Plant-Fire Interactions by Víctor Resco de Dios

Author:Víctor Resco de Dios
Language: eng
Format: epub
ISBN: 9783030411923
Publisher: Springer International Publishing

Lignin (%)

Hemicellulose (%)

Cellulose (%)

Ash (%)

Hardwood stems

18–25

24–40

40–55

<1

Softwood stems

25–35

25–35

45–50

<1

Leaves

0

80–85

15–20

2–8

Grass straw

14–21

24–38

29–43

2–8

Bark

44

30

25

10

Each of these components exhibits very different heating values, which is the amount of energy released during combustion (Table 6.2), hence affecting fire spread. From the lens of fire behavior, the amount of mineral content , or ash, is particularly important. Ashes are difficult to ignite and dampen fire intensity (Varner et al. 2015), while fuels with a larger proportion of mineral content tend to burn slower and have a higher proportion of smoldering (flameless) combustion (Keane 2015). In fact, the mode of action of fire retardants is to diminish fire spread by increasing the fuel mineral content (Giménez et al. 2004; Keane 2015).

Mineral content is the proportion in dry weight of inorganic or mineral material (i.e., without C, H, and O). It is often measured as the ratio of the weight of the ash that is left after a complete combustion, relative to the weight of the unburned dry fuel particle. The five most abundant components in ash are silicon, potassium, calcium, sulfur, and chlorine (Sorek et al. 2014). These are essential macronutrients that play different major physiological roles including defense against pathogens (silicon), regulation of stomatal behavior (potassium or chlorine), amino acid formation (sulfur), or cell wall construction (calcium), among many others.

The contribution of ash varies markedly across tissues: ~10% in bark (Zaja et al. 2018), 2–8% in leaves (Petisco et al. 2008), and < 1% in wood (Zaja et al. 2018). It also varies across species, as pine leaves often show lower ash content (2–6%) than angiosperms (4–8%) (Petisco et al. 2008). The proportion of ash content is not constant in time, and it often shows a unimodal temporal pattern. Ash content increases rapidly during leaf development due to increased accumulation times. However, leaf mineral content often diminishes before leaf or branch senescence because plants have evolved an efficient system of nutrient recycling and minerals stored in older leaves or branches are remobilized and stored or used in other plant parts prior to abscission. Some studies have argued that the reduction in ash content during leaf senescence may have a more profound effect on leaf flammability than the reduction in leaf moisture (Broido and Nelson 1964), but this hypothesis needs further testing, and it is not consistent with modeling results (Fig. 6.6).

Fig. 6.6Ash and live fuel moisture contents are incorporated in Rothermel’s fire behavior model as damping coefficients affecting the reaction intensity. This graph compares the effects of silica-free mineral content and fuel moisture on the damping coefficient. The point on the graph indicates a commonly used value in models

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.