Impacts of timber harvest on aquatic macroinvertebrate
community composition in a northern Idaho watershed
Justin Broglio1, Timothy E. Link2*, Jeffrey Braatne2, John Gravelle2
1
P.O. Box 5574; Incline Village, NV 89450. ph: (208) 596-0838;
broglio838@hotmail.com
2
University of Idaho, College of Natural Resources, 975 W. 6th Street, Moscow,
ID 83844-1133. ph: (208) 885-9465, FAX: (208) 885-6226; tlink@uidaho.edu
*corresponding author
Acknowledgments
The authors express their gratitude to the scientists of Pine Orchard, Inc.
and EcoAnalysts, Inc. who were the independent contractors responsible for data
collection and sample analysis. Appreciation is also extended to the Potlatch
Corporation for designing and implementing the MCEW and for access to the
experimental site and resulting datasets. This research was funded by the
University of Idaho, College of Natural Resources Berklund Undergraduate
Research Award.
2
Abstract
Timber harvest and road construction in mountainous watersheds have
the potential to impact stream temperature, light and flow regimes, primary
production, organic matter, fish and aquatic macroinvertebrates. The effects of
contemporary timber harvest practices on aquatic macroinvertebrates were
studied in a northern Idaho watershed. Macroinvertebrate assemblages are
commonly used to assess the potential effects of timber harvest on stream
ecosystems. In this study, the structure and diversity of macroinvertebrate
assemblages were compared in 50% clear-cut, 50% partial-cut, and control
catchments. Three macroinvertebrate taxa were specifically used as
bioindicators of stream habitat quality: Ephemeroptera (mayflies), Plecoptera
(stoneflies), and Trichoptera (caddis flies), “EPT”. In relation to pre-harvest
conditions, there were no major changes in functional feeding group composition
or species diversity. However, changes were observed in macroinvertebrate
abundance and EPT richness and abundance. Long-term and detailed food web
studies are needed to fully assess these responses to clear-cut and partial-cut
harvesting practices.
KEY TERMS: aquatic macroinvertebrates; water quality; timber harvest; Pacific
Northwest; Mica Creek
3
Introduction and Background
Forest harvest practices have changed dramatically over the last century,
with increased emphasis on methods to decrease adverse impacts on aquatic
ecosystems. Forest harvest can affect several aspects of stream ecosystems
including temperature, light and flow regimes, primary production, organic matter
dynamics, and macroinvertebrate community structure (Stone and Wallace
1998). Forest harvest and road construction in mountainous watersheds also
have the potential to increase the amount of fine sediment entering streams
(Haggerty et al. 2004). These sediment inputs can potentially impact all biotic
components of stream ecosystems (Relyea et al. 2000).
Macroinvertebrates are valuable bioindicators to assess the effects of
forest harvest due to their sensitivity to changes in sediment, organic matter,
temperature, and light levels (Haggerty et al. 2004). Sediment inputs may have
positive, negative, or neutral effects on macroinvertebrate communities,
depending on the quantities involved, geologic characteristics, nature of the
streambed, composition of flora and fauna, and time of year (McClelland 1972).
There are several other environmental variables related to macroinvertebrate
community composition, including sediment composition and particle size
(Peeters et al. 2004), streamside vegetation, hyporheic and near-bed flows, and
longitudinal and downstream hydraulic gradients, that control the input and
dynamics of organic matter, nutrients, temperature, and light (White 1997).
4
The impacts of forest harvest on macroinvertebrate community structure
within a given reach are controlled by complex interactions between species
assemblage, watershed physiography, hydroclimatic regime, and the type and
extent of land cover alteration. In a low gradient sand-bottomed stream, clear-cut
logging was noted to alter species composition, richness and proportional
abundance of functional feeding groups, with an increase in collector-gathers and
scrapers and a decrease in shredders (Kedzierski and Smock 2001). A similar
trend of increasing scraper abundance and a decline in shredder abundance
after clear-cutting was also noted in a low elevation oak (Quercus spp.) and
hickory (Carya spp.) watershed in North Carolina (Stone and Wallace 1998). In a
sub-boreal forest, macroinvertebrate densities increased immediately after clearcutting as a result of increased light levels, which increased primary production
(Fuchs et al. 2003). These studies reveal the range of responses that may arise
between streams, indicating the need to improve our understanding of
macroinvertebrate responses to disturbances both within and between a broad
range of stream ecosystems.
In the relatively pristine (i.e., no significant disturbances for ~70 years)
Mica Creek Experimental Watershed (MCEW), initial biological assessments
revealed considerable variation between the upper, middle, and lower stream
reaches, with shredders and collectors dominating upper reaches (White 1997).
This initial study also determined that taxa richness had no relationship to stream
size, and that collector-filterers were constant among sites. A high degree of
taxonomic variation was observed throughout the watershed, but this variation
5
was related to habitat changes along the stream continuum (White 1997). This
and other studies also established sediment tolerances for macroinvertebrates
(Relyea et al. 2000) and provided a base of knowledge on aquatic insect
community structure and diversity prior to road construction and timber harvest
(White 1997).
The primary objective of this research was to assess temporal differences
in macroinvertebrate community composition and species diversity before and
after timber harvest in a 50% clear-cut catchment and a 50% partial-cut (i.e.
thinned) catchment with 50% canopy removal in harvested areas. The
secondary objective of this research was to assess the degree of post-harvest
disturbance in upper headwater reaches, which were expected to sustain greater
impacts on aquatic macroinvertebrates.
Methods
Site Description
This research was conducted in the Mica Creek Experimental Watershed
(MCEW), a 27 km2 watershed located in Shoshone County, northern Idaho
(Fig. 1). The MCEW is privately owned by Potlatch Corporation and managed
primarily for timber production (Schultz 2000). Streamflow, water quality, and
aquatic ecological conditions have been monitored since 1991 as part of a
comprehensive study of contemporary forest harvest practices on headwater
streams.
6
Mica Creek is a tributary of the St. Joe River and the research area
includes the headwaters of the west fork and main stem of Mica Creek.
Experimental catchments range from 1000 to 1600 m (amsl), with stream
gradients ranging from 5 to 20 percent. Average annual air temperature is 5 oC,
and average annual precipitation is approximately 1450 mm, over half of which
typically falls in the form of snow.
In the early 1900s, approximately 95% of the overstory canopy was
removed from the Mica Creek Basin using historic harvesting techniques
(Schultz, 2000). Large-scale sediment movement was the most common effect
associated with these logging practices. By the early 1930s, logging ceased in
upper Mica Creek. In December 1933, a large rain-on-snow flood event damaged
the central flume beyond repair and flushed a significant amount of sediment
through the Mica Creek stream network (Schultz 2000). The site has remained
relatively undisturbed since the early 1930s and is typical of many second-growth
forests in the region.
Experimental Treatments
Recent harvest activities were initiated in late 1997 with the construction of
a main access spur road. After road construction, four years of post-road data
were collected prior to harvesting in the summer and fall of 2001. The clear-cut
area was broadcast burned and replanted with conifer seedlings in late May
2003. Two of the three sub-watersheds that drain into Flume 4 (Fig. 1) were
harvested using a mobile cable system (steeper sections of the watershed) and
7
rubber tire skidders (lower gradient areas). Timber harvest followed Idaho Forest
Practice Act guidelines, leaving 75 % of existing shade in Class I Stream
Protection Zones (SPZs) and operating equipment outside a 75 foot buffer in the
Class I fish-bearing streams and a 30 foot buffer in the Class II non-fish bearing
streams. Drainage features were also installed along skid trails to control erosion.
The clear-cut catchment (50% canopy removal) drains to Flume 1 (Fig.1),
the partial-cut catchment (25% total canopy removal) drains to Flume 2, the
control catchment drains to Flume 3, and Flume 4 is the cumulative site
downstream of for all three catchments. Physical characteristics for these four
sites are summarized in Tables 1 and 2.
This study used macroinvertebrate data collected over five years near the
four stream-gauging stations. These data were used to assess the cumulative
potential effects of timber harvest techniques on macroinvertebrate populations.
This study also established four new sampling points (paired design) to assess
impacts in upper watershed reaches. This included two sites located in the clearcut zone, one in the partial-cut zone, and one in the control zone. These reaches
were located in the central timber harvest areas, contain smaller riparian buffers
and higher numbers of road/stream crossings. These additional sites provided
EPT abundance data for stream reaches that had not been previously sampled,
but which were expected to sustain greater impacts relative to the flume
sampling sites.
8
Macroinvertebrate Sampling Protocol
Macroinvertebrates were sampled in the thalweg of riffles below the flume
at each gauging site. Sample sites were 40 times the wetted width of the stream
and ranged from 50 to 75 m in length. Five randomly placed benthic samples
were taken at each site with a modified Hess sampler (36 cm diameter sample
area, 250 µm mesh net). These methods were necessary to sample the small
headwater environments within the MCEW. Samples were taken at the lowest
riffle and preceded upstream within the designated stream reach with no more
than one sample per riffle. Samples were placed in one quart glass jars and
preserved in a 70% alcohol solution (White 1997). These sampling protocols
were also followed in upper watershed reaches, though study reaches were
shorter in length (25-50 m).
Four supplemental post-timber harvest macroinvertebrate sample sites
above the flumes were chosen in the headwater regions of Mica Creek in July
2003. These regions of the MCEW are located in the central timber harvest
areas, contain smaller riparian buffers and higher numbers of road/stream
crossings, and stream segments are relatively short in length. These areas in the
MCEW were likely to sustain greater impacts as a result of the disturbances;
therefore, it is important to understand how the aquatic community is structured
across these areas.
9
Data Analysis
Macroinvertebrates collected at the flume sites were identified to genus,
and species (when possible) by EcoAnalysts Inc. (Moscow, ID). Data were sorted
and graphed, with a Multivariate Analysis of Variance (MANOVA) to identify
significant differences in specific taxa (Ephemeroptera, Plecoptera, and
Trichoptera, or EPT) and overall macroinvertebrate abundance. Statistical
analyses were completed using the StatistiXL data analysis package. All data
were ln(x+1) transformed to meet MANOVA assumptions of independence,
normality and homogeneity of variance (Benfield 1996, Chamberlain and Braatne
2006). Average percent composition of macroinvertebrate functional feeding
groups (collectors-filters, collectors-gathers, scrapers, shredders, and predators)
were also sorted and graphed.
In addition to abundance values and functional feeding groups, four other
indices (EPT richness, predator richness, scraper richness, and Shannon-Weiner
H’ log e) were used to determine macroinvertebrate community richness and
species diversity. Indices were sorted and graphed, with a MANOVA to assess
significant differences. EPT richness, defined as the total number of identifiably
distinct taxa in the insect orders Ephmeroptera, Plecoptera, and Trichoptera, was
used to characterize macroinvertebrate richness at flumes 1-4. Predator and
scraper richness was used to characterize changes in allocthanous and
autochthanous inputs. Shannon-Wiener H’ log e, a common community diversity
index, was used to estimate macroinvertebrate diversity.
10
The data that were collected during the year harvesting occurred (2001)
were not included in the statistical analysis of pre- and post-harvest
macroinvertebrate communities. Impacts of harvesting were considered to occur
continuously and increase over the course of this year, whereas the sampling
occurred at a discrete point in time. For example, although the impact of reduced
shade likely affected the headwater streams prior to the macroinvertebrate
sampling, increased sedimentation was not observed until flows increased after
sampling (Karwan and Gravelle, this issue). This year was therefore removed to
eliminate any partial impact effects and to directly compare years that are
representative of actual pre- and post-harvest conditions. It is important to note
that the macroinvertebrate community structure during this year was very similar
to both the pre- and post-harvest conditions.
Taxonomic identification (EPT abundance) of the headwater
macroinvertebrate samples collected in 2003 was completed in the University of
Idaho, College of Natural Resources laboratory. Samples were filtered through a
# 40 U.S.D.A standard testing sieve and then identified to order using keys
provided by Merritt and Cummins (1996). The total numbers of individuals in
each of the three orders of concern were sorted by site and an average was
calculated from the five replicate samples taken at each site.
11
Results and Discussion
Macroinvertebrate Abundance
A distinct increase (P = 0.014) in macroinvertebrate abundance values
followed timber harvest in 2001 (Figure 2). Abundance values in the clear-cut
catchment increased from 250 individuals per site prior to harvest (2000) to 656
(2002) and 600 (2003) individuals per site following timber harvest. These values
represent the overall macroinvertebrate community (e.g. Ephemeroptera,
Plecoptera, Coleoptera, Diptera, Chironomidae, Trichoptera, Lumbricina,
Oligochaeta, Bivalvia, Gastropoda, Ostracoda, Tricladida, and Acari).
The largest increase in macroinvertebrate abundance was observed in the
clear-cut and cumulative sites. This increase could be related to several different
variables, or interactions between altered variables. Because clear-cutting
increased annual water yield by approximately 30 % (Hubbart et al. this issue),
changes in sediment quality and depositional patterns may contribute to
community increases. Increases in fine substrate, amount of riparian cover,
slash, stream cover, and mean water temperature are highly correlated with
variation among macroinvertebrate assemblages in headwater streams (Banks et
al. 2005). Clear-cutting above Flume 1 increased stream temperatures in
harvested reaches (by 1.6 to 3.5 °C), but slightly reduced (by ~0.3 °C) stream
temperatures at the flume sites (Gravelle and Link this issue). Temperature
changes, coupled with increased flows that may have increased oxygenation,
may have contributed to increased population densities. Additional research is
needed to identify the specific processes underlying these observations.
12
EPT Abundance
Average EPT abundance increased significantly (P = 0.001) following
timber harvest (Fig. 3). The most dramatic increases were seen in the clear-cut
and cumulative catchments. EPT abundance values in the clear-cut catchment
increased from 97 individuals prior to harvest, to 276 individuals after harvest.
EPT abundance values in the cumulative catchment increased from 471
individuals prior to harvest, to 801 individuals after harvest.
Although a small increase in EPT abundance was seen in the control
reach, it was not as dramatic as the 179 individuals increase observed in the
clear-cut catchment. Therefore, it can be assumed that cumulative effects of
timber harvest (i.e., increased flows, changes in sediment quality and
depositional patterns, temperature and light changes) increased populations of
Ephemeroptera, Plecoptera, and Trichoptera. Jackson et al. (2005) found that
EPT abundance increased after timber harvest in six clear-cut catchments in the
Washington Coast Range, which was related to increased primary productivity
from decreased slash cover and increased insolation. EPT abundance increased
during and after harvest in all study reaches, and returned to pre-treatment levels
two years (2003) after harvest, therefore supporting the assumption that timber
harvest increased EPT abundance.
13
EPT Richness
Average EPT richness values (Fig. 4) were compared at each sample site
over a four-year period before and after timber harvest. There were no significant
differences between clear-cut and partial-cut reaches and the control reach (P =
0.676). However, EPT richness values at the cumulative site (Flume 4) declined
moderately after timber harvest, later increasing toward pre-treatment values by
2003. Because Flume 4 is downstream of catchments 1, 2, and 3, this
downstream decline in EPT richness may be associated with the increased flows
(Hubbart et al. this issue), or sediment flux (Karwan and Gravelle this issue)
related to timber harvest. This decline in downstream EPT richness could also be
linked to the observed decrease in scrapers or an increase in predators
(described below).
Shannon-Wiener H (log e) – Diversity Index
Shannon-Wiener values are a common index of species diversity. The
Shannon-Wiener Index can be estimated with the natural log (ln), log 2, or log 10
data transformation. In this study, these values were natural log transformed to
meet independence, normality and equality of variance assumptions associated
with statistical analyses.
The Shannon-Wiener (log e) values were higher than 2.5 in all sample
years (Fig. 5), indicating high levels of species diversity in all study reaches.
Diversity values at Flume 1 (clear-cut) and Flume 4 (cumulative) both correspond
to the natural variation observed at Flume 3 (control stream). Patterns observed
14
in the control reach showed a progressive increase from 2.96 to 3.22 after
harvest (2002), and again from 3.22 to 3.35 (2003). There was a significant
difference between all the Shannon-Wiener values (P = 0.039), therefore
suggesting the increase in Shannon-Wiener diversity values can be related to
natural variation.
Functional Feeding Groups
Functional feeding groups (e.g. collector-gatherers, collector-filterers,
shredders, scrapers, and predators) were quantified at each study site from 1999
through 2003 (excluding the 2001 harvest year). The dominant functional feeding
group at all four flume sites was collector-gatherers (Fig. 6). Collector-gatherer
compositions were high (52 % on average) before and after timber harvest and
therefore do not appear to be impacted by harvest disturbances (Fig. 6). White
(1997) also observed collector-gatherer dominance prior to timber harvest.
An increase in predators was observed during the study period, but this
pattern was also seen at the control site (Flume 3). Thus, increases appear to be
due to natural population cycles, climatic variability, and concomitant impacts on
flow and sedimentation (Fig. 6).
The dominant functional group associated with most headwater streams
are shredders, while collectors are generally associated with network stream
systems (Gomi et al. 2002). However, scrapers might predominate in streams
impacted by recent clear-cuts, with shredders dominating streams with denser
riparian canopies (Fuchs et al. 2003). Collector-gatherers are correlated with fine
15
particles and commonly found in depositional areas. Kedzierski and Smock
(2001) noted that an increase in both collector-gatherers and scrapers, and a
decrease in shredders can be attributed to timber harvest. Stone and Wallace
(1998) found that collectors were three times more abundant in clear-cut stream
reaches. They also noted a marked drop in shredder abundance immediately
after clear-cutting. The functional feeding group data observed in the MCEW
differs from these studies, as collector-gathers dominated each sample site and
scrapers declined in the clear-cut, control, and cumulative catchments. This
result could be due to several interacting factors, including the geologic,
hydroclimatic and biophysical characteristics of this area.
The composition of functional feeding groups in the MCEW were related
directly to the studies by Herlihy et al. (2005) and Cole et al. (2002). Herlihy et al.
(2005) found that almost half (49 %) of functional feeding group assemblages in
headwater streams were composed of collector species, whereas the remainder
where evenly divided among scrapers, shredders and predators. Cole et al.
(2002) found that collector-gatherers where the most abundant functional feeding
group, averaging 45 % of the sampled assemblages.
Scraper and Predator Richness
Average scraper and predator richness values are shown in Figure 7 for
each site from 1999 to 2003. There was an increase in predator richness from
2000 through 2003 in all catchments. Since there was no statistical significance
between the experimental catchments (P = 0.184), this observation suggests that
16
this pattern was not related to timber harvest. This increase in predator richness
follows the increase in predator abundance noted above, but since the control
sites showed the same trend as the experimental treatment sites, this increase
appears unrelated to timber harvest.
Declines in scraper richness after timber harvest (2002, 2003) were not
statistically significant (P = 0.487). In contrast to the study by Kedzierski and
Smock (2001), there was a decrease in scrapers and an increase in predators.
Kedzierski and Smock (2001) sampled a low gradient sand-bottomed stream,
whereas stream gradients of MCEW ranged from 5 to 20 %. The streambed
geology in the MCEW is also gneiss/quartzite parent material, overlain by silty
loams and would probably not contain the same macroinvertebrate assemblages
found by Kedzierski and Smock. Hence these differences appear related to
differences in the biophysical environments of these two study areas.
Headwater Data
Since upper headwater sites were only sampled once, longer-term data
were not available for temporal comparisons. However, these data were useful to
assess macroinvertebrate assemblages along more heavily impacted reaches.
EPT abundance was used as a bioindicator in both disturbed and undisturbed
headwater reaches of Mica Creek (Fig. 8). In comparision with Herlihy et
al.(2005), who found that 55 % of the taxa observed in headwater reaches were
in the orders Ephemeroptera, Plecoptera, or Trichoptera, EPT values in the
additional MCEW headwater sites followed more natural patterns of abundance.
17
There were slightly higher EPT abundance values in the control relative to the
clear-cut reaches (Figure 8a) and a much higher abundance of Plecoptera at all
four sites (Figure 8b). Plecoptera abundance values in the clear-cut headwaters
and the control headwaters were 13 % higher than partial-cut headwaters.
Overall, Plecoptera abundance values in the headwater regions of the MCEW
were 132 % higher than Ephemenoptera abundance values and 48 % higher
than Trichopetra abundance values. Futher investigation is warranted to
determine a more comprehensive impact on the invertebrate communities in the
headwater regions of the MCEW.
Future directions
The objectives of this investigation were to assess the general changes on
the macroinvertebrate communities before and after timber harvest, and how the
degree of disturbance in the directly impacted headwater reaches was reflected
in the macroinvertebrate assemblages. There are a number of future
investigations beyond the scope of this initial assessment that would be useful to
explore to more fully understand the subtleties of macroinvertebrate response to
disturbance. Specifically, it would be beneficial to examine specific taxa, such as
Baetis, Perlidae, and Limnephilidae sp., which are more sensitive to habitat
change. Isolation of dominant taxa in each functional feeding group could also
help explain why collector-gathers dominate the upper catchments of the MCEW.
It would also be useful to assess the specific mechanisms that produced the
observed changes through multidisciplinary investigations of the biophysical,
18
biogeochemical and ecological changes associated with timber harvest in
headwater systems. Ongoing investigations include an assessment how
macroinvertebrate changes are propagated to higher trophic levels through
riparian food web analyses in systems with a range of disturbance intensity.
Conclusions
Overall, macroinvertebrate communities were relatively stable. There were
no major changes in functional feeding groups or EPT richness values in relation
to timber harvest. The only statistically significant changes in community
structure were increases in macroinvertebrate and specific taxa (EPT)
abundance. Although a decrease in EPT richness was observed at the
cumulative site, it was not significant and further research is needed to identify
the specific mechanisms that are likely to have produced these observed
changes. Further research is also needed to determine if the observed changes
will remain in the years following forest harvest and if the increased abundance
values will alter food webs or other stream ecosystem components.
19
References
Banks, J., A.T. Herlihy, and J. Li. (2006- in preparation). Influence of forest
harvest on aquatic insect emergence from perennial and intermittent headwater
streams in the central Oregon Coast Range.
Benfield, E.F. 1996. Leaf breakdown in stream ecosystems. P. 579 – 589 in
Methods in Stream Ecology, Hauer, F.R. and G.A. Labertii (eds.). Academic
Press Inc., San Diego.
Chamberlain, E. and J.H. Braatne. (2006 – in press). Leaf decomposition and
stream macroinvertebrate colonization of Japanese knotweed, an invasive plant
species. Hydrobiologia.
Cole, M.B., K.R. Russell, and T.J. Mabee. 2003. Relation of headwater
macroinvertebrate communities to in-stream and adjacent stand characteristics in
managed second-growth forests of the Oregon Coast Range mountains. Can. J.
For. Res. 33:1433-1443.
Fuchs S.A., S.G. Hinch, and E. Mellina. 2003. Effects of streamside logging on
stream macroinvertebrate communities and habitat in the sub-boreal forests of
British Columbia, Canada. Can. J. For. Res. 33:1408-1415.
20
Gomi T., R.C. Sidle, and J.S. Richardson. 2002. Understanding processes and
downstream linkages of headwater systems. Bioscience 52(10):905-915.
Haggerty, S.M., D.P. Batzer, and C.R. Jackson. 2004. Macroinvertebrate
response to logging in coastal headwater streams of Washington, U.S.A. Can. J.
Fish. Aquat. Sci. 61:529-537.
Herlihy, A.T., W.J. Gerth, J. Li, and J.L. Banks. 2005. Macroinvertebrate
community response to natural and forest harvest gradients in western Oregon
headwater streams. Freshwater Biol. 50:905-919.
Hubbart, J.A., T.E. Link, J.A. Gravelle, and W. Elliot. (2006 – in review). Timber
harvest impacts on hydrologic yield in the continental/maritime hydroclimatic
region of the U. S. For. Sci. this issue.
Jackson, R.C., D.P. Batzer, S.S. Cross, S.M. Haggerty, and C.A. Sturm. (2006 in preparation). Abiotic and biotic responses of headwater streams to adjacent
timber harvest: Results of a four-year manipulative study.
Karwan, D.L. and J. A. Gravelle. (2006 – in review) Effects of current timber
harvest practices on suspended sediment loads in Mica Creek, Idaho. For. Sci.
this issue.
21
Kedzierski W.M. and L.A. Smock. 2001. Effects of logging on macroinvertebrate
production in a sand-bottomed, low gradient stream. Freshwater Biol. 46:821833.
McClelland, W.T. 1972. Effects of introduced sediment on the ecology and
behavior of stream insects. Ph.D. dissertation, Univ. of Idaho, Moscow, ID.
Merritt R.W. and K.W. Cummins (eds). 1996. Aquatic insects of North America.
Kendall Hunt Publishing Company, Dubuque, Iowa. 862 p.
Peeters, E.T.H.M., R. Gylstra, and J. Vos. 2004. Benthic macroinvertebrate
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University of Idaho.
http://www.cnr.uidaho.edu/micacreek/publications/MC_History.pdf. January 15,
2006
22
Stone M.K. and J.B. Wallace. 1998. Long-term recovery of a mountain stream
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23
Table 1. Watershed characteristics and experimental treatments
Watershed/
Size
Flume Number
(acres)
1
350
Treatment
50% of watershed area clearcut, 2
cutblocks, 180 acres total
2
400
50% of watershed area partial cut, with
50% canopy removal in cut areas, 200
acres total
3
500
Control (no impact)
4
1250
Cumulative site comprised of
watersheds 1-3
24
Table 2. Aquatic macroinvertebrate sample site characteristics
Wetted Width
Bankfull width
Gradient
Substrate size
Flume
(m)
(m)
(%)
(d50, mm)
1
1.5
2.1
5
50
2
2
2.4
8
50
3
2
2.5
14
70
4
3
3.9
3
40
25
Table 3. Statistical significance of post-harvest changes to
macroinvertebrate metrics
Metric
P value
Overall Abundance
0.014
EPT Abundance
0.001
EPT Richness
0.676
Shannon-Wiener (H)
0.039
Scraper Richness
0.487
Predator Richness
0.184
26
Figure Captions
Figure 1. Map of the Mica Creek experimental area indicating areas of timber
harvest treatments, long term aquatic macroinvertebrate sampling sites ( [ ) and
post-harvest headwater sampling sites ( # ).
Figure 2. Macroinvertebrate abundance results for pre- and post-harvest
periods.
Figure 3. Average number of individuals per site in the orders Ephemeroptera,
Plecoptera, and Trichoptera for pre- and post-harvest periods.
Figure 4. Average number of taxa per site in the orders Ephemeroptera,
Plecoptera, and Trichoptera for pre- and post-harvest periods.
Figure 5. Shannon-Wiener H' (log e) macroinvertebrate diversity index
for pre and post-harvest periods.
Figure 6. Average percent composition of macroinvertebrate functional feeding
groups for pre and post-harvest periods at the four long-term sampling sites.
Figure 7. Average number of macroinvertebrates identified as scrapers and
predators for pre and post-harvest periods.
27
Figure 8. Total and average number of individuals per site in the orders
Ephemeroptera, Plecoptera, and Trichoptera at the four post-harvest headwater
sites.
28
WS3
#
3
[%
3
4
[%
2
1
[%
[%
#
2
WS2
#
1-A
[%
#
1-B
WS1
Long-term monitoring site
Post-harvest sites (2003)
Road
Stream
Mica Creek study area
Watershed boundary
Partial cut (2001)
Clearcut (2001)
0
Figure 1.
#
500
N
1000
1500 Meters
29
Overall Macroinvertebrate Abundance
Average Abundance
(corrected for subsampling)
3000
2500
2000
ClearCut
Partial Cut
Control
Cumulative
1500
1000
500
0
1999
2000
Before Harvest
Figure 2.
2002
2003
After Harvest
30
Average EPT Abundance
Aveage Abundance
(corrected for subsampling)
1000
900
800
700
Clear cut
Partial cut
Control
Cumulative
600
500
400
300
200
100
0
1999
2000
Before Harvest
Figure 3.
2002
2003
After Harvest
31
Aveage EPT Richness Values
Average EPT Richness
40
35
30
Clear cut
Partial cut
Control
Cumulative
25
20
15
10
5
0
1999
2000
Before Harvest
Figure 4.
2002
2003
After Harvest
32
Shannon-Wiener H' (log e)
Shannon-Wiener H' (log e)
Values
4
3.5
3
Clear cut
Partial cut
Control
Cumulative
2.5
2
1.5
1
0.5
0
1999
2000
Before Harvest
Figure 5.
2002
2003
After Harvest
33
Flume One - 50 % clear-cut catchment
Average Percent Composition
100%
80%
60%
40%
20%
0%
1999
2000
Before Harvest
% Shredders
% Scrapers
% Predators
2002
2003
After Harvest
% Coll-Gatherers
% Coll-Filterers
Flume Two - 50 % partial-cut catchment
Average Percent Composition
100%
80%
60%
40%
20%
0%
1999
2000
Before Harvest
% Shredders
Figure 6.
% Scrapers
% Predators
2002
2003
After Harvest
% Coll-Gatherers
% Coll-Filterers
34
Flume Three - Control
Average Percent Composition
100%
80%
60%
40%
20%
0%
1999
2000
2002
Before Harvest
% Shredders
% Scrapers
% Predators
2003
After Harvest
% Coll-Gatherers
% Coll-Filterers
Flume Four - Cumulative
Average Percent Composition
100%
80%
60%
40%
20%
0%
1999
2000
Before Harvest
% Shredders
Figure 6. (continued)
% Scrapers
% Predators
2002
2003
After Harvest
% Coll-Gatherers
% Coll-Filterers
35
Scraper Richness Values
Average Scraper Richness
12
10
Clear cut
Partial cut
Control
Cumulative
8
6
4
2
0
1999
2000
Before Harvest
2002
2003
After Harvest
Average Predator Richness
Predator Richness Values
20
18
16
14
Clear cut
Partial cut
Control
Cumulative
12
10
8
6
4
2
0
1999
2000
Before Harvest
Figure 7.
2002
2003
After Harvest
36
Average EPT Abundance at each site
Average Abundance
60
50
40
30
20
10
0
Clear Cut
Control
Clear Cut
Impact
Partial Cut
Control
Upper Catchment Average EPT Abundance
45
Average Abundance
40
35
30
Ephemenoptera
25
Plecoptera
20
Trichoptera
15
10
5
0
Clear Cut
Control
Figure 8.
Clear Cut Partial Cut
Impact
Control