Seasonal Forage Availability and Potential Vegetation Limitations to a Mountain Goat Population, Olympic National Park

Abstract

In the Olympic Mountains, mountain goats reach their highest summer density (13.8 animals km-2) on Klahhane Ridge. This area has large rock outcrops that serve for escape. There are 10 plant community types used by the goats in the snowfree season. The primary factors influencing plant community distribution are soil stability and time of snowmelt. In May-June the goats feed in the S-facing meadows where snow melts early in the season. During July-August, the relatively hot and dry season, they feed more intensively in the cooler, N-facing meadows. From mid-August to November they feed throughout the area. The most intensive grazing occurred in the herbaceous communities near rock outcrops (CT 2) early in the season and in five communities on the N side of the ridge in midsummer. Of 51 plant species measured, goats selectively grazed 13 and avoided 18 species. Festuca idahoensis and Carex spectabilis are preferred species and these species dominate some plant communities. Data from exclosures (5 year-s) indicated that Festuca declined in vigor with grazing. Although plants on the N side of the ridge grow more rapidly in midsummer, due to meltwaters from snow, the total forage available to goats is only 35 % of that available on S slopes in spring. Based upon areal extent of meadows and estimates of annual aboveground net production, the availability of forage in midsummer on the N slopes is most limiting to this goat population in the snow-free season. INTRODUCTION Mountain goats (Oreamnos americanus) were introduced into the Olympic Mountains in the late 1920s. Since then the population has grown and spread throughout the alpine and subalpine areas (Moorhead, 1977), reaching a current population of 500-700 animals. They are concentrated in Olympic National Park, where the goats have been protected from hunting since 1938 (Stevens, 1979). Mountain goat densities vary within the Olympic Mountains with the abundance of animals being related to the availability of steep rocky terrain for escape and cover, open subalpine or alpine meadows for forage, and cool areas in which goats can escape summer heat (Stevens, 1979). The highest density occurs on Klahhane Ridge in the NE part of Olympic National Park (470 59'30 N, 123 27'30 W), In 1980 approximately 180 goats shared a snow-free (May-November) range of ca. 13 kM2; a density of 13.8 goats km-2. Mountain goat densities are estimated to be 2.5-3 goats km-2 for populations in the Royal Basin and Lake Constance areas of the Park (Stevens and Taber, 1980). These densities compare with summer estimates of 2.8 and 0.5 goats km-2 (Chadwick, 1977; Singer, 1975, respectively) for natural mountain goat populations in Glacier National Park. Despite the high densities of mountain goats on Klahhane Ridge, indications of severe damage to their habitat by overgrazing, such as the prevalence of unpalatable species, are lacking. The most obvious effect of the goats on their habitat has been the creation of dust baths (wallows) which have become quite extensive (Harter, 1983). While wallows are common and the composition of plant communities is changed in their immediate vicinity (Pfitsch, 1981; Reid, 1983), the wallows do not appreciably reduce the amount of forage available to the goats. Klahhane Ridge is an E-W-trending ridge, 4 km long, with an average elevation of ca. 1800 m. Trees occur to the top of the ridge, interspersed with rock outcrops and subalpine meadows. Parent materials are interbedded sedimentary and basaltic rock.