Fire in the Mediterranean Basin - Fire in Mediterranean Ecosystems - page 89

(Pausas & Ferna´ ndez-Mun ˜ oz 2011 ). Prior to this shift, mediterranean landscapes
were shaped by agriculture, livestock and other land uses that maintained low
levels of highly fragmented fuels. Progressive changes in land use switched from a
fuel-limited fire regime to a drought-driven fire regime (Pausas & Ferna´ ndez-
Mun˜ oz 2011 ). Indeed, recent large fires in the Mediterranean Basin have
been related to extreme warm and dry weather (Pausas 2004 ; Trigo et al. 2006 ;
Founda & Giannakopoulos 2009 ).
In the Mediterranean Basin southern rim countries, as well as in some eastern
rim countries such as Turkey, a large proportion of the population continues to be
rural, and heavy use of the land (e.g. overgrazing) continues to be a dominant
force behind many land degradation and desertification problems (Mairota et al.
1998 ; Camci C¸ etin 2007 ). Consequently, in these areas, fuels are maintained at low
levels and the annual area burned has remained fairly constant over the last few
decades. Industrialization and rural depopulation are just beginning in North
Africa, where we might expect a similar shift in fire regimes as observed in the
northern rim countries. Such a shift is already occurring in Algeria as there is a
current depopulation of rural areas for safety reasons, thus fuels are increasing
and fires are becoming more prevalent.
Fuel Patterns and Structure
Most vegetation types (shrublands and woodlands) are sufficiently dense to
sustain active crown fires. Surface fires are currently rare but they sometimes
occur in mountain areas with coniferous forests. It is quite probable that surface
fire regimes were more common in forests in the distant past, but recent forest
management activities, including fire suppression, have made these ecosystems
vulnerable to low-frequency crown fires. Some low shrubs, arid grasslands and
open woodlands rarely burn because of the low amount and continuity of fuel
loads. In open oak woodlands the low fuel values are the result of the grazing
pressure by livestock or the other management actions (e.g. shrub clearing for
cork extraction). In subshrubs and arid grasslands the low fuel volume appears to
be the result of millenia of overgrazing pressure; thus it may be that some of these
landscapes had more frequent fires in the past.
Fuel amounts vary with vegetation type (see Table 2.1 ) . They also vary with fire
history, with climatic and topographic conditions, and, in old-fields, with the time
since abandonment. For instance, in old-fields of eastern Iberia (Spain), biomass
(live and dead, Mg ha 1 ) varies from about 1.5 (1 year postfire) to 18 (unburned)
in Brachypodium grasslands (Caturla et al. 2000 ; see also Table 2.1 ) , and from 13-
59 Mg ha 1 from the third to the seventeenth postfire year in Ulex parviflorus
(gorse) shrubland (de Luis et al. 2004 ; Baeza et al. 2006 ). Fuel loads vary not only
with the time since last fire but also with the fire history previous to the last fire, as
has been demonstrated in Quercus coccifera garrigue (Delitti et al. 2005 ). In the
western part of Iberia, where rainfall is high but there is still a summer drought,