Agriculture Reference
In-Depth Information
Lenihan
et al.
2008
; Giannakopoulos
et al.
2009
). Indeed, some contend that
climate-driven changes have already occurred in fire regimes of western North
American forests (e.g. Westerling
et al.
2006
), although such conclusions may be
premature as they are based on short-term datasets and the data are consistent
with other explanations. In montane forested environments it has been postulated
that increasing temperatures over the twentieth century have caused earlier snow-
melt and that this change has increased fire activity. However, as of yet this
pattern is not consistent for the western USA (Medler
et al.
2002
; Michaels
2006
). Likewise, in the Mediterranean Basin temperatures over the past several
decades have risen, but this change has not been correlated with increased area
burned (Pausas
2004
).
Global climate-forcing mechanisms such as El Nin˜ o-Southern Oscillation
(ENSO) are known to affect fire activity primarily through effects on precipita-
tion. Predicting future impacts is complicated by the observation that this ENSO
effect on fires has changed over time and thus is not always a reliable indicator of
fire occurrence (Yocum
et al.
2010
).
Predicting global change impacts on fire is complicated by the complexity of
potential interactions. Higher temperatures will create greater atmospheric water
deficits and decreased fuel moisture during the fire season. However, these same
water deficits may reduce fine fuel production, thus reducing fire frequency in
some vegetation types (Pausas & Bradstock
2007
). Over time this could result in
fewer but more intense fires. In other cases fire frequency may increase and
contribute to type conversion of woody vegetation to herbaceous systems, ultim-
ately decreasing fire intensity. In addition, direct effects of elevated CO
2
poten-
tially may confound or reinforce these effects (Bradstock
2010
). As CO
2
rises one
might expect increased primary productivity and thus increased fuel loads, but as
CO
2
increases, direct effects on stomatal behavior may act to decrease drought
stress and thus increase fuel moisture.
Predicting future climate and fire interactions is extremely difficult because
current models lack the necessary complexity to capture the multitude of eco-
logical interactions that will occur as environments change. This is illustrated by
the climate envelope models that attempt to predict future demographic patterns
of species based on climate alone (e.g. Loarie
et al.
2008
) and are likely to come to
very different conclusions once we have the ability to incorporate other, and often
more important, ecosystem factors (e.g. Loehle & LeBlanc
1996
; A.J. Davis
et al.
1998
; Pimm
2007
).
Climate change is only one of a multitude of global changes for which we need to
plan. For example, populations are increasing faster in MTC regions than are
temperatures, and since ignitions are largely anthropogenic, and fires are often
ignition limited, we should expect population growth to have a huge impact on future
fire regimes. Modeling studies show that climate scenarios for southern California are
predicted to have minimal impact on persistence of a non-resprouting chaparral
shrub relative to the substantial impact of increases in fire frequency (Lawson
et al.
2010
). Also, increasing nitrogen deposition in most MTC regions may increase
