Agriculture Reference
In-Depth Information
invasive trees and shrubs, especially conifers, but also Australian
Hakea
and
Acacia
species. The Working for Water program, launched in 1995, has made a
major contribution to controlling invasive woody plants in the Cape region
(van Wilgen
et al.
1996
). Water is a key constraint on urban and rural develop-
ment in the Cape and the initial motivation for the program was to reduce the
impacts of invasive trees on streamflow (Le Maitre
et al.
1996
). The success of
the program, and the large level of state support, is owed mostly to its success in
creating work opportunities for the unemployed (van Wilgen
et al.
1996
) but
recent analyses indicate that it is proving to be cost effective for promoting
streamflow (Marais & Wannenburgh
2008
). Fires are also burned for biodiver-
sity objectives following widespread recognition, since the 1980s, that fynbos is a
fire-dependent vegetation. On the WUI fringe, the main objective is protection
from fire damage to property. This is achieved by clearing fire breaks (firebelts)
and by early suppression of fires, primarily by aerial methods (helicopters with
fire buckets).
Prescribed burning from the 1970s was initially based on fixed fire return
intervals of
12 yrs in spring. The spring fire season was based on the idea that
soils should be moist when burned to reduce soil organic matter losses. Fire
regimes became more flexible with increasing knowledge, especially of seroti-
nous Proteaceae, with a shift to longer fire return intervals where maturation
rates were slow and with a shift to autumn burns because of the negative effects
of spring burns on protea recruitment observed in the southern and southwes-
tern Cape (van Wilgen
et al.
1992
a,
1994
;Kraaij
2010
). In the last decade, more
variable fire regimes have been favored, partly because of management con-
straints on burning at fixed seasons and frequencies, but also because of the
realization that different species and functional groups are promoted by differ-
ent fire intervals and events (season and intensity). However, variability in
frequency, season and intensity of fires in a particular area are monitored within
aframeworkof
thresholds of potential concern
(Rogers & Biggs
1999
; Bond &
Archibald
2003
). These are upper and lower thresholds set for fire frequency,
season, intensity, area, and so on. For example, if a fire burns a large area of
fynbos or renosterveld at
∼
6 yr, then this activates a threshold of potential
concern because most individuals in serotinous protea populations would not yet
have developed seedbanks, resulting in poor recruitment. On reaching such a
threshold, managers either re-evaluate the basis for this threshold or intervene;
in this example by preventing the area from burning again before proteas have
matured. The scope for intervention remains strongly constrained by human and
financial resources. Over the last few years, a new organization, Working on Fire
(spawned from the very successful Working for Water program) has been
initiated with trained firefighting teams that can be sent to different parts of
the country (
www.workingonfire.org
)
. This promises a more proactive fire man-
agement than the reactive mode of the preceding decade when resources were
often too limited to influence fires. It is also providing many job opportunities
and work skills.
