Fire in California - Fire in Mediterranean Ecosystems - page 124

Box 5.1 ( cont. )

25

20

Baja Calif.

15

10

So. Calif.

5

0

Jan Mar May July

Month

Fig. B5.1.3 Monthly average temperatures at approximately 2000 m in the San Pedro Ma´rtir
of Baja California (from Alvarez & Maisterrena 1977 ) and in the San Bernardino Mountains of
southern California (at Big Bear Lake; NOAA 1998) .

climate change impacts on both forest structure and fire regimes. At compar-
able elevations the Baja California San Pedro Ma´ rtir is substantially warmer
than sites north of the USA-Mexico border ( Fig. B5.1.3 ).Thedegreeofglobal
warming that Westerling et al. ( 2006 ) suggested would result in major changes
in fire regime throughout the western United States is far less than the present
difference between Baja and southern California forests. Since the greatest
temperature differences between Baja California and southern California occur
in winter, this likely has profound impacts on snowpack, a factor that poten-
tially has substantial impacts on fire regimes (Westerling et al. 2006 ). Some
climate forecasts predict changes in seasonal distribution of precipitation for
California that may impact fire regimes (Fried et al. 2008 ) and the substantial
differences in seasonal distribution between Baja California forests, which
receive substantial summer rains, and southern California forests may also
prove of some value as a potential model system for understanding future
climate change impacts in California.

150 people km 2 ) and extensive road infrastructure, which leads to
frequent and widespread ignitions ( Table 5.1 ) . The much lower fire frequency in
the San Francisco east bay area is tied to the higher rainfall and shorter droughts,
which have contributed to a more limited window of time when shrublands provide
available fuels for burning. In the southern half of the Sierra Nevada the lower
population density has likely played some role in limiting fire ignitions. In addition,
the lack of passes and the high peaks to the east appear to hold foehn winds aloft,
and thus the chaparral-dominated foothills are not subjected to this extreme fire

density ( >