Agriculture Reference
In-Depth Information
combust the needle layer and affect soil conditions for postfire germination
(Pausas
et al.
2008
). In eastern Spain, Pausas
et al.
(
2002
,
2003
) found no differ-
ences in seedling densities between different fire severities measured by crown
scorch, but both seedling height and biomass were higher on high fire severity sites
where most litter was consumed. Fire severity was also correlated with higher
postfire soil phosphorus content, as a consequence of increased microbial activity
(Fierro
et al.
2007
).
In North Africa,
P. halepensis
may coexist with another conifer,
Tetraclinis
articulata
(closely related to the Australian
Callitris
). It is believed that in the
past
Tetraclinis
was a very common tree throughout the area, but the high
quality of its wood (it is both aromatic and resistant to rotting) made it valuable
to past civilizations. In spite of this, we can still find open woodlands of
Tetraclinis
, thanks to its resprouting from a lignotuber after cutting and fire
(Naveh
1975
). However, even these burls, which become massive after recurrent
coppicing and burning, have been extensively collected for their quality and
beauty (Charco
1999
).
Pinus pinaster
(maritime pine) is a highly variable species and some of this
variation is likely tied to past fire regimes. North African populations are highly
serotinous and have thin bark typical of pines from crown fire regimes, whereas
Atlantic coast populations have low serotiny and thick bark suggesting a surface
fire regime (Tapias
et al.
2004
). Unlike
P. halepensis
,
P. pinaster
can survive with a
high proportion of the crown scorched (Botelho
et al.
1998
). Under surface fire
regimes dendrochronology studies record a mean fire interval of 14.5 yrs for
P. pinaster
over the last 180 yrs (Vega
2000
). Given that
P. pinaster
is used for
wood production, some Atlantic stands are maintained at very high tree densities
and under a fire exclusion policy, so that when burned, they produce high-
intensity crown fires. Even in these cases, recruitment seems to be relatively
good (P. Fernandes personal communication), although Pe´ rez
et al.
(
1997
)
observed almost no regeneration of
P. pinaster
after a single fire in the subhumid
central part of Spain, and attributed this to competition with the shrub
Cytisus
eriocarpus
.
Pinus pinea
(stone pine) has characteristics of pines from a surface fire regime. It
has thick bark and no branches in the lower portion of the tree due to self-pruning
of dead branches. It readily survives surface fires, and can survive crown fires with
more than 80% of the crown volume scorched (Rigolot
2004
; Catry
et al.
2010
).
As is the case with other pines from surface fire regimes it does not have serotinous
cones (Keeley & Zedler
1998
). It has some immediate postfire regeneration
(
Fig. 4.7
) due to the annual seed crop being protected in thick cones and by a
dense seed coat (Escudero
et al.
1999
). Due to the fact that this pine produces
edible nuts, it has been planted for a very long time, and thus its natural distribu-
tion and habitat are uncertain. It seems to have been originally limited to poor
sandy soils in dune ecosystems where understory fuels were low. However, its
current distribution includes dense forests that sustain crown fires. In such condi-
tions a general decline has been observed in some areas (Rodrigo
et al.
2007
).
