U. S. Department of the Interior

Bureau of Land Management

Alaska Open File Report 112

BLM/AK/ST-07/011+6700+020

June 2007

Offsetting versus Overlapping Ice Road Routes 

from Year to Year: Impacts to Tundra Vegetation

Dave Yokel, Darek Huebner, Randy Meyers, Debbie Nigro and Jay Ver Hoef

BLM

Alaska
The BLM Mission

The Bureau of Land Management sustains the health, diversity and productivity of the public lands for 

the use and enjoyment of present and future generations.

Cover Photo

Ice road path on low shrub tussock tundra vegetation near the Ublutuoch River in the National 

Petroleum Reserve - Alaska. Photo by Scott Guyer.

Authors

Dave Yokel and Debbie Nigro are wildlife biologists with the Bureau of Land Management, Fairbanks 

District Office, in Fairbanks, Alaska. Darek Huebner was formerly a natural resource specialist in the 

same office and is now an environmental engineer for Barrick Goldstrike Mines, Inc., in Elko, Nevada. 

Randy Meyers was a surface protection specialist at the Bureau of Land Management’s Kotzebue 

Field Station in Kotzebue, Alaska and is now retired. Jay Ver Hoef is a statistician with Ver Hoef 

Statistical Consulting Services in Fairbanks, Alaska.

Disclaimer

The mention of trade names or commercial products in this report does not constitute endorsement or 

recommendation for use by the Federal government.

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at www.blm.gov/ak/st/en/prog/jrmic.
BLM-Alaska Open File Report 112

June 2007

U. S. Department of the Interior

Bureau of Land Management

Offsetting versus Overlapping Ice Road 

Routes from Year to Year:

Impacts to Tundra Vegetation

Dave Yokel, Darek Huebner, Randy Meyers, Debbie Nigro and Jay Ver Hoef



Abstract

In the Record of Decision for the Northeast National Petroleum Reserve – Alaska Integrated Activity 

Plan (1998), the Bureau of Land Management stipulated that the location of ice roads be offset from 

year to year. The rationale for this requirement was based on the assumption that it is environmentally 

preferable to spread the impact over a greater area of tundra because in that way the tundra vegetation 

will recover more quickly, i.e., a less severe impact over a greater area is preferable to a more severe 

impact over a smaller area. This study was intended to test a part of that assumption: additive impacts 

occur to tundra vegetation with subsequent years of ice road construction.

We established transects across ice road paths with four plots per transect: control (outside the road 

boundaries) and three treatments (2001 road only, overlap area of 2001 and 2002 roads, and 2002 road 

only). In each of three summers (2002–2004), we measured depth of thaw, proportion of tussocks damaged, and percent ground cover by eight vegetation cover types to see if greater impacts occurred in the 

overlap-road plots than in the single-year road plots.

No statistically significant differences in depth of thaw were found among control and treatment plots 

or between single-year plots and overlap plots. The only significant result among the thaw data was a 

“year effect”: the thaw depths for all treatments became deeper with each successive year.

The data for proportion of tussocks damaged showed significant overall differences among the control 

and treatments, due mostly to the marked difference between the control by itself and the three road 

treatments combined. More importantly, the overlap treatment displayed a marginally greater level of 

damage than the two single-year treatments. However, a significant year effect due to a decrease in damaged tussocks from one year to the next suggested the resilience of tussocks to some types of damage.

The percent of ground cover by eight vegetation cover types showed no significant difference between 

the overlap-road plots and the single-year road plots when data from three years were combined, but did 

display a significant additive effect in the overlap-road plots for one year (2003) when the three years 

were analyzed separately.

Data from this three-year study provided only minimal evidence of additive impacts from building ice 

roads over the same path in two subsequent years. Given the observed recovery of the tundra during the 

three years of study, it is doubtful that any significant environmental benefit would be gained by requir-

ing that all ice roads be completely offset from paths of previous years. A more appropriate mitigation 

would be to require that ice road routes follow the wetter habitats to the greatest extent possible without 

significantly increasing their length.

iii

Table of Contents

Abstract.................................................................................................................................................... i

Introduction..............................................................................................................................................1

Study Area and Methods..........................................................................................................................1

Results......................................................................................................................................................3

Depth of Thaw.......................................................................................................................................3

Damage to Tussocks..............................................................................................................................4

Ground Cover........................................................................................................................................4

Discussion..............................................................................................................................................10

Depth of Thaw.....................................................................................................................................10

Damage to Tussocks............................................................................................................................12

Ground Cover......................................................................................................................................13

Conclusions and Management Implications..........................................................................................16

Literature Cited ......................................................................................................................................19

Appendix A—List of Species and Growth Forms.................................................................................21

Figures

Figure 1. Examples of scuffed and crushed Eriophorum vaginatum tussocks .....................................2

Figure 2. Examples of healthy, undamaged Eriophorum vaginatum tussocks, displaying 

a substantial component of standing dead sedge blades........................................................2

Figure 3. Mean depth of thaw for pooled data from 2002–2004 ..........................................................3

Figure 4. Effect of year on thaw depth within each of four treatments.................................................3

Figure 5. Mean depth of thaw in each of three years............................................................................4

Figure 6. Proportion of tussocks that were damaged, by treatment type, for pooled data 

from 2002–2004.....................................................................................................................4

Figure 7. Effect of year on proportion of tussocks damaged within each treatment.............................5

Figure 8. Proportion of tussocks damaged in each of three years.........................................................5

Figure 9. Cover category loadings on the first principal component for pooled data 

from 2002–2004.....................................................................................................................6

Figure 10. Means of the first principal component for the control and three treatments for 

pooled data from 2002–2004.................................................................................................6

Figure 11. Cover category loadings on the first principal component for data from 2002 .....................6

Figure 12. Means of the first principal component for the control and three treatments for 

data from 2002.......................................................................................................................6

Figure 13. Cover category loadings on the first principal component for data from 2003 .....................7

Figure 14. Means of the first principal component for the control and three treatments for 

data from 2003.......................................................................................................................7

Figure 15. Cover category loadings on the first principal component for data from 2004.. ...................7

Figure 16. Means of the first principal component for the control and three treatments for 

data from 2004.......................................................................................................................7

Figure 17. Cover type loadings on the first principal component for data by species in 2004...............9

Figure 18. Means of the first principal component for the control and three treatments for 

data by species in 2004........................................................................................................10

Figure 19. Cover category loadings on the second principal component for pooled data 

from 2002–2004...................................................................................................................10

Figure 20. Means of the second principal component for the control and three treatments for 

pooled data from 2002–2004...............................................................................................10

Figure 21. Cover category loadings on the second principal component for data from 2003 ..............10

Figure 22. Aerial photo of one of the tussock tundra study sites (TT-18), taken August 8, 2002 ........ 11

Figure 23. Aerial photo of TT-18 taken August 2, 2004 .......................................................................12

Figure 24. Aerial photo of TT-18 taken July 28, 2005..........................................................................15

Introduction

Studies of impacts to vegetation from seismic 

exploration in the Arctic National Wildlife Refuge 

(ANWR) in 1984 and 1985 suggested that greater damage occurred to tundra where camp-train and seismic

vehicle trails overlapped than where either occurred

alone (Jorgenson et al., 1996). Greater damage also 

occurred where multiple vehicles moved along a 

single, narrow trail rather than along dispersed trails 

(Jorgenson, 2000). Beginning in at least the mid1980s, the Bureau of Land Management (BLM) stipulated for seismic operations in the National Petroleum 

Reserve – Alaska (NPR-A) that “care shall be taken to 

ensure that when multiple trips over the same trails are 

taken, that vehicles will not utilize exactly the same 

tracks... ” (Meares, Don; pers. comm.). In the Record of

Decision for the Northeast NPR-A Integrated Activity Plan /Environmental Impact Statement (1998),

the BLM revised that stipulation somewhat to require

that vehicles avoid using the same trails for multiple

trips. Transferring that same logic from seismic exploration to ice road construction, it was also stipulated that 

the location of ice roads be offset from year to year.

The rationale for this logic is not presented in these 

BLM documents, but is presumably based on the following assumption; it is environmentally preferable to 

spread the impact over a greater area of tundra because 

in that way the tundra vegetation will recover more 

quickly, i.e., a less severe impact over a greater area is 

preferable to a more severe impact over a smaller area. 

This has been verified for seismic camp trains in the 

Arctic National Wildlife Refuge, where the bulldozers 

pulling heavy trailers on skids can result in ruts in the 

tundra (Jorgenson, 2000). Resultant depression of the 

tundra mat may cause wetter soils and a conversion to 

more hydrophilic vegetation that persists for at least 

14 years and possibly much longer.

From the 1940s until the late 1960s, overland travel 

in the NPR-A and other parts of northern Alaska was 

often accomplished simply by bulldozing trails across 

the tundra in both winter and summer (Lawson et al., 

1978; Lawson, 1982). Ice roads were recognized to 

cause less damage to tundra, and they have been used 

on Alaska’s North Slope and the adjacent Yukon and 

Northwest Territories since the early 1970s (Adam 

and Hernandez, 1977; Fisher, 1978; Lawson, 1979, 

1986; Walker et al., 1987), although gravel pads and 

roads were still commonly used for oil exploration 

activities during this period. In the 1990s, exploratory 

drilling activities moved almost exclusively to the use 

of ice roads and pads (Hazen, 1997), yet relatively few 

studies have addressed their impacts (Jorgenson, 1999; 

Guyer and Keating, 2005; Pullman et al., 2005).

Of those studies that have looked at impacts from 

ice roads, none has tested the above assumption inherent to the rationale for requiring ice roads to be offset 

from one year to the next. This study was intended to 

test part of that assumption; additive impacts occur to 

tundra vegetation with subsequent years of ice road 

construction. It was not envisioned that three years of 

study would be long enough to determine if any additive impact would result in a longer recovery period.

Study Area and Methods

Following the 1998 Record of Decision, the first 

exploratory drilling in the NE NPR-A occurred in 2000 

in an area west of the village of Nuiqsut, Alaska, and 

east of Judy Creek. Additional drilling occurred in each 

of the following two years, and all of it was supported 

by ice roads. This study began in the summer of 2002, 

using paths of ice roads constructed and used in the 

periods of January through April, 2001 and 2002. Study 

sites ranged from 8 to 30 km west of Nuiqsut.

The study design required areas of partial overlap between the roads of the two years. In this way, a transect 

placed across the roads could provide a control (outside 

the road boundaries) and three treatments: 2001 road 

only, overlap area of 2001 and 2002 roads, and 2002 

road only. Since the lessees were required to offset 

the roads from year to year, there were very limited 

opportunities to establish transects with a segment of 

overlap. Opportunities arose when the roads were too 

close together, and thus overlapping, or when the 2002 

road crossed at an oblique angle from one side of the 

2001 road to the other.

Our previous summertime observations of seismic 

trails and ice road paths, along with those of others 

(Felix and Raynolds, 1989), indicated that the wetter the vegetation type, the less the impacts during 

winter travel. This is due to the protection provided 

by the solidly frozen ground, or even ice above the 

soil substrate. Flooded and wet tundra types typically 

display little to no impact from winter travel, preclud-

ing the possibility of additive impacts from multiple 

seasons of use. For this reason, we confined this study 

to moist tundra types. Between the two restrictions of 

road layout and moist vegetation types, very limited 

possibilities existed for establishing transects for study 

sites. We found only five suitable sites, four of which 

were tussock (Eriophorum vaginatum) tundra with 

relatively few shrubs and one of drier E. vaginatum

tussocks dominated by dwarf shrubs.
We established transects at 90° to the ice road paths 

and marked control/treatment boundaries with wooden 

stakes. Because those boundaries were more easily observed from the air, we double-checked our initial stake 

placement from a helicopter, noted corrections, and 

then reset the stakes accordingly after landing again. 

Subsequent photographs taken from the air confirmed 

the correct placement of the stakes. Nonetheless, we 

collected no data within 0.5 m of any control or treatment boundary to reduce the possibility of assigning 

data incorrectly to control/treatment type.

We collected three types of data on the control and 

each of three treatments at each of the five study sites: 

depth of thawed soil, proportion of tussocks damaged 

and percent ground cover by eight vegetation/cover 

types. Data collection occurred within the periods 

of August 8–9, 2002; July 28–August 2, 2003; and 

July 30 –August 6, 2004. We measured thaw depth 

and tussock damage within 1 m of, and on the same 

side of, the transect line in each of the three years. We 

collected vegetation cover data within 2 m on either 

side of the transect line.

We measured thaw depth to the nearest cm by press-

ing a pointed steel probe into the ground until encountering hard, frozen soil. To maintain consistency within 

the highly variable microtopography of tussock tundra, 

we only took measurements between tussocks and not 

on them. We took 10 measurements within the control 

and each of three ice road treatments during each of 

the three years.

We categorized tussocks in one of two classes: undamaged or damaged, with the latter including both 

scuffed and crushed tussocks (Figure 1). All tussocks 

within a rectangle made of the transect line, a parallel 

line 1 m away and lines 0.5 m from either end of the 

treatment zone were included in the sample. Tussocks 

bisected by the rectangle boundaries were included 

if on the left or trailing edges, and excluded if on the 

right or leading edges.

We categorized ground cover into eight classes: bare 

ground, litter, live moss or lichen, dead moss or lichen, 

live graminoid (sedges and grasses), dead (but stand-

ing) graminoid, live shrub/forb or dead shrub/forb. 

Healthy, undamaged tussocks (Figure 2), as well as 

other undamaged sedges and grasses, included a substantial component of standing dead biomass from 

previous years. Litter consisted of dead biomass that 

had become detached from a plant of any of the classes, 

whether naturally or by the physical action of ice road 

construction and use. We used the same eight cover 

classes in each of the three years, but our method of 

estimation from the first year differed in the following 

two years. In 2002 we made ocular estimates from a 

0.25 m2 quadrat randomly placed within the treatment. 

Pre-sampling (off-site) suggested that the variation 

within a treatment could be adequately sampled 

using this small a frame, but after completion of our 

first field season we decided to come prepared in the 

following year to use a more precise and accurate 

technique (and a more time-consuming one, hence 

the greater number of days involved). In the follow-

ing two years, we sampled the ground cover using a 

pin frame. Within each treatment, we sampled a 2 x 4 

m grid of 200 points with 20 cm even spacing using a 

starting point randomly located along the length of the 

transect line and within 20 cm of the line. We dropped 

sharpened pins through the frame and recorded the first 

cover class struck by the pin. Thus the data represent 

the “canopy” cover for each treatment.

We went one step further in 2004 and recorded each 

Figure 2. Examples of healthy, undamaged Eriophorum 

vaginatum tussocks, displaying a substantial component of 

standing dead sedge blades.

Figure 1. Examples of scuffed and crushed Eriophorum 

vaginatum tussocks.
pin “hit” to genus, or when possible species, in addition 

to one of the eight cover classes. We were rarely able 

to identify mosses to genus, and most often classified 

them by growth form (cushion or feather). Similarly, 

we identified crustose lichens by growth form only, 

but identified foliose and fruticose lichens to genus or 

species. A complete list of growth forms and species 

appears in Appendix A.

We analyzed depth of thaw data using analysis of 

variance (ANOVA) tested against the F (three- or 

four-way comparisons) or Student’s t (two-way comparisons) distributions. We used a logistic regression 

model to analyze the proportion of tussocks categorized 

as damaged in 2002. The most parsimonious model 

was selected by using likelihood ratio tests against the 

chi-square (χ2) distribution. Pooling 2002 data with 

those from 2003 and 2004 in later years, and adding 

a “year effect,” altered the covariance structure and 

required the use of a different test. Thereafter we analyzed damage to tussocks with a simultaneous Wald 

test, which is compared against the F or Student’s t 

distributions. We analyzed the cover data, with eight 

cover types as variables, using principal components 

analysis of covariance matrices. Plot scores (also 

known as factor scores) were computed for each plot 

for each principal component, and these plot scores 

were analyzed using ANOVA tested against the F or 

Student’s t distributions. We loosely used an alpha 

level of 0.05 as a threshold for statistical significance. 

By “loosely,” we mean that results were not ignored 

if alpha was slightly greater than 0.05, but that they 

provided us less confidence.

Figure 4. Effect of year on thaw depth within each of four treatments.

-32.15

-29.49

-30.48

-29.57

-32.50

-32.00

-31.50

-31.00

-30.50

-30.00

-29.50

-29.00

-28.50

-28.00 Control 2001 Overlap 2002

Treatment Type

Depth (cm)

Figure 3. Mean depth of thaw for pooled data from 

2002–2004. Note the Y-axis does not begin at zero, giving 

an impression of greater difference among treatments than 

really exists.

Control 2001 Overlap 2002

-40.00

-35.00

-30.00

-25.00

-20.00

-15.00

-10.00

-5.00

0.00

Treatment Type

Depth (cm)

8/8-9/2002

7/28/2003

7/30-31/2004

Results

Depth of Thaw

No statistically significant differences in depth of 

thaw were found among control and treatment plots 

for pooled data from 2002–2004 (F = 0.84, p = 0.50; 

Figure 3). It follows, then, that the test of most interest 

to the study’s purpose, whether or not the two-year 

road overlap treatment had significantly deeper thaw 

than the 2001 and 2002 single-road treatments, was 

also not significant (t = 0.21, p = 0.84). In fact, the 

sample data suggest less thaw in the overlap than in 

the 2001 treatment. The only significant result among 

the pooled data was the year effect (F = 101.76, 

p < 0.0001; Figure 4), i.e., the thaw depths for all 
-26.52

-27.72

-29.00

-27.90

-29.50

-29.00

-28.50

-28.00

-27.50

-27.00

-26.50

-26.00

-25.50

-25.00 Control 2001 Overlap 2002

Treatment Type

Depth (cm)

Figure 5. Mean depth of thaw in each of three years.

-28.02

-29.08

-28.00

-31.52 -32.00

-31.00

-30.00

-29.00

-28.00

-27.00

-26.00 Control 2001 Overlap 2002

Treatment Type

Depth (cm)

separately by year. Nonetheless, the same trends were 

evident among years (Figure 5).

Damage to Tussocks

The pooled data from 2002–2004 for proportion of 

tussocks damaged showed significant overall differences among the control and treatments (F = 68.2, 

p < 0.0001; Figure 6). Most of this is due to the marked 

difference between the control by itself and the three 

road treatments combined (<3% damaged vs. >50% 

damaged; t = 13.7, p < 0.0001). In contrast to the 

data for depth of thaw, the 2001 road treatment (51% 

damaged) displayed less impact than the 2002 road 

treatment (63% damaged; t = 3.93, p = 0.0003). Most 

important to the purpose of the study is the comparison 

between the two single-year treatments combined and 

the overlap treatment, which was marginally significant 

(t = 1.88, p = 0.07). These combined data for the three 

years also showed a significant year effect (F = 44.4, 

p < 0.0001; Figure 7) due to a significant decrease in 

damaged tussocks from one year to the next (2002 vs. 

2003: t = 6.06, p<0.0001; 2003 vs. 2004: t = 3.22, 

p = 0.002).

Despite the year effect, the same general trends 

were evident when the data for each sampling year 

were analyzed separately (Figure 8). The difference 

between the 2001 and 2002 single-road treatments 

was significant in two of three years (2002: χ2 = 8.96, 

p = 0.003; 2003: t = 0.87, p = 0.40; 2004: t = 2.36, 

p = 0.04), with the 2001 treatment displaying less damage. The 2001 treatment also displayed significantly 

less damage than the overlap treatment in the same two 

out of three years (2002: χ2 = 7.11, p = 0.008; 2003:

t = 1.30, p = 0.22; 2004: t = 2.20, p = 0.05). In two of 

three data collection years, the trends for the difference 

between the overlap treatment and the two single-road 

treatments combined fit the expected pattern for an 

additive impact in the overlap treatment, but none of 

the three years showed a significant difference (2002: 

χ2 = 2.08, p = 0.15; 2003: t = 1.01, p = 0.33; 2004: 

t = 1.36, p = 0.20).

Ground Cover

The first principal component (PC1pooled) for the 

pooled cover data (2002–2004) explained 46% of the 

variance in the data. The live graminoid class loaded 

strongly positive on PC1pooled, and dominated the 

characteristics of that component (Figure 9). Dead 

(standing) graminoids, litter and live shrubs/forbs were 

weakly positive and dead moss/lichen loaded weakly 

negative. There was significant difference among the 

mean plot scores for the control and three treatments 

0.635 0.630

0.511

0.026

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

Control 2001 Overlap 2002

Treatment Type

Proportion

Figure 6. Proportion of tussocks that were damaged, by 

treatment type, for pooled data from 2002–2004.

-35.92

-32.76

-33.96

-34.64

-36.50

-36.00

-35.50

-35.00

-34.50

-34.00

-33.50

-33.00

-32.50

-32.00

-31.50

-31.00 Cont rol 2001 Overlap 2002

Treatment Type

Depth (cm)

2002

2003

2004

treatments combined differed significantly among the 

three years in which data were collected. These differences were also significant between pairs of data 

collection years (2002 vs. 2003: t = 2.79, p = 0.008; 

2003 vs. 2004: t = 10.65, p < 0.0001), and displayed an 

increase in depth of thaw (~5–7 cm) over two years.

No significant differences among control and 

treatments were found when the data were analyzed 
for PC1pooled, but only marginally so 

(Figure 10; F = 2.73, p = 0.05). The control was significantly more positive than 

the three treatments combined (t = 2.39, 

p = 0.02), but no other comparisons 

were statistically significant, including 

the one of most interest, the two singleroad treatments versus the overlap treatment (t = 0.38, p = 0.71).

Most notable among these pooled 

data was a highly significant year 

effect (F = 140.03, p < 0.0001). It was 

expected that, because the coverage 

estimation technique changed between 

2002 and 2003, the data collected in 

2002 (PC1pooled mean = –17.56) might be dissimilar 

from the following two years (2003 PC1pooled mean = 

–15.72; 2004 PC1pooled mean = 33.27). However, there 

was no difference between 2002 and 2003 (t = 0.53, 

p = 0.60) and the major change causing the year 

effect occurred between 2003 and 2004; the PC1pooled

mean plot score in 2004 was significantly different 

from the previous two years (2002 vs. 2004: t = 14.75, 

p<0.0001; 2003 vs. 2004: t = 14.22, p<0.0001).

Because of the strong year effect, it is worthwhile 

to look at the analyses for data collected in each year 

separately. The first principal component (PC102) for 

the 2002 cover data explained 44% of the variance 

in the data. The live graminoid, live shrub/forb and 

live moss/lichen classes all loaded strongly negative 

on PC102, whereas the dead moss/lichen and litter 

classes both loaded strongly positive (Figure 11). Dead 

graminoids were weakly negative and bare ground 

and dead shrubs/forbs were weakly positive. There 

was significant difference among the mean plot scores 

for the control and three treatments for PC102 (Figure 

12; F = 8.36, p = 0.003), and the control was significantly more negative than the three treatments combined 

(t = 4.35, p = 0.0009). The comparison of the two singleroad treatments versus the overlap treatment showed 

the expected trend, but was not significant (t = 1.41, 

p = 0.18). There was, however, a marginally significant 

difference between the 2001 single-road treatment and 

the other two (2001 vs. overlap: t = 2.24, p = 0.04; 

2001 vs. 2002: t = 2.04, p = 0.06). There was no difference between the mean plot scores of the overlap and 

2002 single-road treatments (t = 0.20, p = 0.84).

The first principal component (PC103) for the 2003 

cover data explained 49% of the variance in the 

data. The live shrub/forb and dead graminoid classes 

loaded strongly negative on PC103, whereas the litter, 

dead shrub/forb and dead moss/lichen classes loaded 

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

Control 2001 Overlap 2002

Treatment Type

Proportion

2002

2003

2004

Figure 7. Effect of year on proportion of tussocks damaged within each 

treatment.

0.487

0.579

0.031

0.633

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

Control 2001 Overlap 2002

Treatment Type

Proportion

0.799

0.014

0.772

0.644

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

Control 2001 Overlap 2002

Treatment Type

Proportion

0.495 0.478

0.355

0.046

0.00

0.10

0.20

0.30

0.40

0.50

0.60

Control 2001 Overlap 2002

Treatment Type

Proportion

Figure 8. Proportion of tussocks damaged in each of 

three years.

2002

2003

2004
Figure 11. Cover category loadings on the first principal component for data from 2002.

0.658

0.318

0.127

0.078

-0.414

-0.434

-0.047

-0.285

-0.600 -0.400 -0.200 0.000 0.200 0.400 0.600 0.800

Moss/Lichen Dead

 Litter

 Bare Ground

 Shrub/Forb Dead

 Graminoid Dead

 Moss/Lichen Live

 Shrub/Forb Live

 Graminoid Live

Cover Class

Loading Factor

Figure 12. Means of the first principal component for the control 

and three treatments for data from 2002.

11.98

10.56

-3.79

-18.75

-10.00-15.00-20.00-25.00

-5.00

5.000.00

15.0010.00

Control 2001 Overlap 2002

Treatment Type

PC1 Means

5.82

1.53

-4.55

-2.80

-2.00-4.00-6.00

8.006.004.002.000.00

Control 2001 Overlap 2002

Treatment Type

PC1 Means

Figure 10. Means of the first principal component for the control 

and three treatments for pooled data from 2002–2004. Figure 9. Cover category loadings on the first principal component for pooled data from 2002–

2004.

0.289

0.215

0.126

0.047

0.004

0.915

-0.121-0.010

-0.200 0.000 0.200 0.400 0.600 0.800 1.000

Graminoid Live

Graminoid Dead

Litter

Shrub/Forb Live

Shrub/Forb Dead

Moss/Lichen Live

Bare Ground

Moss/Lichen Dead

Cover Class

Loading Factor
11.56

3.81

2.94

-18.31

-10.00-15.00-20.00

-5.00

5.000.00

15.0010.00

Control 2001 Overlap 2002

Treatment Type

PC1 Means

Figure 14. Means of the first principal component for the control 

and three treatments for data from 2003.

-30.61

17.36 15.99

-2.73

-10.00-20.00-30.00-40.00

0.00

20.0010.00

Control 2001 Overlap 2002

Treatment Type

PC1 Means

Figure 16. Means of the first principal component for the control 

and three treatments for data from 2004.

Figure 15. Cover category loadings on the first principal component for data from 2004.

0.667

0.207

0.064

0.040

-0.617

-0.267

0.112

-0.206

-0.800 -0.600 -0.400 -0.200 0.000 0.200 0.400 0.600 0.800

Litter

Shrub/Forb Dead

Moss/Lichen Dead

Moss/Lichen Live

Bare Ground

Graminoid Dead

Shrub/Forb Live

Graminoid Live

Cover Class

Loading Factor

-0.800 -0.600 -0.400 -0.200 0.000 0.200 0.400 0.600 0.800

Loading Factor

Cover Class

Figure 13. Cover category loadings on the first principal component for data from 2003.

0.274

0.232

0.043

0.019

-0.423

-0.167

-0.565

0.586

-0.800 -0.600 -0.400 -0.200 0.000 0.200 0.400 0.600 0.800

Litter

Shrub/Forb Dead

Moss/Lichen Dead

Moss/Lichen Live

Bare Ground

Graminoid Live

Shrub/Forb Live

Graminoid Dead

Cover Class

Loading Factor
strongly positive (Figure 13). Live graminoids were 

weakly negative and live moss/lichen and bare ground 

were positive but so weakly as to be insignificant to 

PC103. There was significant difference among the 

mean plot scores for the control and three treatments 

for PC103 (Figure 14; F = 29.91, p < 0.0001), and 

the control was significantly more negative than the 

three treatments combined (t = 9.03, p < 0.0001). The 

comparison of the two single-road treatments versus 

the overlap treatment not only showed the expected 

trend, but this time it was statistically significant 

(t = 2.86, p = 0.01). Both of the single-road treatments 

were significantly different from the overlap treatment 

(2001 vs. overlap: t = 2.61, p = 0.02; 2002 vs. overlap: 

t = 2.34, p = 0.04). There was no difference between 

the means of the two single-road treatments (t = 0.26, 

p = 0.80).

The first principal component (PC104) for the 2004 

cover data explained 57% of the variance in the data, 

which was the highest level among the three years of 

data. The live graminoid class loaded strongly negative on PC104, whereas the litter class again loaded 

strongly positive (Figure 15). Dead graminoid and live 

shrub/forb were moderately negative, dead shrub/forb 

was moderately positive, and dead moss/lichen, live 

moss/lichen, and bare ground were progressively more 

weakly positive on PC104. There was significant difference among the mean plot scores for the control 

and three treatments for PC104 (Figure 16; F = 10.31, 

p = 0.001), and the control was significantly more 

negative than the three treatments combined (t = 5.07, 

p = 0.0003). The comparison of the two single-road 

treatments versus the overlap treatment was not significant (t = 1.02, p = 0.33). The 2001 single-road treatment 

was marginally different from the overlap treatment 

(t = 1.90, p = 0.08) and the 2002 single-road treatment 

(t= 2.04, p = 0.06). There was no difference between 

the means of the 2002 single-road and overlap treatments (t = 0.14, p = 0.89).

Recording the ground cover pin “hits” to species 

rather than one of the eight cover classes resulted in 

86 variables instead of eight. Two of the 86, litter and 

bare ground, were identical to the litter and bare ground 

classes of the prior method involving eight total classes. 

Many of the other 84 classes, however, occurred rarely 

among the 4,000 data points from four treatments 

across five study transects. With their consequently 

low covariances, the loadings of many of these (64 of 

86) on the first principal component (PC1sp) for data 

by species ranged between -0.01 and 0.01 (Figure 17). 

Litter loaded strongly positive while E. vaginatum (tussock sedge) live and dead (#42 and #46, respectively, 

in Figure 21) loaded strongly negative. E. vaginatum

was by far the most frequently occurring species among 

the sedges and grasses. Cushion mosses were the most 

common moss type, and loadings for both live (#3) and 

dead (#7) cushion mosses were, relative to other moss 

classes, significantly positive. Live shrubs tended to 

load negatively, and dead shrubs tended to load positively. However, both live and dead forbs tended to 

load positively. Not surprisingly, the means for the 

control and three treatments for PC1sp (Figure 18) displayed nearly the same pattern as did those for PC104. 

There was significant difference among the control 

and three treatments (F = 10.04, p = 0.001), and the 

control was significantly more negative than the three 

treatments combined (t = 5.00, p = 0.0003). Although 

the trend for PC1sp better fit the hypothesis of an 

additive effect in the overlap treatment than did 

PC104, the comparison of the two single-road treatments versus the overlap treatment was still not significant (t = 1.59, p = 0.14). The 2001 single-road treatment 

was more negative than the overlap treatment (t = 2.19, 

p = 0.05), but not significantly more so than the 2002 

single-road treatment (t = 1.62, p = 0.13). There was no 

difference between the means of the 2002 single-road 

and overlap treatments (t = 0.57, p = 0.58).

The second principal component (PC2pooled) for 

the pooled cover data (2002–2004) explained 26% 

of the variance in the data. The litter class loaded 

strongly positive on PC2pooled, dead shrub/forb and 

dead moss/lichen were weakly positive, and bare 

ground and live moss lichen were positive but relatively insignificant (Figure 19). Live shrub/forb was 

moderately negative and the live and dead graminoid 

classes were even less strongly negative. There was 

significant difference among the means for the control and three treatments for PC2pooled (Figure 20; 

F = 21.57, p < 0.0001), and the control was significantly more negative than the three treatments combined 

(t = 7.68, p < 0.0001). The expected relationship 

among the two single-road treatments and the overlap 

was apparent, but not statistically significant (t = 1.82, 

p = 0.09). The 2001 single-road treatment was significantly different from the overlap treatment (t = 2.34, 

p = 0.04), but neither of the other two paired comparisons of treatments were.

There was also a significant year effect for PC2pooled

(F = 7.62, p = 0.002). As for PC1pooled, this was 

due to a difference between the data from 2004 and 

those of the other two years (2002 vs. 2004: t = 3.78, 

p = 0.0005; 2003 vs. 2004: t = 2.74, p = 0.009). There 

was no difference between 2002 and 2003 (t = 1.03, 

p = 0.31).
Loadings on Principal Component 1

2004 Data Recorded by Species

-0.800 -0.600 -0.400 -0.200 0.000 0.200 0.400 0.600 0.800

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

51

53

55

57

59

61

63

65

67

69

71

73

75

77

79

81

83

85

Plant Species

Loading Factor

Dead Shrub

Live Shrub

Dead Forb

Live Forb

Dead Grass

Live Grass

Dead Sedge

Live Sedge 

Dead Lichen 

Live Lichen

Dead Moss

Live Moss

Litter 

Bare Ground

Figure 17. Cover type loadings on the first principal component for data by species in 

2004. See Appendix A for key to plant species identifying numbers.
Despite the year effect, it is of little value to look 

at PC2 for data collected in each year separately. 

PC2 accounted for 24% to 33% of the variance in the 

three individual, yearly data sets. This is a significant 

proportion of the overall variance, but unfortunately it 

is difficult to interpret what characteristics of ground 

cover are represented by PC2 for any of these analyses 

(see “Discussion” section). For example, the live shrub/

forb class loads significantly negative on PC203 for the 

2003 data, but live and dead (still standing) graminoid 

classes both load positively (Figure 21). Having these 

different indicators of healthy tundra vegetation on 

opposite ends of the spectrum is not readily explainable, i.e., the variance explained by PC203 is not likely 

an effect of the treatments. For this reason, no further 

analyses of PC2 data are presented.

Discussion

Depth of Thaw

Studies conducted in the ANWR following seismic 

exploration in 1984 and 1985 showed that the depth 

of thaw was significantly greater in seismic trails 

than in control plots in the initial summer following 

disturbance, and that thaw depths increased between 

the initial summer and 1988 (Felix et al., 1992). 

Differences between controls and trails were up to 

12 cm, and usually in the range of 7–12 cm. Depth of 

thaw was positively correlated with disturbance level. 

Although thaw depth was significantly greater in trails 

than in controls for all study sites combined, about 25% 

of the study sites had no significant difference, and six 

highly disturbed sites showed depth of thaw shallower 

than their controls in 1991 (Emers et al., 1995). In 

the latter sites, dead sedge leaves may have increased 

insulation of the ground. Sample sizes were larger for 

these ANWR studies than for this study.

In the path of an ice road built in the NPR-A in 

1978, thaw depths were greater than on nearby control 

plots during the first summer following construction 

(Lawson, 1979) and ranged from imperceptible to 

4–6 cm on some slopes while being 4–20 cm in poorly 

drained areas. Pullman et al. (2005) found significantly 

greater thaw depths (2–5 cm) in ice road plots versus 

controls in the first summer following road construction, 

but no significant differences in the second summer. 

Observations of ice roads in Canada (Everett, K.R., unpublished data, in Walker et al., 1987) suggest that thaw 

depths return to pre-impact depths within a few years.

There are several possible hypotheses for why depth 

of thaw may differ between ice road plots and controls. 

During spring thaw, the ice road may remain on the 

-30.16

19.10

13.53

-2.47

-40.00

-30.00

-20.00

-10.00

0.00

10.00

20.00

30.00

Control 2001 Overlap 2002

Treatment Type

PC1 Means

0.867

0.222

0.149

0.058

0.021

-0.383

-0.088

-0.141

-0.600 -0.400 -0.200 0.000 0.200 0.400 0.600 0.800 1.000

Litter

Shrub/Forb Dead

Moss/Lichen Dead

Bare Ground

Moss/Lichen Live

Graminoid Live

Graminoid Dead

Shrub/Forb Live

Cover Class

Loading Factor

8.90

12.89

1.36

-23.15 -25.00

-20.00

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

Control 2001 Overlap 2002

Treatment Type

PC2 Means

0.671

0.258

0.090

-0.647

-0.021

-0.022

-0.139

-0.190

-0.800 -0.600 -0.400 -0.200 0.000 0.200 0.400 0.600 0.800

Graminoid Dead

Graminoid Live

Moss/Lichen Dead

Bare Ground

Litter

Shrub/Forb Dead

Moss/Lichen Live

Shrub/Forb Live

Cover Class

Loading Factor

Figure 18. Means of the first principal component for the 

control and three treatments for data by species in 2004.

Figure 19. Cover category loadings on the second principal 

component for pooled data from 2002–2004.

Figure 20. Means of the second principal component 

for the control and three treatments for pooled data from 

2002–2004.

Figure 21. Cover category loadings on the second principal 

component for data from 2003.

10
tundra for a week or more after the surrounding snow 

has melted. This would result in greater depth of thaw 

in control plots, but the opposite was found in both 

of the above ice road studies. Perhaps any effect of 

delayed melt is present for only a brief time in early 

summer.

Alternatively, compressed or dead vegetation in the 

path of a previous winter’s ice road may provide less 

insulation from summer air temperatures or less shad-

ing from the sun than undisturbed vegetation, leading 

to greater depth of thaw on disturbed plots. Color 

changes in the tundra surface caused by vegetation 

death, delayed vegetation green-up, or exposure of 

soil could change solar input to the ground. Depend-

ing on whether color changes to a darker or lighter 

cast compared to surrounding tundra, this may lead 

to a greater or lesser depth of thaw. Our observations 

(Figure 22) were that vegetation in the path of a previous winter’s ice road has a light brown cast compared 

to the surrounding tundra in the first summer following 

ice road construction, but a dark gray cast in following 

summers.

Regardless, our study failed to demonstrate any 

additive impacts from two years of ice road construction in the overlap treatment, or any other significant 

relationship among control and treatments. Since the 

same trend among treatments is apparent in each of the 

three years, it is possible that a larger sample size could 

result in statistically significant differences. However, 

the range of difference among control and treatments in 

any one year is only 2.5–3.5 cm. Pullman et al. (2005) 

argued that since inter-annual variation in thaw depths 

(8–13 cm) was greater than within-year/between-treatment differences (2–5 cm), the latter were probably not 

ecologically relevant.

Also, even if our observed differences are real, the 

trend among the three ice road construction treatments 

(depth in 2001 > overlap > 2002) does not reflect an additive effect of two years of road in the overlap. If real, 

it may reflect some difference in construction methods 

or technique between the two years, with greater impacts resulting from the 2001 road (but see “Damage 

to Tussocks” results and discussion). We do not know, 

however, if there were any differences in construction 

technique. Alternatively, if depth of thaw increases with 

time in disturbed areas (Felix et al., 1992), the 2001 

treatment has had an extra year of thawing. However, 

that would not explain the shallower depth of thaw in 

Figure 22. Aerial photo of one of the tussock tundra study sites (TT-18), taken August 8, 2002. Arrows point to wooden 

stakes marking the treatment boundaries. (A-B: 2001; B-C: overlap; C-D: 2002; D-E: control)

11
the overlap treatment. Perhaps the lighter color of the 

ice road path in the first summer following construction (Figure 22), before the dead vegetation weathers 

and darkens, increases the albedo and temporarily 

counteracts any effect of the disturbance. This might 

explain the trend observed in 2002, but fails to explain 

the continuation of that trend in following years when 

there is no apparent difference in color among treatments (Figure 23).

There was a significant overall increase in depth of 

thaw (5–7 cm) during the study period (2002–2004; 

Figure 4). This is twice the difference observed, though 

not statistically significant, for comparisons among 

treatments within years (Figure 5). This cannot be 

explained by the time of data collection during each 

summer. Data were collected more than one week later 

in 2002 than in the other two years, allowing more 

time for the ground to thaw before measurement, yet 

2002 displayed the shallowest thaw of the three years. 

This could be explained by increased depth with time 

(Felix et al., 1992; but see Walker et al., 1987, above) 

or a change in weather over the three years, i.e., an 

increasingly greater accumulation of heating degree 

days. The latter is consistent with the overall pattern of 

warming observed in the Alaska Arctic over the last few 

decades. Perhaps both factors are at work here, since 

increased depth of thaw also occurred in the control, 

but less so than in any of the treatments.

Damage to Tussocks

The large difference between the control and the 

three ice road treatments in terms of damaged tussocks 

was not only expected, but known from observations 

of previous ice roads by us and others. Lawson (1979) 

referred to tussocks as being compressed, torn, or 

ripped, and Walker et al. (1987) referred to tussocks 

from the same study as being abraded or crushed. Similar damage was observed in two studies implemented 

simultaneously to this one (Guyer and Keating, 2005; 

Pullman et al., 2005). Indeed, that is why areas with 

tussocks, as opposed to wet or flooded tundra, were 

important to this study. Tussocks are predisposed to 

damage because they represent microrelief on the 

tundra susceptible to flattening (Walker and Webber, 

1980). Noel and Pollard (1996) similarly recognized 

strangmoor ridges as another form of higher microtopography that can be affected by ice construction 

through scraping and compression.

As for the data on depth of thaw in this study, our 

measure of tussock damage failed to demonstrate an 

Figure 23. Aerial photo of TT-18 taken August 2, 2004. Arrows as in Figure 22.

12
additive impact in the area with two years of road construction versus those areas with only one year. This 

comparison was marginally significant when the data 

for all three years were pooled, but this is largely due 

to the much lower level of damage in the 2001 treatment versus the overlap or the 2002 treatments. The 

same contrast was apparent for the tests of each year 

analyzed separately, but none of these even approached 

the level of significance.

The analysis of tussocks had another aspect in common with the analysis of depth of thaw data in that there 

was a significant change from year to year. The most 

likely explanation in this case, however, has little if 

anything to do with differences in weather. The reduced 

level of damage to tussocks measured from one year to 

the next is best explained by recovery of the tussocks. 

The same trend was apparent in each of the treatments 

but not in the control, which implies it was a phenomenon occurring in the impacted areas only, and not 

widely across the tundra. Although crushed tussocks 

remained crushed over this short a period, scuffed 

tussocks often moved out of the “damaged” category 

due to new growth. Walker et al. (1987) noted that tussocks damaged by an ice road built and used in 1978 

were recovering when they returned three years later 

in 1981. However, there remained areas of numerous 

dead tussocks comprised mostly of those that had been 

severely crushed or broken. These observations were 

similar to ours. In 2002, Guyer and Keating (2005) 

looked at the same 1978 ice road route and reported 

the ice road trace “was difficult to locate because of 

its faint to non-existent signature on the ground after 

24 years of vegetation recovery.”

The observed, but not statistically significant, trend 

for greater damage in the overlap treatment as compared to the two single-year road treatments may also 

be due to recovery over time more so than to additive 

impacts in the overlap treatment. In 2002, the measured 

damage was actually slightly greater in the 2002 than 

the overlap treatment, and both were significantly 

greater than the 2001 treatment. In this case, only the 

2001 treatment had had more than a partial growing 

season to recover between impact and measurement. 

In 2004, the 2001 treatment again showed significantly 

less damage than the other two. By this time it had 

benefited from recovery during 3+ growing seasons as 

opposed to only 2+ growing seasons for the other two. 

In none of the three years were the differences between 

the overlap and 2002 treatments significant. Thus recovery time is a more efficient explanation of any differences, perceived or real, among the three treatments 

than is additive impact in the overlap treatment.

The results of the depth of thaw measurements suggested that the 2001 road construction had a greater 

impact on the tundra than did the 2002 construction. 

This was not corroborated by the tussock damage data, 

which displayed the opposite trend. Even if recovery 

time has a strong effect on observed tussock damage, 

it seems unlikely that it could not only mask but reverse any greater impact of construction in the winter 

of 2001. The best explanation for the greater depth of 

thaw in the 2001 treatment may remain sampling error, 

i.e., random chance, although increasing depth of thaw 

with time cannot be ruled out as a potential factor.

Ground Cover

Since the dead graminoid class primarily represents 

standing dead biomass of undisturbed sedges and 

grasses (Figure 2), it makes intuitive sense that it would 

load on PC1pooled in association with the live graminoid, live shrub/forb, and perhaps the live moss/lichen 

classes, and that this group would contrast with an 

alternative group consisting of the dead moss/lichen, 

bare ground, and dead shrub/forb classes (Figure 9). 

However, it does not make sense that the litter class 

would load in association with the “less disturbed” 

classes. Litter certainly occurs in undisturbed tundra, 

but it is more obvious in disturbed areas, where the 

canopy of graminoids and shrub/forbs has been reduced 

and the litter can more readily be seen from above 

(Pullman, 2005). The same is true for the bare ground 

and dead moss/lichen classes, and to a lesser extent, 

even the live moss/lichen class.

Principal components analysis of the cover data from 

all three years pooled does not support the hypothesis 

that additive impacts occur from building an ice road 

over the top of the path from the previous year’s road. 

It is reassuring to see that the control is influenced 

more heavily by the “less disturbed” classes than are 

any of the three treatments (Figure 10) for PC1pooled, 

but nonetheless, additive impacts are not demonstrated 

by an appropriate trend among treatments. Such a trend 

would have the overlap treatment as most divergent 

from the control, with the two single-road treatments 

at some intermediate level. Not too much can be made 

of the apparent differences among treatments, however, since none of those comparisons are statistically 

significant.

Because the very strong year effect for PC1pooled may 

be masking some differences among treatments within 

a year, we also examined the data on a year-by-year 

basis. The eight cover classes load onto PC102 (Figure 

11) in the associations intuitively expected (above), to 

include litter among the “more disturbed” grouping. 

13
Furthermore, the apparent trend among the control and 

three treatments (Figure 12) also matches the relationship expected given the hypothesis of additive impacts 

in the overlap treatment, but this trend is not significant. 

Again, the analysis fails to reject a hypothesis of no 

additive impact in the overlap treatment. It is possible 

that in fact there is no such effect, or that our sample 

size of five study sites has insufficient power to detect 

that effect from among the other variance, or “noise,” 

in the data.

There is one indication that comes out of the 2002 

cover data with a higher degree of certainty. The singleroad treatment from 2001 displays less indication of 

disturbance than does either the 2002 treatment or 

the overlap. This could be due to either a difference 

in construction techniques between the two years, 

or an extra growing season for recovery by the 2001 

treatment, or some combination of both. A difference 

in construction techniques is somewhat questionable, 

given the contradiction seen between the depth of thaw 

data and the tussock damage data, but the depth of thaw 

difference was not significant and the tussock damage 

data agree with the relationship seen here in the cover 

data. Both explanations still have some merit.

In the cover data from 2003, when the data were 

collected using a more rigorous technique (i.e., the 

pin frame rather than ocular estimation), the eight 

cover classes again load in the expected associations 

(Figure 13). The live moss/lichen loads very weakly 

with the “more disturbed” classes, but as explained 

above, that likely results from the removal of some of 

the canopy layer. The means of the PC103 data display 

a picture-perfect trend in support of the hypothesis for 

additive impacts in the overlap treatment, and this time 

the overlap shows significantly more disturbance than 

the two single-road treatments. The mean for the 2001 

treatment shows slightly less disturbance than does the 

2002 treatment, as was the case for the data collected 

in the previous year, but the difference does not approach any level of significance. It may be that no real 

difference exists among the two, or that another year 

of recovery for the younger (2002) treatment allowed 

it to “catch up” with the 2001 treatment (but see 2004 

discussion below).

The same general associations seen for 2002 and 

2003 appear again in how the cover data load on PC104 

(Figure 15). But as for the 2002 data, the means of 

PC104 for the control and three treatments do not support the hypothesis for additive impacts in the overlap 

treatment because the overlap and 2002 single-road 

treatments show similar levels of disturbance. Both 

show significantly more disturbance than the 2001 

single-road treatment, raising again the question as to 

whether the extra season post-disturbance has allowed 

the 2001 treatment substantial time for additional 

recovery.

Recording ground cover to genus or species does not 

provide any significant benefit in testing the hypothesis for additive impacts in the overlap treatment. The

expected trend among control and treatments is apparent, but not statistically significant. However, 

this extra effort not only pays off in terms of distinctions

within the eight cover classes, as seen in the dominance 

of E. vaginatum and cushion mosses, but especially 

in separating shrubs from forbs. After doing so, the 

live forbs load positively, reflecting an association 

with disturbed areas, and the means of PC1sp better fit 

the hypothesis of additive effects than do the means 

of PC104. This fits our observations of forbs coloniz-

ing areas where shrubs had been killed, and to a lesser 

extent, areas of damaged tussocks. Ebersole (1985) also 

described forbs as colonizers following disturbance.

Earlier studies of ice road impacts are not only few 

in number but also provide little quantitative detail of 

changes in ground cover. Walker et al. (1987) did note 

that an especially apparent impact was the alteration 

or destruction of the inter-tussock plant community. 

This is also apparent when comparing Figures 1 and 2. 

In contrast to the earlier studies, Pullman et al. (2005) 

provided quantitative data on nine cover classes that are 

subsets of ours: bare ground, litter, moss, lichen, sedge, 

grass, evergreen shrub, deciduous shrub, and forbs. 

Rather than comparing road overlap areas to singleyear road paths, they compared two single-year paths 

constructed at different times during the same winter. 

In the summer immediately following construction, 

they found inconsistent differences between the two 

treatments. However, when comparing the two treatments to their controls, they observed within tussock 

tundra treatment plots significant increases in cover of 

bare ground and litter; significant decreases of moss, 

sedge, evergreen shrub and forbs; and a marginally 

significant decrease in deciduous shrub. Guyer and 

Keating (2005) described damage to grasses, shrubs, 

forbs and bryophytes, and especially to tussock sedges. 

The results of these two studies are generally comparable to ours.

To summarize the discussion of PC1, its mean plot 

scores in each of the three years of data collection 

indicate it has served as a good indicator of the relative level of disturbance among the control and three 

treatments. In each of the three years, the mean plot 

scores for PC1 reflect a far greater level of disturbance 

in the three treatments than in the control. PC1 also 

14
displays in all three years less disturbance in the 2001 

treatment than in the overlap or 2002 treatments, suggesting some recovery from disturbance, although 

those differences are not consistently significant. But 

in only one of those three years (2003) does the pattern 

among treatments support the hypothesis for additive 

impacts in the overlap treatment.

PC2pooled appears to tell the same general story as 

PC1. Its cover class loadings again show the now 

familiar associations reflecting a relative scale of disturbance (Figure 19), and the control again scores on 

the “undisturbed” side of the scale, whereas the three 

treatments fall on the “disturbed” side (Figure 20). 

The expected trend appears in support of additive impacts in the overlap treatment, but without convincing 

statistics, and once again the 2001 treatment displays 

less disturbance than do the other two. There is also a 

significant year effect as for PC1, but this time things 

quickly fall apart when trying to interpret the PC2 

loadings for any of the individual years of data collection. The relatively neat associations of cover classes 

into “disturbed” versus “undisturbed” groupings are not 

apparent (e.g., Figure 21). In the absence of any obvious interpretation of PC2, the most efficient explanation is that it reflects noise in the data.

Is there any additive impact associated with a second 

year of ice road construction? In the summer immediately following construction of the second ice road, the 

overlap area could be visibly distinguished from the 

two single-road areas (Figure 22). So there is an effect 

of overlap, but recovery of some of the vegetation occurs rapidly, making the ice road paths difficult to see 

in photography after two (Figure 23) or three (Figure 

24) years. Crushed tussocks are still crushed, though 

they may have some new growth, but scuffed tussocks may have significant new growth. As observed 

on seismic trails (Felix and Raynolds, 1989), dwarf 

shrubs are affected greatly by ice road construction 

and may show little recovery in two years, but forbs 

may colonize that space (see above), returning the 

tundra to a perception of health. Any additive effects 

of building one ice road over the top of the previous 

road’s path may be obscured in just a few years by 

recovery of the tundra.

Recovery in the short term has been demonstrated 

by other studies. Although their work occurred in the 

Figure 24. Aerial photo of TT-18 taken July 28, 2005. Arrows as in Figure 22. This photo was taken under better light 

conditions than the one in Figure 23. It also differs from both of the prior photos in that more “cotton-grass” flowers 

(Eriophorum spp.) were evident across the landscape.

15
boreal forest region of the Northwest Territories rather 

than on arctic tundra, Adam and Hernandez (1977) 

reported that live-plant cover increased from 11% to 

16% in the summer immediately following disturbance to 31% to 44% in the following summer. Evidently 

the road construction technique used at that place and 

time, which included using a bulldozer to clear the land 

of trees before constructing the road, caused greater 

overall impacts than modern construction techniques on 

treeless arctic tundra. A better comparison to our study, 

conducted at roughly the same time and only 50 km 

to the east (Pullman et al. 2005), noted a 48% to 63% 

reduction in total live-plant cover in the ice road path 

compared to reference plots during the summer 

immediately after construction. In the following 

summer, total live-plant cover in ice road plots was 

only 23% to 43% less than in reference plots. By the 

time of our final data collection (2004), when the photograph in Figure 23 was taken, our study plots had 

had 1–2 additional years to recover than did those in 

the two studies above.

Conclusions and 

Management Implications

There are at least three important questions this study 

was not designed to answer either completely or at all. 

The first is whether it is better following two or more 

years of ice road construction to have less area with 

more severe impacts or more area with less severe 

impacts. Had we found strong evidence of additive 

impacts in the overlap treatment, we would have confirmed the validity of the question but still would not 

have known the answer. Instead, we found minimal 

evidence of “more severe” impacts, almost making the 

question moot. In addition, since there are no consistent 

differences between the overlap treatment and the 2002 

single-road treatment, each of which received its last 

or only disturbance, respectively, in 2002, the results 

suggest they are recovering at similar rates. 

All of this seems to make the case that ice roads may 

overlap from one year to the next with no significant 

additional impact to tundra vegetation other than 

retarding recovery by another year. It is important 

to remember, though, that these results do not prove 

there are no effects of overlap; all we can say for sure 

is that we failed to find any such effects. It would be 

prudent to keep this question in mind, observe these 

and additional ice road paths over the ensuing years as 

exploration and development expand in the NPR-A, 

and note any anecdotal evidence that suggests a reason to return to this question. It may also be of value 

to return to these plots again in a few years and see if 

depth of thaw has continued to increase, or whether 

the treatments have become similar to the control, as 

suggested by Walker et al. (1987).

The second unanswered question, and the ultimate 

one in terms of environmental consequences, is whether it makes any difference to the ecology of an area to 

have less tundra experiencing more severe impacts or 

more tundra with less severe impacts. Since this study 

was not designed to address this question at all, the 

response here is only speculation, but the answer is 

likely to be scale-dependent. If there are any additive 

effects of overlapping ice roads, despite our inability to 

measure them, there may be a consequence to populations of organisms whose range approximates the width 

of the ice road. These may include some invertebrates, 

but might be limited to non-animal organisms such 

as fungi or bacteria. Given the small proportion of 

the local or regional area that is affected by ice road 

construction, and the apparent rate of recovery to a 

level that can provide some cover and support some 

herbivory, it seems unlikely that overlapping versus 

offsetting ice roads would have any consequence to 

vertebrate wildlife. So at the scale at which the BLM 

seeks to manage the NPR-A, there is likely no difference to ecological communities.

The third question relates to impacts of overlapping 

ice road paths for three or more years. There is potential 

for this to occur if the requirement for offsetting paths 

from year to year is removed. The same ice road route 

could be used for many consecutive years during exploration and subsequent field development. Not only 

would this delay recovery, but perhaps it could make 

recovery occur at a slower rate once ice road use ends. 

Our anecdotal observations of the Alpine field ice road 

(east of the NPR-A), which was used in several consecutive years, do not suggest this is a concern, but no 

rigorous test of this possibility has been conducted.

Data from this three-year study provide, at best, 

minimal evidence of additive impacts from building 

ice roads over the same path in two subsequent years. 

Increased depth of ground thaw may be a result of 

ice road construction, but these data show no additive effects at all. Yet this is the measure that may be 

most important to tundra vegetation in the long term. 

Deeper thaw can lead to changes in soil moisture that 

may translate into a change in plant species composition. The proportion of tussocks that were damaged 

do provide weak evidence of an additive effect, but 

only when the data for all three years are pooled. An 

additive effect is displayed by the ground cover data, 

but only in one of three years. It is conceivable that 

16
increasing the sample size of this study (beyond five 

transects) could lead to more convincing statistics 

in one direction or the other, but that would not be 

possible without an effort to purposely build overlapping roads. It is not likely that increasing the number 

of years of data collection in the short term would 

provide more conclusive evidence of an additive 

effect in overlap areas because of the ongoing recovery of the vegetation during the years of data collection. 

However, if depth of thaw increases in the long term, 

it may be measurable and cause a significant change in 

ground cover. If so, it would likely show an effect of ice 

road construction in general, but not an additive effect 

of overlapping ice roads. Most importantly, given the 

fairly rapid recovery of the tundra, it is doubtful that 

any significant environmental benefit will be gained by 

requiring that all ice roads be completely offset from 

paths of previous years. A more appropriate mitigation 

would be to require that ice road routes follow the 

wetter habitats to the greatest extent possible without 

significantly increasing their length.

17

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.

20
Species Name or Growth Form I.D. No. Live I.D. No. Dead

Bare Ground n/a 1

Litter n/a 2

Mosses

 Cushion mosses (>50% Aulacomnium turgidum? Next most common: Ceratodon 

purpureus?)

 cushion moss 3 7

 Polytrichum spp. 5 9

 Feather mosses 4 8

 Sphagnum spp. 6 10

Lichens

 lichen (dead; not discernible) 21 35

 Crustose lichens 14 28

 Foliose lichens

 Peltigera apthosa 22 36

 Peltigera scabrosa 23 37

 Fruticose lichens

 Alectoria ochroleuca 11 25

 Cetraria cucullata 12 26

 Cetraria islandica 13 27

 Cladina rangiferina 16 30

 Cladina spp. 15 29

 Cladonia spp. 17 31

 Cladonia squamulosa 18 32

 Dactylina arctica 19 33

 Evernia perfragilis 20 34

 Thamnolia spp. 24 38

Monocots

 Sedges (Cyperaceae)

 Carex aquatilis 39 43

 Carex bigelowii 40 44

 Eriophorum angustifolium 41 45

 Eriophorum vaginatum 42 46

 Grasses (Poaceae)

 Arctagrostis latifolia 47 51

Appendix A. 

List of species and growth forms included among the ground cover data from 2004, 

and the identification number for each as seen in Figure 17.

21
Species Name or Growth Form I.D. No. Live I.D. No. Dead

Dicots

 Forbs

 Pedicularis capitata 56 62

 Polygonum bistorta 55 61

 Pyrola grandiflora 57 63

 Saussurea angustifolia 58 64

 Senecio atropurpureus 59 65

 Stellaria laeta 60 66

Shrubs

 Arctostaphylos rubra 67 77

 Betula nana 68 78

 Cassiope tetragona 69 79

 Dryas integrifolia 70 80

 Empetrum nigrum 71 81

 Ledum palustre ssp. decumbens 72 82

 Rubus chamaemorus 73 83

 Salix planifolia ssp. pulchra 74 84

 Salix rotundifolia 75 85

 Vaccinium vitis-idaea 76 86

22