Environmental Engineering Reference
In-Depth Information
used (e.g. straw, wood and bark chip, shredded wood,
rock fragments, paper sheets or other organic mater-
ials). For post-fire conditions, on-site slash may be a
good and cheap alternative. In some cases, especially
when erosion risk is high and seedlings are not likely
to stop it, so-called first-aid or jump-starting restora-
tion must include site stabilization by above-ground
obstruction structures (e.g., rocks, logs, branches,
brush piles, etc). These obstruction structures also
retain organic matter, nutrients and propagules, and
thus promote plant establishment and regeneration
(Ludwig & Tongway 1996, Tongway & Ludwig 1996).
For instance, site stabilization is sometimes needed in
steep mountain slopes when old terraces collapse,
often occurring as a result of the loss of vegetation
cover after a wildfire.
Seeding species mixtures usually include commer-
cially available seeds of native or naturalized her-
baceous species, combining perennials with annuals,
and grasses with legumes. Annuals show rapid germ-
ination, whereas perennials allow longer persistence.
Differences in life-history traits, such as rooting
depth and the potential for N fixation in legumes
justify the use of mixtures. In the experiment men-
tioned above (Vallejo & Alloza 1998), seeded plots
showed plant recovery within 2 months of application.
However, field observations and measurements taken
6 and 18 months after seeding showed a short-lived,
transient increase in plant cover, especially signific-
ant under semi-arid conditions, with almost all intro-
duced species having disappeared after 18 months.
Therefore, no inhibition of native-species regrowth was
observed in those plots. Hence, the technique proved
to be efficient in protecting vulnerable ecosystems after
fire.
Seeding and mulching can be used on a large scale
or in remote areas by aerial applications, although their
efficiency and cost-effectiveness in these situations can
be questioned (Robichaud
et al.
2000).
5.0
control
seeding + mulch
mulch only
2.0
1.0
0.5
0.2
0.1
Pine woodland
Shrubland
Shrubland
Fig. 14.3
Total sediment yield (Mg ha
−1
yr
−1
; log scale)
in three different burned slopes (one pine woodland
and two shrublands) in Benidorm, south-eastern
Spain, subject to three different treatments: control
(untreated), mulch only (200 g m
−2
of straw) and
mulch plus seeding (grasses and legumes). The area
was burned in August 1992 and the sediment yield
was recorded from May 1993 to November 1994.
Elaborated from Bautista
et al.
(1996).
seeders (species unable to resprout after fire), grow-
ing preferentially on marl substrates and, especially,
on south-facing slopes, commonly show low early post-
fire recovery (Pausas
et al.
1999) and thus higher
erosion and runoff risk.
To provide rapid soil protection, two main (non-
exclusive) techniques can be applied:
(i)
seeding
with herbaceous species and (ii)
mul-
ching
; that is, protection of soil surface with various
kinds of materials. Both seeding and mulching reduce
soil losses (Fig. 14.3), surface crusting and water
evaporation, and enhance water infiltration. For
instance, in a post-fire pine woodland in eastern Spain,
control plots had 7.2-times-higher soil losses than plots
with a straw mulching treatment (200 g m
−2
of straw;
Bautista
et al.
1996; Fig. 14.3). In an experiment with
both seeding (legumes and grasses) and mulching
(straw), the reduction in soil depletion was, on aver-
age, 12 Mg ha
−1
yr
−1
(Vallejo & Alloza 1998), which is
well above the level of tolerable soil loss for shallow
and erodible soils with low rates of soil formation (2-
5Mgha
−1
yr
−1
; Smith & Stamey 1965, Arnoldus 1977).
There are many different types of mulch that can be
14.3.4 Woodland restoration
To ensure long-term restoration, in most cases it is
necessary to introduce woody species. We now briefly
review some of the most prominent and promising
of physical and biological tools being tested in
