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Glacial Maximum (LGM), when cold dry conditions limited the amount of biomass produc-
tion (Spessa et al. 2003, Whitlock et al. 2010, Daniau et al. 2012). The benchmark for fire restor-
ation therefore shifts depending on the timescale of observation, as vegetation and fire
regimes continue to reorganize in response to climate change and vegetation feedbacks
(Pauly 1995, Jackson 2006, Jackson and Hobbs 2009).
Understanding the interplay between fire and climate is a vital consideration when plan-
ning fire management in the face of global warming, especially as some current fire regimes
are still influenced by the fire deficit' that was created by fire suppression policies in the
twentieth century (Marlon et al. 2008, Daniau et al. 2012, Marlon et al. 2012). Fire regimes can
be thought of as the interaction between fire frequency, extent (spatial scale), intensity, and
seasonality over space and time. These factors create a fire template within which biotas and
human societies have co-evolved (Bowman et al. 2011). Climate affects fire by determining
the amount of fuel (biomass) available and whether a fire is likely to start (Murphy et al. 2011).
In arid climates, fires are unlikely to occur because productivity is low and there is insuffi-
cient fuel, whereas in wet climates the chances of ignition are low (Figure 4.3a). Fire is thus
limited by productivity in arid climates and by fire conditions in very wet climates. Therefore,
fire regimes in some systems will be more sensitive to changes in biomass availability while
others will be more sensitive to fire conditions; a similar increase in rainfall could thus
increase fire in some, biomass limited ecosystems while reducing fire in ignition limited sys-
tems (Moritz et al. 2012). At intermediate rainfall, climate, vegetation, and people interact to
determine fire regimes. Humans can influence fire regimes through manipulating the avail-
ability (amount, type, and spatial distribution) of biomass, by controlling ignitions, and by
choosing the season and weather in which burning takes place (Archibald et al. 2009, Le Page
et al. 2010, Coughlan and Petty 2012, Laris 2013) (Figure 4.3b).
Understanding the relationship between climate, fire, and vegetation productivity helps in
predicting how systems will respond to climate change. Long-term records suggest that
warmer periods like the like the MWP and MHA provide more realistic analogues for the cli-
mate of the twenty-first century, than the colder conditions of the LIA, immediately prior to
the Anthropocene. The palaeoecological record suggests that we might see dramatic changes
as we move into warmer, more fire-prone climates, and cold-adapted assemblages are
replaced. The old-growth forests of today are legacies of the climate and fire regimes of the
LIA, and it seems likely that some may not survive warming climate and associated fire
regimes. To plan for the future, site-specific histories are needed that show how ecosystems
and fire responded to changing rainfall, temperatures, and fire.
Past warm periods saw not only changes in fire regimes, but also dramatic changes in eco-
system composition and structure, and these changes can be studied in the palaeoecological
record. In the forests of the Sierra Nevada, California, for example, fire frequency was higher
in the MWP, and firs became dominant in high-elevation communities. In the LIA, fire fre-
quency was lower, and lodgepole pine trees became more abundant. The recent re-emer-
gence of young red firs echoes forest composition in the MWP (Millar and Woolfenden 1999,
Millar et al. 2007).
Looking further back in time, in British Columbia, charcoal and pollen records show that
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