Table 11—Fire regime severity/frequency classes within the Basin Assessment area.
Frequency Severity Class
Historic
percent
—
0.0
14.2
14.2
Lethal frequent
21.5
6.0
-15.6
Lethal infrequent
20.4
34.5
14.1
Lethal very infrequent
3.2
8.1
4.9
Lethal extremely infrequent
2.2
1.5
-0.8
Mixed very frequent
0.6
0.0
-0.6
Mixed frequent
6.2
3.8
-2.5
Mixed infrequent
9.3
16.8
7.5
Mixed very frequent
1.3
0.0
-1.3
24.3
1.4
-22.9
Nonlethal frequent
6.9
2.3
-4.6
Nonlethal infrequent
2.7
10.0
7.3
Rarely
1.3
1.5
0.2
No Data
0.1
0.1
0.0
100.0
100.0
Lethal very frequent
Nonlethal very frequent
Total
Comparing fire severity between historic and
current times for forested potential vegetation
groups on FS- and BLM-administered lands show
an increase in lethal fire from 20 to 50 percent of
the area and a reduction in non-lethal fires from
40 to 15 percent (fig. 14). Subregional differences
exists; although eastern Oregon and Washington
as well as Idaho and western Montana show decreases in non-lethal fire, and increases in lethal
fire, the drop in non-lethal fires in Oregon and
Washington is greater than in Idaho and Montana.
The increase in lethal fires has been greater in
Idaho and Montana than in Oregon and Washington.
Altered fire regimes have been largely responsible
for more homogeneous forests and rangeland
landscapes. Large wilderness or unroaded areas
62
Change
Current
prevail in ERUs such as the Central Idaho Mountains, Northern Glaciated Mountains, Northern
Cascades, and Owyhee Uplands. Even in wilderness and unroaded areas, where fire exclusion
alone has been the primary management influence, fire, insect, and pathogen disturbance regimes have been significantly altered. Despite
these disturbance regime changes, wilderness and
unroaded areas are among those least altered by
management. Predicted road densities vary greatly
across the Basin (fig. 15). Examples of road densities within subwatersheds are shown in figure 16.
Roads are correlated with many changes in vegetation, land use, and hazards, yet a consistent inventory of roads across all ownerships within the
Basin does not exist. Roads are important from
both an ecological and socioeconomic perspective.
This file was created by scanning the printed publication.
Text errors identified by the software have been corrected;
however, some errors may remain.
Figure 12—Changs in Basin fire regimes from historic to current by severity class.
63
Figure 13—Changes in Basin fire regimes from historic to currem by frequency class.
64
Figure 14—Fire Severity for FS- and BLM-administered Forested Potential Vegetation Groups.
65
Figure 15—Predicted road density classes.
66
Figure 16—An example of road density categories for subwatersheds within the Basin.
67
Aquatic/riparian10
Seven key salmonids were selected for detailed
analysis. These are bull trout, westslope cutthroat
trout, Yellowstone cutthroat trout, and redband
trout; steelhead; and ocean-type and stream-type
chinook salmon. Less area within the basin is
currently occupied by three or more key salmonids
(fig. 17) than existed historically (fig. 18). Figure
19 shows the distribution of subwatersheds with
by one or more key salmonid species stonghold.
Key salmonid strongholds are subbasins that
support strong populations based on the consideration of life history forms, trends in population
numbers and relative abundance of individuals.
Strong populations (fig. 20) are associated with
higher-elevation forested lands, and the proportion declines with increasing road densities (fig.
21). The largest areas of contiguous watersheds
supporting strong populations of key salmonids
are associated with the Central Idaho Mountains,
the Snake Headwaters, and the Northern Cascades
ERUs. Important but more restricted areas are
found in the Blue Mountains, Upper Clark Fork,
and the Northern Glaciated Mountains ERUs.
Strongholds varied between 32 percent of the
occupied range for Yellowstone cutthroat trout
and less than 1 percent for stream-type chinook/
salmon (table 12).
Many of the aquatic strongholds occur in areas of
low road density (the definitions of road density
categories are in figure 16). The higher the road
density, the lower the proportion of subwatersheds
that support strong populations of key salmonids
(fig. 21). There is an apparent difference in the
response of aquatic systems between FS-administered lands and all other lands at very low road
densities. Strongholds within the "all lands"
category decline more quickly as road density
increases. Strongholds on FS-administered lands
remain stable or slightly increase. At higher road
densities FS-administered lands provide a greater
proportion of strongholds. For the Basin,
56 percent of the unroaded area is in key
10
Details on historical trends and current status of the Basin's
aquatic/riparian ecosystem are in the Component Assessment—
Aquatic chapter (Lee and others 1996).
68
salmonid strongholds but the proportion varies
from a high of 76 percent in the Snake headwaters
to none in the Upper Klamath (table 13).
Designated wilderness and potentially unroaded
areas are important anchors for strongholds
throughout the Basin. More than 19 million
acres (8 million ha) (27%) of FS- and BLMadministered lands in the Basin contain strongholds (40% FS and 4% BLM). These stronghold
subwatersheds contain large areas of unroaded
land (about 11.6 million acres/4.7 million ha),
averaging 58 percent of the area of an individual
subwatershed.
The use of intensive forest management to re-establish more natural landscape patterns and disturbance
regimes has variable risks and benefits across the
landscape. However, the consequences of large fires
are dependent on habitat conditions and the inherent resiliency of local populations. Damage to
aquatic ecosystems from fire may be most severe
when they have been seriously degraded and fragmented. Intensive management of watersheds that
support healthy populations may pose greater risk
for disruption of watershed processes and degradation of habitats than does fire.
Rehabilitation of depressed populations of anadromous salmonids cannot rely on habitat improvement alone but requires a concerted effort to
address causes of mortality in all life stages. These
include freshwater spawning and rearing, juvenile
migration, ocean survival, and adult migration.
Thus, to realize the benefits of improved migration and ocean survival, there must be maintenance of good-quality freshwater habitats and
healthy populations as well as increases in the
distribution of high-quality spawning and early
rearing habitats. Federal land management plays
a key role in spawning and rearing habitats.
Analysis of the extensive stream inventory data
reveals that major decreases in pool habitat, both
frequency of pools and deep pools, have occurred
over the last 40 to 60 years. These are attributable
to losses in riparian vegetation, road and highway
construction, timber harvest, grazing, farming,
Figure 17—Current number of key salmonid species present within the Basin.
69
CONTINUED