Slim-Tumuch Fish-Forestry Study (1971-1975)
Project Initiation - 1971
Until 1971, little information was available concerning the effects of forest
harvesting on aquatic habitat and salmonid productivity in the central interior
of British Columbia. Most fish-forestry studies had been conducted in
coastal regions, and fisheries managers in interior regions had incorporated
into forest harvest plans measures for stream protection that were derived from
coastal experiences. However, because coastal regions differ from interior
regions with respect to climate, hydrology, soils, forest cover, and logging
methods, this approach was frequently questioned by both foresters and
biologists who recognized the need for data applicable to interior
regions. Accordingly, in 1971 a study (generally referred to as the Slim-Tumuch
Fish-Forestry study) was initiated by the federal Fisheries and Marine Service
(now the Department of Fisheries and Oceans [DFO]) and the B.C.
Department of Recreation and Conservation (now the Ministry of Water, Land and
Air Protection) to provide short-term (< 5 years) data on the possible effects
of forest harvesting on water quality and fish habitat in the central interior
of British Columbia in order to use these data for the integrated management of
forest and fisheries resources.
The Slim Creek valley looking towards the Fraser River from
the Centennial Creek valley (February 1987).
Slim Creek is located 80 km east of Prince George at 54° N latitude and 121°
W longitude, and flows from Shandy Lake through a broad flat-bottomed valley
bordered by rolling hills. Approximately 3 km below Shandy Lake, Centennial
Creek and Donna Creek flow into the mainstem of Slim Creek, which then flows
into Tumuch Lake. The Slim watershed area is ~ 560 km2, although the main focus
of the study during the 1971-1975 period was a smaller area (186 km2) upstream
of Tumuch Lake that included Centennial Creek and its tributaries (Rosanne and
Karolyn Creeks), as well as Donna Creek, as the primary streams of interest.
Study sites were also established along Leaner Creek (a tributary to Tumuch
Lake), as well as along two additional tributaries (Hah and Hee Creeks) to the Bowron River and one tributary (Hungary Creek) to the Fraser River. Soils in the
Slim watershed are diverse and include well-sorted sandy gravels, poorly sorted
tills, and silty-sandy loams, the latter occurring mainly in the valley bottoms
and lower slopes of Donna, Centennial, and Slim Creeks. Slopes are 20-30% on
valley side-walls but are grading (Centennial, Donna) or near level (Slim) in
the valley bottoms. Precipitation is ~ 100 cm annually and is about equally
divided between rain and snow. Forest cover at unharvested sites is overmature,
with white spruce (Picea glauca) being dominant in association with subalpine
fir (Abies lasiocarpa), western redcedar (Thuja plicata), alders (Alnus spp.),
poplars (Populus spp.), and lodgepole pine (Pinus contorta). Streamside
vegetation ranges from conifers to alder, willow, and marsh grasses. The streams
and lake system supports large populations of chinook salmon (Oncorhynchus
tshawytscha), rainbow trout (O. mykiss), Dolly Varden char (Salvelinus malma),
kokanee (O. nerka), mountain whitefish (Prosopium williamsoni), pygmy whitefish
(P. coulteri), and burbot (Lota lota), in addition to cyprinid and cottid
fishes. With the exception of a reach stretching ~ 1 km upstream of its
confluence with Slim Creek, Centennial Creek and its tributaries (Rosanne and
Karolyn) were not inhabited by fish, owing to a waterfall obstruction. This was
unknown during the planning phase of forest harvesting and the headwaters were
subsequently stocked in 1972 and 1973 with rainbow trout. Leaner Creek is
probably a minor spawning area for rainbow trout and kokanee that are resident
in Tumuch Lake. Streamflows peak in spring during the snowmelt-dominated freshet
with a second peak in autumn, and are lowest in winter and during the month of
August. For example, during 1973 and 1974, flows in Centennial and Donna Creeks
peaked at 6-8 m3/sec in May and June, gradually decreasing to 0.7 and 0.35
m3/sec by mid-summer and winter, respectively. Flows in Rosanne Creek peaked at
1.1-1.4 m3/sec in May and June, decreasing to 0.1-0.2 m3/sec during the summer.
Overview of the Slim Creek watershed study area.
Slim Creek near the Yellowhead Highway.
primary experimental approach that was adopted for the Slim-Tumuch study
consisted of an extensive post-treatment design in which logged areas were
compared to unharvested (forested control) areas. Control sites included streams
along which no timber harvesting had occurred (e.g., Donna Creek
and the mainstem of Slim Creek), as well as sites upstream of logged reaches
(e.g., Rosanne, Karolyn, and Leaner
Creeks). Additional pre- and post-logging
surveys were also carried out in Rosanne Creek to assess changes in
stream-bottom composition. The study was initiated in 1971, but this phase
entailed only photo and aerial reconnaissance for the selection of study and
reference (control) sites. In the fall of 1971, a road was constructed along
Centennial Creek, and logging was started near Roseanne Creek
(a tributary to Centennial Creek) during the winter of 1971–1972. By the summer
of 1973, six cutblocks along Centennial Creek and four cutblocks along Slim
Creek to Tumuch Lake had been harvested. Additional
harvesting was conducted northwest of Tumuch Lake
from 1973 to 1975. Monitoring of physical and biological attributes was started
in the spring of 1972 and continued until September 1975.
||Slim Creek just below the Centennial Creek
confluence. (Photo taken in February 1987.)
||Roseanne Creek. The watershed was logged in
1971-1972. (Photo taken in February 1987.)
||Roseanne Creek. This section contains little organic
debris after logging. (Photo taken in February 1987, 14 years after
Timber harvesting treatments
Forest harvesting in the study reaches involved construction of a main
haul road, clearcutting, and extraction of timber using tractor and
rubber-tire skidders. Standard road-building practices were utilized, in
which a 30- to 45-m opening was cleared and local material used for the
sub-grade. Haul roads were more than 100 m from streams except at
crossings (where steel pipe culverts were installed), and, whereas
secondary roads and landings were pre-located on cutting plan permits,
skidtrail layouts were largely left to the judgement of logging
contractors. Clearcutting of ~ 121-ha cutting units was carried out in
late 1971-1973 in the Centennial Creek watershed, although other
cutting units throughout the study watersheds varied in size and ranged
from 80-160 ha in the Slim and Hungary Creek watersheds to ~ 200 ha in
Hah and Hee Creeks. The principal species harvested were white spruce
and some subalpine fir. Cedar and subalpine fir were also cut but
frequently left behind as slash owing to core decay. Whole trees were
skidded to landings for bucking, sorting, and loading, and logging was
carried out during summer and winter months but was interrupted during
spring melt and autumn freezing due to poor road conditions.
Detailed view of the cutting units and sampling stations in the upper
Slim-Tumuch watershed showing the forest harvesting sequence.
Main haul road along Centennial Creek. The second growth is widely
spaced and has little undergrowth (February 1987).
Streamside practices in the study reaches varied as a result of
different contractors, inclusion of stream protection clauses inserted
into some of the cutting permits, season of cut, and different terrain.
Four main streamside logging practices were applied within the stream
Reserve strip, whereby a streamside strip varying
in width from 20 to 200 m and comprising coniferous and deciduous
trees was retained.
Selective strip, whereby a streamside 20-m strip
of vegetation comprising non-commercial trees and leaning commercial
conifers was left standing. Equipment operation was also restricted
within this zone.
Directional falling and skidding, whereby timber
was fallen and skidded away from streams whenever feasible. This
practice also retained deciduous (e.g., alder and willow) and most
non-commercial conifers. Landings tended to be located to minimize
stream crossings and streambank encroachment.
Non-directional falling and skidding, whereby no
attempt was made to control the direction in which trees were felled
and skid trails were not laid out to minimize bank encroachment or
the number of stream crossings.
Aerial photograph of Tumuch Lake (1985). An example of the logging treatments
applied around the lake. (North is towards the top of the
Adjacent to the main streams
(Slim and Centennial), conifer and deciduous leave (buffer) strips of
variable width were left standing. Practices near tributary streams
(watersheds > 26 km2) ranged from selective cutting with few skidder
crossings during summer logging in the upper reaches (e.g., Leaner Creek
and the upper reaches of Karolyn Creek) to clearcutting with frequent
in-stream falling and skidding during winter logging in the lower
reaches (e.g., Rosanne Creek and the lower reaches of Karolyn Creek). A
summary of the streamside practices undertaken along the study streams
during 1972-1974 is presented below.
The following responses of a variety of stream physical and biological attributes
to streamside logging practices were monitored as part of the Slim-Tumuch
study: 1) water quality parameters (suspended sediment,
discharge, water temperature, dissolved oxygen, total dissolved solids,
and nutrient concentrations); 2) stream channel changes (debris
accumulations, bank slumpage, and habitat and substrate
characteristics); 3) invertebrate responses (benthic production and drift
abundance); and 4) salmonid responses (survival and growth of stocked juvenile [age-0
and age-1] rainbow trout, and the survival of trout eggs). Limnological surveys were also carried out to compare water quality,
plankton densities, and fish abundances in a lake around which logging
was carried out (Tumuch Lake) and one whose riparian zone was not logged
|Slim Creek above
Donna Creek, site1.
The main findings of the 1971-1975 studies are summarized below:
Suspended sediment levels downstream of logged
areas were 5-10 times higher than levels in unharvested reaches
during peak spring flows in Centennial, Donna, and upper Slim
Creeks. The main source of sediment in the Centennial Creek
watershed was from a lacustrine silty loam deposit, and most of the
erosion was due to disturbance of these deposits by the main haul
road (although secondary roads and skidder trails were also
Centennial Creek, site 1.
||Centennial Creek jam, September 1990.
- Water temperatures increased in logged reaches by a few degrees when
compared to unharvested reaches.
- Cation levels were similar in the logged and unharvested reaches, and
some nutrient concentrations in logged reaches were up to five times those
recorded in unharvested reaches.
- Of the four logging practices, non-directional falling and skidding
caused the greatest channel disturbance, followed by directional falling and
skidding, selective strips, and reserve strips.
||Rosanne Creek, above bridge (summer logging),
||Rosanne Creek, beaver
pond, September 1990.
- Sediment deposition in areas downstream of logged reaches was associated
with reductions in benthic invertebrate densities, particularly in riffles.
A strong negative correlation was found between sediment concentrations and
invertebrate densities. Invertebrate drift was also lower in the logged
reach of Rosanne Creek when compared to control reaches.
- Increased sediment deposition on riffle gravels has implications for
trout egg-to-fry survival rates. However, rainbow trout eggs planted in
gravels downstream of logged reaches in Rosanne Creek had good survival
rates to the pre-emergent stage, despite sediment loadings that were similar
to those used under controlled experimental conditions at the Loon Lake
Hatchery (where reductions in survival were observed). Higher water
velocities in Rosanne Creek relative to the controlled experiment may have
resulted in less sediment deposition.
- Rainbow trout juveniles (age-0 and age-1) stocked in Rosanne Creek were
found to have higher growth rates when compared to unharvested reaches,
although other intrinsic but undocumented factors (e.g., differences in flow
and cover) may also have played a role in these results. However,
late-summer densities of age-0 trout were lower in the logged reaches when
compared to the unharvested reach, although the reverse pattern was found
for age-1 trout.
- Turbidity was higher in Tumuch Lake (around which logging was conducted)
when compared to Shandy Lake (control), and this was attributed to higher
concentrations of suspended sediment enetring the lake during the spring.
Productivity was also lower in Tumuch Lake (possibly due to the higher
turbidities and resulting lower transparency of the water column) despite
slightly higher nutrient levels.
- There were no consistent differences in zooplankton, phytoplankton, and
fish populations between Tumuch Lake and Shandy Lake, although benthic
invertebrate densities were lower than expected at the Slim Creek inlet to
Tumuch Lake (possibly due to higher rates of sediment deposition).
|Slim Creek, site 1.
||Tumuch Lake / Slim Creek.
The Slim-Tumuch Fish-Forestry study was the first to examine the physical and
biological responses of stream ecosystems to clearcut logging practices in the
central interior of British Columbia. The study highlighted the differences
between coastal and interior stream ecosystem processes and drew attention to
their potentially different responses to streamside clearcut logging. Moreover,
although the study provided valuable preliminary data that were sorely needed to
enable foresters and biologists to make scientifically defensible management
decisions, there is an acknowledged dearth of information regarding the impacts
of streamside logging in temperate, interior regions, and future fish-forestry
studies in these regions of British Columbia are therefore encouraged.
In recent years (from the early 1980s to the early 1990s), the Slim Creek
watershed continued to be subjected to relatively intense timber harvesting
activities, in part to combat a bark beetle infestation. The federal DFO
Salmonid Enhancement Program initiated further studies in the Slim Creek
watershed in 1980 and 1981 to collect information for a planned enhancement
facility on the Bowron River. Data on migration timing, size distribution, and
morphology of adult and juvenile chinook salmon were collected along with
physical and chemical observations on the streams and lakes. In early 1987, DFO
initiated a limited survey to assess channel morphological changes caused by
logging as well as to gather preliminary data on the winter distribution of
chinook salmon. During the period from 1990 to 1994, DFO was again involved in
monitoring water quality (streamflow, suspended sediment, nutrients, dissolved
oxygen, water temperature) and salmonid densities and distributions within the
Slim Creek watershed, but to date these data have not yet been compiled or
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Updated February 2009