Comparing Flammability of Southern Plants

Several studies have compared the overall flammability of different plants, but few have included southern species. The information that does exist is summarized below and presented in BROKEN-LINK Table: Flammability characteristics of southern species I, and BROKEN-LINK Table: Flammability characteristics of southern species II. This section concludes with a summary of the limitations of plant flammability research.

Fuel characteristics of saw palmetto (Serenoa repens) and gallberry (Ilex glabra) are the most extensively studied in the southeast. For the chemical characteristics, gallberry appears to be more flammable than saw palmetto (see BROKEN-LINK Table: Energy content of gallberry and saw palmetto). This is confirmed by Burgan and Susott (1991) in a comparison of flammability characteristics for saw palmetto, gallberry, and wax myrtle (Myrica cerifera). Combusted at temperatures ranging from 300^oC to 500^oC, gallberry burned the most intensely, followed by saw palmetto and then wax myrtle (Burgan and Susott 1991). Gallberry has a very high volatile extractive content (Shafizadeh et al. 1977, Burgan and Susott 1991), which contributes greatly to combustion (Shafizadeh et al. 1977). In contrast, saw palmetto has a low volatile extractive content, so combustion can be attributed to unextractable components such as lignin and cellulose (Shafizadeh et al. 1977).

Plant flammability can help determine the general flammability of community types. For example, Behm (in press) found that understory plants in pine flatwoods (saw palmetto, gallberry, and Lyonia lucida) have greater ignitability, sustainability, and combustibility than understory plants in hardwood hammocks (beautyberry, Callicarpa americana). The results of this study and similar studies have important implications for wildfire hazard to wildland-urban interface (WUI) structures near these different forest types.

Bark, terminal branch, and foliage of Melaleuca have greater energy content (5.621, 4.585, and 5.146 kcal∙g-1) than bark, terminal branch, and foliage of Eucalyptus (4.009, 4.497, and 4.894 kcal∙g-1) (Wang and Huffman 1982). Melaleuca and Eucalyptus are exotics from Australia found in South Florida.

Longleaf pine (Pinus palustris) needles burn faster and more intensely than needles from South Florida slash pine (Pinus elliotii var elliotii) although both are highly flammable (Fonda 2001). Sand pine needles had a significantly longer flame time than longleaf or South Florida slash, but were generally less flammable (Fonda 2001). Longleaf pine litter produces slightly more energy per weight than slash pine litter possibly due to lower mineral content and higher surface area-to-volume ratio for longleaf pine litter (Hough and Albini 1978). No more distinctions between pines can be made at this time, although the observed energy content of the evergreen Juniperus ashei (2.6 kcal∙g-1) was much lower than other evergreen species that have been studied (Owens et al. 1998).

Data on other southern species are much more limited. Based on reported specific leaf area (leaf area per mass), red maple foliage is more flammable than chestnut oak followed by scarlet oak (Rieske et al. 2002). However, the information for these species was not gathered in order to quantify flammability and other information on flammability characteristics is not available. In addition, flammability comparisons between species from different studies are difficult due to differences in environmental conditions and horticultural practices. Although leaf area per plant has been measured for mountain laurel (Thackston et al. 1982) and rosebay rhododendron (Starrett et al. 1993), they are not comparable due to different horticultural production of the nursery plants. The lack of studies comparing flammability characteristics among species precludes any further comments concerning other fuel components of the south.