North American Journal of Fisheries Management 26:983–994, 2006
Ó Copyright by the American Fisheries Society 2006
DOI: 10.1577/M05-114.1
[Article]
Effects of Wildfire and Subsequent Hydrologic Events on
Fish Distribution and Abundance in Tributaries of
North Fork John Day River
PHILIP J. HOWELL*
U.S. Department of Agriculture, Forest Service, Forestry and Range Sciences Laboratory,
1401 Gekeler Lane, LaGrande, Oregon 97850, USA
Abstract.—Recent large wildfires in western states have fueled increasing concerns of resource managers
and the public about the effects of fire, including risks to fish, particularly endangered species. However, there
are few empirical studies on the response of fish to fire and none that include anadromous species. The Tower
Fire was one of four large fires in the upper John Day River basin in Oregon in 1996. Much of the area burned
at moderate to high severity, consistent with the pattern of increasing fire severity and size projected for the
region. Intense spring storms in 1997 and 1998 triggered large floods, landslides, and debris torrents that
affected streams within and downstream of the fire. We investigated the effects of the fire and ensuing floods
on fish distribution and abundance in three streams immediately after the fire through 2003. Immediately after
the fire, no fish were found in moderate- and high-intensity burn areas. Fish began to repopulate defaunated
reaches the year after the fire, and within 4 years distribution of juvenile steelhead (anadromous rainbow trout
Oncorhynchus mykiss) and resident rainbow trout was similar to that before the fire. Juvenile spring Chinook
salmon O. tshawytscha also began to use lower reaches of one of the streams after the flood, which had
eliminated a culvert near the mouth of the stream suspected to be a barrier. Densities in most burned reaches
and in unburned reaches downstream of the fire have rebounded to levels similar to or greater than densities in
reference streams outside of the fire. An isolated introduced population of brook trout Salvelinus fontinalis
also recovered. Thus, despite the size and severity of the fire, postfire hydrologic events, and human-induced
changes to watersheds, fish populations were highly resilient.
Two issues that dominate natural resource management in the Pacific Northwest are species listed under the
Endangered Species Act (ESA) and wildfires. Large fires
in the region, such as the Yellowstone fire in 1988 and
more recent fires between 1996 and 2003, have received
national attention. The declines of Pacific salmon
Oncorhynchus spp., steelhead (anadromous rainbow
trout O. mykiss), bull trout Salvelinus confluentus, and
other native fishes have also been widely recognized.
These two issues have merged into concern about risks to
these species from wildfire (e.g., Bisson et al. 2003;
Rieman et al. 2003). The concern has been magnified in
response to both the direct experience of recent large
wildfires and anticipation of increased frequency,
magnitude, and severity of future fires (Hann et al.
1997; Hessburg and Agee 2003). This has prompted a
number of initiatives to reduce levels of forest vegetation
assumed to fuel wild fires, reestablish forest vegetation
more in keeping with common perceptions of historic
fire regimes, and bolster fire suppression capacity to
reduce potential losses of fiber, property, fish, and other
species (e.g., USDA 2000; HFRA 2003).
* E-mail: [email protected]
Received July 21, 2005; accepted May 15, 2006
Published online November 30, 2006
Effects of high-severity fires on the landscape and
aquatic habitat can be dramatic, such as the loss of
riparian vegetation and mass erosion and debris flows
after storm events. Direct mortality of fish can also
occur (e.g., Minshall and Brock 1991; Rieman et al.
1997), although the cause of mortality is uncertain. On
the other hand, many species in fire-prone environments are adapted to periodic disturbance (Gresswell
1999). Fires and other natural disturbances may
ultimately benefit aquatic species by contributing to
habitat complexity (Reeves et al. 1995; Benda et al.
2003; Rieman et al. 2003).
There have been few empirical studies of the effects
of fire and postfire storms on fishes (see Gresswell
1999; Dunham et al. 2003), none of which have
included anadromous salmonids. Those effects have
ranged from extirpation of small populations (Rinne
1996) to at least short-term increases in production
(Novak and White 1990). Data from those studies,
coupled with theories of biological response to
disturbance and studies of physical processes related
to fire, suggest that a number of biological and physical
factors influence the effects of fire on fishes (Dunham
et al. 2003; Rieman et al. 2003). Prominent factors
include the severity and extent of the fire and the
storms that follow, the distribution and connectivity of
983
984
HOWELL
FIGURE 1.—Map of the study area in the upper North Fork John Day River basin, Oregon, 1996. Study streams inside the
Tower Fire area (shaded) and reference streams outside the fire area are underlined.
adjacent populations, and effects of past land and water
management.
The Tower Fire, which burned about 20,640 ha
during mid-August through early September 1996, was
one of four fires during that year in the headwaters of
the North Fork of the John Day River that burned a
total of 42,330 ha. The Tower Fire was the largest fire
ever documented on the Umatilla National Forest
(USDA 1997). Fire crews observed dead fish in
streams during fire suppression activities. Floods and
debris flows in 1997 and 1998 greatly accentuated the
physical effects in some of the burned streams after the
fire. Streams within the fire contained populations with
a range of characteristics: widely distributed, highly
migratory steelhead and Chinook salmon O. tshawytscha and small, isolated populations of nonnative
brook trout Salvelinus fontinalis. Steelhead, the
primary species found in streams within the fire, are
listed as threatened in the John Day River basin under
the ESA; at the time of the fire, populations in the
North Fork John Day River were classified as
depressed (Lee et al. 1997). The North Fork John
Day River also supports the only remaining wild
population of spring Chinook salmon in the Columbia
River basin classified as strong (Lee et al. 1997). Thus,
the Tower Fire provided an opportunity to add to the
limited empirical data on the response of fish
populations to wildfire, especially where the fire
appeared to fit the projected pattern of increased
severity and extent and to relate that response to a
number of physical and biological factors hypothesized
to influence it. Specific objectives of the study were to
document the effects of the Tower Fire on fish
distribution and abundance and to monitor recovery
of the populations after the fire.
Study Area
The study area was located in the North Fork John
Day River basin in the Blue Mountains of northeastern
Oregon. Study streams that were within the Tower Fire
were Oriental, Texas Bar, South Fork Cable, and North
Fork Cable creeks (Figure 1). The lower 22% and 21%
of Texas Bar and North Fork Cable Creek watersheds,
respectively, were outside of the fire (USDA 1997).
Only 1% of Oriental Creek watershed and 3% of South
Fork Cable Creek watershed were unburned (Table 1).
Much of the Tower Fire was a convection crown
fire, a particularly hot fire that rapidly burns through
the forest canopy (USDA 1997). It is also believed that
a so-called downburst occurred, where winds blow
outward near the ground as the convection column
collapses, which can greatly increase fire intensity and
spread at ground level. About 40% of the fire area
burned during the 24-h period when this fire behavior
occurred. Burn intensities (i.e., fire effects on ground
vegetation and soils) were mapped by the U.S. Forest
Service (USFS) as low, moderate, or high according to
USFS criteria (USDA 1995). Within the fire perimeter,
riparian burn intensities were predominantly moderate
and high along most of the streams, except for
primarily lower reaches along the fire perimeter. South
Fork Cable Creek also had a low-intensity ‘‘island’’ in a
meadow reach between the study reaches (Figure 2).
Burn intensities throughout the upland portions of the
Texas Bar, Oriental, and South Fork Cable watersheds
were also mainly moderate and high (Table 1).
Mortality of overstory trees in moderate- and high-
985
WILDFIRE EFFECTS ON FISH DISTRIBUTION
TABLE 1.—Area, elevation, and burn intensity of subwatersheds of the upper North Fork John Day River basin, Oregon, in the
study area.
Percentage burned by intensity
Subwatershed
Burned
Texas Bar Creek
Oriental Creek
South Fork Cable Creek
North Fork Cable Creek
Reference
Battle Creek
Sponge Creek
Frazier Creek
Area (ha)
Mean
elevation (m)
Low
Moderate
High
Total
2,548
1,246
2,449
4,968
1,378
1,456
1,577
1,519
34
16
32
46
33
69
46
21
11
13
19
13
78
99
97
79
1,458
896
1,525
1,692
1,707
1,588
intensity areas was estimated at 95% (USDA 1997).
Tree mortality was complete or nearly complete in 45%
of the area. The understory riparian vegetation often
was also consumed, particularly in high-intensity areas.
In some cases, exposed woody debris in the stream
channel burned.
Forest vegetation in Texas Bar and Oriental creeks
was largely composed of dry types (ponderosa pine
Pinus ponderosa and Douglas-fir Pseudotsuga menziesii; USDA 1997). Mortality in those stand types in the
fire was 2.5–4 times the levels typified by short fire
return intervals (1–25 years) and expected low
mortality of overstory trees (0–20%; Agee 1993;
USDA 1997). In contrast, South Fork Cable Creek
watershed contained principally cool–moist and cold–
dry stand types and stands of lodgepole pine Pinus
contorta with expected longer fire return intervals and
60–80% mortality of large trees from fire (Agee 1993);
actual mortality of these types was lower (31–50%;
USDA 1997).
Streamflows are dominated by snowmelt; however,
thunderstorms can have profound effects in localized
areas. A severe thunderstorm, flood, and debris flows
occurred in the spring of 1997 in the North Fork Cable
Creek watershed. A similar event occurred in the spring
of 1998 and extensively affected Oriental Creek and, to
a lesser degree, the upper reaches of South Fork Cable
Creek (Figure 2). Large debris flows also accompanied
the flood in Oriental Creek. A culvert contained in a
deeply filled road crossing located just upstream of a
study reach in Oriental Creek plugged during the event,
creating a dam-burst flood, which greatly magnified the
effect of the flood and debris torrent on the lower half of
the stream. A culvert and road crossing near the mouth
of the creek were also destroyed. The storm produced a
large amount of hail in upper South Fork Cable Creek.
Deposition of hailstones was approximately 1.7 m deep
along the channel in the upper study reach, but there was
little evidence of channel scouring downstream. A
0
0
0
landslide adjacent to Texas Bar Creek, which also
occurred in 1998, substantially altered the channel along
a study reach. A section of hiking and off-road vehicle
trail washed out in the spring of 2000 and introduced a
large amount of sediment in South Fork Cable Creek,
just upstream from the middle sampling reach.
The Oriental Creek watershed is underlain by
granitic geology, subject to increased surface and mass
erosion and slope instability (USDA 1997). Texas Bar
and South Fork Cable Creek watersheds contain
primarily pyroclastic geology, which is comparatively
less erosive and more stable.
Timber harvest has occurred in all of the study
watersheds within the fire, particularly the Texas Bar
and Oriental watersheds. The extent of timber harvest
has not been compiled, but road densities provide an
indication since the roads were built primarily for
timber harvest. Road densities in Texas Bar and
Oriental Creek watersheds were 3.0 and 2.0 km/km2
(USDA 1997), respectively, which would be classified
as high (1.7–4.7 km/km2) according to criteria for the
interior Columbia River basin (Lee et al. 1997). Much
of the South Fork Cable and upper North Fork Cable
Creek watersheds are within a roadless area. Road
densities in those watersheds were 1.1 and 0.9 km/km2,
respectively. Before the fire, all of the study watersheds
in the fire area were also used for livestock grazing.
Rainbow trout are found in all of the study streams and
are the predominant and most widely distributed fish
species. Anadromous (steelhead) and purely freshwater
forms (stream resident and fluvial) potentially occur.
They will be referred to collectively as O. mykiss because
juvenile steelhead and small resident rainbow trout
found at the time of sampling were indistinguishable.
Nonnative eastern brook trout inhabit the upper reaches
of South Fork Cable Creek. Spring Chinook salmon
spawn and rear in the main stem and larger tributaries of
the North Fork John Day River. Juvenile Chinook
salmon can occasionally be found in the lower reaches of
986
HOWELL
FIGURE 2.—Burn intensities during the Tower Fire (1996), sampling locations, and features affected by postfire disturbances in
Texas Bar, Oriental, North Fork Cable, and South Fork Cable creeks in the upper North Fork John Day River basin, Oregon.
Years indicated by final two digits.
smaller tributaries of the North Fork John Day River
during summer (Lindsay et al. 1986). Sculpins Cottus
spp. and speckled dace Rhinichthys osculus are also
found in portions of the study streams.
Methods
Abundance.—In both Texas Bar and Oriental creeks,
two sites for sampling population densities were
located in high-intensity burn areas and two ‘‘un-
987
WILDFIRE EFFECTS ON FISH DISTRIBUTION
burned’’ sites were located downstream (Figure 2).
Sample sites were longitudinally distributed in the
burned and unburned areas. The riparian area next to
one of the unburned sites on Texas Bar Creek had a
few small spots of very low-intensity ground fire that
did not influence the stream channel. The three sites on
South Fork Cable Creek burned at high intensity.
Reference sites for comparing population densities in
unburned streams unaffected by the fire included
Frazier Creek (a tributary of Camas Creek, which
enters the North Fork John Day River downstream of
Texas Bar Creek) and Sponge and Battle creeks
(tributaries of Desolation Creek, which flows into the
North Fork John Day River near the mouth of Camas
Creek; Figure 1). Sampling reaches and watersheds of
the reference streams generally had similar characteristics as those sampled in the fire (Tables 1, 2). Like
Texas Bar and Oriental creeks, Battle and Sponge
creeks were dominated by O. mykiss, and Frazier Creek
contained a mix of O. mykiss and brook trout similar to
South Fork Cable Creek. Three reaches (one reach per
stream) were sampled in the reference streams. Sites in
the fire area were sampled in 1996 within several
weeks of the fire, in 1997–2000, and in 2003.
Reference sites were sampled in 1998–2000 and in
2003.
Sample reaches were approximately 100 m in length.
Block nets were installed at the upper and lower
boundaries of each reach before sampling. Population
abundances were estimated with backpack electrofishers, pulsed DC (30 Hz), and multiple-pass removal
methods (Armour et al. 1983). Between two and five
passes per sample reach were made until a reduction of
at least 67% from the catch of the previous pass was
achieved. Fish were anesthetized with tricaine methanesulfonate (MS-222; 60 mg/L), and salmonids were
measured to the nearest millimeter (fork length). Any
O. mykiss and brook trout larger than 75 mm were
classified as age 1 and older; 75-mm and smaller O.
mykiss and brook trout were classified as age 0. Wetted
channel widths were measured at 10-m intervals, and
channel areas were calculated to determine fish
densities. Sites were sampled during base flows in
August and September.
We initially analyzed the densities of age-1 and older
O. mykiss by use of a repeated-measures analysis of
variance (Maceina et al. 1994) to compare streams in
the fire with reference streams. However, the analysis
had low statistical sensitivity to detect differences
because the progressive upstream recolonization and
density fluctuations due to the flood and debris flows
resulted in high variation in O. mykiss density among
streams and among years. Consequently, densities
(fish/100 m2) of age-1 and older O. mykiss in study
TABLE 2.—Mean wetted widths and gradients of density
sampling reaches.
Stream
Oriental Creek
Texas Bar Creek
South Fork Cable Creek
Sponge Creek
Battle Creek
Frazier Creek
Reach
Unburned
Unburned
Burned 1
Burned 2
Unburned
Unburned
Burned 1
Burned 2
Burned 1
Burned 2
Burned 3
Reference
Reference
Reference
1
2
1
2
1
2
3
Mean
width (m)
Gradient
(%)
2.1
1.9
1.3
0.4
2.2
1.8
1.9
1.4
2.1
2.6
1.4
2.3
1.9
2.5
4
4
6
7
4
4
6
6
3
3
3
3
5
4
reaches were compared with density classes (low [5],
moderate [6–19], and high [20]) developed by
Dambacher and Jones (in press) for O. mykiss in 82
eastern Oregon streams and with densities in other
unburned tributaries of the North Fork John Day River
(n ¼ 43; Kostow 2003).
Distribution.—Before the fire, fish distribution (i.e.,
presence of fish species along the stream length) was
previously determined in Texas Bar Creek in 1992 and
in Oriental and North Fork Cable creeks in 1993 by
systematically sampling stream habitat units through
electrofishing or snorkeling (sensu Hankin and Reeves
1988). Distribution was sampled immediately after the
fire in Texas Bar and Oriental creeks by electrofishing
without block nets in 100-m reaches distributed
throughout moderate- and high-intensity burn areas.
Salmonids had been visually observed in the lowintensity burned meadow reach of South Fork Cable
Creek between the upper two study reaches during fire
intensity mapping. Fish distribution in Texas Bar,
Oriental, and North Fork Cable creeks was subsequently sampled in 1999–2000 in 100-m reaches at
intervals of one reach per stream kilometer using
single-pass electrofishing without block nets until the
upper limit of distribution was determined (two or
more successive reaches with zero catch).
Results
Abundance
Mean density of age-1 and older O. mykiss in the
reference streams in 1998–2000 was 15 fish/100 m2
(SD ¼ 6.3; Figure 3) and corresponded with the
‘‘moderate’’ densities (6–19 fish/100 m2) observed in
other streams in eastern Oregon (Dambacher and Jones,
in press). Densities of age-1 and older O. mykiss in
other tributaries of the North Fork John Day River
outside of the fire were similar to those in reference
sites, averaging 18 fish/100 m2 (range ¼ 5–28 fish/100
988
HOWELL
FIGURE 4.—Densities (with upper 95% confidence limits) of
O. mykiss and brook trout in South Fork Cable Creek Oregon,
after the Tower Fire in 1996. Reaches are oriented
downstream to upstream from left to right for each year.
Note differences in the scales of the y-axes. Dashed reference
lines indicate density classes for age-1 and older steelhead and
rainbow trout (Dambacher and Jones, in press): low (0–5),
moderate (6–19), and high (20).
FIGURE 3.—Densities (with upper 95% confidence limits) of
O. mykiss in Oriental Creek, Texas Bar Creek, and reference
streams after the Tower Fire in 1996. Reaches in burned
streams are oriented downstream to upstream from left to right
for each year. Note differences in the scales of the y-axes.
Dashed reference lines indicate density classes for age-1 and
older fish (Dambacher and Jones, in press): low (0–5),
moderate (6–19), and high (20).
m2) in 1990–1992, 1994, and 1996 (Kostow 2003). In
2003, mean densities of age-1 and older O. mykiss in
the reference streams were double or triple those
amounts (39 fish/100 m2; SD ¼ 19.2).
No live fish were found in burned reaches sampled
for abundance or distribution shortly after the fire in
Texas Bar and Oriental creeks (Figure 3). Fish were
found in only one sample reach of South Fork Cable
Creek (Figure 4). However, O. mykiss, the only species
sampled in Texas Bar and Oriental creeks, were found
in both sample reaches downstream from the fire in
those streams at densities similar to or higher than
reference streams. This, coupled with observations of
dead fish in streams by fire suppression crews during
the fire, suggests that mortality of fishes in moderateand high-intensity burn areas was high, although
downstream emigration was possible since upper
reaches of all three streams burned at moderate to high
intensity and no fish were encountered during sampling
of those reaches. Repopulation of defaunated reaches
began the year after the fire. Oriental and Texas Bar
creeks contained exclusively larger (165 mm), age-1
and older fish. In 2003, high densities of O. mykiss in
most reaches of all three streams in the fire were
consistent with high densities in the reference streams
that year (Figures 3, 4).
WILDFIRE EFFECTS ON FISH DISTRIBUTION
The study streams provide a mix of fire and postfire
hydrologic disturbances for comparison. After the fire
in 1996 and in 1997 but before the flood and debris
torrent in Oriental Creek, densities of age-1 and older
O. mykiss in the unburned reaches were moderate to
high (range ¼ 6–37 fish/100 m2). Three months after
the flood in 1998, O. mykiss density in those reaches
had plummeted to 1 fish/100 m2 (Figure 3), and density
of age-1 and older O. mykiss in the unburned reaches
remained generally low thereafter (8 fish/100 m2).
Total abundance in the unburned reaches rebounded
the year after the flood but consisted primarily of age-0
fish, a pattern that has continued since then. Surprisingly, density in the lower burned reach after the debris
torrent (5 fish/100 m2) was higher than densities in the
unburned reaches, was the same as levels in 1997 after
the fire, and also consisted of all age-1 and older fish.
The reach was located just downstream of the culvert
and road crossing that caused the dam-burst flood.
Densities of age-1 and older fish in the burned reached
were moderate to high (11–21 fish/100 m2) after 1999.
Fish did not recolonize the uppermost burned reach
until 2000, and densities there have remained low (2–5
fish/100 m2).
Although O. mykiss densities in the unburned
reaches of Oriental Creek dropped to low levels the
same year after the flood and debris torrent, juvenile
spring Chinook salmon first appeared in those reaches
that year (Figure 5). The density of Chinook salmon in
the lower unburned reach (47 fish/100 m2) at that time
was highest at any point after the fire. Juvenile
Chinook salmon continued to occur in the unburned
reaches in all years after the spring 1998 flood (Figure
5).
Texas Bar Creek did not experience a postfire flood
and debris flows like Oriental Creek, but a landslide
from the side slope impinged the channel where the
lower burned sampling reach was located (Figure 2). In
Texas Bar Creek, densities of age-1 and older O.
mykiss in unburned reaches were high, exceeding 20
fish/100 m2 in most years since the fire (Figure 3).
Recolonization patterns in both burned reaches were
similar. Densities of age-1 and older O. mykiss have
been moderate to high (mean ¼ 15 fish/100 m2) since 2
years after the fire, similar to the reference sites. The
landslide had no apparent effect on abundance in the
lower burned reach. Unlike Oriental Creek, samples
from the burned reaches of Texas Bar Creek have
generally consisted of a mix of age-0 and age-1 and
older fish.
Densities of age-1 and older O. mykiss in the two
lower reaches of South Fork Cable Creek exceeded 20
fish/100 m2 since the year after the fire (Figure 4).
Production of age-0 O. mykiss in these reaches was
989
FIGURE 5.—Juvenile Chinook salmon density (with upper
95% confidence limits) in Oriental Creek after the Tower Fire
in 1996. Reaches are oriented downstream to upstream from
left to right for each year.
particularly high in 1999 and 2003. Like the uppermost
sample reach in Oriental Creek, the uppermost reach in
South Fork Cable Creek was not recolonized by O.
mykiss until 2000. Despite this delay, the density of
age-1 and older O. mykiss in the upper reach was
particularly high (43 fish/100 m2) in 2003. Similar to
the pattern in Oriental and Texas Bar creeks, initial
recolonizers were small numbers of larger age-1 and
older fish (Figures 3, 4). Initial recolonizers in the
upper reach of South Fork Cable Creek and the burned
reaches of Oriental and Texas Bar creeks ranged in size
from 165 to 205 mm (n ¼ 10). However, O. mykiss
sampled from all reaches of streams in the fire for all
years were predominantly less than 140 mm (Figure 6).
Like O. mykiss, brook trout were found only in the
middle reach of South Fork Cable Creek immediately
after the fire in 1996 (Figure 4). They recolonized the
upper reach a year later but were absent in 1998 after
the storm. All three reaches have contained brook trout
since 1999. Densities of brook trout have remained low
in the middle and lower reaches since the fire;
however, they are similar to the densities found in
Frazier Creek, the reference stream containing brook
trout (for 1998–2003, mean density of age-1 and older
fish ¼ 1 fish/100 m2; mean density of age-0 fish ¼ 2
fish/100 m2). Since 1999, densities of age-1 and older
brook trout were relatively high (19 fish/100 m2) in
the upper reach, where most of the age-0 fish have been
found and where there was also a high density of age-1
and older O. mykiss in 2003.
In summary, despite apparent extensive mortality of
fishes during the Tower Fire, the defaunated stream
segments generally were recolonized within 2 years
and have maintained moderate to high trout densities
since then. In Texas Bar Creek and in two of the three
reaches of South Fork Cable Creek, densities of age-1
990
HOWELL
FIGURE 6.—O. mykiss length frequency as a percentage of
fish sampled (n ¼ 3,353) in Texas Bar, Oriental, and South
Fork Cable creeks in the upper North Fork John Day River
basin, Oregon, 1996–2003.
and older O. mykiss have been high (mean 6 SD ¼ 22
6 14 and 36 6 17 fish/100 m2) since 1998, 2 years
after the fire. Densities in these reaches have been
similar to or higher than reference streams since 1998.
Even in the remaining upper reach of South Fork Cable
Creek, the density of age-1 and older O. mykiss was
high (43 fish/100 m2) in 2003, despite high densities of
introduced brook trout since 1999 and effects of the
storm in 1998. Reproduction in those streams, as
evidenced by relative densities of age-0 fish, has also
been high, similar to that observed by Rieman et al.
(1997) in the Boise River basin.
In Oriental Creek, which was extensively and
severely affected by the flood and debris flows in
May 1998, O. mykiss recovered more slowly and at
lower densities than in the other study streams. The
timing of that event coincided with O. mykiss spawning
and incubation. Age-0 fish were also only found in one
of the burned reaches in 1999–2000 and at low
densities. Conversely, age-0 fish densities in the
unburned reaches have been higher or similar to
reference streams, but the corresponding low densities
of older fish may be indicative of lower survival. The
low densities in the upper burned reach may also be
related to its location near the upper end of O. mykiss
distribution and its smaller channel width and higher
gradient (Table 2). A positive effect of the flood and
debris flows was the appearance of juvenile Chinook
salmon in lower Oriental Creek. This is probably
related to the displacement of a road culvert near the
mouth during the flood. The culvert was suspected by
the USFS to be a passage barrier at low flows. Juvenile
Chinook salmon had not been observed there in
previous surveys (USFS, unpublished data). Tributaries, such as Oriental Creek, may provide coolwater
refuges during summer for juvenile Chinook salmon
spawned in the main-stem John Day River (Lindsay et
al. 1986). The maximum 7-d average daily temperature
in Oriental Creek, for example, was 5.68C cooler than
the main-stem North Fork John Day River during
1991–1996 (USDA 1997).
The initial recurrence of age-1 and older O. mykiss
exclusively in the burned reaches of Oriental and Texas
Bar creeks and the upper reach of South Fork Cable
Creek suggests immigration of juveniles rather than
reproduction. Although O. mykiss in South Fork Cable
Creek reestablished most slowly in the upper reach,
brook trout rebounded most rapidly in that reach. The
low densities of brook trout in the lower two reaches of
South Fork Cable Creek may be related to their
location in the watershed and associated habitat
characteristics, such as water temperature, rather than
an effect of the fire. Densities in those reaches were
similar to densities in Frazier Creek, the reference
stream containing brook trout. Brook trout in other
streams in the John Day River subbasin and other
basins in northeastern Oregon are typically more
abundant in the upper reaches of the watersheds.
Distribution
After initial postfire sampling in 1996, fish distribution was resurveyed in Texas Bar and Oriental creeks
in 1999 and in North Fork Cable Creek in 2000.
Distribution of O. mykiss, the only species occurring in
the moderate- to high-intensity burned areas in these
streams, was similar to that reported before the fire
(USFS, unpublished; Figure 7). Juvenile Chinook
salmon also appeared for the first time in both
unburned lower reaches of Oriental Creek after the
flood and debris torrent in 1998.
Discussion
Mortality of fishes, particularly salmonids, from
wildfires has been reported in several other studies.
Extirpation or high mortality in more intensely burned
reaches is consistent with that observed by McMahon
and deCalesta (1990) and Rieman et al. (1997).
Extirpation of small populations is possible. Small,
isolated populations of endangered Gila trout O. gilae
and introduced O. mykiss and brook trout in the
Southwest were eliminated after fire (Rinne 1996;
Brown et al. 2001). However, recolonization can be
rapid, as evidenced in most of the stream reaches in this
study. Novak and White (1990) and Rieman et al.
(1997) reported similar responses of rainbow trout. In
most other studies, fish densities observed within a few
WILDFIRE EFFECTS ON FISH DISTRIBUTION
FIGURE 7.—Distribution of O. mykiss in North Fork Cable,
Texas Bar, and Oriental creeks before and after the Tower Fire
in 1996.
years after the fires were similar to or greater than those
measured before the fire (Gresswell 1999).
Mortalities have also been associated with postfire
floods, landslides, and debris flows after intense
rainstorms, similar to what occurred in Oriental and
Cable creeks. In fact, most of the reported incidents of
wildfire-related fish mortality also involve flooding and
debris flows (Novak and White 1990; Propst et al.
1992; Bozek and Young 1994; Rinne 1996; Rieman et
al. 1997). Probabilities of flooding and erosion are
substantially greater after severe fires because of
reduced infiltration rates of precipitation and more
bare soil (Wondzell and King 2003). Consequently,
even smaller storms with less precipitation but higher
frequency of occurrence may exceed the infiltration
capacity in recently burned areas. This strongly
suggests that wildfire effects on fish need to be
considered in the context of potential confounding
effects of subsequent storms. Landscape characteristics
(e.g., topography, geology, soils) may be useful in
assessing the risks of landslides and debris flows from
postfire storms on stream channels (Miller et al. 2003).
As evident in Oriental Creek, roads and other aspects
of management history that could accentuate flood and
debris flow effects should also be considered. However, evaluation of the risks associated with postfire storm
events and ensuing erosion and stream channel
alteration, like the more direct effects of fire alone,
must be tempered by the potential longer-term
contribution of these processes to habitat complexity
and corresponding biological benefits. What initially
appears to be physically ‘‘catastrophic’’ may not be so
for the fish (Bisson et al. 1988; Reeves et al. 1995;
Roghair et al. 2002).
Dry forests (primarily ponderosa pine and Douglasfir species) historically dominated the Tower Fire area,
including the Texas Bar and Oriental creek drainages
991
(USDA 1997). Fire regimes during the 1500s to the
1800s have been typified as frequent low-severity fires
(Agee 1993). The composition, structure, and pattern
of forests, particularly dry forests, have been extensively altered since Euro-American settlement. Such
alteration has changed the historical fire regimes to
projected larger, higher-severity fires (Hann et al. 1997;
Hessburg and Agee 2003). Thus, the Tower Fire has
been described as more severe than would have
occurred under ‘‘natural’’ conditions (USDA 1997).
However, recent research suggests that mixedseverity fire (i.e., low–high) was common historically
in dry forests in the region (Hessburg et al. 2005). Fire
regimes of the past in dry forests have also varied with
climate and included periods with high-severity fires
and large debris flows, such as occurred during 950–
1350 AD (Pierce et al. 2004; Whitlock 2004). Despite
the debate over historical fire regimes and the role of
climate in influencing those patterns, fish populations
in the Tower Fire demonstrated remarkable resilience
to high-severity fire and ensuing hydrological events,
regardless of how consistent one considers them to be
with natural patterns.
A complex array of physical and biological factors
influences the effects of fire on fishes and subsequent
recovery. Physical factors include the nature of the fire
and postfire storms (e.g., severity, extent, patchiness,
timing), past management (e.g., roads, fish passage,
fire suppression; Rieman et al. 2003), and the quantity,
quality, and connectivity of the habitat (Dunham et al.
2003). Biological factors include proximity of other
populations, life history diversity (particularly migratory forms), and nonnative species (Dunham et al.
2003). All of these factors were evident in this study. In
this case, a large fire eliminated fish in moderate- to
high-intensity burned reaches, and postfire floods and
debris flows had similar and perhaps longer-lasting
effects in the most severely affected reaches, as might
be expected. However, connectivity and biological
characteristics of the populations resulted in rapid
recovery from both forms of disturbance.
Unburned reaches and reaches that burned at low
intensity and maintained fish after the fire were
downstream of the more intensely burned reaches with
high mortality. There was also a low-intensity burned
reach in a meadow section of upper South Fork Cable
Creek, where fish survived the fire that was interspersed among high-intensity burn areas. As apparent
from the dispersal of older age-classes of O. mykiss and
brook trout as initial recolonizers of defaunated
reaches, these refuges probably were a source of
recolonization to adjacent reaches where mortality was
high. A similar pattern was reported by Rieman et al.
(1997).
992
HOWELL
Although multiple life history forms of O. mykiss
were potentially present, steelhead were probably the
most common. Of the O. mykiss sampled, 95.0% were
smaller than 140 mm and 0.3% were 200 mm and
larger. This is consistent with other sampling in the
John Day River basin, in which 98% of the O. mykiss
were smaller than 140 mm (ODFW 2001). This
contrasts with the size composition of resident O.
mykiss in tributaries of the Snake River in southwestern
Idaho. Many Snake River tributaries that might have
once contained steelhead now only contain resident
forms as a result of blockage of anadromous fish at
Hells Canyon Dam; 32% of the fish sampled from
those streams during the 1990s were larger than 150
mm and 5% were 200 mm and larger (Zoellick et al.
2005). The contribution of fluvial life history forms
was also probably low since few fluvial fish have been
observed in the main-stem John Day River and changes
in main-stem habitats have made them suitable
primarily as migratory corridors (Kostow 2003). These
data suggest that most of the O. mykiss in the study
streams were juvenile steelhead.
It appears that the initial recolonization and
continued recovery of O. mykiss were not driven by
high escapements of steelhead, however. Steelhead
redd counts in the North Fork John Day watershed
during 1995–1999 were some of the lowest recorded
since surveys were started in 1959 (ODFW, unpublished data). High densities in 2003 do reflect higher
steelhead escapements in 2001–2003. These results
suggest that steelhead, even at depressed adult
numbers, may have facilitated the recovery of O.
mykiss. This may be particularly applicable to steelhead
and other species, where overall adult abundance may
be low but the populations are widely dispersed.
Steelhead and other migratory fish may be particularly
important for maintaining populations subject to fire,
since adults and juvenile migrants may be in waters
outside of the fires, or in larger main-stem reaches
where mortality and other effects from fire, such as
debris flows, are lower (Gresswell 1999). Rieman et al.
(1997) also attributed the recovery of bull trout in
burned areas of the Boise River basin to the
contribution of migratory forms.
Although recovery of O. mykiss did not appear to be
limited by restricted access for adult steelhead, the
appearance of Chinook salmon juveniles in lower
Oriental Creek after the flood and displacement of the
road culvert near the mouth suggests upstream access
by juveniles was limited by the culvert during low
flows. The pattern of upstream recolonization from
juveniles and spawning adults in this study indicates
that maintaining well-distributed populations in connected habitats is key to fish resilience to disturbance.
Dunham et al. (2003) proposed that the vulnerability
of fish to fire effects is directly related to the habitat
specificity of the species and that the degradation,
isolation, and fragmentation of the habitats are
inversely related to habitat size. Oncorhynchus mykiss
are dominant in most tributaries of the North Fork John
Day River. They are noted for being habitat generalists
and are potentially more tolerant of some habitat effects
of fire, such as increases in temperature. The recovery
of O. mykiss in Texas Bar Creek and, to a lesser extent,
Oriental Creek, is also remarkable, given the habitat
condition and history of land management effects, such
as roads (USDA 1997). The recovery of brook trout,
which occurred in South Fork Cable Creek as an
isolated resident population with narrow distribution
and more specific habitat requirements than O. mykiss,
is also noteworthy. Resident populations, especially
where they occur in small streams in areas with higher
probabilities of fire occurrence (Arno 1980) and
potential for direct mortality from fire and effects of
postfire storms (Swanson et al. 1990), may be more
vulnerable to fire since they lack the support of
migratory forms for recolonization. Effects of fire on
small, isolated populations are probably dependent on
fine-scale fire severity patterns and the magnitude of
effects from postfire weather events. The increased
vulnerability of resident populations, especially under a
scenario of increasing size and severity of fires, also
underscores the need to maintain and restore broadly
distributed populations.
Dunham et al. (2003) argued that fire may favor
nonnative species, but they acknowledged that the
reverse may also be true. In this study, both nonnative
brook trout and native O. mykiss recovered to relatively
high densities in South Fork Cable Creek, and there
appeared to be no displacement or depression of
abundance of O. mykiss by brook trout.
The results of this and most other studies of fire
effects on fish indicate that some populations,
including ESA-listed species, can be resilient to large,
severe fires, floods, and debris flows, even in
landscapes with legacy effects of past management.
However, we do not know what the long-term effects
on habitat and productivity will be. Most physical
effects of fire occur within the first decade, except for
long-term recruitment of large wood and in cases
where large floods and debris flows result in substantial
channel reorganization (Gresswell 1999). The role of
fire in stream processes that create and maintain diverse
and productive habitats is also an important consideration in evaluating the effects of fire on fishes.
The appearance of juvenile Chinook salmon in
Oriental Creek after elimination of the culvert at the
mouth and the contribution of roads to flood effects in
WILDFIRE EFFECTS ON FISH DISTRIBUTION
that drainage emphasize that there may be threats to
aquatic species other than fire that warrant management
attention. Restoring landscapes and disburbance patterns to more closely resemble what native species
evolved with may also be beneficial (e.g., Rieman et al.
2000), to the extent that is possible, especially given
current climate trajectories (Meyer and Pierce 2003;
Whitlock et al. 2003; Pierce et al. 2004). Managers
need to carefully consider the risks and justification for
fire-related forest management as well as other actions
that may be of more immediate or greater consequence
for aquatic species. Understanding how fish respond to
fire is an important step in assessing those risks.
Acknowledgments
Pam Arbogast, Chelsie McFetridge, Randy Scarlett,
Christine Hirsch, David Crabtree, and several other
USFS employees assisted with the fieldwork. Mary
Buckman, Oregon Department of Fish and Wildlife,
helped with the statistical analysis. Funding was
provided by the USFS. Thanks to John Sanchez,
USFS, for support. Bruce Rieman, Peter Bisson,
Robert Gresswell, Michael Young, and an anonymous
reviewer provided helpful suggestions on the manuscript.
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