Technical Report

Elk Ecology and Management Perspectives at Mount Rainier National Park
William P, Bradley, Chas. H. Driver


The elk research program initiated by the Park Service spawned a new era in understanding of elk ecology and movement in Mount Rainier National Park and the surrounding area. Space limitations and the intent of this paper do not permit thorough examination of all the results of this research; only the highlights as they are pertinent to our understanding of the Mount Rainier elk situation will be given here. The actual data on which the following statements are based, however, can be found in annual reports by Driver and Danielson (1974), Bradley et al. (1975), Bradley and Driver (1976), and Bradley (1978a, 1978b, and 1978c). These individual reports are presently being condensed into one volume detailing the Mount Rainier elk investigations.

Abundance and Distribution

To provide accurate data on the present distribution and number of elk currently utilizing sub-alpine environments in Mount Rainier a unique aerial survey technique was developed. The aerial survey involved flying over the sub-alpine meadow complexes in the two hours immediately prior to sunset on repeated aerial flights throughout the summer. The technique was field tested in the summer of 1973 and then used repeatedly during the summers of 1974 through 1976 without deviation.

The results of this survey, shown in Figure 2, indicate that the entire eastern half of the park is occupied by summering elk populations. The arrows in this figure point to recent observations of elk in the relatively unoccupied western portion of the park. Most of these observations are found in the low elevation riparian corridors along the major stream sources. These observations were not surprising as elk were known to inhabit the river drainages on the west of the park boundary prior to the start of the present study. However, observations were also made in sub-alpine habitats on Mazama Ridge and Indian Henry's Hunting Ground during the course of the study. These observations may indicate a westward expansion of the present Mount Rainier elk population.

Figure 2. Present distribution of summer elk populations in Mount Rainier National Park (stippled area). Arrows indicate recent observations of elk in the eastern region of the park.

The number of elk utilizing sub-alpine habitats in Mount Rainier were estimated by the same aerial census technique. These data showed between 1300 and 1700 elk utilizing park habitats throughout the course of the study during summer months. The abundance of elk within park habitats was much higher than was previously thought by either the National Park Service or other outside management agencies. The data also showed that the total elk herd was still increasing with the highest rate of increase found in the north herd segment.

Patterns of Elk Movement and Migration

To answer the important questions concerning the movement and migration patterns of this elk herd, study personnel and NPS staff live-trapped and individually marked elk within the boundaries of the park. By the spring of 1977, 193 elk had been individually marked through this program and the subsequent re-sightings of marked elk within and outside the boundaries of Mount Rainier National Park provided this much needed managerial information. The data confirmed the fact that the summering elk population was indeed a migratory herd which wintered outside park boundaries.

Elk movement into the park from outside winter ranges was documented by road surveys along Carlton Creek, adjacent to the southeast boundary of the park. The peak build-up of elk on winter ranges adjacent to the park boundary occurred in the month of May. Elk continued to move through this winter range area and into the park throughout the month of June. By the end of July in each year, sightings on the winter range road surveys had dwindled to zero, indicating that all elk had moved into and occupied habitats within the park. The build-up of elk within the park and the rate of occupation of high sub-alpine summer ranges is shown in Figure 3; it clearly indicates the gradual movement of elk into the high summer ranges through the months of June and early July. The figure also indicates the period of peak occupation of the sub-alpine zone to be from July 15th to approximately September 10th, declining rapidly thereafter. Re-sightings of marked elk within the park boundaries also showed conclusively that there are two distinct herds inhabiting the park. The north herd winters in the White River drainage while the south herd winters in the upper Cowlitz River drainage. Although the range of these two distinct herds comes together in the park in the vicinity of Cayuse Pass, there is little interchange between them. Similarly, there was shown to be little interchange between Mount Rainier elk herds and elk herds summering on the crest of the Cascades, adjacent to the eastern boundary of the park.

Figure 3. Number of elk observed on subalpine ranges during individual aerial surveys, 1974-76. The graph illustrates the temporal pattern of elk migration and occupation of summer range units within the park.

Re-sightings of elk marked in the park on winter ranges outside the boundaries are shown in Figure 4 for the south herd area. Additional documentation substantiating the migratory nature of the elk herd is shown in Figure 5. This figure was obtained by plotting the known death sites from all sources of mortality obtained for individually marked elk during the course of the study. Of the forty individually marked elk trapped within the park boundaries whose death sites were known, 90 percent of them died outside the park. Migrational distances from winter range outside park boundaries to summer range Inside park boundaries averaged from eight to twelve miles, although distances of up to 25 miles were recorded.

Figure 4. Winter and early spring re-location of individually marked elk caught in the Backbone and Ohanapecosh traps within the boundaries of Mount Rainier National Park. Concentration areas reflect degree of observation time and may not indicate true densities.

Figure 5. Known death sites of forty individually marked elk recovered from the South Rainier herd area during the course of study.

Impacts on Vegetation

The research effort documented the obvious physical impacts of elk, such as wallowing, trailing and denudation of vegetated areas. Small vegetation exclosures were erected around intensive use areas to measure the rate of recovery and the response of vegetation in the absence of grazing pressure from elk. Although these techniques measured an obvious and certainly substantial impact, the real question we sought to answer was the ore subtle effects of elk grazing and trampling on the floristic dynamics of the meadows themselves. Measuring this elusive relationship proved difficult, for virtually all of the subalpine meadow areas on the eastern side of the park had already been impacted by the presence of the elk. It was decided that similar sub-alpine areas on the west side of the park could not be used, as the influence of different weather patterns on the vegetative structure would not yield comparable results.

It was decided to approach this question with a uniquely designed simulation study. Two small areas unaffected by the presence of elk were located. Random plots were laid out and elk foraging was simulated by clipping with grass shears, while elk trampling was simulated by physically trampling the vegetation with an artificially constructed elk hoof. Nine different combinations of clipping and trampling, ranging from control plots with neither impact to plots receiving both heavy clipping and heavy trampling, were built into the experiment. Other treatments evaluated different areas of use, different intensities of use (one treatment vs. two treatments per year), different soil substrates and different vegetative communities. Impacts on specified soil parameters were also evaluated. Vegetative cover was chosen as the main unit of measurement and this was broken down by forage class and by individual species.

The response of total vegetative cover to the simulations on all plots is shown in Figure 6 for two years of treatment. Heavy trampling alone resulted in a 44 percent loss of vegetative cover by the second year of treatment. The combined effects of heavy trampling and heavy foraging resulted in a 60 percent loss of vegetative cover through the second year of treatment. The analysis was further broken down into forage classes of woody browse, grass and grasslike plants, and forbs. These results were even more enlightening. In all the different treatments measured, the forb component of the meadow systems sustained the greatest damage due to the simulated presence of elk. In those plots treated twice per year, the forb component of the meadow system decreased almost 77 percent by the end of the second year of treatment. The woody browse plants, mostly Vaccinium spp., were most affected by trampling and least affected by foraging. Grasses and grasslike plants showed a large decline in percent vegetative cover the first year of treatment but held their own or increased slightly during the second year of treatment. As vegetative cover decreased, accumulated surface organic litter also decreased, exposing more bare mineral soil. After the second year of treatment the plots were allowed to rest for one year and then were re-measured. This recovery phase never attained the vegetative cover found on the sites previously and was characterized by a rapid invasion of the disturbed sites by species not previously found in the vegetative association. These species were characteristic of drier, more arid sites found in other areas of the park.

Figure 6. Response of total vegetative cover to varying degrees of simulated elk foraging and trampling over a two-year time span. (For each pair of bars on the graph, the bar on the left represents percentage for 1975 and the bar on the right represents percentage for 1976.)

Concurrently with the simulation experiment, we conducted studies on the food habits of elk within the park. These studies corroborated our observations in the simulation experiment in that those forb species most consumed by elk were the same species that were disappearing on the simulation sites, while the Invading species were of a less palatable nature.

Although the results of any simulation experiment can never be presumed to exactly mimic the situation as found in nature, the treated plots closely resembled those meadows found In high use concentration areas. We feel that the presence of elk in Mount Rainier sub-alpine environments is definitely changing the floristic composition of the sub-alpine meadow system.

The Effects of Sport Hunting

Because of the potential of sport hunting around the periphery of the park to regulate the Mount Rainier elk herds and the differing opinions on whether the "park" elk constituted any segment of the huntable population, studies were carried out to determine the impact of sport hunting on the Mount Rainier elk herd. Check stations were set up in strategic areas outside the park boundary. This effort was concentrated In the south herd area.

Monitoring the sport hunting season further documented the migratory nature of the Mount Rainier elk herd and also pointed out the effects of weather on these movements and their influence on the success or failure of the general elk hunting season. In both 1974 and 1976, early winter storms did not occur until mid-November. In both these years, few elk were harvested in the area from Packwood north to the park boundary. In 1975, however, early winter storms came in the middle of October. By the beginning of elk season in the first week of November, elk had already started their migration out of the park to the lower winter ranges. This resulted in a harvest five times greater than that occurring in the two years of good weather. In addition, hunters observed and harvested many elk that had been individually marked within the boundaries of Mount Rainier National Park. Succeeding storms during the 1975 hunting season also allowed documentation on the effect of inclement weather in triggering additional waves of elk migrating out of the park boundary with each passing weather front. This fact was reflected both in the observations of elk and in the harvest of elk. These data showed fairly conclusively that, in the south Rainier herd area, the success of the sport hunting season is dependent largely on the inclusion of the Mount Rainier herd in the harvest and that this herd's presence or absence is determined largely by the severity of early winter weather patterns.

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Last Updated: Monday, 01-Dec-2003 20:10:54
Author: Natural & Cultural Resources Division

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