Agriculture Reference
In-Depth Information
Contemporary MTC Fire Regimes
MTC plant communities are among the most fire-prone woody vegetation types in
the world (Chuvieco et al. 2008 ). This is the result of wet winters with moderate
temperatures, which are conducive to biomass production sufficient to carry fires,
and an annual summer drought, which converts this biomass to available fuels.
The low to moderate productivity of these communities generates large expanses
of shrubland or woodland fuels that are conducive to high-intensity crown fires.
MTC alone does not make this vegetation fire-prone, as demonstrated by the
distribution of fire-prone mediterranean-type vegetation (MTV) outside MTC
regions; pines in North America and Eucalyptus in Australia are good examples.
The primary difference with fire regimes in sclerophyll vegetation in other climates
is that in MTC regions there is an annual fire season, making these landscapes
vulnerable to fires every year, whereas under other climates, this vegetation type
may experience high fire danger at longer intervals, for example every 2 yrs
(Hasson et al. 2009 ) or longer (Vines 1974 ) in southeastern Australia.
Large, high-intensity fires have long been associated with MTC vegetation (see
the discussion of paleohistory in Chapter 10 ), and it is the colonization of
these landscapes by people that creates a fire problem. MTC regions are highly
attractive to people and all regions have high-density metropolitan areas closely
juxtaposed to flammable landscapes. All MTC communities have roots to Euro-
pean societies and this has contributed to substantial transfer of culture and land
management philosophy, strategies and tactics between regions. In all cases there
is a clear recognition of the fire danger inherent in these landscapes and the need
to reduce community vulnerability to fires, but at the same time protect natural
resources. These ideas, however, have emerged at different times and in response
to different events in each MTC landscape.
Human Impacts on Fire Regimes
Humans have had a multitude of impacts on fire regimes that include changes in
frequency and timing of ignitions and changes in fuel load and landscape patterns
of fuel distribution (Keeley et al. 2009a ). In MTC regions where natural ignitions
are frequently limiting, increased population growth has generally been associated
with increased fire frequency. Humans have the ability not just to change numbers
of ignitions but also to shift the natural season of burning to periods of severe fire
weather with high winds and high temperatures. Fuel structure has been altered in
diverse ways. When a policy of suppressing fires has been successful in excluding
fires over broad regions for extended periods of time, fuels have accumulated
beyond their historical levels. Fuels are also altered under intensive livestock
grazing regimes in diverse ways. On rangelands this has the potential for reducing
fine fuels and thus reducing fire events. In savannas this may be coupled with
increased woody fuels, although this is a function of recruitment strategies of local
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