U. S. Department of the Interior

Bureau of Land Management

BLM Alaska Open File Report 114

BLM/AK/GI-10/002+6516+F031

November 2009

Dall Sheep Use of Areas of Critical Environmental 

Concern in the Utility Corridor Management Area, 

Alaska

Tim Craig and Paul Leonard

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

A Dall sheep ewe and two lambs near the Dalton Highway at the head of the Atigun River valley. This and other 

report photographs by BLM/Tim Craig.

Author

Tim Craig is a wildlife biologist at the BLM Fairbanks District Office in Fairbanks, Alaska. Paul Leonard 

served as a Fairbanks District Office intern through the Conservation and Land Management Internship 

Program of the Chicago Botanic Garden.

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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A bibliography of scientific reports is online at www.blm.gov/ak. 
Dall Sheep Use of 

Areas of Critical Environmental Concern 

in the Utility Corridor Management Area, Alaska

Tim Craig and Paul Leonard

BLM-Alaska Open File Report 114

November 2009

U. S. Department of the Interior

Bureau of Land Management

i

We thank Marty Webb for his expert service as a pilot and as an 

observer. Cindy Hamfler and Jon Syder flew several habitat survey 

flights. Erica Craig provided advice on habitat analyses. Richard 

Kemnitz provided helicopter time for our survey, and Kyle Joly, Craig 

McCaa, Cindy Hamfler, and Jim Herriges offered editorial comments 

on the manuscript. 

Acknowledgments

From summer 2000 through summer 2006, we sporadically searched 

for Dall sheep (Ovis dalli) and/or evidence of their habitat use in 5 

Areas of Critical Environmental Concern (ACECs) on Bureau of Land 

Management-administered lands in the eastern Brooks Range of northern Alaska. The purpose of our work was to determine (1) when sheep 

use the ACECs, (2) how many sheep use the ACECs, and (3) which 

areas within the ACECs were of special importance to sheep. 

We found that sheep used all 5 ACECs year-round. We determined 

that lambing takes place in, or very near, all of the ACECs, and that 

ewes selected habitat near escape terrain and foraging areas to lamb. 

In each ACEC, sheep occupied locations with shallow snow, such as 

windswept ridges or south-facing, steep slopes during the winter. We 

were not able to accurately estimate the sheep population in the ACECs 

during this season because of the difficulty in detecting white sheep in 

the snow. However, the number of tracks we found suggested that far 

fewer sheep occupy the ACECs in the winter than in the summer. 

The highest number of sheep we observed during the summer on 

any one survey was in the Snowden Mountain ACEC (N = 173), and 

the lowest numbers were in the Galbraith Lake and West Fork Atigun 

ACECs (N = 6 and 8, respectively). Generally, we found sheep at high 

elevations during the summer and in selected habitat where vegetation was low and sparse, such as the earth cover classes Low Shrub, 

Low Shrub – Lichen, Dwarf Shrub, Dwarf Shrub – Lichen, and Rock/

Gravel. The relative density of tracks during the winter indicated that 

the Snowden Mountain and Poss Mountain ACECs hosted the greatest 

number of sheep during these months, while the West Fork Atigun and 

Nugget Creek ACECs held the least. 

Sheep were observed 1212 times in the ACECs during our surveys, 

but we made many more observations of sheep immediately outside 

ACEC boundaries. In addition, we located previously unreported potential sheep licks in the Snowden Mountain and the West Fork Atigun 

ACECs.

Our results indicate that the sheep population within the ACECs 

may fluctuate annually without known causation, a phenomenon that 

is reflected in surveys of the greater sheep population elsewhere in the 

Brooks Range. The population structure in the ACECs is within the 

ranges of both historic and contemporary values determined for sheep 

elsewhere in the Brooks Range. The data collected during our work can 

be used for future population comparisons and as a baseline for sheep 

habitat use within the ACECs.

Abstract

Contents

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

Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Summer Habitat Use Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Winter Habitat Use Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Population Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Earth Cover Use Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Poss Mountain ACEC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Summer Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Winter Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Populations Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

Earth Cover Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Nugget Creek ACEC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Summer Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Winter Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Population Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Earth Cover Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Snowden Mountain ACEC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Summer Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Winter Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Population Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Earth Cover Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

West Fork Atigun ACEC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Summer Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Winter Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Population Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Earth Cover Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Galbraith Lake ACEC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Summer Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Winter Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Population Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Earth Cover Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

General Observations and Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Appendix A. Alaska Earthcover Classification Class Descriptions . . . . . . . . . . . . . . . . . . . . . . 27

Tables

Table 1. Habitat surveys of Dall sheep and sheep licks observed during summer . . . . . . . . 6

Table 2. Winter surveys of Dall sheep and sheep tracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Table 3. Summer population surveys of Dall sheep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Table 4. Chi-square analysis of earth cover use by Dall sheep . . . . . . . . . . . . . . . . . . . . . . . 11

Table 5. Summer Dall sheep surveys in the upper Chandalar drainage . . . . . . . . . . . . . . . 16

Table 6. Areas used by Dall sheep rams in 4 ACECs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

iii
iv

Figures

Figure 1. Location of the 5 ACECs in the Utility Corridor Management Area . . . . . . . . . . . . 3

Figure 2. Dall sheep tracks in winter in the Poss Mountain ACEC . . . . . . . . . . . . . . . . . . . . 4

Figure 3. Dall sheep observations in the Poss Mountain ACEC . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 4. Dall sheep at a mineral lick in Victor Gulch, Poss Mountain ACEC . . . . . . . . . . . . 9

Figure 5. Dall sheep observations in the Nugget Creek ACEC . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 6. Dall sheep band in escape terrain in the Nugget Creek ACEC . . . . . . . . . . . . . . . 12

Figure 7. Dall sheep observations in the Snowden Mountain ACEC . . . . . . . . . . . . . . . . . . 14

Figure 8. Rugged terrain on the western side of the Snowden Mountain ACEC . . . . . . . . . 15

Figure 9. Previously unreported Dall sheep lick in the Snowden Mountain ACEC . . . . . . . 15

Figure 10. Dall sheep observations in the West Fork Atigun ACEC . . . . . . . . . . . . . . . . . . . . 17

Figure 11. Previously unreported Dall sheep lick in the West Fork Atigun ACEC . . . . . . . . 18

Figure 12. Dall sheep lick in the West Fork Atigun ACEC . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 13. Dall sheep observations in the Galbraith Lake ACEC . . . . . . . . . . . . . . . . . . . . . . 20

Figure 14. Terrain in southwestern Galbraith Lake ACEC . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 15. Dall sheep habitat at Black Mountain, Galbraith Lake ACEC . . . . . . . . . . . . . . . 22
BLM Open File Report 114 • November 2009 1

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

Introduction

The Bureau of Land Management (BLM) 

is responsible for management of public lands 

around the Dalton Highway and adjacent 

Trans-Alaska Pipeline System between mileposts 56 and 300 on the Dalton Highway. 

This area is managed under the guidance of 

the BLM’s Utility Corridor Resource Management Plan (BLM 1989), which was implemented 

in 1991. The BLM unit that administers this 

land is the Central Yukon Field Office of the 

Fairbanks District Office. 

The Federal Land Policy and Management 

Act of 1976 (FLPMA) provides for the establishment of Areas of Critical Environmental 

Concern (ACECs) on BLM-managed public lands. FLPMA defines an ACEC as an 

area “within the public lands where special 

management attention is required (when 

such areas are developed or used or where 

no development is required) to protect and 

prevent irreparable damage to important 

historic, cultural or scenic values, fish and 

wildlife resources, or other natural systems 

or processes...” The Utility Corridor Resource 

Management Plan delineated 5 ACECs totaling 42,005 ha specifically to protect Dall sheep 

(Ovis dalli) habitat and other resources.

Dall sheep (hereafter referred to as “sheep” 

in this report) are found throughout the 

Utility Corridor where appropriate habitat 

occurs, but the sheep density is highest in the 

northern third of the corridor. The public has 

a great appreciation for mountain sheep 

(Summerfield 1974). This interest includes 

the recreational viewing of sheep and their 

harvest under both sport and subsistence 

regulations. One measure of this interest is 

the harvest of 120 to 134 rams by hunters 

in the general area from 1998 to 2000 

(Stephenson 2002). In addition, visitors to the 

Arctic Interagency Visitor Center in Coldfoot 

commonly comment favorably about sightings 

of sheep when they travel through the area 

(Lisa Jodwalis, BLM, pers. comm.).

The sheep population in portions of the 

eastern Brooks Range declined during the 

early 1970s and then rebounded in the 1980s 

(Stephenson 2002). Another steep population decline occurred in the early 1990s 

(Brubaker and Whitten 1998; Lenart 2002; 

Lawler 2004), this time in both the eastern 

Brooks Range and the Alaska Range. The 

reason for the declines, up to 40% in portions 

of the eastern Brooks Range, is thought to 

be weather-related; the declines correlate 

with winters of deep snow during this time 

period (Stephenson 2002). The Alaska Range 

population rebounded during the relatively 

mild winters during the late 1990s, while 

the Brooks Range sheep numbers did not. 

Therefore, other limiting factors are probably 

controlling recovery of the sheep population in 

this area (Steve Arthur, Alaska Department 

of Fish and Game, written comm.). 

In 1993, the Alaska Department of Fish 

and Game (ADFG) established a conservative management approach for sport sheep 

hunting throughout the area by establishing 

a “full-curl-ram-only” regulation. This has 

helped improve the population structure 

of sheep in the Eastern Brooks Range by 

increasing the number of breeding-age rams 

(Stephenson 2002), although the population 

size has not increased.

In addition to the sport hunts administered by the ADFG, the BLM administers 2 

Federal Subsistence sheep registration hunts 

in the Utility Corridor. Both of these hunts 

are within the Dalton Highway Corridor 

Management Area (the State designation for 

an area extending 8 km (5 miles) from either 

side of the Dalton Highway). One hunt occurs 

to the south of Atigun Pass and one to the 

north. The harvest limit for these hunts is 

one 7⁄8-curl ram per year per hunter. Recent 

harvest reports from these hunts show that 

the reporting hunters took 2 to 5 sheep annually for subsistence use and that most of these 

sheep were killed in the hunting unit south of 

Atigun Pass. Five to seven unsuccessful hunts 

were reported annually as well. However, 

because the same hunter could participate in 

both hunts, double reporting might have 

occurred if a person was successful in one 

hunt and not in the other.

Other researchers have conducted surveys 

of sheep and their habitat on BLM-administered public land in the Utility Corridor 

and on adjacent lands administered by 

other entities (Summerfield 1974; Daum 

1982; Jakimchuk et al. 1984; Stephenson 

2002). However, to our knowledge, no one 
2 BLM Open File Report 11

 has published inventories of sheep habitat or 

sheep use specifically in BLM ACECs in the 

Utility Corridor. 

Declining sheep populations throughout 

northeast Alaska in the last half-century have 

increased the importance of identifying and 

monitoring significant sheep habitats. Such 

research not only helps land managers assess 

the efficacy of management actions designed 

to protect sheep, but it provides data that can 

be used to modify and improve those efforts.

Study Area 

Our study occurred in the 5 ACECs established for the protection of sheep habitat in 

the Brooks Range (Figure 1). Three of these 

ACECs are located on the southern slopes of 

the Brooks Range: Poss Mountain (3237 ha), 

Nugget Creek (1335 ha), and Snowden 

Mountain (11,331 ha). Poss Mountain and 

Nugget Creek lie on opposite sides of the 

Middle Fork Koyukuk River valley. The 

Snowden Mountain ACEC is about 35 km 

north of these ACECs within the Dietrich 

River drainage, a major tributary of the 

Middle Fork Koyukuk River. These ACECs 

and nearby mountain valleys host a variety of 

largely undisturbed habitats native to interior 

Alaska, including low shrub communities 

(dominated by Salix spp., Betula spp . and 

Vaccinium spp.), riparian areas (dominated by 

Picea glauca), patchy spruce (P. glauca and P. 

mariana) bogs, and deciduous forests (dominated by Populus tremuloides, P. balsamifera, 

and Betula papyrifera). At higher elevations, 

habitat is predominated by treeless dwarf 

shrub communities and sparsely vegetated 

(Carex spp . and forbs) escarpments and scree . 

The remaining 2 ACECs are located on the 

north slope of the Brooks Range. The West 

Fork Atigun ACEC (3440 ha) is in the upper 

Atigun River drainage while the Galbraith 

Lake ACEC (22,662 ha) is on the northern 

edge of the mountain range near the Arctic 

Foothills physiographic province (Wahrhaftig 

1965). These study sites are largely covered 

with treeless, dwarf shrub vegetation communities. Vertical escarpments and scree, 

sparsely vegetated with Carex spp. and forbs, 

are predominant habitat features in the West 

Fork Atigun and Galbraith Lake ACECs.

4 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

The topography in the general area of all 5 

ACECs is mountainous. Most are bordered 

by broad, glacier-carved mountain valleys 

that are fed by steeply incised tributaries. 

Elevations within the ACECs range from 600 m

in the bottoms of the rugged side-canyons to 

nearly 2000 m on the nearby jagged peaks. 

The lithic material in the study areas is 

predominated by Precambrian and Paleozoic 

limestone/marble, quartzite, schist, conglomerate, sandstone, and shale (Brosgé and 

Reiser 1964; Brosgé et al. 1979). 

 An arctic climate characterizes all of the 

ACECs. The warm temperatures and continuous daylight of summer contrast sharply with 

the extreme cold temperatures and abbreviated light of winter in the study area. The 

annual changes between summer and winter 

can be abrupt at this high latitude; spring 

and fall are often abridged. The average July 

temperature in Wiseman, Alaska, the village 

nearest the study area, is 14 °C while the 

average temperature in January is –27 °C 

(Natural Resources Conservation Service, 

Anchorage, written comm.). Annual precipitation at nearby Bettles, Alaska, averages about 

35 cm (National Weather Service data). 

Methods

Surveys and observations were conducted 

in the ACECs during various seasons from 

2000 to 2006. Techniques used to determine 

habitat use and population size of sheep in the 

ACECs are detailed below. 

Summer Habitat Use Surveys

Although snow can be present at any time 

of the year at high latitudes, we classified as 

“summer” surveys those that were conducted 

during the months that are most often snowfree (May–August). Summer habitat surveys 

were conducted in helicopters (Eurocopter 

AS350 AStar and Bell 206B) and fixed-wing 

aircraft (Bellanca Scout or Piper PA-18). 

Logistical challenges caused us to conduct 

surveys opportunistically, resulting in uneven 

spatial and temporal coverage among ACECs. 

The Galbraith Lake and West Fork Atigun 

ACECs, the 2 northernmost units, were each 

visited 2 times, the Nugget Creek ACEC 4 

times, and the remaining 2 ACECs 3 times 
At gi un River

North Fork Cha ndalar River Dietrich River

Koyu

kuk

River

Atigun Pass

Galbraith

Lake ACEC

Snowden 

Mountain

ACEC

Poss

Mountain ACEC

West Fork 

Atigun ACEC

Nuggett 

Creek

ACEC

Wiseman

Bettles

Anchorage

Fairbanks

STUDY AREA

GATES OF THE ARCTIC 

NATIONAL PARK

ARCTIC NATIONAL

WILDLIFE REFUGE

Middle Fork

Dalton Highway

Trans Alaska Pipeline

BLM Open File Report 114 • November 2009 3

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

Figure 1. Location of the 5 ACECs within the Utility Corridor Management Area, Alaska.

N

0 10 km
4

 

BLM Open File Report 114 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

each. We collected no data in 2001 due to lack 

of funding. In total we spent about 530 min 

surveying the ACECs during summer months. 

We did not record the time spent conducting 

population surveys within individual ACECs 

because summer surveys were part of a continuous survey of the larger area. 

During fixed-wing surveys the pilot and 

1 passenger made observations; during most 

helicopter surveys the pilot and 2 passengers made observations. Observers recorded 

geospatial data on 1:63,600 U.S. Geological 

Survey topographic maps or used a handheld 

Global Positioning System (GPS) unit to mark 

electronic waypoints. An exhaustive survey 

of the sheep populations in the ACECs was 

not made during these flights. To minimize 

disturbing animals and potentially causing 

abandonment of habitat (Lawler et al. 2005), 

we avoided approaching sheep closely and did 

not hover over bands longer than necessary. 

As a result, we classified sheep into only 2 

age/sex categories: (1) ewe/lambs

(includes ewes, lambs, and rams that 

were indistinguishable from ewes, i.e, 

usually less than half-curl) and 

(2) rams half-curl or larger. 

Habitat features like mineral licks 

have been shown to be very important 

components of sheep habitat (Heimer 

1973). Licks provide sheep with nutrients and facilitate social interactions 

among individuals (Jakimchuk et al. 

1984). Therefore, we recorded all licks 

observed during our flights. When 

sheep were not present, we identified 

licks based on the presence of multiple 

trails leading to areas where disturbed 

soil was obvious (Daum 1982). 

We also recorded locations where we 

observed ewes with newborn lambs in 

late May and early June, the reported 

peak of lambing in the area (Daum 

1982). It is assumed for this report that 

these animals were spotted near natal 

sites.

Winter Habitat Use Surveys

The annual movement of sheep from 

winter to summer range is related to 

decreasing snow depth and increasing 

temperatures (Jakimchuk et al. 1984). 

Therefore, we surveyed the 3 southernmost 

ACECs via fixed-wing aircraft (Bellanca 

Scout or Piper PA-18) during early spring 

2003, when snow depths for that winter were 

at their maximum extent (exceeding 70 cm 

on level ground). In 2003 and 2004 we also 

surveyed the 2 northernmost ACECs in late 

September (snow depth, 30+ cm), after sheep 

were known to have moved back to winter 

range in the Atigun River valley (Summerfield 

1974). The purpose of these flights was to 

determine if sheep over-winter in the ACECs. 

We flew approximately 275 min to survey the 

areas. We did not attempt to count individuals 

during these surveys because of the difficulty 

of seeing sheep in a snow-covered landscape. 

Rather, we searched for and recorded all 

sheep tracks within the ACECs (Figure 2). 

We recorded observations in 2 categories 

that we could distinguish from the air: 

(1) tracks of sheep bands of less than 5 

animals and (2) tracks of bands of more than 

Figure 2. These barely discernible Dall sheep tracks 

(indicated by arrows) illustrate one of the challenges of 

winter sheep observations in the Brooks Range. Photo 

taken in Poss Mountain ACEC.
BLM Open File Report 114 • November 2009 5

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

5 animals. Depending on snowfall and wind, 

sheep tracks can remain visible for long 

periods. Consequently, we were not able 

to definitively determine the winter sheep 

population in the ACECs, although we were 

able to estimate habitat use from the presence of tracks that appeared to be of similar 

ages. The meandering nature of the tracks, 

which were usually localized on wind-blown 

ridge tops and steep, south-facing rocky 

slopes, prevented us from attempting to map 

complete usage areas based on the tracks 

we observed. We did record any sightings of 

sheep we made during these flights. In 

addition, we included some opportunistic 

observations we made from vehicles on the 

Dalton Highway.

Population Surveys

From 2002 through 2006, the ADFG inventoried sheep in the eastern Brooks Range in 

an effort to monitor the sheep population in 

the general area. Its survey data are included 

in the Results and Discussion section of this 

report. The BLM helped fund the surveys in 

2002, 2003, and 2006. Most of the ADFG’s 

survey effort was concentrated in a large 

survey unit located in the Chandalar River 

drainage, east of the Dalton Highway. This 

unit included the Snowden Mountain ACEC 

and was near the Poss Mountain ACEC. As 

a result, the Snowden Mountain and Poss 

Mountain ACECs were surveyed more often 

than the others, producing uneven population 

data for the 5 ACECs. In addition, the ADFG’s 

2002 and 2003 surveys included location 

data on sheep sightings that occurred in the 

Snowden Mountain ACEC. In 2006 ADFG 

researchers recorded this information for all 

of the ACECs. We used these data along with 

our own observations in the analyses of sheep 

habitat preferences. 

In conducting these surveys, the ADFG 

employed its typical techniques for surveying 

sheep (Whitten 1997). In short, researchers 

used fixed-wing, 2-place aircraft (Piper PA-18) 

with both the pilot and the passenger acting 

as observers. The ADFG mostly conducted 

surveys when winds were calm and visibility 

was good. However, conditions sometimes 

changed during this effort. The ADFG aborted 

surveys when environmental conditions 

became unsafe for flying or appreciably 

impeded observations. Researchers attempted 

to locate all sheep within units during each 

survey. However, extensive cliffs and rockslides complicated observations in some parts 

of the ACECs and reduced survey accuracy by 

an unknown factor. The ADFG flew surveys 

along contour lines in the ACEC, and on most 

flights, researchers recorded the locations 

of sheep via the aircraft’s GPS. Sheep were 

classified into 4 age/sex categories: (1) ewes 

or ewe-like (includes rams that were indistinguishable from ewes, i.e., usually less than 

half-curl), (2) lambs-of-the-year, (3) sub-adult 

rams (half-curl to full-curl rams), and (4) fullcurl and larger rams. 

Earth Cover Use Analysis

The earth cover images dataset used in 

this report was generated from a Landsat 

sensor image collected 2 July 1999 and 

23 June 2001. The earth cover classification 

incorporated methodology developed by the 

BLM and cooperators as described in BLM et 

al. (2003), as well as an existing Alaska 

Vegetation Classification system (Viereck et 

al. 1992). Vegetation compositions for the 

classifications are provided in Appendix A. 

The classified earth cover grid has a spatial 

resolution of 30 m. The overall classification 

accuracy reported in BLM et al. (2003) was 

74.6%. For our analysis the overall classification accuracy is assumed to be 100%; the 

impact of this assumption will not be evaluated. We analyzed sheep habitat preferences 

by generating random points (1 for every 2 

ha of land) in each ACEC and attributing 

those points to their associated earth cover 

type. These points were then compared with 

the observed sheep earth cover use and 

tested for heterogeneity or independence via 

a chi-square test. This enabled us to determine if sheep were using earth cover types 

at the same frequency that they occur in the 

ACECs. For each ACEC, earth cover classes 

were combined into 3 categories to perform 

the chi-square test (see Results and Discussion; Table 4). Lumping occurred in instances 

where we did not observe sheep in a class 

(All Other), where only one sheep location 

was recorded and that earth cover class was 

dissimilar from other classes (All Other), or 
6

 

BLM Open File Report 114 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

where multiple sheep locations were characterized by similar classes (e.g., Low Shrub, 

Dwarf Shrub, etc.). 

Because sheep rams are of particular 

importance to the public, we focused on their 

habitat use within each ACEC. To do this, we 

determined the range of elevation at which all 

rams were found within the ACECs, buffering 

observations by 50 m to account for any error 

associated with the digital elevation model 

data (e.g., pixel size and any inherent error in 

the base data) as well as GPS location error. 

Within the elevation range, we measured the 

area covered by the 5 earth cover types where 

rams were most often found, and determined 

the percent of the total ACEC area that met 

these criteria.

Results and Discussion

Summary data for the summer, winter, and 

habitat surveys are presented in Tables 1, 2, 

and 3. The next section describes our findings 

for each ACEC and is followed by our general 

observations, a summary of our findings, and 

our recommendations for further study.

Table 1. Habitat surveys of Dall sheep and sheep licks observed during the summer in 5 ACECs in the 

Utility Corridor Management Area, Alaska. *Partial survey

Visit site Date Duration Rams

Ewes/

lambs Total Licks

Poss 

Mountain

28 Jul 2000 10 min 1 15 16

28 Jun 2002 19 min 60 60

1 Jun 2004 29 min 5 55 60

25 Jul 2006 12 min 1 14 15 1

Subtotal (min) 70 7 144 151

Nugget 

Creek

11 Aug 2000 10 min 5 14 19

28 Jun 2002 7 min 1 11 12

27 Jun 2003 6 min 11 11

1 Jun 2004 5 min 8 20 28

25 Jul 2006 3 min 9 - 9

Subtotal (min) 31 23 56 79

Snowden 

Mountain

7 July 2002 57 min 7 158 165 1

27 Jun 2003* <5 min 17 11 28 1

1 Jun 2004 79 min 35 57 92

25 Jul 2006 58 min - 34 34 1

Subtotal (min) <199 59 260 319

West Fork 

Atigun

26 Jun 2003 20 min - 2 2 2

22 May 2004 37 min - 2 2

25 Jul 2006 8 min - 17 17

Subtotal (min) 65 - 21 21

Galbraith 

Lake

27 Jun 2003 80 min - 9 9

22 May 2004 85 min 16 113 129

25 Jul 2006 39 min - 0 0

Subtotal (min) 164 16 122 138

Total <530 105 603 708 6 
BLM Open File Report 114 • November 2009 7

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

Table 2. Winter surveys of Dall sheep and sheep tracks in 5 ACECs in the Utility Corridor Management 

Area, Alaska. *Partial survey

Visit site Date Duration

Tracks 

<5

Tracks 

5+ Rams Ewes Lambs

Total 

Sheep 

Spotted

Poss 

Mountain

25 Apr 2003 18 min 3 5 6 6

23 Sep 2003* < 5 min 1 3 7 2 12

Nugget Creek 25 Apr 2003 3 min 1 1 1 2

Snowden 

Mountain 25 Apr 2003 32 min 7 3 4 4

West Fork 

Atigun

23 Sep 2003 25 min 1 2 2

22 Apr 2004 62 min 1 1 1 2

Galbraith 

Lake

23 Sep 2003 45 min 6 1 1

22 Apr 2004 90 min 4 5 18 23

Total 275 min 22 10 11 37 4 52

Table 3. Summer population surveys of Dall sheep observed by ADFG in 5 ACECs in the Utility 

Corridor Management Area, Alaska.

Visit site Date Duration Rams Ewes Lambs Total

Poss 

Mountain

23 Jun 2004 Not recorded 0 26 7 33

28 Jun 2006 Not recorded 4 22 4 30

Nugget Creek 28 Jun 2006 Not recorded 11 21 3 35

Snowden 

Mountain

22 Jun 2004 Not recorded 0 59 13 72

29 Jun 2005 Not recorded 10 119 44 173

27 Jun 2006 Not recorded 3 75 29 107

West Fork 

Atigun 11 Jul 2006 Not recorded 2 6 0 8

Galbraith 

Lake 11 Jul 2006 Not recorded 1 4 1 6

Total 31 332 101 464

Poss Mountain ACEC

Summer Use

The Poss Mountain ACEC (Figure 3) is 

located on the western end of a rugged, mountainous ridgeline and encompasses roughly 

the west half of Poss Mountain itself. The 

principal vegetated cover types in the ACEC 

are Low Shrub and Dwarf Shrub. However, 

the non-vegetated classification Rock/Gravel 

comprises over one-quarter of the entire land 

cover in the ACEC. While the majority of the 

sheep habitat on Poss Mountain lies outside 

the ACEC boundary, the ACEC does include 

an important sheep mineral lick (BLM 1989) 

as well as nearby important escape terrain on 

the northwest side of Poss Mountain. Most of 

the animals we observed during our surveys 

were either close to this lick or were in the 

escape terrain (Figure 4).

We surveyed sheep habitat use in the Poss 

Mountain ACEC once each in 2000, 2002, 

2004, and 2006. When we totaled all of the 

sheep observations from these flights and the 
3

1

8

12

10

18

6

7 4

6

3

4

2

9

6

20

22

Earthcover

Clear Water

Dwarf Shrub

Dwarf Shrub - Lichen

Low Shrub

Low Shrub - Lichen

Low Shrub Tussock Tundra

Low Shrub Willow / Alder

Rock/Gravel - Non-Vegitated Soil

Snow

Sparse Vegetation

Tall Shrub

Tussock Tundra

Tussock Tundra - Lichen

0 0.5 1

Miles

 LEGEND

Habitat Survey Ewes

Lambing Sites

Population Survey Ewes

Population Survey Rams

Sheep Outisde ACEC

Mineral Lick

ACEC Boundary

Victor Gulch

Tracks

<5

>5 -Vegetated

Outside

 

BLM Open File Report 114 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

8

Figure 3. Dall sheep observations in Poss Mountain ACEC, Utility Corridor Management Area, Alaska.
BLM Open File Report 114 • November 2009 9

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

results of the ADFG population surveys, we 

recorded only 10 rams. These rams, which 

accounted for 5% of our total sheep observations, were all found in the central and 

northern half of the ACEC in Low Shrub or 

Low Shrub – Lichen habitat. 

We found 3 lambing areas containing a 

total of 38 ewes and 17 lambs in the Poss 

Mountain ACEC in 2004. These sites were in 

the central and southern portion of the ACEC 

near the lick and escape cover. The overall 

ewe:lamb ratio for the ACEC was 4.1:1 (24 

lambs/100 ewes).

Winter Use

We found that sheep used the Poss 

Mountain ACEC during the winter. In fact, 

winter sheep sign was more concentrated in 

the ACEC than anywhere else on Poss 

Mountain and its nearby associated highlands. It appeared from tracks left in the snow 

that up to 20 animals may have wintered in 

the ACEC in April 2003. Again, we observed 

most of the winter use in and around the 

ACEC near the mineral lick in the head of 

Victor Gulch and in the nearby escape 

terrain. On 23 September 2003 we attempted 

to survey the Poss Mountain ACEC again, 

but were only able to reach the northwestern 

edge of the ACEC due to high winds. The only 

sheep we observed during the flight was a 

band (7 ewes, 2 lambs, and 3 rams) near the 

known lick in Victor Gulch. It should be noted 

that on both of our winter visits, we spotted 

sheep trails in the snow between the Victor 

Gulch lick and another heavily used mineral 

lick northwest of the ACEC in Gold Creek. 

Population Surveys

The ADFG surveyed the Poss Mountain 

ACEC in 2004 and 2006, locating 33 and 

30 sheep, respectively, in the ACEC. Again, 

researchers spotted few rams (0 and 4, 

respectively). The highest productivity 

observed during the ADFG flights occurred 

in 2004 (27 lambs/100 ewes). 

Earth Cover Use

Statistical analysis of sheep habitat selection data for Poss Mountain ACEC (Table 4) 

Figure 4. Dall sheep (indicated by arrow) at a mineral lick in Victor Gulch within 

the Poss Mountain ACEC, Utility Corridor Management Area, Alaska.
5

9 1

8

1

10

7

21

Earthcover Classes

Closed Birch

Closed Mixed Needleleaf Deciduous

Closed Needleleaf

Dwarf Shrub

Dwarf Shrub Lichen

Low Shrub

Low Shrub Lichen

Low Shrub Tussock Tundra

Low Shrub Willow / Alder

Open Birch

Open Mixed Needleleaf Deciduous

Open Needleleaf

Rock/Gravel - Sparse Vegetation

Snow

Tall Shrub

Tussock Tundra

Tussock Tundra Lichen

Woodland Needleleaf

Woodland Needleleaf Lichen

0 0.5 1

Miles

Habitat Survey Rams

 LEGEND

Habitat Survey Ewes

Lambing Sites

Population Survey Ewes

Population Survey Rams

Sheep Outisde ACEC

Mineral Lick

ACEC Boundary

Tracks

<5

>5

Outside

10

 

BLM Open File Report 114 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

Figure 5. Dall sheep observations in Nugget Creek ACEC, Utility Corridor Management Area, Alaska.
BLM Open File Report 114 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

11

revealed that sheep used earth cover classes 

in the All Other category less than they were 

available ( χ2 = 7.25, df = 2, P = 0.026). The 

Rock/Gravel class was used more than available, and the Low Shrub categories provided 

no significant relationship between available 

and used habitat. Hansen (1996) found that 

ewes in the Brooks Range fed primarily on 

forbs and grasses during summer. Because 

most of our observations were made during 

the warm season of the year, these results 

probably demonstrate that animals were 

selecting habitats that host graminoids 

(grasses and grass-like plants) and forbs—

but that also lie in close proximity to escape 

cover. We may have flushed sheep into these 

areas when approaching in the aircraft, and 

therefore their associated locations fell into 

the Rock/Gravel earth cover class.

Nugget Creek ACEC

Summer Use

The Nugget Creek ACEC (Figure 5) is the 

smallest of the 5 ACECs and is essentially 

comprised of a single, isolated mountain. 

The topography on the southeast side of 

this mountain is very steep. Cliffs and scree 

predominate, providing the only escape

cover in the greater area. The north side of 

the mountain is largely open, gentle terrain 

covered by graminoids and low shrubs. The 

dominant earth cover type in these portions 

of the ACEC is Low Shrub. The juxtaposition of steep escape terrain and the open, 

foraging habitat on the north side of the 

mountain creates an island of good sheep 

habitat in an otherwise inhospitable landscape (Figure 6).

We visited the Nugget Creek ACEC in 

2000, 2002–2004, and 2006, successfully 

locating sheep on each visit (Table 1). Generally, the animals we spotted were foraging in 

Low Shrub habitat when we arrived, but in 

most cases, they immediately began moving 

toward the nearby security habitat when the 

aircraft approached. We spotted all 3 age/

sex classes of sheep in the ACEC. However, 

because of the limited amount of habitat 

available in the area, we spotted few sheep in 

this ACEC during any one visit. The number 

of sheep observed during habitat surveys 

ranged from 9 to 28.

We searched for lambing areas in the ACEC 

in late spring 2004 and found 15 ewes and 5 

lambs at one location. This ewe/lamb group 

was located at the highest elevation in the 

ACEC and near its most rugged topography.

Table 4. Chi-square analysis of earth cover use by Dall sheep in 3 ACECs in the Utility 

Corridor Management Area, Alaska.

ACEC Earth Cover Chi-Square P Value

Poss 

Mountain

Low Shrub, Low Shrub – 

Lichen, Dwarf Shrub

7.25 0.026 Rock/Gravel

All Other

Snowden 

Mountain

Low Shrub, Low Shrub – 

Lichen, Dwarf Shrub, 

Dwarf Shrub – Lichen, 

Low Shrub – Willow/Alder 13.66 0.001

Sparse Vegetation, Rock/

Gravel

All Other

Galbraith 

Lake

Dwarf Shrub, 

Dwarf Shrub – Lichen

3.13 0.209 Rock/Gravel

All Other
12

 

BLM Open File Report 114 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

The same lambing area had been identified 

by Daum (1982) 20 years earlier, perhaps 

indicating long-term consistency of lambing 

in the Nugget Creek ACEC. Escape terrain, 

known to be a critical component of lambing 

habitat (Rachlow and Bowyer 1998; Lawson 

et al. 1982), is particularly important where it 

occurs near good foraging areas, as it does in 

the Nugget Creek ACEC. 

Ewes and rams in the Nugget Creek ACEC 

shared very similar territory, and although 

gender-exclusive groups were sometimes seen, 

we observed both at overlapping locations. 

When we tallied sheep observations for all of 

our surveys, rams accounted for 23.5% of the 

total observations in the ACEC.

The Utility Corridor Resource Management 

Plan identified one mineral lick on the steep, 

rugged southeast side of the mountain in the 

Nugget Creek ACEC. We did not see sheep 

using this lick, nor did we detect recent sign 

of sheep use of the area during our observations. Summerfield (1974) has indicated that 

mineral licks can be divided into 2 categories. 

“Primary” licks are used regularly, while 

“secondary” licks are only used occasionally 

or when primary licks cannot be accessed for 

some reason. Perhaps the identified lick in the 

Nugget Creek ACEC falls in the “secondary” 

lick category.

Winter Use

Sheep winter habitat is dependent on snow 

depth, which is related to the physical 

geography of an area (Heimer et al. 1994). 

During the winter, sheep seek locations 

where snow is shallow so they can forage 

while expending minimal energy (Summerfield 1974). As a result, sheep are sometimes 

confined to microsites on windswept highlands 

and/or the lee side of ridges during winter. 

We found that one small group of sheep used 

the Nugget Creek ACEC during the winter of 

2003 (Table 2). The tracks of these animals 

were confined to a small area on the brink of 

a steep escarpment near the single peak in 

the ACEC.

Population Surveys

Because the Nugget Creek ACEC is so 

small, each of our visits to the ACEC can be 

considered a complete census of the area. The 

largest number of sheep seen during the study 

period was a mixed band of 35 animals, found 

Figure 6. Dall sheep band (indicated by arrow) in escape terrain in the 

Nugget Creek ACEC, Utility Corridor Management Area, Alaska. View is 

toward the north with the Middle Fork Koyukuk River and Dalton Highway 

in the background.
BLM Open File Report 114 • November 2009 13

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

during the 2006 ADFG population survey 

(Table 3). Later that summer, we conducted a 

habitat survey in the ACEC and found only 9 

rams. The fluctuation in the number of sheep 

inhabiting the ACEC between the ADFG 

population survey and our habitat survey 

a month later indicates considerable movement of sheep in and out of the Nugget Creek 

ACEC. 

Earth Cover Use

Due to the small number of observed sheep 

locations in the Nugget Creek ACEC, the chisquare analysis offered inconclusive results. 

However, we were able to draw broad conclusions from data collected in the ACEC. Five 

of the six unique sheep locations in the ACEC 

were in the Rock/Gravel classification, which 

covers the southeast side of the main peak in 

the ACEC. The other sheep observation was 

in the Low Shrub habitat on the north side of 

this mountain. These data echo our observations that sheep foraged in close proximity to 

escape cover in the ACEC and moved there 

immediately when threatened. 

Snowden Mountain ACEC

Summer Use

The Snowden Mountain ACEC (Figure 7) 

is the largest of the Utility Corridor ACECs 

that were established for the protection of 

sheep habitat on the south slope of the 

Brooks Range. This ACEC is extremely 

rugged (Figure 8), with elevations ranging 

from 600 m to nearly 2000 m. The area, which 

includes 5 peaks over 1500 m, is incised by 3 

third-order tributaries. 

We visited this ACEC once each year in 

2002, 2003, 2004, and 2006. Compared with 

the other ACECs, we counted large numbers 

of sheep during most visits. Analysis of all 

sheep locations, including the ADFG population survey sightings, revealed that ram and 

ewe locations were more segregated in this 

ACEC than in any other, possibly because 

the large size of the ACEC allowed sheep to 

occupy separate, yet suitable, habitat. More 

than 65% of all of the ewes counted were 

concentrated around the center of the ACEC, 

while most (70%) of the rams were found in 2 

areas along the south-central and southeast 

borders. During the summer we usually found 

sheep at high elevations in the ACEC, often at 

the heads of small side drainages. This finding 

concurs with reported sheep movements in 

the Atigun River valley (Summerfield 1974; 

Jakimchuk et al. 1984). 

We found 6 lambing sites in the ACEC 

in 2004 and counted 44 ewes and 13 lambs 

in these areas. These observations were all 

grouped within 2 generalized lambing areas 

that ADFG identified over 30 years ago 

(Linderman 1972). The lambing sites were all 

near steep escape terrain where the prominent earth cover type was Rock/Gravel and 

Dwarf Shrub – Lichen. The overall ewe/lamb 

ratio was 3.6:1 (32 lambs/100 ewes).

The Utility Corridor Resource Management 

Plan and an early ADFG study (Linderman 

1974) identified 2 mineral licks in the Snowden 

Mountain ACEC. We relocated one of these 

licks but did not find sign of recent sheep 

use at the other (which was omitted from 

Figure 7). We did locate 2 new mineral licks 

based on the presence of sheep trails and soil 

disturbance at the sites (Figure 9). 

Winter Use

We found that more sheep used the 

Snowden Mountain ACEC than any other 

during the winter. Heimer et al. (1994) has 

pointed out that windy areas covered with 

light, dry snow are important to wintering 

sheep. Similarly, Summerfield (1974) found 

that ridge tops are important as sheep wintering areas because they are blown free of snow 

and are good grazing sites, while Hansen 

(1996) determined that sheep forage mainly 

on grasses during the winter. We observed 

that winter track densities were greatest in 

the central portion of the Snowden Mountain 

ACEC and that tracks generally were located 

on high, windswept ridges and south-facing 

slopes where snow depth was comparatively 

shallow and graminoids predominate. 

Population Surveys

During June/July 2002–2006 the ADFG 

surveyed about 201,760 ha (779 square miles) 

immediately south of the Chandalar River 

(ADFG field reports, on file with the BLM). 

The results of these surveys varied by roughly 

one-third on consecutive years (Table 5), and 
2

1

2

3

2

2

5

2 1

6

9

2

1

1

2

8 5

9

5

1

3

3

7

20

41

50

21

46

1

1

1

5

5

3 7

1

7 7

9

2

1 2

1

1

17

3

2

4

4

4

2 3

3

2

6

6 4

2 4

25

10

29

45

5

Earthcover Classes

Clear Water

Closed Needleleaf

Dwarf Shrub

Dwarf Shrub - Lichen

Low Shrub

Low Shrub - Lichen

Low Shrub Tussock Tundra

Low Shrub Willow / Alder

Open Mixed Needleleaf Deciduous

Open Needleleaf

Rock/Gravel - Non-Vegetated Soil

Snow

Sparse Vegetation

Tall Shrub

Tussock Tundra

Tussock Tundra - Lichen

Wet Sedge

Woodland Needleleaf

Woodland Needleleaf - Lichen

0 1 2

Miles

Habitat Survey Rams

 LEGEND

Habitat Survey Ewes

Lambing Sites

Population Survey Ewes

Population Survey Rams

Sheep Outisde ACEC

Mineral Lick

ACEC Boundary

Tracks

<5

>5

Outside

14

 

BLM Open File Report 114 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

Figure 7. Dall sheep observations in Snowden Mountain ACEC, Utility Corridor Management Area, 

Alaska.
BLM Open File Report 114 • November 2009 15

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

it appears that the component of the population varying the most between survey years 

was “ewe-like.” 

Because the ADFG did not conduct concurrent sheep surveys in contiguous areas, it 

is not known whether these changes in the 

sheep population resulted from emigration, 

sampling error, or other factors.

The boundary of the ADFG’s large survey 

unit encompasses the Snowden Mountain 

ACEC. Unfortunately, sheep counted exclusively inside the ACEC were only recorded from 

2004 to 2006. Nonetheless, the considerable 

variability in the number of sheep sighted in 

the ACEC during these 3 years—from 72 to 

173 sheep—is perhaps reflective of changes in 

Figure 8. Rugged terrain on the western side of the Snowden Mountain 

ACEC, Utility Corridor Management Area, Alaska. Snowden Mountain 

(shown) reaches an elevation of 1957 m.

Figure 9. One of the two previously unreported Dall sheep licks located in 

the Snowden Mountain ACEC, Utility Corridor Management Area, Alaska. 
16

 

BLM Open File Report 114 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

the larger sample unit. From these associated 

observations we postulate that movement of 

sheep in and out of the ACEC is a common 

event prompted by unknown factors. 

The greatest number of sheep found during 

the ADFG surveys was in 2005, when over 

25% of the total sheep sighted (173) were 

lambs. This high proportion of lambs may 

illustrate the value of the ACEC’s rugged 

escape terrain to lambing ewes.

Earth Cover Use

Sheep within the Snowden Mountain 

ACEC used the grouped Low Shrub category 

(Low Shrub, Dwarf Shrub, etc.) marginally 

more than available and the grouped Sparsely 

Vegetated and Rock/Gravel category much 

more than available (χ2 = 13.66, df = 2, 

P = 0.001). Of all the ACECs analyzed, 

Snowden Mountain showed the greatest use 

of the Rock/Gravel habitat class. Sheep used 

the All Other class moderately less than 

available.

West Fork Atigun ACEC

Summer Use

The West Fork Atigun ACEC (Figure 10) 

is located on the north side of the largest 

tributary of the Atigun River. We do not have 

complete earth cover data for this area.

However, the data we do possess indicate 

that the ACEC is largely composed of the nonvegetated category Rock/Gravel. The more 

vegetated areas are dominated by Dwarf Shrub 

and Dwarf Shrub – Lichen communities.

We conducted habitat and population 

surveys in the West Fork Atigun ACEC in 

2003, 2004, and 2006. In nearly every survey 

visit, we found fewer sheep than in the other 

ACECs. 

We conducted one sheep habitat survey in 

late June 2003 and another in mid-July 2006. 

Although the 2003 survey occurred after sheep 

usually move to summer range (Summerfield 

1974), deep snow throughout the upper 

elevations of the ACEC prevented sheep from 

occupying most of the ACEC. As a result, we 

located only 2 small bands of sheep (one of 

rams, one of ewes) in the ACEC during that 

visit. However, we also spotted 5 other herds 

of sheep just outside the ACEC boundary. 

These animals were on the west-facing slopes 

across the West Fork Atigun River, where 

snow depth was much lower. In contrast, 

during our July 2006 flight, when snow levels 

were very low, we found 17 sheep in the ACEC. 

Summerfield (1974) also found that snow depth 

greatly influences sheep movements in the 

Atigun River valley, with sheep generally 

following small tributaries upward as snow 

melts during the summer until they ultimately 

arrive at the level of the remaining glaciers.

During 2003 and 2006 habitat survey 

flights, we spotted ewes near 2 licks in adjacent ravines in the ACEC. Only one of these 

licks had been previously reported (BLM 

1989); the other is a new, heretofore 

unreported lick (Figures 11 and 12). Both 

of these mineral licks were located in black 

shale substrate similar to that described in 

Jakimchuk et al. (1984). 

Jakimchuk et al. (1984) identified a lambing area on the south-facing slopes of the 

mountains west of Atigun River and near the 

confluence of the Atigun and West Fork 

Atigun rivers. This lambing area is just outside 

the West Fork Atigun ACEC to the northeast. 

Table 5. Sheep surveys in the upper Chandalar drainage (201,760 ha), June/

July 2002–2006. Data taken from ADFG field reports, on file with the BLM.

Year

“Ewelike” LambsLamb/

100 ewes Rams Total

2002 884 221 25 434 1539

2003 621 114 18 254 989

2004 908 180 20 372 1460

2005 636 214 34 249 1099

2006 857 224 26 436 1517
1

1

6

6

2

1

2

11

Earthcover

Water

Cloud - Cloud Shadow - No Data

Dwarf Shrub

Dwarf Shrub - Lichen

Low Shrub

Low Shrub - Lichen

Low Shrub Tussock Tundra

Low Shrub Willow / Alder

Rock/Gravel - Non-Vegitated Soil

Snow

Sparse Vegetation

Tall Shrub

Tussock Tundra

Tussock Tundra - Lichen

0 10.5

Miles ±

! Population Survey Ewes

# Population Survey Rams

Tracks

ACEC Boundary

Mineral Lick

! Sheep Outisde ACEC

LEGEND

! Habitat Survey Ewes

<5

>5

Outside

-Vegetated

BLM Open File Report 114 • November 2009 17

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

Figure 10. Dall sheep observations in West Fork Atigun ACEC, Utility Corridor Management Area, 

Alaska.
18

 

BLM Open File Report 114 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

While we found no evidence of lambing within 

the ACEC proper, we did encounter ewes and 

lambs just outside the ACEC boundary to the 

southeast. The nearest escape terrain to these 

ewes and lambs was located within the West 

Fork Atigun ACEC, so we infer that these 

animals lambed within its boundaries. 

Winter Use

We located the tracks of one group of 

sheep in the West Fork Atigun ACEC 

during a survey flight in September 2003 

and spotted 2 rams at a different location. In 

April 2004, 7 months later, we found sheep 

tracks in another area and again spotted 2 

Figure 11. Previously unreported Dall sheep lick (indicated by arrow) in 

the West Fork Atigun ACEC, Utility Corridor Management Area, Alaska. 

Another lick reported by BLM (1989) is located in the next ravine to the 

right (southwest) and is shown in Figure 12 below. 

Figure 12. Dall sheep lick reported by BLM (1989) in the West Fork Atigun 

ACEC, Utility Corridor Management Area, Alaska. 
BLM Open File Report 114 • November 2009 19

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

rams in the ACEC. In January 2004, we made 

ground-based observations from the Dalton 

Highway near the ACEC’s eastern boundary. 

During these sightings we again observed 2 

rams in the ACEC, but also spotted 11 other 

sheep just east of the boundary and nearer 

the highway.

These observations reveal that the West 

Fork Atigun ACEC was consistently used 

throughout that winter. They also show that, 

unlike the sheep that winter in the Snowden 

Mountain ACEC on windswept ridges, the 

sheep in the West Fork Atigun ACEC winter 

at lower elevations on toe slopes. In spite of 

this apparent contrast, snow depth probably 

drove the wintering sheep’s habitat selection in both ACECs; ridge tops and steep, 

south-facing toe slopes hold less snow than 

surrounding habitats. Summerfield (1974), 

who found that sheep in the Atigun River 

valley wintered on low-elevation, southfacing slopes, postulated that these sites 

attracted sheep due to higher temperatures 

and shallower snow, which increases foraging 

efficiency. 

In summary, our observations indicate 

that deep snow forces sheep to select from 2 

strategies to survive the harsh winters in 

the Brooks Range: reside on wind-swept 

ridges or move to lower elevations with a 

southern exposure. Sheep in the West Fork 

Atigun ACEC appear to select the second 

strategy. While only a few sheep winter in 

the ACEC proper, more use the area just 

outside the ACEC boundary at even lower 

elevations.

Population Surveys

The ADFG surveyed this ACEC once during the study period (2006) and found only 8 

sheep. However, ADFG researchers counted 

many individuals (126) near the northeast 

and southwest boundaries of the ACEC.

Earth Cover Use

Due to the small number of observed 

locations in the West Fork Atigun ACEC, 

the chi-square analysis offered inconclusive 

results. However, we were able to draw broad 

conclusions from data collected. Of the 10 

sheep locations documented in surveys, 7 were 

in the Rock/Gravel class. The remaining 3 

were in the Sparse Vegetation, Dwarf Shrub – 

Lichen, and Cloud classes. We conclude from 

these data that sheep in the West Fork Atigun 

ACEC, like those in the other ACECs, mostly 

used areas with little vegetation at high elevation (x = 1451 m ± 227 m). 

Galbraith Lake ACEC

Summer Use

The Galbraith Lake ACEC (Figures 13 and 

and 14), the largest of the 5 ACECs, contains 

Galbraith Lake and 3 large drainages that 

feed the lake. The ACEC encompasses the 

Atigun River valley and portions of the mountains on both sides of the valley. The major 

vegetation communities in the ACEC are 

Dwarf Shrub and Dwarf Shrub – Lichen.

We conducted aerial habitat surveys in this 

ACEC 3 times (2003, 2004, and 2006). We 

found only 2 herds of sheep (ewes and lambs) 

in the summer of 2003 and no sheep in the 

summer of 2006. Similarly, ADFG researchers spotted few sheep during their population 

survey in July 2006. In contrast, during the 

habitat flight in late May 2004 we spotted 129 

sheep, 17 of which were lambs. 

The differences in the number of sheep 

observed during these flights probably reflect 

a pattern in the sheep’s seasonal movement 

rather than actual changes in the sheep 

population among years. Jakimchuk et al. 

(1984) observed that sheep use the westand south-facing slopes on the east side of 

the Atigun River valley near Atigun Gorge 

during the spring as lambing-nursery areas, 

where they find an early flush of green 

plants in the spring (Summerfield 1974). 

In fact, BLM employees have counted up 

to 200 sheep in the area known as “Black 

Mountain” (Figure 15) in the spring when 

green vegetation is just beginning to emerge 

(Roger Delaney, BLM, pers. comm.). We 

made ground-based observations of sheep 

in the northern part of the ACEC from the 

Dalton Highway in June 2000 and 2003 and 

noted 27 and 54 sheep (small rams and ewes/

lambs, respectively) in the area around Black 

Mountain.

Our observations confirm that the foothills 

east of Galbraith Lake are valuable to sheep 

in the early spring, both as a lambing area 
1

1

3

2

9 1

5

2

1

3

1

14

8

5

5

7

33

10

13

Earthcover Classes

Water

Cloud - Cloud Shadow - No Data

Dwarf Shrub

Dwarf Shrub - Lichen

Low Shrub

Low Shrub - Lichen

Low Shrub - Tussock Tundra

Low Shrub Willow / Alder

Mesic/Dry Sege Meadow

Rock/Gravel - Non Vegitated Soil

Snow

Sparse Vegetation

Tall Shrub

Tussock Tundra

Tussock Tundra - Lichen

Wet Sedge

0 1.5 3

Miles

 LEGEND

Black Mount ain Atigun Gorge Atigun Valley

Habitat Survey Rams

Habitat Survey Ewes

Lambing Sites

Population Survey Ewes

Population Survey Rams

Sheep Outisde ACEC

ACEC Boundary

Tracks

<5

>5

-Vegetated

Outside

20

 

BLM Open File Report 114 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

Figure 13. Dall sheep observations in Galbraith Lake ACEC, Utility Corridor Management Area, 

Alaska.
BLM Open File Report 114 • November 2009 21

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

and as a spring foraging area, particularly 

for nursing ewes. (Of the 17 total lambs 

spotted in the ACEC, 10 were in this area.) 

Summerfield (1974) noted that as the summer season progresses, sheep move to higher 

elevations in the Atigun River drainage. 

Similarly, our observations suggest that 

there is a seasonal movement of animals 

from lower-elevation spring foraging areas to 

higher elevations in, or even out of, the ACEC 

each summer.

Summerfield (1974) and Daum (1982) had 

previously identified a potential mineral lick 

in the ACEC. However, we did not observe 

sign of recent use of this, or any other mineral 

lick, in the Galbraith Lake ACEC during our 

surveys. 

Winter use

We found sheep tracks in 6 locations in 

the ACEC during a flight in September 2003. 

Groups of fewer than 5 animals accounted for 

all of these tracks. We also observed 1 ram 

during this flight. In another winter flight in 

April 2004, we detected 23 individual sheep, 

as well as the tracks of other sheep, in 4 areas 

in the ACEC. Each observation of tracks was 

of fewer than 5 animals. These sightings 

occurred throughout the ACEC either on high 

ridges or low toe-slopes, probably in response 

to snow depth. In addition, we observed the 

ACEC from the ground along the Dalton 

Highway near Black Mountain in November 

2005 and spotted sheep, both ewes and rams, 

using the lower slopes of the northwest portion of the ACEC. 

Population surveys

ADFG surveyed this ACEC once during the 

study period (2006) and found only 6 sheep in 

the ACEC. 

Earth cover use

Clouds obscured several important habitat 

areas in the satellite image that served as the 

basis for the earth cover classification of the 

Galbraith Lake ACEC. Unfortunately, several 

sheep locations were in this Cloud class, and 

analysis provided the least conclusive data 

(χ2 = 3.13, df = 2, P = 0.209) of all of the habitat use analyses we conducted. The data not 

in the Cloud class indicate that dwarf shrub 

classes have no relationship between availability and sheep use, as we found in the Poss 

Mountain ACEC. As with most of the other 

ACECs, sheep used the Rock/Gravel class 

marginally more than available but used the 

All Other class marginally less than available.

Figure 14. View to the northeast from the southwestern border of the 

Galbraith Lake ACEC, Utility Corridor Management Area, Alaska. 

Galbraith Lake is visible in the background.
22

 

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Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

General Observations and Summary

We determined that all of the ACECs were 

used by sheep year-round for summering, 

wintering, and lambing areas. Our surveys 

were conducted opportunistically due to funding, weather, and other logistical reasons. As 

a result they were both spatially and temporally uneven. Nonetheless, we found that the 

Nugget, Poss Mountain, and Snowden Mountain ACECs and the northeastern portion of 

the Galbraith Lake ACEC are of particular 

importance to sheep, probably because these 

areas contain a great deal of escape terrain 

juxtaposed with foraging habitat compared to 

areas outside the ACECs. Of these 4 ACECs, 

the Snowden Mountain ACEC consistently 

hosted the greatest number of animals during 

our survey visits. Snowden Mountain ACEC 

also contains proportionally more of these 

critical habitats than the other ACECs. 

We found that sheep generally selected 

summer habitats that were in the Rock/Gravel 

and/or Sparse Vegetation classes. Similarly, 

we usually found lambing ewes in habitat that 

was in or near escape terrain, which also falls 

into these classes. This behavioral trait has 

been observed elsewhere by others (Rachlow 

and Bowyer 1998). It is important to note that 

the Rock/Gravel and Sparse Vegetation classes 

are not devoid of vegetation. By definition, 

vegetation makes up less than 20% of the 

cover in the Rock/Gravel earth cover class 

and between 20% and 50% in the Sparse 

Vegetation class. Sheep are known to inhabit 

open, rocky, relatively dry habitats at high 

elevations, where predation and competition 

for forage from other ungulates are reduced 

(Lawson and Johnson 1982). Vegetation is 

characteristically sparse in areas that meet 

those criteria in the ACECs we studied.

Due to public interest in sheep rams, we 

analyzed data on their occurrence in the 

ACECs to develop information on their habitat preferences. Throughout the entire study, 

we counted rams 144 times. These comprised 

11.7% of the total sheep sighted during the 

study. Although each ACEC contains unique 

topography, we found that the elevations 

and habitat used by rams during summer 

months were somewhat uniform across all 

ACECs. Over 97% of all rams counted were 

found in 5 earth cover classes: Low Shrub, 

Low Shrub – Lichen, Dwarf Shrub, Dwarf 

Shrub – Lichen, and Rock/Gravel. The mean 

elevations used by rams in all study areas 

was 1194 m (±265 m), and the elevations 

at which rams were spotted did not vary by 

more than 175 m in any of the ACECs. (We 

omitted West Fork Atigun ACEC from this 

analysis because so few rams were observed 

there.) Because elevation and earth cover 

class were so diagnostic, we estimated how 

much habitat rams were using in each 

Figure 15. Up to 200 Dall sheep have been sighted in the vicinity of Black Mountain, located on the 

northeastern boundary of Galbraith Lake ACEC appoximately 2 km northeast of the lake. 
BLM Open File Report 114 • November 2009 23

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

ACEC (Table 6). We found that although the 

Nugget Creek ACEC is by far the smallest 

ACEC in both area and percent area used, it 

appears to be very important to rams. In fact 

it accounted for only 3% of the total ACEC 

land area but contained 19% of the rams 

observed. In the Nugget Creek ACEC the 

ratio of ram to units of used habitat (ha) was 

1:6, in contrast to ratios of 1:97 or higher for 

the other ACECs. 

Sheep were not using some of the previously 

reported sheep licks in the ACECs during our 

study. However, they were using other licks 

that had not been previously reported. This 

finding probably does not negate the importance of the historic licks, but rather, shows 

that there is some variability in the use of 

licks by sheep over time.

Sheep appeared to have 2 strategies in 

selecting wintering areas. They selected 

either high, wind-swept ridges or lower, 

steep slopes that were oriented to the south 

and west. We hypothesize that snow depth is 

the driving factor in selecting both of these 

wintering areas. 

We observed sheep a total of 1212 times 

within the boundaries of the 5 ACECs. In 

addition, we observed hundreds of sheep just 

outside the ACECs’ boundaries. The largest 

numbers of these “extra-ACEC” sheep were 

around the Snowden Mountain and West Fork 

Atigun ACECs. These animals probably use 

the ACECs as well. 

The productivity of sheep in our study 

areas, when all years and all ACECs were 

combined, was 30.4 lambs / 100 ewes 

(R = 0 – 39; SD ±12.58). The productivity 

of sheep in the Atigun River valley has 

previously been reported to be 43 lambs /

100 ewes (Jakimchuk et al. 1984), 36 

lambs / 100 ewes (Summerfield 1974), and 

30.8 lambs / 100 ewes (Nichols 1978). The 

productivity of the sheep population in a 

large survey unit on the south side of the 

Brooks Range averaged 24.6 lambs / 100 

ewes over 5 years from 2002 to 2006 

(R = 18 – 36; SD ±6.23; ADFG survey 

results on file with the BLM). 

Unfortunately, budget and environmental constraints precluded repeated 

surveys in each year and consistent survey 

effort on each survey. As a result, sources of 

sampling error cannot be discounted in our 

population data. However, it appears that 

the sheep populations in the ACECs fluctuate markedly. It also appears that the 

Snowden Mountain ACEC had a particularly large population shift in consecutive 

years, similar to the fluctuations detected 

by the ADFG in its surveys in the nearby 

Chandalar drainage survey unit, which 

encompasses the Snowden Mountain ACEC. 

The factors that affect production of sheep 

and drive the aforementioned fluctuations in 

the sheep population are not known. Further 

study is needed to determine the contribution 

of seasonal and annual movements, fecundity, and lamb mortality to the dynamics of 

the sheep populations within the ACECs and 

in the general area.

Table 6. Areas used by Dall sheep rams in 4 ACECs in the Utility Corridor Management 

Area, Alaska.

Visit Site

Size of ACEC 

(ha)

Area Used 

(ha)

% of Total 

Used 

Rams:Area 

Used (ha)

Poss Mountain 3237 975 30.1% 1:98

Nugget Creek 1335 151 11.3% 1:6

Snowden 

Mountain 11,331 6999 61.8% 1:97

Galbraith Lake 22,662 6858 30.3% 1:298
24

 

BLM Open File Report 114 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

Literature Cited

[BLM] Bureau of Land Management. 1989. 

Utility Corridor Proposed Resource Management Plan and Final Environmental 

Impact Statement. Arctic District Office, 

Fairbanks, Alaska.

[BLM et al.] Bureau of Land Management, 

Ducks Unlimited, Inc., and Spatial Solutions. 2003. Dalton Highway earth cover 

classification. Unpublished Technical 

Report. BLM-Alaska State Office, Anchorage, Alaska. 

Brosgé, W.P. and H.N. Reiser. 1964. Geologic 

map and section of the Chandalar quadrangle, Alaska. U.S. Geological Survey Miscellaneous Geologic Investigations Map I-375, 

scale 1:250,000.

Brosgé, W.P., H.N. Reiser, J.T. Dutro, Jr., 

and R.L. Detterman. 1979. Bedrock geologic 

map of the Philip Smith Mountains quadrangle, Alaska. U.S. Geological Survey 

Miscellaneous Field Studies Map MF879-B, scale 1:250,000.

Brubaker, R. and K.R. Whitten. 1998. 1996 

Dall sheep (Ovis dalli dalli) survey, Gates 

of the Arctic National Park and Preserve, 

Alaska. U.S. Department of the Interior, 

National Park Service, Technical Report 

NPS/AR/NRTR-98/35, Alaska Region.

Daum, D. 1982. Central Brooks Range Dall 

sheep lambing area and mineral lick project. Internal Report. U.S. Department of 

the Interior, Bureau of Land Management, 

Fairbanks District, Alaska.

Hansen, M.C. 1996. Foraging ecology of 

female Dall’s sheep in the Brooks Range, 

Alaska. PhD thesis. University of Alaska 

Fairbanks, Fairbanks, Alaska. 

Heimer, W.E. 1973. Dall sheep movements 

and mineral lick use. Alaska Department 

of Fish and Game, Federal Aid in Wildlife 

Restoration Final Report, Project W-17-2, 3, 

4, 5; Job 6.1R, Juneau, Alaska. 

Heimer, W.E., F.J. Mauer, and S.W. Keller. 

1994. The effects of physical geography on 

Dall sheep habitat quality and home range 

size. In: Pybus, M. and B. Wishart, editors. 

Proceedings of the Biennial Symposium of 

the Northern Wild Sheep and Goat Council 

9:144–148. 

Jakimchuk, R.G., D.J. Vernam, and L.G. 

Sopuck. 1984. The relationship between 

Dall sheep and the Trans-Alaska Pipeline 

in the northern Brooks Range. Unpublished 

report to Alyeska Pipeline Service Company, 

Renewable Resources Consulting Services 

Ltd., Sidney, British Columbia, Canada.

Lawler, J.P. 2004. Demography and home 

ranges of Dall’s sheep in the central Brooks 

Range, Anaktuvuk Pass, Alaska: Gates of 

the Arctic National Park and Preserve. U.S. 

Department of the Interior, National Park 

Service, Technical Report NPS/AR/NRTR2004-43, Alaska Region. 

Lawler, J.P., B. Griffith, D. Johnson and 

J. Burch. 2005. The effects of military 

jet overflights on Dall’s sheep in interior 

Alaska: report to the Department of the Air 

Force, 11th U.S. Air Force, Elmendorf Air 

Force Base, Alaska. U.S. Department of the 

Interior, National Park Service, Technical 

Report NPS/AR/NRTR-2005-50; NPS D-31, 

Alaska Support Office, Anchorage, Alaska. 

Lawson, B. and R. Johnson. 1982. Mountain 

sheep. In: Chapman, J.A. and G.A. 

Feldhamer, editors. The wild mammals of 

North America: biology, management, and 

economics. Baltimore, Maryland: The Johns 

Hopkins University Press. pp.1036–1055. 

Lenart, E. A. 2002. Game Management 

Units 24 West, and portions of 23 and 26A 

(15,717 mi2). In: Healy, C., editor. Dall 

sheep management report of survey-inventory activities: 1 July 1998–30 June 2001, 

Alaska Department of Fish and Game, 

Project 6.0, Juneau, Alaska, pp. 155–171.

Linderman, S. 1972. A report on the sheep 

study at the Dietrich River headwaters. 
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Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

Appendix 3. In: Nichols, L. and W. Heimer, 

editors. Sheep report, vol. 13. Alaska 

Department of Fish and Game, Federal 

Aid in Wildlife Restoration Annual Project 

Report W-17-3 and W-17-4, Juneau, 

Alaska.

Nichols, L. 1978. Dall sheep reproduction. 

Journal of Wildlife Management 42:570–

580.

Olendorff, R.R., D.D. Bibles, M.T. Dean, 

J.R. Haugh, and M.N. Kochert. 1989. 

Raptor habitat management under the 

U. S. Bureau of Land Management 

multiple-use mandate. Raptor Research 

Reports 8:1–80. 

Olendorff R.R. and M.N. Kochert. 1992. 

Raptor habitat management on public 

lands. Bureau of Land Management, 

Report to the Chief, Division of Wildlife 

and Fisheries, BLM/SC/PT-92/009+6635, 

Washington D.C. 

Rachlow, J.L. and R.T. Bowyer. 1998. Habitat 

selection by Dall’s sheep (Ovis dalli): maternal trade-offs. Journal of Zoology (London) 

245:457–465. 

Stephenson R.O. 2002. Game Management 

Units 24 East, 25A, 26B, and 26C (49,600 

mi2). In: Healy, C., editor. Dall sheep management report of survey-inventory activities: 1 July 1998–30 June 2001, Alaska 

Department of Fish and Game, Project 6.0, 

Juneau, Alaska, pp. 172–185.

Summerfield, B.L. 1974. Population dynamics 

and seasonal movement patterns of Dall 

sheep in the Atigun Canyon area, Brooks 

Range, Alaska. M.S. Thesis. University of 

Alaska Fairbanks, Fairbanks, Alaska.

Viereck, L.A., C.T. Dyrness, A.R. Batten, 

and K.J. Wenzlick. 1992. The Alaska 

Vegetation Classification. U.S. Department 

of Agriculture, Forest Service, Pacific

Northwest Research Station, General 

Technical Report PNW-GTR-286, Portland, 

Oregon.

Wahrhaftig, C. 1965. Physiographic divisions 

of Alaska. U.S. Geological Survey Professional Paper 482. 

Whitten, K.R. 1997. Estimating population 

size and composition of Dall sheep in Alaska: asessment of previously used methods 

and experimental implementation of new 

techniques. Alaska Department of Fish and 

Game, Federal Aid in Wildlife Restoration. 

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W-24-4, and W-24-5, Study 6.11, Juneau, 

Alaska.
 
BLM Open File Report 114 • November 2009 27

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

Appendix A. Alaska Earth Cover Classification Class Descriptions 

(BLM et al. 2003)

1.0 Forest

Needleleaf and Deciduous Trees

The needleleaf species generally found 

were white spruce (Picea glauca) and black 

spruce (P. mariana). White spruce tended to 

occur on warmer sites with better drainage, 

while black spruce dominated poorly drained 

sites and was more common in the interior of 

Alaska. The needleleaf classes included both 

white and black spruce. 

The deciduous tree species generally found 

were paper birch (Betula papyfera), aspen 

(Populus tremuloides) and cottonwood (P. 

balsamifera and P. trichocarpa). Black cottonwoods (P. trichocarpa) were generally found 

only in river valleys and on alluvial flats. 

Under some conditions willow (Salix spp.) and 

alder (Alnus rubra) formed a significant part 

of the tree canopy. Deciduous stands were 

found in major river valleys, on alluvial flats, 

surrounding lakes, or most commonly, on 

the steep slopes of small hills. Mixed deciduous/coniferous stands were present in the 

same areas as pure deciduous stands. While 

needleleaf stands were extensive, deciduous 

and mixed deciduous/coniferous stands were 

generally limited in size. The only exception to 

this rule was near major rivers, where relatively extensive stands of pure deciduous trees 

occurred on floodplains and in ancient oxbows.

1.1 Closed Needleleaf 

At least 60% of the cover was trees, and 

>75% of the trees were needleleaf trees. 

Closed needleleaf sites were rare because 

even where stem densities were high, the 

crown closure remained low. Generally, closed 

needleleaf sites were found only along major 

rivers.

1.2 Open Needleleaf

From 25% to 59% of the cover was trees, 

and >75% of the trees were needleleaf. This 

class was very common throughout the interior of Alaska. A wide variety of understory 

plant groups were present, including low and 

tall shrubs, forbs, grasses, sedges, horsetails, 

mosses, and lichens.

1.21 Open Needleleaf – Lichen

From 25% to 59% of the cover was trees, 

>75% of the trees were needleleaf, and > 20% 

of the understory was lichen.

1.3 Woodland Needleleaf

From 10% to 24% of the cover was trees, 

and >75% of the trees were needleleaf. 

Woodland understory was extremely varied 

and included most of the shrub, herbaceous, 

or graminoid types present in the study 

area.

1.31 Woodland Needleleaf – Lichen

From 10% to 24% of the cover was trees, 

>75% of the trees were needleleaf, and > 20% 

of the understory was lichen. The lichen often 

occurred in small, round patches between 

trees. Within the study area, this class was 

generally found along ridgetops or on riparian 

benches.

1.4 Closed Deciduous (Mixed Deciduous 

Species 1.45)

At least 60% of the cover was trees, and 

>75% of the trees were deciduous. Occurred 

in stands of limited size, generally on the 

floodplains of major rivers, but occasionally 

on hillsides, riparian gravel bars, or bordering 

small lakes. This class included paper birch, 

aspen, or cottonwood.

1.41 Closed Birch

At least 60% of the cover was trees, >75% 

of the trees were deciduous, and >75% of the 

deciduous trees were paper birch.

1.42 Closed Aspen

At least 60% of the cover was trees, >75% 

of the trees were deciduous, and >75% of the 

deciduous trees were aspen. Stands of pure 

aspen occurred, but were generally no larger 
28

 

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Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

than a few acres. They were found on steep 

slopes, with particular soil conditions, and on 

river floodplains.

1.43 Closed Poplar

At least 60% of the cover was trees, >75% 

of the trees were deciduous, and >75% of the 

deciduous trees were cottonwood.

1.44 Closed Deciduous – Willow Complex

At least 60% of the cover was trees, >75% 

of the trees were deciduous, and >60% of the deciduous trees were of the Salix genus, tree form.

1.5 Open Deciduous (Mixed Deciduous 

Species 1.55)

From 25% to 59% of the cover was trees, 

and >75% of the trees were deciduous. There 

was generally a needleleaf component to this 

class, though it was less than 25%. This was a 

relatively uncommon class. 

1.51 Open Birch

From 25% to 59% of the cover was trees, 

>75% of the trees were deciduous, and >75% 

of the deciduous trees were paper birch. This 

class was very rare. No examples of this class 

were found in the study area.

1.52 Open Aspen

From 25 to 59% of the cover was trees, 

>75% of the trees were deciduous, and >75% 

of the deciduous trees were aspen.

1.53 Open Cottonwood

From 25% to 59% of the cover was trees, 

>75% of the trees were deciduous, and >75% 

of the deciduous trees were cottonwood.

1.54 Open Deciduous – Willow Complex

At least 25%–59% of the cover was trees, 

>75% of the trees were deciduous, and >60% 

of the deciduous trees were of the Salix genus, 

tree form.

1.6 Closed Mixed Needleleaf/Deciduous

At least 60% of the cover was trees, but neither needleleaf nor deciduous trees made up 

>75% of the tree cover. This class was uncommon and found mainly along the meanders of 

major rivers.

1.7 Open Mixed Needleleaf/Deciduous

From 25% to 59% of the cover was trees, 

but neither needleleaf nor deciduous trees 

made up >75% of the tree cover. This class 

occurred in regenerating burns, on hill slopes, 

or on the borders of lakes.

2.0 Shrub

The tall and low shrub classes were dominated by willow species, dwarf birch (B. nana

and B. glandulosa) and Vaccinium species,

with alder being somewhat less common. 

However, the proportions of willow to birch 

and the relative heights of the shrub species 

varied widely, which created difficulties in 

determining whether a site was made up of 

tall or low shrub. As a result, the height of the 

shrub species making up the largest proportion of the site dictated whether the site was 

called a low or tall shrub. The shrub heights 

were averaged within a genus, as in the case 

of a site with both tall and low willow shrubs. 

Dwarf shrub was usually composed of dwarf 

ericaceous shrubs and Dryas species, but often 

included a variety of forbs and graminoids. 

The species composition of this class varied 

widely from site to site and included rare 

plant species. It is nearly always found on 

hilltops or mountain plateaus and may have 

included some rock.

2.1 Tall Shrub

Shrubs made up 25%–100% of the cover 

and shrub height was >1.3 m. This class 

generally had a major willow component that 

was mixed with dwarf birch and/or alder, but 

could also have been dominated by nearly 

pure stands of alder. It was found most often 

in wet drainages, at the head of streams, or on 

slopes.

2.21 Low Shrub – Willow/Alder 

Shrubs made up 25%–100% of the cover, 

shrub height was .25–1.3 m, and >75% of the 

shrub cover was willow and/or alder. 

2.22 Other Low Shrub/Tussock Tundra

Shrubs made up 25%–100% of the cover, 

shrub height was .25–1.3 m, and >35% of the 

cover was made up of tussock-forming cottongrass (Eriophorum vaginatum). This class 
BLM Open File Report 114 • November 2009 29

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

was found in extensive patches in flat, poorly 

drained areas. It was generally made up of 

cottongrass, ericaceous shrubs, willow and/or 

alder shrubs, other graminoids, and an occasional black spruce.

2.23 Low Shrub – Lichen Other

Shrubs made up 25%–100% of the cover, 

shrub height was .25–1.3 m, and >20% of the 

cover was made up of lichen. This class was 

found at mid- to high elevations. The shrub 

species in this class were nearly always dwarf 

birch. 

2.24 Low Shrub – Other

Shrubs made up 25%–100% of the cover, 

and shrub height was .25-1.3 m. This was the 

most common low shrub class. It was generally composed of dwarf birch, willow species, 

Vaccinium species, and Ledum species.

2.31 Dwarf Shrub – Lichen

Shrubs made up 25%–100% of the cover, 

shrub height was <.25 m, and >20% of the 

cover was made up of lichen. This class was 

generally made up of dwarf ericaceous 

shrubs and Dryas species, but often included 

a variety of forbs and graminoids. It was 

nearly always found at higher elevations on 

hilltops, mountain slopes and plateaus. This 

class may be more open than the Dwarf Shrub

– Other class.

2.31 Dwarf Shrub – Other

Shrubs made up 25%–100% of the cover, 

and the shrub height was <.25 m. This class 

was generally made up of dwarf ericaceous 

shrubs and Dryas species but often included a 

variety of forbs and graminoids, and some rock. 

It was nearly always found at higher elevations 

on hilltops, mountain slopes, and plateaus. 

3.0 Herbaceous

The classes in this category included 

bryoids, forbs, and graminoids. Bryoids and 

forbs were present as a component of most 

of the other classes but rarely appeared in 

pure stands. Graminoids such as Carex spp., 

Eriophorum spp., or bluejoint grass (Calamagrostis canadensis) may have dominated a 

community.

3.11 Lichen

Composed of >40% herbaceous species, 

<25% water, and > 60% lichen species.

3.12 Moss

Composed of >40% herbaceous species, 

<25% water, and >60% moss species.

3.21 Wet Graminoid

Composed of >40% herbaceous species, 

<25% water, and where >60% of the herbaceous cover was graminoid and >20% of the 

graminoid cover was made up of Carex aquatilis. This class represented wet or seasonally 

flooded sites. It was often present in stands 

too small to be mapped at the current scale.

3.31 Tussock Tundra

Composed of >40% herbaceous species, 

<25% water, where >50% of the herbaceous 

cover was graminoid and >35% of the graminoid cover was made up of tussock-forming 

cottongrass. Tussock tundra often included 

ericaceous shrubs, willow and/or alder shrubs, 

forbs, bryoids, and other graminoids. This 

class was usually found at lower elevations in 

flat, poorly drained areas.

3.311 Tussock Tundra/Lichen

Composed of >40% herbaceous species, 

<25% water, where >50% of the herbaceous 

cover was graminoid, >20% of the cover was 

lichen, and >35% of the graminoid cover was 

made up of tussock-forming cottongrass. 

Tussock tundra often included ericaceous 

shrubs, willow and/or alder shrubs, forbs and 

other graminoids. This class, usually found at 

lower elevations in flat, poorly drained areas, 

included a major component of lichen.

3.34 Mesic/Dry Graminoid

Composed of >40% herbaceous species, 

<5% water, with >50% graminoids excluding tussock-forming cottongrass and Carex 

aquatilis. This class was not common and was 

found generally only at high elevations. 

3.35 Mesic/Dry Forb

Composed of >40% herbaceous species, <5% 

water, with <50% graminoids. Regenerating 

burn areas dominated by fireweed (Epilobium 

angustifolium) fell into the mesic/dry forb 
30

 

BLM Open File Report 114 • November 2009

Dall Sheep Use of ACECs in the Utility Corridor Management Area, Alaska

category. However, forb communities without 

significant graminoid or shrub components 

were generally rare in the interior of Alaska.

4.0 Aquatic Vegetation

The aquatic vegetation was divided into 

Aquatic Bed and Emergent classes. The Aquatic 

Bed class was dominated by plants with leaves 

that float on the water surface, generally pond 

lilies (Nuphar polysepalum). The Emergent 

Vegetation class was composed of species that 

were partially submerged in the water, and 

included freshwater herbs such as horsetails 

(Equisetum spp.), marestail (Hippuris spp.), 

and buckbean (Menyanthes trifoliata).

4.1 Aquatic Bed

Aquatic vegetation made up >20% of the 

cover, and >20% of the vegetation was composed of plants with floating leaves. This class 

was generally dominated by pond lilies.

4.2 Emergent Vegetation

Aquatic vegetation made up >20% of 

the cover, and >20% of the vegetation was 

composed of plants other than pond lilies.

Generally included freshwater herbs such as 

horsetails, marestail, or buckbean.

5.0 Water

5.1 Clear Water

Composed of >80% clear water.

5.2 Turbid Water

Composed of >80% turbid water.

6.0 Barren

This class included sparsely vegetated 

sites, e.g., abandoned gravel pits or riparian 

gravel bars, along with non-vegetated sites, 

e.g., barren mountaintops or glacial till.

6.1 Sparse Vegetation

At least 50% of the area was barren, but 

vegetation made up >20% of the cover. This 

class was often found on riparian gravel 

bars, on rocky or very steep slopes, and in 

abandoned gravel pits. The plant species were 

generally herbs, graminoids, and bryoids.

6.2 Rock/Gravel

At least 50% of the area was barren, >50% 

of the cover was composed of rock and/or 

gravel, and vegetation made up less than 20% 

of the cover. This class was most often made 

up of mountaintops or glaciers.

6.3 Non-vegetated Soil

At least 50% of the area was barren, >50% 

of the cover was composed of mud, silt or 

sand, and vegetation made up less than 20% 

of the cover. This type was generally along 

shorelines or rivers.

7.0 Urban

At least 50% of the area was urban. This 

class was only found in the study area within 

the village of Ruby.

8.0 Agriculture

At least 50% of the area was agriculture. 

This class was not found in the study area.

9.0 Cloud/Shadow

At least 50% of the cover was cloud or 

shadow.

9.1 Cloud 

At least 50% of the cover was made up of 

clouds.

9.2 Cloud Shadow

At least 50% of the cover was made up of 

cloud shadows.

9.3 Terrain Shadow

At least 50% of the cover was made up of 

terrain shadows.

10.0 Other

Sites that did not fall into any other category were assigned to Other. For example, 

sites containing 25%–80% water, <25% shrub, 

and <20% aquatic vegetation were classed as 

Other. Sites classed as Other may have also 

included extensive areas of vegetative litter, 

such as downed wood.