Agriculture Reference
In-Depth Information
and spiny shrublands. Most of these vegetation types are susceptible to active
crown fires (see
Chapter 2
), except in semi-arid conditions where the low fuel
load and continuity limits fire spread. Understory fires, although they are
currently relatively rare, may occur in mountain coniferous forests.
However, these climatic patterns interact with past land use and geology in
determining fire response (Pausas
et al.
1999
). Many areas with rocky bedrocks
such as hard limestones and karsts were not terraced in the past because they have
very shallow and decarbonated soils with abundant rock outcrops. They do have
abundant cracks that allow deep-rooted plants to access water and, thus, deep-
rooted postfire obligate resprouters dominate these soils. On these substrates
broadleaf evergreen garrigue and maquis are common on drier sites and evergreen
oak woodlands on more mesic sites with deeper soils. Previous land uses were
related to gathering forest products, including wood, charcoal, cork, mushrooms,
kermes and acorns, and livestock grazing.
In contrast, landscapes with relatively soft bedrocks (e.g. marl-limestone
colluviums) were extensively cleared and terraced or intensively grazed in the past.
Many of these croplands and grasslands have been abandoned and old-fields are a
dominant feature of such landscapes (
Fig. 4.2
). Under these conditions are shrub-
lands dominated by small-leaved and/or malacophyllous species, which are
frequently non-resprouters, and early colonizers; evergreen resprouting species
appear later in the succession (see below). Mixed shrublands, with both broadleaf
evergreen and small-leaved species also occur. All of these shrublands may have
pines (
P. halepensis
,
P. pinaster
,
P. brutia
) with variable densities. In most Medi-
terranean Basin countries, massive plantations, especially with native conifers
(mainly pines) but also with non-native conifers and
Eucalyptus
, have been planted
on these substrates during the last century, and many of these afforestations were
conducted in old-fields (Pausas
et al.
2004a
,
2008
).
In brief, at low elevations landscapes often comprise a mixture of: (1) never-
terraced broadleaf evergreen shrublands and forest, (2) old-fields of variable age,
often dominated by small-leaved shrubs, and sometimes afforested with pines,
and (3) low shrublands resulting from long-term overgrazing or in arid condi-
tions. In the first and second cases, crown fires are common, while in the third
they are rare due to low fuel values. Transitions and intermixed mosaics are
frequent.
Broadleaf Evergreen Shrublands (Maquis and Garrigue)
Broadleaf evergreen sclerophyllous shrubs and small trees dominate areas that
were never terraced, typically hard limestone landscapes at low elevations. This
maquis shrubland includes species of
Pistacia
,
Phillyrea
,
Olea
,
Ceratonia
,
Quercus
,
Rhamnus
,
Arbutus
,
Myrtus
and
Viburnum
among others (
Table 4.3
). All are strong
postfire obligate resprouters and belong to lineages whose origin is tied to
the Tertiary Madrean-Tethyan sclerophyllous vegetation that was broadly
distributed in North America and Eurasia (Laurasia, see
Chapter 10
). The most
