Effects of Alternatives to

Clearcutting on Invertebrate

and Organic Detritus

Transport From Headwaters

in Southeastern Alaska

Jake Musslewhite and Mark S. Wipfli

United States

Department of

Agriculture

Forest Service

Pacific Northwest

Research Station

General Technical

Report

PNW-GTR-602

April 2004
Jake Musslewhite is a biologist, U.S. Department of Agriculture, Forest Service,

Pacific Northwest Research Station, Forestry Sciences Laboratory, 2770 Sherwood

Lane, Juneau, AK 99801; Mark S. Wipfli was a research ecologist, Forestry Sciences

Laboratory, 1133 N Western Ave., Wenatchee, WA 98801. Wipfli is now with USGS

Cooperative Fish & Wildlife Research Unit, Institute of Arctic Biology, 216 Irving I

Building, University of Alaska Fairbanks, Fairbanks, AK 99775.

Authors
Musslewhite, Jake; Wipfli, Mark S. 2004. Effects of alternatives to clearcutting on

invertebrate and organic detritus transport from headwaters in southeastern

Alaska. Gen. Tech. Rep. PNW-GTR-602. Portland, OR: U.S. Department of

Agriculture, Forest Service, Pacific Northwest Research Station. 28 p.

We examined the transport of invertebrates and coarse organic detritus from headwater streams draining timber harvest units in a selective timber harvesting study,

alternatives to clearcutting (ATC) in southeastern Alaska. Transport in 17 small

streams (mean measured discharge range: 1.2 to 14.6 L/s) was sampled with 250-

μm-mesh drift nets in spring, summer, and fall near Hanus Bay at an ATC installation

on Catherine and Baranof Islands. Samples were taken before (1996) and after

(1999, 2000) nine timber harvesting treatments were applied. Invertebrate and organic detritus drift densities and community composition were used to assess treatment

effects. A comparison of drift densities before and after treatment showed year-toyear differences comparable to natural variation at other sites in this study, but no

clear relationship to intensity or type of timber harvest treatments. Natural variation 

in drift densities prevented detection of any potential timber harvesting effects.

Coefficients of variation showed transport was most variable among streams, 

followed by seasons and then days. A trend toward an increase in the proportion of

true flies (Diptera) and a decrease in the proportion of mayflies (Ephemeroptera) was

seen in more intensive treatments. Although transport rates were extremely variable,

a mean of 220 mg invertebrate dry mass and 18 g detritus per stream per day was

being transported downstream. The transport of this material suggests that headwaters are potential source areas of aquatic and terrestrial invertebrates and detritus,

linking upland ecosystems with habitats (commonly fish bearing) lower in the 

catchment.

Keywords: Alternatives to clearcutting, headwater streams, invertebrates, organic

detritus, riparian.

Abstract
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Document continues on next page.

.
River continuum theory implies that headwater streams are tightly linked to and

dependent upon surrounding terrestrial ecosystems (Vannote et al. 1980). Autotrophic

production in these streams is often low, but the streams typically receive large inputs

of coarse particulate organic matter in the form of leaves, woody debris, and other

organic material (Bilby and Likens 1980, Iverson et al. 1982). Coarse particulate

organic material is subject to physical and microbial processing (Hall and Meyer

1998) and macroinvertebrate processing (Cummins et al. 1989), which produce fine

particulate organic matter. This processed material can serve as food for macroinvertebrate communities, both within the headwater stream and in downstream habitats

(Cummins 1974). The flow of detritus and macroinvertebrates from these headwater

production zones may represent a valuable subsidy to downstream fish and associated food webs (Wipfli and Gregovich 2002).

Headwater streams produce a range of benthic invertebrates and much particulate

detritus (Stone and Wallace 1998; Wallace et al. 1986, 1997). The high gradient and

velocity typical of headwater streams facilitate the movement and drift of this material,

especially during freshets (Anderson and Lehmkuhl 1968). Invertebrates are often

common in drift (Allan 1995) with aquatic insect densities ranging from fewer than 

1 to 116 individuals per cubic meter of water (O’Hop and Wallace 1983, Waringer

1992; see Giller and Malmqvist 1998). Wipfli and Gregovich (2002) reported from 

pretreatment data that headwater streams draining alternatives-to-clearcutting (ATC)

installations were transporting both aquatic and terrestrial invertebrates that originated in upland habitats. These headwater streams were discovered to house a wide

range of invertebrate taxa, including mayflies, stoneflies, caddisflies, midges, crane

flies, beetles, and mites, as well as many less common taxa.

Southeastern Alaska’s steep topography and abundant precipitation produce numerous small headwater streams. Previous studies of the effects of timber harvesting 

on southeastern Alaska streams have largely focused on higher order, fish-bearing

streams, especially those containing salmonids, and have commonly shown that 

loss of large wood for fish habitat can be a negative consequence of logging (Bryant

1985). Although larger, fish-bearing streams are intensively studied, the structure 

and function of the region’s headwater streams are poorly understood (Wipfli and

Gregovich 2002).

The ATC demonstration project was established in the early 1990s with the goal of

understanding the ecological consequences of various timber harvesting practices 

in old-growth forests of southeastern Alaska (McClellan et al. 2000). Major study 

components included silviculture, avian ecology, hydrology, slope stability, and aquatic

ecology. The aquatic ecology component of the ATC project focused on the transport

of aquatic and terrestrial invertebrates and organic detritus in headwater streams

before and after timber harvesting. Specifically, we wanted to measure the change 

in (1) invertebrate and organic detritus drift densities and (2) invertebrate taxonomic

composition in response to ATC timber harvesting.

Southeastern Alaska has a maritime climate, moderate temperature, and much 

precipitation (which can exceed 500 cm/year) (Harris et al. 1974). The mountainous

landscape supports a temperate rain forest dominated by Sitka spruce (Picea

sitchensis (Bong.) Carr) and western hemlock (Tsuga heterophylla (Raf.) Sarg.),

mixed with occasional Alaska yellow-cedar (Chamaecyparis nootkatensis (D. Don)

Spach), western redcedar (Thuja plicata Donn ex D. Don), black cottonwood 

Introduction

Methods

Study Sites

1
2

(Populus trichocarpa Torr. & Gray), mountain hemlock (Tsuga mertensiana (Bong.)

Carr.), red alder (Alnus rubra Bong.), and willow (Salix L. spp.). The soils range from

shallow organic and mineral accumulations over bedrock and glacial till to well-developed spodosols (Harris et al. 1974). A mosaic landscape of forest, peat bogs, and

alpine vegetation is drained by numerous small, fishless headwater streams that drain

into larger streams containing coho (Oncorhynchus kisutch), pink (O. gorbuscha),

chum (O. keta), sockeye (O. nerka), and chinook (O. tshawytscha) salmon, cutthroat

(O. clarki) and steelhead trout (O. mykiss), Dolly Varden char (Salvelinus malma),

sculpin (Cottus spp.) and stickleback (Gasterosteus spp.).

Hanus Bay is one of three ATC installations in southeastern Alaska (fig. 1). We report

here on results from the Hanus Bay ATC installation only, because postharvest data

have not been collected at the second installation (Portage Bay), and harvesting has

not occurred at the third installation (Lancaster Cove) as yet.

Figure 1—Alternatives-to-clearcutting study sites in southeastern Alaska.
3

The Hanus Bay installation, located on Catherine and Baranof Islands, consists of

nine experimental harvest units of approximately 16 ha each that were selected to be

representative of productive upland old-growth forest (McClellan et al. 2000) (fig. 2).

The units are generally steep (30 to 45 percent slope) and have elevations ranging

from 61 to 526 m. Prior to timber harvest, all the units were forested primarily with

western hemlock (62 percent by basal area) and Sitka spruce (16 percent), along

with yellow-cedar (11 percent) and mountain hemlock (11 percent) (Hennon and

McClellan, in press).

Timber harvesting took place during 1997 across the nine units. Each unit received 

a different timber harvest prescription ranging from an uncut control to conventional

clearcutting (McClellan et al. 2000). Intermediate harvest regimes included various

spatial arrangements and proportions of unharvested trees (fig. 3). In these intermediate treatments the distribution of retained trees formed gaps, clumps, or was uniform throughout the unit. In units where retention was uniformly distributed, harvested

trees were individually selected (ITS, or individual tree selection), and 5, 25, or 75

percent of the original basal area was retained. Units receiving clump or gap treatments retained 25 or 75 percent of the original basal area, and harvested trees were

either part of a harvested patch or individually selected from the surrounding matrix.

Figure 2—Alternatives-to-clearcutting experimental units in Hanus Bay, Alaska.
4

Figure 3—Schematic representation of alternatives-to-clearcutting experimental treatments (from McClellan

et al. 2000).
Seventeen headwater streams were selected from within these nine units. Two

streams were selected within each unit, except for one unit having only one suitable

stream. Study streams were located within 6 km of each other and were spread

among three watersheds. These streams were high gradient and small (mean bankfull

width 2.5 m) (table 1). The length of stream between its origin and the sampling site

was generally less than 0.5 km. All streams contained some surface flow (mean, 4.7

L/s) during all sampling bouts, albeit negligible flow for some streams during dry 

periods (down to 0.04 L/s).

Permanent sampling stations were established for each stream. The station was

located on or close to the lowest elevation along the unit boundary in order to sample

the stream after it had flowed through as much of the unit as possible. In many cases,

the stream originated within the unit and eventually flowed into fish habitat.

At each sampling station, invertebrates (aquatic and terrestrial) and organic detritus

(≥250 μm) were sampled with a 250-μm-mesh net attached to one end of a 75-cm

long, 10-cm diameter plastic pipe that rested on the stream bottom. The pipe with

attached net was secured in the middle of each stream with sandbags. Facilitated by

5

Table 1—Physical characteristics and timber harvest prescriptions of study streams

at the Hanus Bay alternatives-to-clearcutting installation, southeastern Alaska

Mean (range) Mean

estimated bankfull Silvicultural Basal area 

Unit Stream discharge width treatment retention

Liters per second Meters Percent

1 1 2.0 (0.07-6.7) 0.90 Gap 25

2 1 3.8 (0.5-12.9) 1.64 Clump 25

2 5.1 (0.6-14.3) 1.84

3 1 3.5 (0.3-11.2) 1.98 ITS 75

2 7.4 (0.5-44.8) 2.83

4 1 3.4 (0.2-17.6) 2.46 Clump 75

2 2.0 (0.5-7.5) 1.33

5 1 9.4 (2.3-17.5) 4.73 Gap 75

2 9.1 (0.5-29.7) 2.98

6 1 4.3 (0.2-23.8) 6.03 Wildlife trees 5

2 14.6 (2.2-48.7) 5.20

7 1 1.2 (0.04-5.1) 1.47 ITS 25

2 1.7 (0.2-4.8) 2.62

8 1 3.8 (0.2-8.8) 1.60 Control 100

2 3.3 (0.2-8.1) 1.92

9 1 2.8 (0.2-9.2) 1.97 Clearcut 0

2 1.7 (0.07-5.5) 1.10

Mean of all streams 4.7 2.51

Note: ITS = individual tree selection.

Sampling Procedures
6

high stream gradient, the downstream end of each horizontal pipe rested above the

stream surface. Discharge through the pipe was determined by recording the time

required to fill a container of known volume. Discharge was measured at the beginning and end of each sampling period, and these values were used to estimate the

total volume of water that passed through the pipe over the sampling period. The total

volume sampled was used to calculate invertebrate and detritus drift densities. Many

of the streams were sufficiently small for the entire streamflow to pass through the

pipe. If not, the percentage of the total streamflow passing through the pipe was 

estimated, and this fraction was used to estimate the total discharge of the stream.

Streams were sampled seasonally (spring, summer, fall). One year (1996) of pretreatment sampling was conducted, followed by two years (1999, 2000) of posttreatment

sampling. In 1996, each seasonal sampling bout consisted of three samples for each

stream, collected over consecutive 24-hour periods. This was modified in posttreatment sampling to two 48-hour sampling periods for each season. Owing to time 

constraints, only the first of these two 48-hour samples was used for 2000 data. The

sampling period for each stream began and ended at approximately the same time 

of day in order to minimize the effect of diel variation in invertebrate drift. Stream 

temperature was recorded hourly with temperature loggers placed near the sampling

sites. These were placed in the stream during the first sampling of each year and

removed following the last sampling of the year.

Samples, once collected and returned to the laboratory, were preserved in 70 

percent ethanol. A plankton splitter was used to subsample unusually large samples.

Invertebrates were sorted from detritus, identified to the lowest reliable taxon, and

their body lengths measured to the nearest millimeter. Their dry mass was estimated

by using taxon-specific length:dry mass regression equations (Burgherr and Meyer

1997, Meyer 1989, Rogers et al. 1977, Sample et al. 1993, Smock 1980; M. Wipfli,

unpublished data). The remainder of the sample (detrital component) was ovendried,

weighed, ashed (at 500 ̊ C for 5 hours), and reweighed to determine ash-free dry

mass (AFDM).

Drift densities were calculated for each unit and seasonal sampling bout. Drift density

of individuals was calculated as the total of all invertebrates captured in the unit over

the seasonal sampling bout divided by the volume of water sampled (number of 

invertebrates/m3). Biomass (mg invertebrates/m3) and organic detritus (g AFDM/m3)

densities were calculated in the same fashion. Mean drift densities for each unit and

year were computed from the three corresponding seasonal drift density estimates.

These were used to compare pretreatment drift densities to each posttreatment year’s

drift densities.

The spatial and temporal variation in drift densities was measured with coefficients 

of variation (CV). Because the intent was to measure the amount of natural variation

(i.e., not owing to treatment effects), only pretreatment data were used. For these 

calculations, drift densities were calculated for individual samples rather than from

estimates at the unit level as described above.

Temporal variability was determined from pretreatment data by using both day-to-day

and seasonal CVs. Day-to-day CVs measured the daily variation in drift densities

seen within a single stream; seasonal CVs measured the seasonal variation within a

Sample Processing

and Data Analysis
7

single stream. The three consecutive 24-hour samples from each stream’s seasonal

sampling bout were used to calculate each day-to-day CV, which were then averaged

across all streams and sampling bouts. Seasonal CVs for each stream were calculated from the mean drift density of the three consecutive samples taken each season.

The seasonal CVs from each stream were then averaged across all streams. Spatial

variability was measured by using stream-to-stream CVs, which measured the 

variation in drift densities between all study streams on the same day. A CV was 

calculated for each sampling day by using the samples for all 17 streams, and then

averaging these across all sampling days.

There did not appear to be a relationship between harvest treatment prescriptions

and subsequent changes in mean drift density. Drift densities of both invertebrate

individuals and biomass were generally lower in posttreatment years than in the pretreatment year (including in the control treatment), but in a different pattern for each

of these two responses (fig. 4). Biomass density differences appeared to be more

consistent across treatments and years, whereas density differences for individuals

appeared to differ more from treatment to treatment and between years. The only

positive changes in drift densities following treatment were seen in the GAP75 and

ITS25 treatments in one year only.

As for invertebrate drift densities, mean posttreatment organic detritus drift densities

for most harvest units were lower than those seen in pretreatment (including in the

control treatment) (fig. 5). However, in 1999 the units with 25 percent retention had

densities much higher than before treatment; in 2000 only the ITS25 treatment had

mean organic drift densities higher than pretreatment means.

Invertebrate drift density showed a seasonal pattern: mean density was highest in

summer (2.85 invertebrates/m3, 0.90 mg/m3), lowest in spring (1.31 invertebrates/m3,

0.38 mg/m3), and intermediate in fall (1.63 invertebrates/m3, 0.38 mg/m3). The mean

drift density of individuals across all sampling was 1.95 invertebrates/m3, with a 

corresponding biomass density of 0.57 mg/m3. Organic detritus densities were also

seasonal, but the pattern was different than that of invertebrates. The highest mean

detritus densities were in fall, at 0.06 g AFDM/m3; the lowest were in summer (0.03

g/m3); and spring had intermediate densities at 0.05 g/m3. Overall, the mean organic

detritus density was 0.05 g/m3.

The transport rate of invertebrates from each stream averaged 830 individuals and

220 mg biomass per day. The largest transport rate occurred in spring, when an average of 1,500 individuals and 400 mg biomass per stream per day were transported

by that season’s typically larger discharges. In comparison, the low discharges of

summer transported a stream average of 520 individuals and 130 mg biomass per

day, which translated to substantially higher drift densities than in the higher flows of

spring. Mean transport rates per stream in fall were the lowest at 400 individuals and

110 mg biomass per day. Organic detritus transport followed a similar pattern of higher mean stream transport rates in spring (34 g AFDM per day) than in fall (17 g per

day) or summer (3 g per day). The overall mean stream transport rate of organic

detritus was 18 g per day.

Results

Drift Densities
8

1996 to 1999 1996 to 2000

Figure 4—Difference between pretreatment (1996) and posttreatment (1999, 2000) mean invertebrate individual (A,B) and biomass (C,D)

drift densities at the Hanus Bay alternatives-to-clearcutting installation, Alaska. Differences are expressed as a percentage of the pretreatment value; a negative value indicates a decrease in density.

A B

C D
9

1996 to 1999

1996 to 2000

Figure 5—Difference between pretreatment (1996) and posttreatment (1999, 2000) mean organic

detritus drift densities at the Hanus Bay alternatives-to-clearcutting installation, Alaska. Differences are expressed as a percentage of the pretreatment value; a negative value indicates a

decrease in density. Note differences in scales of vertical axes.
10

Pretreatment invertebrate drift densities were highly variable both spatially and temporally (fig. 6). Spatial CVs were the highest, followed by seasonal and then day-today CVs. This pattern was similar for drift densities of both individuals and biomass.

Mean spatial CVs for drift density of individuals were highest in fall (84 percent) and

lowest in spring (50 percent), whereas summer was intermediate at 60 percent. For

biomass drift density, spatial CVs were highest in summer (90 percent), and spring

and fall CVs were similar at 67 and 73 percent, respectively. The largest mean day-today CVs for drift densities of both individuals and biomass were seen in the fall (58

and 49 percent). The lowest day-to-day CVs occurred in spring (27 and 24 percent),

whereas summer day-to-day CVs were 32 and 45 percent.

Invertebrate Drift

Density Variability

Figure 6—Comparison of pretreatment day-to-day, seasonal, and spatial coefficients of variation (± standard error) for invertebrate individuals (top) and biomass (bottom) drift densities at

the Hanus Bay alternatives-to-clearcutting installation, Alaska.
Mayflies (Ephemeroptera, primarily Baetis) and dipterans (primarily Chironomidae)

were the most abundant taxa captured (table 2). Coleopterans (primarily Amphizoa,

hydrophilids, and dytiscids) were numerically only 2.6 percent of the total, but nearly a

quarter of the biomass owing to their larger size. Collembolans, mites, and ostracods

composed nearly a quarter of the total invertebrates captured, but together were only

3.3 percent of the biomass. A detailed list of taxa and their relative proportions is

given in the appendix.

There is an apparent relationship between treatment intensity (i.e., basal area retention) and the relative proportions of mayflies and dipterans, the two dominant taxa

(fig. 7). In the first year (1999) of posttreatment sampling, the proportion of mayflies

tended to decrease, and the proportion of dipterans increased. The magnitude of this

change seemed to be related to treatment intensity, with little or no change seen in

the control unit, and the largest change seen in the CLEAR5 (wildlife trees) treatment.

In the following year, these proportions tended to revert to closer to their pretreatment

condition. In the CLEAR5 treatment, an exceptionally large number of chironomid 

larvae captured in the summer of 1999 was primarily responsible for the increase in

the proportion of dipterans for that year.

11

Invertebrate

Community

Composition

Table 2—The most abundant orders of invertebrates collected in headwater

stream drift samples at the Hanus Bay alternatives-to-clearcutting installation,

southeastern Alaska 

Order Number Biomass

Percentage of total (rank)

Ephemeroptera 38.0 (1) 27.0 (1)

Diptera 25.3 (2) 19.3 (3)

Ostracoda 10.5 (3) .4

Acarina 7.6 (4) .3

Plecoptera 7.2 (5) 11.0 (5)

Coleoptera 2.6 24.1 (2)

Trichoptera 1.7 11.3 (4)
12

CONTROLIndividualsBiomass

1996 1999 2000

Figure 7aFigures 7a-7i—Proportions of invertebrate taxa captured in headwater streams at the Hanus Bay alternatives-toclearcutting installation, Alaska, for each year and treatment. Units are (A) number of individuals and (B) mg drymass. The “other” category is the aggregate of all taxa composing less than 5 percent of the total.
13

ITS75Individuals

Biomass

1996 1999 2000

Figure 7b
14

CLUMP75

IndividualsBiomass

1996 1999 2000

Figure 7c
15

GAP75

IndividualsBiomass

1996 1999 2000

Figure 7d
16

ITS25

Individuals

Biomass

1996 1999 2000

Figure 7e
17

CLUMP25Individuals

Biomass

1996 1999 2000

Figure 7f
18

GAP25

Individuals

Biomass

1996 1999 2000

Figure 7g
19

CLEAR5Individuals

Biomass

1996 1999 2000

Figure 7h
20

CLEAR0

Individuals

Biomass

1996 1999 2000

Figure 7i
21

Mean water temperatures across all treatments rose by about 1 °C after treatment

(table 3). More change was seen in more intensive treatments, such as clearcut and

wildlife trees; less change was seen in less intensive treatments, such as the control

and units with 75 percent retention. Intensive treatments also tended to be associated

with a larger change in maximum water temperature.

Although there were large differences in mean invertebrate drift density between 

pretreatment and posttreatment sampling, there was little indication that these differences were due to treatment effects. There was no obvious relationship between the

intensity and spatial arrangement of timber harvest and subsequent magnitude of

invertebrate drift density change. In fact, the largest differences were often seen in

the uncut control unit. Large pretreatment to posttreatment differences also were

seen in organic detritus drift densities, but these, too, had little apparent relationship

to the applied treatments. Although drift density measurements were an inconclusive

measure of the impacts of treatment, the taxonomic composition of the drift did seem

to show changes following treatment. Focusing on the two dominant taxa present, we

observed an apparent increase in the proportion of dipterans and a decrease in the

proportion of mayflies after treatment. This change seemed to be related to the intensity of harvest, although we could not confirm this statistically.

Drift densities in these streams were highly variable both spatially and temporally,

which, along with lack of replication, made detection of treatment effects problematic.

Any change in drift densities as a result of treatment would have to have been large

to be distinguished from natural year-to-year variation. Pretreatment data from two

other ATC installations, Portage Bay and Lancaster Cove, were used to assess the

natural year-to-year variation in drift densities (Wipfli and Gregovich 2002). Neither 

of these locations had data spanning 2 complete years, so seasonal comparisons

were made, i.e., comparing a unit’s summer drift densities of one year to that unit’s

summer drift densities of the next year. In this comparison, mean invertebrate drift

densities differed by an average of 95 percent between years. Some units had drift

Table 3—Temperature of headwater streams at the Hanus Bay alternatives-toclearcutting installation, southeastern Alaska before (1996) and after (1999,

2000) timber harvest 

Pretreatment mean Posttreatment mean Change in mean 

Treatment (range) (range) temperature

Degrees Celsius

Control 7.5 (2.5–12.1) 7.8 (2.0–12.4) 0.3

Clump75 7.9 (3.4–11.3) 8.1 (3.6–12.6) .2

Gap75 5.8 (3.7–8.1) 6.3 (4.4–11.2) .5

ITS75 8.2 (2.2–15.4) 8.3 (2.3–13.5) .1

Clump25 8.0 (1.8–12.9) 8.5 (1.8–13.6) .5

Gap25 7.3 (1.3–10.9) 7.6 (0.8–11.5) .3

ITS25 6.3 (2.3–10.2) 8.2 (1.8–16.9) 1.9

Wildlife trees 7.4 (2.5–12.9) 8.9 (3.0–15.2) 1.5

Clearcut 7.5 (3.1–10.6) 9.7 (3.9–15.3) 2.2

All treatments 7.4 (1.3–15.4) 8.4 (0.8–16.9) 1.0

Note: Data are from continuous hourly measurements taken from May through September.

Stream Temperature

Discussion
22

densities that changed 300 to 800 percent from year to year. This is in excess of 

the 60 percent average yearly difference seen in Hanus Bay. Year-to-year differences

between pretreatment and posttreatment drift densities at Hanus Bay, although large,

fit within the range of natural variation seen at other sites when using the same sampling methodology as in this study.

Seasonal variation within a stream was expected as a consequence of seasonal 

differences in temperature and sunlight, and of the various life histories of drifting

organisms. The amount of day-to-day variation seen within a stream, although less

than seasonal variation, was considerable. This degree of day-to-day variation

appears to be a prominent feature of drift and has been reported by others (Shearer

et al. 2002, Williams 1980). Variability across streams on the same sampling date 

was even larger than seasonal variation, suggesting that localized factors such as

gradient, substrate, or aspect may play a large role in productivity and the amount 

of invertebrate and organic matter transported.

We, like others, have found that considerable sampling effort is necessary to achieve

meaningful results (Allan and Russek 1985, Matthaei et al. 1998, Shearer et al.

2002). Drift sample processing is time consuming, so careful consideration of the

amount of natural variation and the analytical requirements of any drift sampling project is critical. Drift sampling was used here because of the potential of headwater

stream transport to affect downstream, fish-bearing communities. Other measures,

such as benthic invertebrate abundance, may be better indicators of changes owing

to timber harvest.

Drift density measures were used as a tool to compare the transport of material in

streams of different sizes. Drift density measures have typically been used in larger

rivers, where it is impossible or impractical to sample the entire drift (Allan and

Russek 1985, Brittain and Eikeland 1988). In this study, we were usually able to 

capture all or most of the stream’s surface flow, so obtaining a reasonably accurate

estimate of total transport was possible. However, estimates of total transport are of

little use when making comparisons between streams whose discharges can differ 

by an order of magnitude. The use of drift density measures facilitated these comparisons, but we suggest some caution when using this technique. Extremely high and

low discharges were associated with a concentration or dilution of the sample so that

the drift density seemed to be more related to the volume of water sampled than to

the abundance of the invertebrates it carried. Samples obtained during periods of

extremely low discharge, or in very small streams, tended to have misleadingly high

densities despite containing few invertebrates. For example, the samples with the

highest and second-highest drift densities of individuals (19.6 and 12.7 invertebrates/m3) collected during low flows (0.50 and 0.24 m3/day) at the Portage Bay ATC

installation had only 10 and 3 invertebrates, respectively. Both of these samples were

collected at the same stream on consecutive days. Conversely, samples taken in 

larger streams or in streams at high flows tended to have lower densities. The stream

with the highest observed densities in Portage Bay was also the source of the sample

with the lowest observed density (0.02 invertebrates/m3). This sample was collected

during a period of higher discharge, estimated at 144 m3/day, and contained three

invertebrates. Clearly, the use of drift density measures does not negate the effect 

of streamflow differences and must be used carefully by investigators.
23

The objective of this study was to measure the effects of various timber harvest treatments on the invertebrate and organic detritus transport from headwater streams.

These effects were measured by comparing drift densities and community composition before and after timber harvest. Large natural spatial and temporal variability 

prevented detection of possible treatment effects from timber harvesting in this study.

When developing experimental studies and monitoring plans for headwater streams

such as these in the future, considerations of low statistical power resulting from high

natural variability along with the large amount of time and money needed to achieve

suitable replicates and information from drift sampling should be carefully balanced.

Nonetheless, these streams have much potential to influence downstream habitats

through the energy (food) they deliver to these habitats year round. Understanding

these linkages more fully should aid ecosystem management in regions containing

upland forests, headwater streams, and critical fish habitat.

This report is a contribution from the USDA Forest Service study, Alternatives to

Clearcutting in the Old-Growth Forests of Southeast Alaska, a joint effort of the

Pacific Northwest Research Station, the Alaska Region, and the Tongass National

Forest. Special thanks are given to Dave Gregovich, Alison Cooney, Kim Frangos,

John Hudson, Maria Lang, Shuly Millstein, and the USDA Forest Service personnel 

at the Sitka Ranger District. Thanks to Tim Max and John Caouette for statistical

advice. We thank Adelaide Johnson, Jack Piccolo, John Hudson, and Brenda Wright

for helping improve earlier versions of this paper. Thanks also to Bob Wisseman for

taxonomic assistance and to Frances Biles for preparation of the study sites maps.

When you know: Multiply by: To find:

Millimeters (mm) 0.0394 Inches

Centimeters (cm) .394 Inches

Meters (m) 3.28 Feet

Kilometers (km) .6215 Miles

Cubic meters (m3) 35.3 Cubic feet

Micrometers (μm) .0000394 Inches

Hectares (ha) 2.47 Acres

Grams (g) .0352 Ounces

Milligrams (mg) .0000352 Ounces

Liters (L) 1.057 Quarts

Liters per second (L/s) .265 Gallons per second

Celsius degrees (°C) 1.8C+32 Fahrenheit degrees

Allan, J.D. 1995. Stream ecology: structure and function of running waters. London:

Chapman and Hall. 388 p.

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Fisheries and Aquatic Sciences. 42: 210-215.

Anderson, N.H.; Lehmkuhl, D.M. 1968. Catastrophic drift of insects in a woodland

stream. Ecology. 49(2): 198-206.

Bilby, R.E.; Likens, G.E. 1980. Importance of organic debris dams in the structure

and function of stream ecosystems. Ecology. 61(5): 1107-1113.

Conclusions

Acknowledgments

English

Equivalents

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26

Macroinvertebrate taxa collected from headwater streams at the Hanus Bay

alternatives-to-clearcutting installation, southeastern Alaska

Taxona Number Biomass

Percentage of total

Annelida

Oligochaeta 0.4 0.9

Arthropoda

Chelicerata

Arachnida

Acari 7.6 .3

Araneae .3 1.5

Pseudoscorpiones <.1 <.1

Crustacea

Isopoda <.1 <.1

Ostracoda 10.5 .4

Uniramia

Diplopoda <.1 .3

Chilopoda <.1 .2

Insecta

Collembola 5.8 2.6

Ephemeroptera .2 .3

Ameletidae

Ameletus .7 .5

Baetidae 31.9 14.1

Ephemerellidae <.1 <.1

Caudatella .1 .3

Drunella .3 2.2

Heptegeniidae .2 .3

Cinygma .1 .8

Cinygmula .9 1.4

Epeorus .7 2.0

Rhithrogena .1 .7

Leptophlebiidae

Paraleptophlebia 2.8 4.3

Plecoptera .3 .2

Capniidae .8 .2

Chloroperlidae .2 .2

Kathroperla <.1 <.1

Sweltsa 1.7 5.4

Leuctridae 1.2 2.2

Nemouridae .9 .7

Podmosta 1.1 .7

Zapada .8 1.0

Visoka .4 .4

Perlidae <.1 <.1

Perlodidae <.1 <.1

Hemiptera <.1 <.1

Aphididae <.1 <.1

Appendix 1
27

Taxona Number Biomass

Percentage of total

Homoptera <.1 <.1

Trichoptera .1 .2

Brachycentridae <.1 <.1

Micrasema .2 .2

Glossosomatidae <.1 .2

Hydropsychidae <.1 .5

Limnephilidae .1 .4

Chyranda .2 1.1

Cryptochia <.1 .2

Ecclisocosmoecus <.1 .3

Homophylax <.1 <.1

Imania <.1 <.1

Neophylax <.1 <.1

Psychoglypha <.1 <.1

Philopotamidae .2 .7

Polycentropodidae <.1 <.1

Rhyacophilidae .7 7.6

Lepidoptera <.1 .2

Coleoptera .4 1.1

Misc. terrestrial .2 3.7

Amphizoidae .2 12.8

Curculionidae <.1 .2

Dytiscidae 1.0 1.9

Elmidae <.1 <.1

Hydrophilidae .1 1.2

Ametor <.1 .5

Hydrovatus .6 1.4

Staphylinidae .2 1.3

Diptera 4.7 4.2

Ceratopogonidae <.1 <.1

Chaoboridae <.1 <.1

Chironomidae 19.0 9.7

Culicidae <.1 <.1

Dixidae .4 .2

Empididae <.1 .1

Ephydridae <.1 <.1

Mycetophilidae <.1 <.1

Psychodidae <.1 <.1

Sciaridae .3 .5

Simuliidae .2 .2

Tipulidae .1 1.4

Dicranota .3 .1

Pedicia <.1 .5

Tipula <.1 2.0

Hymenoptera .2 .2

Formicidae <.1 <.1

Orthoptera <.1 <.1
28

Taxona Number Biomass

Percentage of total

Psocoptera <.1 <.1

Thysanoptera .1 <.1

Mollusca

Gastropoda <.1 .4

Nematomorpha <.1 <.1

Platyhelminthes

Turbellaria <.1 .2

a Macroinvertebrates were identified to the lowest reliable taxon (i.e., individuals that could not be positively

identified to a certain taxonomic level were assigned to the next higher category), so percentage of relative

abundance by count or biomass of a higher taxon (i.e., family) does not include those from the taxon or

taxa below them (i.e., genus).
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