Fuel composition influences fire characteristics and understorey hardwoods in pine savanna

Abstract

Summary1. Fuels in the groundcover of frequently burned south-eastern pine savannas include shed leaves of trees. Flammable needles of longleaf pine (Pinus palustris) potentially increase maximum fire temperatures and durations of heating, negatively affecting other trees within the groundcover. Less flammable leaves that accumulate around the bases of understorey stems of hardwood trees such as mockernut hickories (Carya alba) in the fall potentially depress maximum fire temperatures and durations of heating, enhancing post-fire recovery. 2. We experimentally manipulated amounts of pine and hickory leaves beneath understorey hickory stems in a pine savanna, measured temperatures during prescribed fires and assessed combustion of fuels and survival and regrowth of hickory stems. 3. Pine needles increased fire temperatures and durations of heating relative to herbaceous fuels and increased combustion of hickory leaves. Hickory leaves, however, neither increased nor decreased fire characteristics relative to herbaceous fuels. 4. All hickories survived fire by resprouting. When pine needles were absent, most hickories resprouted from buds located above-ground along the stem at heights inversely related to temperature increase. In contrast, resprouting occurred only from underground root crowns when pine needles were present. Such differences in locations of resprouts influenced sizes of stems at the end of the growing season. 5. Synthesis. Groundcover fuels containing flammable leaves shed by pyrogenic species of savanna trees affect local fire characteristics and resprouting of non-pyrogenic understorey trees. Thus, local variation in flammable fuels produced by pyrogenic species can engineer landscape dynamics of other trees in savannas.

Flammability of litter sampled according to two different methods: comparison of results in laboratory experiments

“…However, some flammability variables (flame height, flame temperature and rate of consumption) were highly affected by the construction of litters that decreased the litter aeration, except for very compacted litters like those of pure pine. The burning of the pine litters released the highest temperature, regardless of the sampling method and this result was consistent with the work of Ellair and Platt (2013). The negative relationship between rate of spread and flaming duration shown in the co-inertia analysis was consistent with other works dealing with mixed litters (de Magalhães and Schwilk 2012); however, none of these variables varied significantly between vegetation types.…”

Pyrogenic fuels produced by savanna trees can engineer humid savannas

“…Recurring fires fueled by C 4 grasses thus produce “fire traps,” demographic bottlenecks that reduce chances that woody plants will reach the overstory (e.g., Bond and Midgley , Higgins et al. , Werner and Franklin , Grady and Hoffmann , Ellair and Platt , Werner and Prior ). Nonetheless, variation in fire weather conditions (e.g., rainfall and drought conditions; Beckage et al.…”

Testing Vegetation Flammability: The Problem of Extremely Low Ignition Frequency and Overall Flammability Score

“…Thus, to avoid complete preignition combustion of a sample an increased amount of material should be considered at low heat fluxes. Epiradiator testing of leaf litter samples bigger than 1 gram is justified as leaf litter naturally occurs in layers, presenting more or less continuous fuel patches, which even in very fragmented state have mass bigger than 1 gram and a fuel load higher than that corresponding to testing 1 gram at epiradiator with 10-centimetre diameter [18,22,51,52]. …”

“…Due to rising importance of reliable vegetation flammability information numerous researchers worked on quantifying it with studies ranging from field burning experiments [17,18] and burning tables/benches [19][20][21][22] to individual leaf testing [16,23]. In this effort a high number of testing procedures and measured parameters were associated with vegetation flammability.…”