5th Symposium on Fire and Forest Meteorology and the 2nd International Wildland Fire Ecology and Fire Management Congress

Monday, 17 November 2003: 3:30 PM
Fuel composition and consumption in subtropical South Florida slash pine forests
James R. Snyder, USGS, Ochopee, FL; and H. Belles, S. Koptur, M. S. Ross, and J. Sah
A series of experimental fires have been conducted in South Florida pinelands to examine effects of season of burning. The studies have been conducted in three locations: 1) Key Deer National Wildlife Refuge on Big Pine Key (BPK) in the Lower Florida Keys, 2) the Long Pine Key (LPK) area of Everglades National Park, and 3) the Raccoon Point (RP) area of Big Cypress National Preserve. The BPK and LPK sites are true pine rocklands in that the substrate is Miami oolitic limestone, whereas the RP pinelands are found where there is a thin (~20cm) layer of sandy soil on top of Tamiami limestone. The South Florida climate can be characterized as having a hot, rainy wet season from May to October and a cooler and relatively dry season from November through April.

The dominant tree throughout is South Florida slash pine, Pinus elliottii var. densa. The understories contain palms in all three areas. The RP pinelands contain cabbage palm and saw palmetto, both temperate palms. These same species are the dominant palms in LPK, but there are also significant numbers of silver palm, a tropical palm, in parts of LPK. The dominant palm in BPK is the tropical thatch palm, with substantial amounts of silver palm and very limited numbers of saw palmetto and cabbage palm. The hardwood shrub flora is least diverse and most temperate in RP and more diverse and tropical in LPK and BPK. The herbaceous layer is dominated by grasses and sedges in all three areas.

We estimated fuel loading with clipped quadrats and sorted dead material into fine (<6 mm) and coarse (6-25 mm) litter components and live vegetation into herbs, palm fronds, and hardwoods (leaves and stems < 6 mm diameter). Total fuel loading ranged from a high of 1660 g/m2 (1555 g/m2 litter and 105 g/m2 vegetation) in BPK to a low of 1050 g/m2 (875 g/m2 litter and 175 g/m2 vegetation) in RP. LPK was intermediate with a fuel loading of 1460 g/m2 (1310 g/m2 litter and 150 g/m2 vegetation). It is thought that the Keys pinelands have lower productivity than those on the mainland, however, the pinelands on Big Pine Key had been unburned for 8 years or more, while those in the National Park Service areas had burned about 4 years previously on average.

The live component of fuels was dominated by herbs in the RP pinelands with very little contributed by hardwood shrubs. The opposite was true in LPK and BPK where live fuels were dominated by the diverse shrubby understory. The preponderance of herbaceous fuels in Big Cypress pinelands may be attributed to their hydric nature, as they are often flooded with several centimeters of water during the wet season.

In all cases the dominant component consumed by fire was the fine litter component, which is predominantly pine needles. Fuel consumption at RP ranged from a mean of 645 g/m2 in 6 wet season burns to a mean of 810 g/m2 in 6 dry season burns. In four LPK burns fuel consumption ranged from 950 to 1450 g/m2. In BPK, loss of fuel ranged from 380 to 1270 g/m2 and fuel consumption as a percentage of initial fuel loading ranged from 40 to 72%. Only two of the 10 burns conducted on BPK were carried out in the dry season and they did not have appreciably different fuel consumption than adjacent wet season burns. The uneven, rocky substrate in the LPK and BPK pinelands allows rapid drying of fuels so that wet season burns can result in higher fuel consumption than the seasonal rainfall pattern would otherwise suggest.

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