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ŠUMARSKI LIST 11-12/2015 str. 69     <-- 69 -->        PDF

magnitude difference between observed and estimated fireline intensity was found for tall maquis, which is due to the very low amount of dead fuel in relation to live fuel. The reason for this disagreement is the fact that Rothermel’s model was developed using only dead fuels and it was mathematically extended to live fuels, where the live fuel component burns only when the complex contains enough dead fuel to sustain live fuel combustion (Catchpole & Catchpole 1991). For both low and tall maquis, fire spread rate is overpredicted by more than 50%, which is also consistent with the importance of live fuels in these vegetation types.
Comparatively, the predictions for the remaining fuel complexes, which are entirely composed of dead fuels, are in closer agreement with observed fire characteristics. Slash fuel fire behavior exhibits a clear and marked temporal trend, with important decreases with slash age. As time passes and foliage retention decreases, the fuel bed packing ratio decreases up to a point where the available fuel does not optimize combustion.
Within the wind range adopted for simulation (0–20 km h–1), the response of rate of fire spread to wind was relatively linear, in accordance with most empirical models of fire spread in shrubland (Vega et al. 1998; Fernandes, 2001; Bilgili & Saglam, 2003; Saglam et al. 2008b; Anderson et al. 2015). From Figure 1, it is quite apparent that the difference is marked in potential fire spread between maquis, especially low maquis, and the horizontally-dominated fuel beds. Rate of spread is predicted to be similar between black pine litter and fresh slash particularly at higher wind speeds.
Similarly to wind speed, shrub fuels were more responsive to variation in dead fuel moisture content, indicating that dramatic changes in fire behavior can occur as weather conditions change (Figure 2). Rates of spread in black pine slash and litter varied only within a narrow range of 1–4 m min–1 in response to the comparatively large moisture content range of 4–20%, implying that wind variation would be much more important than moisture content variation in these fuel complexes, in accordance with other studies in pine fuel types (e.g. Küçük et al. 2007; Tanskanen et al. 2007; Küçük et al. 2008; Fernandes et al. 2009).
Figure 3 illustrates the effect of slash age on potential fire spread rate. Initially (month 3) the difference between 8 kg m–2 and 16 kg m–2 treatments is more evident (3.2 versus 2.4 m min–1), but rate of spread decays quite fast and after 9 months it decreases to one third of month 3 values. From the point of view of fire hazard, the changes