Agriculture Reference
In-Depth Information
Grand Prix/Old Fire Complex
65 250 ha
15
Rancho Cucamonga
215
N
San Bernardino
Legend
dNBR value
Severity
0-20
Unburned to low
21-96 Low to moderate
97-173 Moderate
174-249 Moderate to high
250
High
City
County line
Highway
(a)
0
2.5
5
10
15
20
Kilometers
(b)
Fig. 2.3
Landsat TM-based differenced Normalized Burn Ratio (dNBR) indices for two large
wildfires illustrating mosaic of different fire severities. Inset shows these fires (a) and additional
fires burning at the same time (b), all of which are included in the study of fire severities in
Keeley
et al.
2008
. (From Keeley
et al.
2008
.)
Fire intensity and fire severity are operationally tractable measures, but they are
largely of value only so far as they can predict ecosystem responses such as soil
erosion or natural regeneration (
Fig. 2.4
). Such predictions are complicated by the
fact that many biotic and abiotic factors enter into the relationship between fire
intensity, fire severity and ecosystem response (e.g. Peterson & Ryan
1986
; Neary
et al.
1999
; Lentile
et al.
2006
). For example, alien plant invasion may increase
with increased fire severity in forests (Turner
et al.
1999
) but show the opposite
relationship in shrublands (Keeley
et al.
2008
). Degree of fire severity can affect
the extent of postfire resprouting in herbs and shrubs (Flinn & Wein
1977
; Keeley
2006c
) and seedling recruitment (Whelan
1995
; Bond & van Wilgen
1996
; Ryan
2002
; Pausas
et al.
2003
; Keeley
et al.
2005a
; Johnstone & Chapin
2006
) but there
are significant species-specific differences; high fire severity may be inhibitory in
some but stimulatory in others. In some forests fire severity may be correlated
with long-lasting impacts on regeneration (Lecomte
et al.
2006
) but in other
