Agriculture Reference
In-Depth Information
woody species and grazing habits of livestock and of native grazers and browsers.
Timber harvesting also produces changes in fuels that vary with extraction
methods. In some forest types this can lead to much smaller, more flammable
fuels and often increased surface fuels, greatly exacerbating fire hazard.
In the Mediterranean Basin repeated burning of shrublands to expand range-
lands and agricultural lands has been replaced in the late twentieth century by the
abandonment of traditional rural lifestyles, as well as by legislative changes that
outlawed such burning (Henderson
et al.
2005
; Moreira & Russo
2007
). The
resulting recolonization of previously cleared landscapes by woody species has
resulted in increased fuels that have contributed to a greater frequency of large
high-intensity fires (Loepfe
et al.
2010
), and perhaps slower response time to fires
due to fewer eyes to spot fires (Wrathall
1985
) and fewer volunteers to fight fires
(Bassi
et al.
2008
). Due to such fire events, as well as a cultural framework that
prefers dense forests, land management has focused on reducing fires with inten-
sive fire suppression and increasing forest growth (Seijo
2009
). This has the
potential for producing other undesired changes such as loss of native diversity
(He´ dl
et al.
2010
). Momentum is increasing for the replacement of this cultural-
based management with a paradigm focused on sustainability of natural ecosys-
tems within the context of natural fire regimes (Pausas & Vallejo
2008
).
Although the vast majority of fires are anthropogenic, only a small number of
these are intentional. In fact, prescribed burning is only used locally or sporadic-
ally in France, Portugal and Spain, and not allowed in Greece, Turkey and most
of Italy. The technique is well established only in France, where it is used for fuel
reduction of intact woodlands, and for reducing shrubland recolonization of
former pastures (Rigolot
et al.
1998
).
In California the trend since the mid-twentieth century has been toward expan-
sion of metropolitan population centers into wildland areas. This urban sprawl
has placed more and more structures and people at risk and created a highly
vulnerable wildland-urban interface that totals more than 5 million homes across
28 000 km
2
(Radeloff
et al.
2005
; Hammer
et al.
2007
). This is a severe problem in
the southern half of the state where the population density is far higher than in any
other MTC region (
Table 13.1
). In response to this growth pattern most of the last
century has been managed under a policy of rapid deployment of fire suppression
forces against all unplanned fires. Despite this policy, the total area burned in
coastal and foothill landscapes has either remained unchanged or increased over
the last 100 yrs (Keeley
et al.
1999a
; see Fig. 5.10). The success of this policy is
measured by the fact that although the numbers of ignitions have increased
rapidly over this period, in concert with population growth (Sapsis
1999
; Syphard
et al.
2007
), fire suppression has been successful at keeping much of the landscape
within the historical range of fire frequency and so far saved the majority of native
shrublands from type conversion to alien grasslands (see
Chapters 5
and
12
).
In more remote mountain communities embedded in conifer forests throughout
the western USA, the fire suppression policy has had radically different impacts.
Under a fire regime of understory surface fires, fire suppression forces have been
