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...wildfires facilitated moose population growth and range expansion. A hunting season in Montana along the northern boundary of Yellowstone National Park, authorized in 1945 in response to perceived damage by moose to willow stands, evidently reduced the moose population quickly and maintained it at moderate densities through 1988. In 1988, landscape-altering wildfires swept through the Yellowstone ecosystem and impacted old growth forest important for moose survival during winter. The moose population associated with the NYWR declined by 75% or more and has shown no sign of recovery by 2002. Several techniques for assessing population trend for moose on the NYWR were tested. Given the problems associated with monitoring a species at low densities with a dispersed social organization and occupying habitats where visibility is limited, aerial population censuses were not useful. A horseback trail survey, a road survey, and counts of moose in early winter or late spring in larger willow stands had greater potential as indices to moose population changes.
ALCES VOL. 42:133-149 (2006)
Key words: monitoring, moose, Northern Yellowstone Winter Range, population history, Yellowstone
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The Northern Yellowstone Winter Range (NYWR) (Fig. 1) supports over half the wintering ungulates that utilize Yellowstone National Park (YNP) during summer (National Academy of Sciences 2002). While elk (Cervus elaphus) and bison (Bison bison) constitute more than 80% of the ungulate biomass on the NYWR during winter (National Academy of Sciences 2002), this winter range is essential to several less common ungulates, including moose (Alces alces), bighorn sheep (Ovis canadensis), mule deer (Odocoileus hemionus), and pronghorn antelope (Antilocapra americana) (Yellowstone National Park 1997). In 1985, a study (Tyers 2003) was initiated to identify moose habitat needs and population status. This paper summarizes information collected on the history of moose on the NYWR and gives recommendations for monitoring the NYWR moose population.
Accurate assessment of ungulate population dynamics and factors that regulate populations is essential to sound population management (Gasaway et al. 1986, Van Ballenberghe and Ballard 1998). Obtaining reliable demographic information on any free-ranging ungulate population is difficult (McCullough 1984, Saether 1987), but moose are among the most difficult ungulates to monitor because they are the least social North American deer and frequently occupy habitats with poor observability (Schladweiler 1973, Houston 1974).
Moose population size is typically assessed in 3 ways- total area counts, sample estimates, and indices (Timmermann and Buss 1998). Timmermann and Buss (1998) advocated multiple information sources to assess population status. I used historic documents to trace the history of moose populations on the NYWR and multiple population monitoring methods, including aerial surveys, horseback surveys, road surveys, and spatially restricted counts, to determine if vegetation changes associated with massive wildfires in the Yellowstone ecosystem in 1988 precipitated changes in moose population size. The results of my population monitoring efforts during 1985 - 2001 allowed me to evaluate the efficacy of several techniques for developing moose population indices and to identify reasonable techniques for monitoring future population trends.
[FIGURE 1 OMITTED]
STUDY AREA
The NYWR includes parts of YNP, the southern third of the Gardiner Ranger District, Gallatin National Forest, and mixed private and state lands (Fig. 1). The boundary of the NYWR is based on winter distribution of elk (Houston 1982). During this study, elk were the dominant ungulate species (10,000 - 25,000), but mule deer (2,000 - 3,000), bighorn sheep (100- 200), bison (500- 1,000), and pronghorn antelope (100 - 300) also occupied the NYWR. Moose numbers were unknown, but they wintered throughout the study area in scattered areas of suitable habitat, usually at higher elevations than elk.
Vegetation on the NYWR varies from low elevation (< 2,000 m) sage (Artemisia spp.) steppe to high elevation (3,000 m) coniferous forests. Willow (Salix spp.) stands occur along streams and in wet areas within forests. Lodgepole pine (Pinus contorta), Engelmann spruce (Picea engelmannii), subalpine fir (Abies lasiocarpa), Douglas fir (Pseudostuga menzieisii), and whitebark pine (P. albicaulus) are the most common coniferous species in the NYWR. The 1988 Yellowstone fires burned approximately 43,000 ha of the 143,900 ha of mature conifer forest present in the NYWR in 1988, thus converting about 30% of mature forest to early seral stages (Tyers 2003).
METHODS
Historical Documents
Agency files and archives were searched for statements on moose populations specific to the study area. Documents not considered by other authors that provided an historical context for population monitoring were of special interest.
Population Monitoring Techniques
Horseback transect index--In 1947, 1948, and 1949, Montana Fish and Game Biologist Joe Gaab looked for moose each September in the Absaroka Primitive Area (now the Absaroka Beartooth Wilderness) on about 177 km of trail. From 1985 to 2001, other observers repeated his route through the Hellroaring, Buffalo Fork, and Slough Creek drainages 34 times between July and late October to develop a moose population index.
Gaab rode primarily to look for moose. During 1985 through 2001, observers conducted other tasks along the routes (trail maintenance, hunter compliance checks, and outfitter camp inspections) but reported all moose observed. Gaab and more recent observers recorded age (calf or > 1 year of age) and gender (for moose > 1 year of age) of all moose sighted. From 1985 to 2001, the days spent covering the route ranged from 5 to 32, and trails were not traveled in any particular sequence. In both periods (1947-1949 and 1985-2001) observations were restricted to daylight hours and sightings were reported as number of moose seen per day per observer group. Observer group size varied from 1 to 6.
Road transect index--Moose sightings along the 89-km stretch of road from Gardiner to Cooke City, the only road in Y-NP maintained for wheeled vehicles year-round, were used as an index of moose distribution and abundance. Each trip was considered one sample regardless of the direction of travel. No attempt was made to standardize time of day, but at least 4 trips per month were completed in all months. Data collected between January 1987 - December 1992 and January 1995 - December 1997 were used to determine if there were differences in the number of moose seen seasonally and if moose numbers seen along the road differed before and after the 1988 fires.
To determine if changes between pre-and post-fire road counts were consistent across the NYWR, the road was divided into 5 sections. Each section consisted of a road segment that traversed similar vegetation and topography. The first section, Gardiner to Mammoth (8.0 km), included the Gardner River canyon. Topography was broken and the surrounding vegetation was arid grasslands and dry sagebrush unaffected by the 1988 fires. Gardiner was the lowest point along the road (1,585 m).
The second section was from Mammoth to Tower Junction (29.1 km). Topography and vegetation were diverse. Vegetation included open grasslands and Douglas fir, but there were also mature spruce-fir forests, isolated stretches of stunted...
NOTE: All illustrations and photos
have been removed from this article.
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