Agriculture Reference
In-Depth Information
Box 5.1 Comparison of Fire Regimes between Southern California and
Northwestern Mexico (Baja California)
Dodge (
1975
) postulated that burning patterns were likely different in chapar-
ral and coniferous forests on the two sides of the USA/Mexican border because
of different management practices. North of the border fire prevention and fire
suppression were policy, whereas south of the border neither were widely
practiced; indeed, in rural Mexico it was customary to set fire to chaparral,
sage scrub and grasslands as soon as sufficient dead material had accumulated
to carry a fire. Dodge found that the most significant difference between the
vegetation of these two regions was in land use practices; in particular the
intensive grazing and browsing by cows and horses south of the border limited
fuel continuity. He suggested that vegetation patterns and fire behavior in Baja
California were the result of overgrazing and extensive anthropogenic burning.
Minnich (
1983
) used Landsat remote imagery to compare patterns of burning
in southern California shrublands between 1972 and 1980 on both sides of the
border. He concluded that during this 9-year period fires were larger north of the
border; however, fire size was not compared statistically and critics have con-
tended that further analysis shows no difference in fire size (Strauss
et al
.
1989
).
Keeley & Fotheringham (
2001a
) pointed out that the inclusion by Minnich
(
1983
) of two huge fires north of the border, which were outside the study period,
biased the conclusions because they were based on U.S. Forest Service historical
records and such records are not available in Mexico.
In an attempt to compensate for the lack of written records south of the
border, Minnich (Minnich & Dezzani
1991
; Minnich
1995
,
1998
; Minnich &
Chou
1997
) used historical aerial photographs to prove that large fires were
absent from northern Baja California. This conclusion was based on photos
from three time periods over an 80-year period, and these studies have been
criticized because of the lack of demonstration that this photo series, with a
16-18-yr gap between photos, could capture all large historical fires (Keeley &
Fotheringham
2001a
,
2001b
). Further challenges to the notion that Baja
California did not historically have large fires are based on written accounts by
early explorers that described in detail massive wildfires in northern Baja
California (Keeley & Zedler
2009
).
The conclusion from the Baja studies is that the smaller fires south of the
border are reflective of the natural southern California fire regime and larger
fires north of the border are a modern artifact of fire suppression. An important
management conclusion from these studies is that widespread prescription
burning is needed in southern California to return the landscape to its natural
condition with fuel loads insufficient to carry massive fires. In the late twentieth
century this model was readily accepted by fire managers in southern California
as this seemed like a reasonable extension of the western conifer model of fire
suppression causing fuel accumulation which has led to large contemporary
Continued
