Yellowstone's Northern Range - Greater Yellowstone Science ...

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THE NORTHERN RANGE 34 indicates the number of grass, forb, and shrub species on the northern range was the same in grazed and ungrazed sampling plots. Shannon's index to plant species diversity was very similar; 2.38 in ungrazed grasslands compared to 2.30 in grazed grasslands. Community or Beta diversity on the northern range, however, may have experienced a slow decline in the past century due to the decline in aspen and willow stands, but this is somewhat unclear due to the greater Alpha diversity outside the exclosures versus inside the excIosures (Singer 1996a; Coughenour and Singer, Colo. State Univ., and U.S. Geol. Surv., unpubl. data.) Wallace (1991) monitored community structure of five northern range sites, on summer, winter, and transitional ranges, collecting data both inside and outside of exclosures. She found "no significant correlations between changes in diversity and grazing intensities," and concluded that "climate has a stronger control on system structure than does grazing." However, one study of mid-elevation willow communities and nearby grasslands reported significantly more plant species outside the exclosure than inside (Chadde and Kay 1988). According to this study, there were a total of l7 species inside the exc1osure: 1 tree, 5 shrubs, 7 forbs, and 4 graminoids. There were 35 species outside the excIosure: 2 trees, 6 shrubs, 16 forbs, and 11 graminoids. If only native species are considered, there were 15 native species in the ungrazed inside and 31 in the grazed outside. This does not suggest that ungulate grazing decreases species diversity, and seems to suggest that grazing allows for more diversity. In mid-elevation grasslands, climatic variation from year to year caused greater variation in plant species composition than did grazing (Wallace and Macko 1993). In one study, bison and elk grazing were found to be complementary, the two grazers selecting different plants and plant parts (Wallace 1996). Three investigations focused on determining plant species changes after 30 years of protection from grazing in exc10sures (Coughenour et al. 1994, 1996; Reardon 1996; Singer 1996a). Minor changes in species abundance (based on biomass measures) due to grazing were found in the first study (Singer 1996a). Two grasses resistant to grazing, Junegrass and thick-spiked wheatgrass, were more abundant on grazed sites. There was a slight tendency for Sandberg's bluegrass and Hood's phlox to be less abundant on grazed sites, even though Hood's phlox is not known to be a grazed plant. No effects on 127 other plant species were found. A second investigation that monitored plant basal areas found no effect upon any species that could be attributed to grazing (plant basal area is the area occupied by the root crown of the bunch grasses; it is regarded as a more useful long-term indicator of the plant's success than is the area covered by the canopy formed by the plant's leaves, because the canopy is more dramatically affected by yearly variations in moisture) (Reardon 1996). A third study based on plant frequencies showed that total plant frequency, Idaho fescue frequency, and Junegrass frequency increased on grazed areas over the 1958-1981 period, even while elk numbers increased fourfold (Coughenour et al. 1994). As mentioned above, in the 1960s, elk numbers were artificially reduced to less than 4,000 on the northern range. Bison numbers were reduced to 400 parkwide at the same time. Since then, the northern range herds of elk and bison have increased substantially, to as many as an estimated 22,000 elk and 900 bison, their numbers varying depending upon a variety of environmental conditions. Coughenour et aJ. (1994) found that "dominant perennial grasses either maintained their relative abundance or increased. Forbs (broadleaf, herbaceous plants that are neither grasses nor shrubs) decreased in relative abundance, and increased after 1986 both in and out of exclosures, in response to drought. Total plant cover decreased after 1981 due to climatic conditions, as shown by parallel declines both inside and outside excIosures." The authors concluded, "On the basis of these trends, we conclude that elk grazing has not degraded the <strong>Yellowstone</strong> northern winter range."
GRASSLANDS 35 25000 20000 15000 10000 Number of Elk Figure 3. J a. Recent elk numbers all Yellowstolle's northern range. Dark squares: minimum estimated /lumber oj elk ill the fall. Grey squares: total estimated midwinter population as corrected for elk sightability, which varies dlle to differing' winter conditions, adapted from Coughenour et af. (1994) and Singeret al. (1997). 5000 o 1956 1960 1965 1970 1975 1980 1985 1990 1995 Year Total Plant Frequency 60 40 20 B -a- Lower - In --*- Lower - Out --B- Upper-in ~ Upper-out B O~~~~~-L~~~~~~-L~-L~LL~~~L4-L~~ 1956 1961 1966 1971 1976 1981 1986 Figure 3.1 h. Total plant frequencies inside and outside of elk exclosilres all lower and upper elevation sites on the northern range. Note the lack of correlation between elk IIlImbers alld plant frequencies, suggesting that climate, rather thaI! elk, is the determinant of the condition of plant communities. Adapted from Coughenour et al. (1994). Year GRASSLAND PRODUCTION The question of the effect of ungulate grazing on the abundance or biomass of grassland vegetation is central. Several research projects investigated vegetation biomass on a variety of locations and seasonal ungulate ranges (Frank 1990; Frank and McNaughton 1991, 1992, 1993, 1996a, 1996b; Merrill and Boyce 1991, 1996; Singer 1996a).
Page 1: YELLOW"STONE'S NORTHERN RANGE COMPL
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Page 6 and 7: Suggested citation: Yellowstone Nat
Page 8 and 9: c=J Northern Winter Range _ Boundar
Page 10 and 11: Aspen, willows, and biodiversity ..
Page 12 and 13: vii
Page 14 and 15: THE NORTHERN RANGE xii range criter
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Page 18 and 19: THE NORTHERN RANGE 2 Figure 1.1. Ph
Page 20 and 21: THE NORTHERN RANGE tion. There was
Page 22 and 23: THE NORTHERN RANGE 6 Figure 1.6. Gr
Page 24 and 25: THE NORTHERN RANGE 8 Figure 1.8. El
Page 26 and 27: THE NORTHERN RANGE 10 unpopular or
Page 28 and 29: THE NORTHERN RANGE 12 earlier Yello
Page 30 and 31: , ! ~ , I~ " 1 \, • .' '-, , \, ,
Page 32 and 33: THE NORTHERN RANGE 16 Northern rang
Page 34 and 35: Figure 2.3. Sum ot rotal annual riv
Page 36 and 37: THE NORTHERN RANGE 20 Figure 2.4 Tr
Page 38 and 39: THE NORTHERN RANGE 22 dendrochronol
Page 40 and 41: THE NORTHERN RANGE 24 Figure 2.7. A
Page 42 and 43: THE NORTHERN RANGE 26 et al. (1991)
Page 44 and 45: THE NORTHERN RANGE 28 earlier time,
Page 46 and 47: .', P (/ i0~ , • 9 ~ § , , ~ , i
Page 48 and 49: THE NORTHERN RANGE 32 systems-range
Page 52 and 53: THE NORTHERN RANGE 36 Data were gat
Page 54 and 55: THE NORTHERN RANGE 38 grazed and un
Page 56 and 57: THE NORTHERN RANGE showed that graz
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Page 60 and 61: Figure 4.1. Northern range, showing
Page 62 and 63: Figure 4.2. Willow distribution in
Page 64 and 65: THE NORTHERN RANGE 48 Figure 4.4. I
Page 66 and 67: THE NORTHERN RANGE 50 public lands,
Page 68 and 69: THE NORTIlERN RANGE 52 Figure 4.5.
Page 70 and 71: THE NORTHERN RANGE 54 able uncertai
Page 72 and 73: THE NORTHERN RANGE 56 to confirm an
Page 74: THE NORTHERN RANGE 58 RESEARCH RECO
Page 77 and 78: SOIL, EROSION, SEDIMENTS, AND WATER
Page 79 and 80: SOIL, EROSION, SEDIMENTS, AND WATER
Page 81 and 82: ated with ungulate winter ranges. T
Page 83 and 84: ELK POPULATION ISSUES IS YELLOWSTON
Page 85 and 86: ange grazing issue, Yellowstone man
Page 87 and 88: ELK POPULATION ISSUES 71 ... Other
Page 89 and 90: ELK POPULATION ISSUES 73 1996d), so
Page 91 and 92: ELK POPULATION ISSUES 75 the northe
Page 93 and 94: ELK POPULATION ISSUES 77 It has evo
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Page 98 and 99: THE NORTHERN RANGE 82 Competition t
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Figure 7.3. Bison winter range. Sin
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THE NORTHERN RANGE Figure 7.7. Envi
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THE NORTHERN RANGE 88 not aware of
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THE NORTHERN RANGE 90 tion size, an
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THE NORTHERN RANGE 92 activity (95
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THE NORTHERN RANGE 94 pursue the su
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THE NORTHERN RANGE 96 factors were
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THE NORTHERN RANGE Figure 7.13. Num
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THE NORTHERN RANGE 102 complex set
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THE NORTHERN RANGE 104 practically
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THE NORTHERN RANGE 106 appear suppr
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AppendixA. Conferences, Meetings, a
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lJO Year Estimate Comment Source 19
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lJ2 , Estimated # of Elk Year Date
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lJ4 Winter Total Count 1967-68 397
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116 Year Date of Count Parkwide Par
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118 Counts and estimates of mule de
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120 Northern Yellowstone winter ran
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122 Population estimates and reduct
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124 Actual count Inside Outside Est
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Pronghorn counted during spring sur
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128 Year 1939 1940 1941 1942 1943 1
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Ground and aerial counts of bighorn
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REFERENCE LIST NOTES ON THIS REFERE
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Pages 199-210 in Carbyn, L.N., S.H.
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Yellowstone National Park. Technica
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mammal mortality in the 1988 Yellow
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National Park. International Journa
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Mehus, C.A. 1995. Influences ofbraw
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__ , and __ . 1996a. Preburn root b
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Pages 127-138 in F.J. Singer, ed. E
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some northern Yellowstone elk. M.S.
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I I I I I
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