Agriculture Reference
In-Depth Information
Stand-thinning fire regime
50
Individual fire
40
Natural
landscape
30
Perturbed
landscape
20
10
0
0.1
10
Gap size (ha)
10 0 0
Fig. 5.9
Projected gap size in mixed conifer forests of the Sierra Nevada under historical
conditions and perturbed conditions due to a century of fire suppression policy that has excluded
fire
.
(From Keeley & Stephenson
2000
.
)
These forests require management that restores historical fire regimes or utilizes
mechanical thinning to reduce current fuel loads (Franklin
et al.
2006
). These
approaches sound like simple alternatives but there are untold problems behind
both. Prescription burning is a viable option in some parts of California, but due
to human demographics, it is not widely applicable in many areas highly frag-
mented by development. Additionally, atmospheric circulation in most of these
ranges is closely linked with foothill and valley communities and as a consequence
air quality constraints greatly limit the window of opportunity for prescription
burning. Mechanical thinning (i.e. logging) is perhaps the only option in many
forests, but it is costly, particularly if the prescriptions focus on removing those
tree sizes most responsible for fire hazard. Mechanical thinning projects can pay
for themselves, but usually only if large trees are harvested. This scenario creates a
dilemma because removing large trees promotes further in-growth of saplings and
may exacerbate the fire hazard problem, requiring future mechanical thinning at
shorter intervals.
In chaparral, fire suppression has not been effective at eliminating fires. On the
basis of our understanding of historical burning patterns it is apparent that
contemporary fire regimes are not qualitatively different from historical fire
regimes (Keeley
2006a
). However, fire frequency has increased with demographic
growth and the human subsidy of fires has greatly increased fire frequency.
Thus, the lower foothills and coastal plains have not experienced fire exclusion
and in fact the landscape burns far more frequently now than historically was
the case (Keeley
et al.
1999a
). This does not imply that fire suppression has had
no impact. Indeed, without suppression over the past century this landscape
would have burned at a much greater frequency than was the case historically.
Fire management of this landscape is particularly difficult because it is also the
region of greatest human development. The primary management dilemma is
