which is an ecological metric used by federal
agencies, The Nature Conservancy, and others
to determine the degree to which the vegetation
and fire regimes of a given area have changed
compared to reference conditions. As shown on
their map (Fig. 13.5), fire management has significantly changed the fuel levels of many
forests, and concurrently, the frequency and
intensity of fire. About 30 % of all ownerships
(except those related to agriculture, barren, and
urban land) are in high-risk categories (shown in
yellow and red). In many ecoregions this percentage is much higher. For example, in the
mountains of the southwest, as much as 83 % is
moderately to severely altered.
13.5 Why Ecoregions Are Needed
The same forest type can occur in different
ecoregion divisions. For example, ponderosa
pine forest occurs in the northern Rocky
Mountains and in the southwest. This does not
imply that the climate, topography, soil, and fire
regime are necessarily the same. In the southwest, the historical fire regime is of frequent,
low-intensity, surface fires that tend to maintain
open, multi-age forests. Farther north in the
Rocky Mountains, cooler conditions mean
moister forests in which fires burn less readily.
This distinction is important because fire management strategies and restoration protocols are
often applicable only to the local region in which
they were developed. Therefore, management
strategies planned to address the fire and fuel
issue such as those documented in the interagency National Fire Plan should take into consideration ecoregional variation in fire regimes.
This 10-year comprehensive strategy can be
viewed online at: http://www.fireplan.gov.
13.6 Use of Ecosystem Patterns
Within Ecoregions
Macroclimate accounts for the largest share of
systematic environmental variation at the macroscale or ecoregion level. At the mesoscale, physiography (geology and landform) modifies the
macroclimate and exerts the major control over
ecosystem patterns and processes within climatic
zones. With this in mind, Bailey et al. (1994)
used physiographic factors to subdivide the
ecoregion provinces of the United States into
subregional areas, or sections, that have different
landform characteristics. These differences are
important because the character of the landform
with different geology will vary in the climatic
zone. In the same climatic zone, different
geologies, such as granitic mountains or volcanic
plateaus, will weather and erode differently
forming different landform relief. Where this
occurs, the spread of a disturbance like wildfire
may differ among landforms. Swanson et al.
(1990) hypothesized that in forested, steepmountain landforms along the northwest coast
of the United States where landform relief does
not exceed several tree heights (e.g., Coast
Ranges), disturbance agents such as fire and
wind can readily move through the forest with
little regard for topography. Landforms may
have a greater effect on the spread of disturbance
and mosaic structure where relief substantially
exceeds tree height (e.g., Cascade Range). The
classification and mapping of physiography as
was done to delineate ecological subregions at
the section level should provide an important
means of discriminating broad areas with differing fire regimes within a particular ecoregion.
At finer scales, one finds considerable variation in fire regimes in response to local topography, vegetation, and microclimate (cf., Cleland
et al. 2004). As we have seen, local ecosystems
occur in predictable patterns within a particular
ecoregion. Similar fire regimes occur on similar
sites within an ecoregion. Knowledge about fire
regimes on similar sites allows ecological restoration so as to incorporate the natural variability
of fire regimes across the ecoregion.
13.7 Future Range of Variation
The range of variation concept is a useful starting
point, but it is limited for a number of reasons.
First, many systems have been fragmented
because of human disturbance; because of this,
fires will not carry the way they did historically.
134
13 Use of Fire Regimes at the Ecoregion Scale
agencies, The Nature Conservancy, and others
to determine the degree to which the vegetation
and fire regimes of a given area have changed
compared to reference conditions. As shown on
their map (Fig. 13.5), fire management has significantly changed the fuel levels of many
forests, and concurrently, the frequency and
intensity of fire. About 30 % of all ownerships
(except those related to agriculture, barren, and
urban land) are in high-risk categories (shown in
yellow and red). In many ecoregions this percentage is much higher. For example, in the
mountains of the southwest, as much as 83 % is
moderately to severely altered.
13.5 Why Ecoregions Are Needed
The same forest type can occur in different
ecoregion divisions. For example, ponderosa
pine forest occurs in the northern Rocky
Mountains and in the southwest. This does not
imply that the climate, topography, soil, and fire
regime are necessarily the same. In the southwest, the historical fire regime is of frequent,
low-intensity, surface fires that tend to maintain
open, multi-age forests. Farther north in the
Rocky Mountains, cooler conditions mean
moister forests in which fires burn less readily.
This distinction is important because fire management strategies and restoration protocols are
often applicable only to the local region in which
they were developed. Therefore, management
strategies planned to address the fire and fuel
issue such as those documented in the interagency National Fire Plan should take into consideration ecoregional variation in fire regimes.
This 10-year comprehensive strategy can be
viewed online at: http://www.fireplan.gov.
13.6 Use of Ecosystem Patterns
Within Ecoregions
Macroclimate accounts for the largest share of
systematic environmental variation at the macroscale or ecoregion level. At the mesoscale, physiography (geology and landform) modifies the
macroclimate and exerts the major control over
ecosystem patterns and processes within climatic
zones. With this in mind, Bailey et al. (1994)
used physiographic factors to subdivide the
ecoregion provinces of the United States into
subregional areas, or sections, that have different
landform characteristics. These differences are
important because the character of the landform
with different geology will vary in the climatic
zone. In the same climatic zone, different
geologies, such as granitic mountains or volcanic
plateaus, will weather and erode differently
forming different landform relief. Where this
occurs, the spread of a disturbance like wildfire
may differ among landforms. Swanson et al.
(1990) hypothesized that in forested, steepmountain landforms along the northwest coast
of the United States where landform relief does
not exceed several tree heights (e.g., Coast
Ranges), disturbance agents such as fire and
wind can readily move through the forest with
little regard for topography. Landforms may
have a greater effect on the spread of disturbance
and mosaic structure where relief substantially
exceeds tree height (e.g., Cascade Range). The
classification and mapping of physiography as
was done to delineate ecological subregions at
the section level should provide an important
means of discriminating broad areas with differing fire regimes within a particular ecoregion.
At finer scales, one finds considerable variation in fire regimes in response to local topography, vegetation, and microclimate (cf., Cleland
et al. 2004). As we have seen, local ecosystems
occur in predictable patterns within a particular
ecoregion. Similar fire regimes occur on similar
sites within an ecoregion. Knowledge about fire
regimes on similar sites allows ecological restoration so as to incorporate the natural variability
of fire regimes across the ecoregion.
13.7 Future Range of Variation
The range of variation concept is a useful starting
point, but it is limited for a number of reasons.
First, many systems have been fragmented
because of human disturbance; because of this,
fires will not carry the way they did historically.
134
13 Use of Fire Regimes at the Ecoregion Scale