Agriculture Reference
In-Depth Information
little threat to most plant species in these systems because regeneration mostly
depends on dormant seedbanks and resprouting from basal lignotubers (
Box 2.1
).
This generalization, however, may not apply to fauna that must recolonize
burned sites and whose long-term persistence is controlled by metapopulation
dynamics. On highly contemporary fragmented landscapes, metapopulation
dynamics may be compromised and pose severe threats to postfire recovery of
some animal populations (Walter
1977
; Main
1981
; see also
Chapter 8
).
MODIS (Moderate Resolution Imaging Spectroradiometer) is a key instrument
aboard the NASA Terra (EOS AM) and Aqua (EOS PM) satellites that has found
wide use globally in the mapping of wildland fires (Giglio
et al.
2006
; Roy
et al.
2008
), among many other applications. Terra's orbit around Earth is timed so that
it passes from north to south across the equator in the morning, while Aqua passes
south to north over the equator in the afternoon. MODIS image data are acquired
in 36 co-registered spectral bands at moderate spatial resolutions (250, 500, and
1000 meters). Thermal information at 1000-m spatial resolution is collected twice
daily by each sensor (one daytime and one nighttime observation) in the mid to
high latitudes.
The U.S. Forest Service and the international fire monitoring community use
MODIS imagery to provide a near real-time geospatial overview of current wild-
land fire occurrence at regional, national and international scales. These fire data
are integrated with various sources of contextual spatial data and information in a
suite of geospatial data and mapping products and utilized by fire managers to
assess the current fire situation (
http://activefiremaps.fs.fed.us/
)
. These data add-
itionally serve as a decision support tool in strategic decisions relevant to resource
allocation in relation to fire-suppression activities.
Fire Seasonality
As illustrated in
Fig. 2.1
, seasonality is a necessity for converting potential fuels
into available fuels. Rarely are fire-prone ecosystems vulnerable to burning year
round, although some grassland ecosystems may qualify. Most ecosystems have a
particular season when fires are most likely and it is highly variable. For example,
the season of greatest area burned in Mediterranean Basin ecosystems is in the
summer, whereas in southern California it is in the autumn. Fires in non-MTC
ecosystems may peak in other seasons, for example in the winter or spring in
strongly monsoonal climates. Fire seasonality is a function of the coincidence of
ignitions with condition of the fuels. Generally fire seasons center around the
driest time of the year and it is noteworthy that the peak numbers of ignitions do
not always coincide with peak area burned. In the southwestern USA generally the
largest fires are during the driest time of the year, which is late spring and early
summer, whereas the peak numbers of ignitions (mostly from lightning) are in
summer during the monsoon season (late June to early July). Even in regions
where humans dominate the fire ignitions such as in southern California, the
