Agriculture Reference
In-Depth Information
Ecosystem
responses
Erosion
Vegetation recovery
Fire
intensity
Fire or burn
severity
Energy
released
Organic
matter loss
Societal
impacts
Loss of life or property
Suppression costs
Fig. 2.4
Schematic representation relating the energy output from a fire (fire intensity),
the impact as measured by organic matter loss (fire severity, also known as burn severity),
and ecosystem responses and societal impacts that may vary in response to different patterns
of fire severity.
ecosystems severity is not closely tied to short-term or long-term changes in
recovery (
Box 2.1
). In North America some agencies utilize a ground measure-
ment of fire severity known as the CBI or Composite Burn Index (Key & Benson
2006
) but correlation between this metric and dNBR ranges from weak to good
depending on the ecosystem (Gitas
et al.
2009
). Weak correlations are likely tied to
the fact that in some ecosystems CBI mixes both fire severity and ecosystem
response variables (Keeley
2009
).
A major management reason for postfire assessments of fire or burn severity is
because it is thought to be an important indicator of watershed stability (Robichaud
et al
.
2000
; Wilson
et al
.
2001
; Ruiz-Gallardo
et al
.
2004
). Loss of aboveground
biomass exposes more soil surface and increases the kinetic force of precipitation on
the soil surface, which can increase overland water flow (Moody & Martin
2001
).
Also, loss of soil organicmatter alters the binding capacity of soil and results in other
structural changes that can affect erosional processes. Postfire increase in soil water
repellency due to hydrophobic soil layers is tied, albeit sometimes weakly, to fire
severity, although in some ecosystems soil hydrophobicity is unrelated to fire sever-
ity (Doerr
et al.
2006
). In summary, fire
per se
does affect ecosystem hydrology, but
the degree of fire severity may not play a major role relative to the multitude of other
factors that determine postfire hydrological functioning (Robichaud
et al.
2000
;
Doerr
et al.
2006
; Gonza´ lez-Pelayo
et al.
2006
; Pausas
et al.
2008
).
Fire Frequency
Fire frequency
is the number of occurrences of fire within a circumscribed area and
time period of interest. It is commonly expressed as the
fire rotation interval
, which
