Elementos, valores y parámetros del sistema

Rainforest is widely considered to be less flammable than other vegetation types (Jackson 1968; Mount 1979; Bond and van Wilgen 1996; Bowman 2000). Comparisons of the flammability of rainforest components with that of components of adjacent ecosystems have shown lower flammability in some rainforest trees in some locations (e.g. Dickinson and Kirkpatrick 1985) but no difference elsewhere (e.g. Bowman and Wilson 1988).

The flammability of species and litter is critical in predicting the conditions under which rainforest of different types will burn. Flammability consists of four components; ignitability, sustainability, combustability and consumability (Anderson 1970; Martin et al. 1994). These components are not independent of one another (Martin et al. 1994). For example, sustainability, combustibility and consumability are irrelevant in the absence of ignition (White and Zipperer 2010).

Ignitability refers to the delay until ignition occurs, and is the time to first flaming from the time of first exposure to an ignition source (Gill and Moore 1996). Sustainability relates to the ability of fuel to continue burning once ignited, independent of the initial heat source (White and Zipperer 2010). Combustibility describes how rapidly the fuel burns after ignition and is related to the rate of spread and heat of combustion (Behm et al. 2004). Consumability refers to the proportion of mass or volume that is consumed in the combustion process (White and Zipperer 2010). High consumability has been associated with fine fuel biomass and volatile solids (Behm et al. 2004).

Moisture content provides the most dominant influence on foliage flammability, with increased levels of moisture content decreasing flammability (Gill and Moore 1996; Etlinger and Beall 2004; Pellizzaro et al. 2007; Marino et al. 2010). Dimitrakopoulos and Papaioannou (2001) found that 73-94% of the variation in ignitability (time to ignition) could be explained by moisture content alone. The surface area to volume ratio of the foliage is also important (Etlinger and Beall 2004; Dibble et al. 2007). Gill and Moore (1996) found that surface area to volume ratio and moisture content together explained over 80% of the variance in ignitability, with increasing

21 moisture content increasing the ignition delay time, and increasing surface area to volume ratio decreasing it (Gill and Moore 1996).

Leaves are commonly the only plant component that is examined in laboratory flammability studies (e.g. Gill and Moore 1996; Dimitrakopoulos and Papaioannou 2001). This is because they provide uniformity and because they are often considered the most flammable part of the plant due to high surface area to volume ratios and the presence of volatile compounds

(Dimitrakopoulos and Papaioannou 2001). Moisture content of the litter component is also a very important factor in the flammability of ecosystems. Fernandes et al. (2008) found that above 35% moisture content, the in situ litter of maritime pine forests was unable to sustain fire. Gillon

et al. (1995) found similar results for a French pine forest, with fuel moisture levels above 30% unable to sustain ignition in a windless environment within a laboratory. In Australia, a moisture content of below 20% – 25% has been found necessary for fine eucalypt fuel to burn sustainably (Luke and McArthur 1978).

Some other contributors to flammability are heat content (Pellizzaro et al. 2007), chemical composition (Etlinger and Beall 2004), ash content (Dickinson and Kirkpatrick 1985), the

arrangement of fuels in three dimensions (Fernandes et al. 2008), fuel bed porosity and fuel depth (Dibble et al. 2007). The flammability of plants is not only a function of their intrinsic properties but also of their environment, horticultural or management practices and life stage and all these factors vary among individuals of the same species (Gill and Moore 1996). Consistent results have not been found for these contributors to flammability. For example, Gill and Moore (1996) found that mineral content decreased flammability, whereas Etlinger and Beall (2004) found no such relationship. These discrepancies may be due to the large number of methods that have been used in testing the components of flammability as well as a lack of independence between the factors (Behm et al. 2004).

In addition to laboratory studies, fire sustainability experiments may take the form of small-scale experimental field test fires (Lin 1999; Beverly and Wotton 2007; Fernandes et al. 2008; Leonard 2009) or landscape-scale fires (Marsden-Smedley et al. 2001; Gould et al. 2007). Small-scale field- based test fires have the advantage of being inexpensive and capable of being conducted during fire weather conditions that may not be conducive to larger scale fires. While experimental laboratory test fires are advantageous for examining specific fuel properties by manipulating external influences such as weather variables (Beverly and Wotton 2007), unless the natural fuel arrangement is retained and a large enough area is allowed for fire to develop, laboratory results

22 are not necessarily transferable to fire sustainability in the field (Fernandes et al. 2008). Fire sustainability studies have been conducted in numerous vegetation types, including grassland (Leonard 2009), buttongrass moorland (Marsden-Smedley et al. 2001), shrublands (Weise et al.

2005) conifer forest surface fuels (Beverly and Wotton 2007; Fernandes et al. 2008) as well as tropical rainforest surface fuels (Uhl et al. 1988), however the capacity for fire to be sustained within cool-temperate rainforest has not been examined.

This chapter aims to determine if leaf and litter material from species that dominate cool- temperate rainforest and mixed forest are less flammable than leaf and litter material from species that occur in surrounding fire dependent ecosystems, such as Banksia marginata scrubland and Eucalyptus coccifera woodland, as well as determining if it is possible to predict flammability from other fuel properties, such as surface area to volume ratio. The chapter also looks at the fuel moisture conditions in a small-scale field based ignition experiment to see how rainforest litter responds to ignition in situ.