(i.e. prescribed) fire (Ager et al. 2013) (Fig. 2.3d). In many cases, the cost of
mechanical fuel reduction is high and may imply a loss of commercial revenues—
which can be compensated to some extent by biofuel production—or C stocks. In
populated areas, these actions, therefore, tend to be concentrated in restricted,
sensitive areas, often close to the wildland–urban interface (Driscoll et al. 2016).
Consequently, the true trade-off regarding economic cost corresponds to fire
suppression versus fuel reduction options, and the challenge is to optimise the
respective actions through territory and time.
In addition to the fire-vegetation feedback, a fire-driven system is also controlled
by the ambivalent effect of weather, since high temperatures and low humidity
favour the ignition and propagation of fires. However, when these conditions
continue over time they result in chronic drought—as in arid climates—and reduced
fuel load (Loepfe et al. 2014). The increase in dry fuel after extreme drought
episodes that exacerbate vegetation mortality can be considered transitory in the
context of an overall fire regime, although it does represent a temporary window of
opportunity for wildfires (Allen 2007). Thus, as in other ecosystems, the occurrence
and severity of wildfires in mountain forests respond to a network of historical
interactions involving climate, previous fires, management and other disturbances
(e.g. insect outbreaks) (Bigler et al. 2005). Accordingly, a fire regime and its
distribution in a landscape can be analysed by spatially explicit simulation models
that include the characteristics of vegetation and management (Schumacher and
Bugmann 2006; Loepfe et al. 2012). The empirical analysis of fire distribution at a
regional scale reveals that in drier regions wildfires are controlled by fuel load
availability, while in moist regions fire is determined by the occurrence of extreme
dry periods (Loepfe et al. 2014). Therefore, the fuel vs. climate control of a fire
regime can change over time, while the fuel load accumulates and climate changes
(Kloster et al. 2012). In periods in which logging is intense or agricultural activity
predominates, wildfires will mainly be determined by the local accumulation of fuel
load; in contrast, when afforestation dominates a landscape, the limiting factors
would be weather and drought (Pausas and Fernández-Muñoz 2012). In high
mountains, these dynamics would often correspond to pastures and encroachment,
respectively, but they have traditionally been disrupted by humans who have widely
used wildfire to favour grazing (MacNeill 2003; Colombaroli et al. 2010). Thus,
conservation in high mountains should come to terms with fire management, particularly because fire climatic risk is expected to increase in many regions
(Moriondo et al. 2006). In addition to the financial component of the trade-off
between fire suppression and fuel reduction, conservation in these areas should
incorporate analysis of the trade-offs and synergies between biodiversity values and
ecosystem services associated with a fire regime in terms of species composition,
soil and vegetation, C stocks and erosion (Garcia-Pausas et al. 2017). For instance,
while C stock and erosion losses respond similarly to wildfires, species diversity
may be favoured by moderately frequent fires (Coop et al. 2010).
54
F. Lloret
mechanical fuel reduction is high and may imply a loss of commercial revenues—
which can be compensated to some extent by biofuel production—or C stocks. In
populated areas, these actions, therefore, tend to be concentrated in restricted,
sensitive areas, often close to the wildland–urban interface (Driscoll et al. 2016).
Consequently, the true trade-off regarding economic cost corresponds to fire
suppression versus fuel reduction options, and the challenge is to optimise the
respective actions through territory and time.
In addition to the fire-vegetation feedback, a fire-driven system is also controlled
by the ambivalent effect of weather, since high temperatures and low humidity
favour the ignition and propagation of fires. However, when these conditions
continue over time they result in chronic drought—as in arid climates—and reduced
fuel load (Loepfe et al. 2014). The increase in dry fuel after extreme drought
episodes that exacerbate vegetation mortality can be considered transitory in the
context of an overall fire regime, although it does represent a temporary window of
opportunity for wildfires (Allen 2007). Thus, as in other ecosystems, the occurrence
and severity of wildfires in mountain forests respond to a network of historical
interactions involving climate, previous fires, management and other disturbances
(e.g. insect outbreaks) (Bigler et al. 2005). Accordingly, a fire regime and its
distribution in a landscape can be analysed by spatially explicit simulation models
that include the characteristics of vegetation and management (Schumacher and
Bugmann 2006; Loepfe et al. 2012). The empirical analysis of fire distribution at a
regional scale reveals that in drier regions wildfires are controlled by fuel load
availability, while in moist regions fire is determined by the occurrence of extreme
dry periods (Loepfe et al. 2014). Therefore, the fuel vs. climate control of a fire
regime can change over time, while the fuel load accumulates and climate changes
(Kloster et al. 2012). In periods in which logging is intense or agricultural activity
predominates, wildfires will mainly be determined by the local accumulation of fuel
load; in contrast, when afforestation dominates a landscape, the limiting factors
would be weather and drought (Pausas and Fernández-Muñoz 2012). In high
mountains, these dynamics would often correspond to pastures and encroachment,
respectively, but they have traditionally been disrupted by humans who have widely
used wildfire to favour grazing (MacNeill 2003; Colombaroli et al. 2010). Thus,
conservation in high mountains should come to terms with fire management, particularly because fire climatic risk is expected to increase in many regions
(Moriondo et al. 2006). In addition to the financial component of the trade-off
between fire suppression and fuel reduction, conservation in these areas should
incorporate analysis of the trade-offs and synergies between biodiversity values and
ecosystem services associated with a fire regime in terms of species composition,
soil and vegetation, C stocks and erosion (Garcia-Pausas et al. 2017). For instance,
while C stock and erosion losses respond similarly to wildfires, species diversity
may be favoured by moderately frequent fires (Coop et al. 2010).
54
F. Lloret