restoration

In areas that have received fire, continued prescribed burning is used to maintain key attributes of vegetation structure (e.g. low vegetation height, low pine tree density, patches of bare ground). Many of these key attributes are important to the Florida scrub jay and to endemic plants, especially gap specialists. Fires also reduce fuels and that, together with a more convenient structure, helps reduce the intensity and size of subsequent wildfires, a major issue in Florida. Maintenance fires are usually conducted in the spring and summer. Most fire managers tolerate patchiness in these fires. In fact, there is a tendency to be satisfied with lighting the perimeter of burn units and inadequate monitoring of the percent of area burned. Obviously, a burn unit with only 10% of the area actually burned will not be a biologically effective fire, nor will it reduce fuel loads significantly. However, high-intensity crown fires have been prescribed and successfully implemented (e.g., Custer and Thorsen 1993, Outcalt and Greenberg 1998, Main and Menges 1997).

Although prescribed burning has been used aggressively by many land management agencies for decades, large areas of Florida (especially in private hands and near urban areas) continue to be fire suppressed. The dense vegetation can be a fire hazard and does not support the biodiversity of periodically burned areas. As these areas come into ownership by public or private agencies that are able to use fire management, a difficult restoration phase begins. Areas that are extremely overgrown are likely to be particularly difficult to restore using fire (Duncan et al. 1999).

Initial fires in overgrown areas are often conducted during winter months to take advantage of lower humidity and consistent winds that can carry fire through dense vegetation. Most areas are switched to spring and summer maintenance burns after an initial winter burn.

Mechanical pretreatments (or even surrogates) are increasingly used in the restoration phase. These include roller chopping, mowing (with a range of machines), logging, and chain sawing. The goals vary with the type of vegetation and include removing or reducing tree canopies, reducing shrub heights, producing a more uniform fuel bed, and creating a more homogenous fire. These treatments may be designed to reduce fire intensities or, conversely, allow fire-resistant areas to burn. Although many mechanical treatments are being used in scrub and other ecosystems statewide, most are being applied with little monitoring. There are a few ongoing studies on the effects of these treatments on wildlife, vegetation, and rare species showing varying results (Schmalzer and Boyle 1998, Roberts and Cox 1999, Menges et al. 2001, Berish et al. 2002, Schmalzer et al. 2003).

Implementation

Fires are conducted in all seasons in Florida, with a tradition of winter (December-February) burns for restoration and for agriculture and forestry, and spring and early summer (March-July) burns for ecological goals. Few burns are conducted in late summer due to high humidity and rainfall, and fall burns are avoided because they tend to be associated with high pine mortality (Menges and Deyrup 2001).

Fire return intervals (FRI) are often fixed by fire management plans. FRIs for scrub ecosystems are usually designed to match historic ranges (5-20 years), although there is some variation. Some agencies burn on fixed schedules, while some allow more variation in FRI. Fuel reduction concerns have lead some agencies to burn scrub on shorter FRI (5-10 years) although fire suppression in recently acquired lands is still the norm. Lightning ignited fires, accidental fires, and escapes can burn more areas and alter plans for future burning. Likewise, weather and other logistical constraints (including problems obtaining authorizations for various reasons) leave planned burns undone.

Fires are carried out by teams ranging in size from 3-20, by individual agencies or multi-agency task forces, usually with little or no monitoring or associated research. Crews generally depend on vehicles on the ground and hand lighting in Florida scrub. Aerial ignitions, used extensively in Florida in wetland and flatwoods areas, are used in Florida scrub by some agencies. Aerial ignitions often result in a very patchy, low intensity burn. Florida agencies are relatively sophisticated with respect to training, although certainly continued improvement is needed.

Lighting patterns for on-the-ground ignitions usually include backing fires, flanking fires from the edges, and a final head fire (Main and Menges 1997, Outcalt and Greenberg 1998). Many lighters make forays into the burn unit to light spot fires or strip head fires (e.g., Custer and Thorsen 1996). Because Florida scrub is very dense, mown lines are often used within the unit to provide access and to help fires get rolling. Mown lines are often used around the unit to reduce heat on firelines and to facilitate backing fires, which often do not burn well in Florida scrub.

Smoke management is an increasingly important issue in urbanizing Florida. Smoke management planning is now required to obtain burn authorizations from the Florida Division of Forestry. Some tracts of Florida scrub and other vegetation essentially cannot be burned because they are surrounded by roads and other development and there is no place to put the smoke. However, because Florida has a tradition of prescribed fire in agriculture, forestry, and natural lands management, many (most?) Floridians outside of major metropolitan areas tolerate some level of smoke and understand that prescribed burning has benefits despite this inconvenience.

The effectiveness of prescribed burning is not usually measured. Fire coverage, fire intensities, and responses of key species would be useful variables in post-burn monitoring. Most burns are not monitored at all beyond indicating what burn units were lit. Mapping of patchiness of burns using aerial images and GPS might be an eye-opener to land managers. Patchy burns may not provide the same beneficial effects for species that depend on fire (e.g., Satterthwaite et al. 2002).

Additional research on fire behavior, appropriate fuel models for Florida scrub, and the appropriateness of mechanical surrogates and pretreatments for fire would all benefit prescribed fire in Florida scrub (see: Research Gaps).