Agriculture Reference
In-Depth Information
Animal Communities
Other than a few burrowing species, most animals in chaparral shrublands flee
from fires or perish (Cook 1959 ; Lawrence 1966 ; Quinn 1979 ; Fox et al. 1985 ). As
a consequence recovery is dependent on recolonization and thus metapopulation
patterns play a critical role, although this has not been well studied. On contem-
porary landscapes large fires may pose problems for recovery due to habitat
fragmentation and loss of natural corridors.
Coniferous Forest Surface Fire Regime
In mountains above 2000 m in southern California (latitude 33 -34 ) and progres-
sively lower further northward in the state, conifer forests replace shrublands and
associated woodlands (see Fig. 2.2a ) . These forests are dominated by a small
number of species: in the Pinaceae, Pinus ponderosa , P. jeffreyi , P. lambertiana ,
Abies concolor and Pseudotsuga menziesii , and in the Cupressaceae, Calocedrus
decurrens , all of which reach 50-70 m in height (Rundel et al ., 1977 ; Thorne 1977 ;
Minnich 2007 ; Fites-Kaufman et al. 2007 ). Half of these are endemics to the MTC
region and three, P. ponderosa , A. concolor and Ps. menziesii , are widespread
outside this climatic region (Fowells 1965 ). These species assemble in diverse
patterns both locally and regionally, with much variation in landscape mosaics
and fire regime characteristics (Sugihara et al. 2006 ).
Throughout the interior mountain ranges of California two forest types pre-
dominate. Forests dominated by Pinus ponderosa often form open-canopy com-
munities with herbaceous understories at lower elevations, and higher up on
equator-facing exposures. The closed-canopy, Abies concolor dominated, mixed
conifer forests are typically at higher elevations, and on pole-facing slopes at lower
elevations. Much of this landscape is topographically heterogeneous and thus
clusters of closed-canopy forest often form a mosaic with persistent gaps in which
relatively little establishes, as well as mosaics with persistent shrub thickets
(Conard & Radosevich 1982 ; North et al. 2002 ). Both forest types are character-
ized by a surface fire regime or a mixed surface and crown fire regime.
Fuel Structure
High productivity of trees in these forests allows for rapid growth rates and the
capacity to outgrow surface fuels. As a consequence both forest types typically
maintain a separation between the tree canopy fuels and surface fuels, and the
taller the trees the greater the potential separation ( Fig. 5.6a ). This separation of
fuels is enhanced by traits such as self-pruning of dead branches, thick bark and
deep roots (Keeley & Zedler 1998 ).
The character of the surface fuels varies as a function of canopy closure. On the
drier ponderosa pine forest sites, wide spacing of trees results in a more open forest
Search WWH ::




Custom Search