Agriculture Reference
In-Depth Information
Fire Policies and their Impact on Fire Regimes
Among the various approaches to fire management in fynbos is a
natural fire
policy
conducted in
natural fire zones
(Seydack
et al.
2007
). The natural fire zones
are an interesting management experiment in the Cape region. A comparison of
fire regimes under different management policies, including 20 yrs under natural
fire management, has recently been reported by Seydack
et al.
(
2007
) in the
Swartberg Mountain range of the eastern inland ranges of the Cape region. The
Swartberg is a narrow lozenge-shaped mountain rising to 2000 m elevation from
arid shrublands in the lowlands. Because fires in the mountains pose little threat to
adjoining properties, a natural fire management regime was implemented in the
1980s and has been maintained to the present. Fires ignited by lightning and
rockfalls were allowed to burn without interference, whereas human-ignited fires
were prevented from spreading wherever practical (Seydack
et al.
2007
). This
regime contrasts with periods of fire suppression and prescribed burning at
different periods of the twentieth century. The experiment provides a rare per-
spective on determinants of
fynbos fire regimes with and without human
intervention.
The
natural burning zone
management regime was successful in greatly reducing
the area burned by anthropogenic fires (to < 25% per year). Initially the annual
area burned (by lightning-ignited fires) was much lower than the previous era of
prescribed burning, suggesting that natural fires occurred at much longer intervals
than the usual assumption of
15 yrs. However, the impact of fire policies on the
fire regime has to be evaluated against longer-term cycles in area burned.
Seydack
et al.
(
2007
) analysed the data in 5-yr periods from 1941 to 2000. There
were four 5-yr periods when the mean area burned annually equalled or exceeded
10 000 ha. These peak burning periods recurred at intervals of 15, 25 and 15 yrs,
more or less the mean fire return interval for fynbos (
Fig. 7.11
). Seydack
et al.
(
2007
) suggest that the peaks in fire activities are associated with periods of more
active summer convectional storms bringing more summer rain and also lightning
activity. However, periods of high fire activity followed long periods of low
activity under cool moist conditions, during which fuel accumulated. This suggests
that both fuel and weather conditions influenced natural fynbos fire regimes and
the frequency and extent of large fires. Multiyear periodicity of fire activity also
means that the effects of different management policies on fire regimes are difficult
to assess unless maintained for many decades.
For the available data, fires were significantly smaller in eras of fire suppression
(1951-1974) and prescribed block burning (1975-1985) vs. under natural (light-
ning) fires (1986-2002) (mean and median ha burned: suppression era 761, 84;
prescribed era 601, 171; natural era 1430, 276, respectively). The area burned per
year in the three eras was 5612, 9015 and 7907 ha respectively but Seydack
et al.
(
2007
) attributed the variation largely to multi-annual cycles in climate patterns.
The most noticeable differences were changes in fire season, with fires during the
natural fire era shifting to the summer months and fewer fires in spring and
autumn relative to anthropogenic fires.
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