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

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Figure 2.3. Sum ot rotal annual river discharge and precipitation from four rivers and five weather stations in Yellowstone 1983-1994. Note relatively flat precipitation, but declining river discharge. Figure courtesy Irving Friedman and Daniel Norton. THE NORTHERN RANGE 18 600 -,----------------------------------------------, 500 400 I I X X I \ I \ X 1\ I \ \ \ Discharge , I \ I \ I \/ \ li \ \ / , X , , I , I 'x X I \ , , \ X 300 I ')( 200 Precipitation 100 - 7( - Total-discharge: Sum of 4 rivers; Madison, Yellowstone, Snake and Falls rivers. -a- Precipitation-sum of 5 stations; Mammoth, Tower, Lake, Snake R., Old Faithful o 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 Water Year Caremans 1996; Mullenders et a1. 1996). But the changes in climate can be surprisingly abrupt and localized. Yellowstone National Park is large enough and topographically diverse enough to be characterized by significantly different climatic regimes in different areas (Despain 1987, Meyer et a1. 1995, Whitlock et a1. 1995). At the same time, within a given area the variations from year to year can be striking: Summer "monsoonal" precipitation is highly variable on small spatial and temporal scales; thus the potential exists for severe drought and large fires followed within a few years by intensive convective-storm rainfall (Meyer et a1. 1995). The timing of precipitation within a given year has had profound effects on plant growth. Studies of Yellowstone sagebrush-grasslands further indicated that relative productivity of those areas was more dependent upon winter precipitation than upon temperature and precipitation during the growing season (Merrill et a1. 1993). It is in this context of great climatic variability, both long- and short-term, temporal and spatial, that several generations of ecologists and managers have attempted to understand the northern range and its vegetation-ungulate interactions. It is only recently, however, that investigators have fully appreciated the unpredictability of climate, and have attempted to incorporate that unpredictability into their thinking. Though public attention on the
PREHISTORIC AND EARLY HISTORIC SETTING 19 northern range is still focused primarily on animal numbers, it has become clear to scientists that those numbers are largely a response to varying climatic conditions. Though an appreciation for climatic variability and its influences on ecological processes is essential to an understanding of the northern range, certain types of variability have attracted more attention among modern researchers than others. As will be seen in the following sections of this report, a key factor being considered in several northern range issues is changes in climate since the park's establishment. The long-term condition of several key species of plant communities are tied by investigators to possible effects of changing climate in Yellowstone. Long-term precipitation changes can have profound effects on plant communities we see on the landscape today. For example, there are few young Rocky Mountain juniper among stands of old-growth (400+ years) juniper below 6,500 feet elevation on the northern range. Rocky Mountain juniper in the intermountain west are much studied, and it is well known that they survive best in landscapes that receive between 16 and 22 inches of moisture a year (Springfield 1976). The established old-growth juniper stands on the northern range are currently living in a precipitation zone that receives less than 14 inches of moisture a year. However, upslope, between 6,600 to 7,000 feet elevation, juniper are found in many age groups, including very young plants. It is logical to assume then, that the 400+ year-old junipers were established at a time when they were in a zone that received more than 18 inches of precipitation. This suggests that the IS-inch precipitation isobar has moved upslope from several hundred years ago, and the juniper have followed it. A similar manifestation of the variability of climate on Yellowstone's plant communities is found in the current status of tall and robust stands of willows. In general, tall stands of willows occur in the park above 6,SOO to 7,200 feet, in areas with at least 20 inches of annual precipitation. Tall and robust willow stands generally occur above 7,600 feet, in areas with about 30 inches of annual moisture. Historical photographs of northern range in the park in the late ISOOs, at a time when at least several thousand elk were wintering in the park, show tall willows well below 6,SOO feet, where they do not currently exist. This change in willows might indicate a decline in the annual amount of moisture over the past 100 years. While there is considerable uncertainty about what effects such climatic changes may have on northern range vegetation, there is no longer any question that these changes are real and continue today. Yellowstone is blessed with having detailed climatic data for the past century (Farnes 1997), and a variety of other data sets, such as those found in tree-ring studies, complement the information base on the park's climate since its establishment in IS72. Study of these records indicates that over the course of the twentieth century, summer (I.e., fire season) temperatures have been increasing, January-June precipitation is decreasing, and the likelihood of major fire seasons is increasing (Figure 2.4) (Balling et al. 1992a, 1992b). Their results indicate a decline of 1.6'F (16.9'C) and a decline of 2.4 inches of precipitation over a 95-year period. While these declines may seem small and insignificant in the Yellowstone area, small numerical changes may have large effects. As noted earlier, the difference between 16 and IS inches of precipitation may be the difference whether seedling junipers survive or not. Permafrost has been observed and studied in, and adjacent to the park in the Beartooth, North Absaroka, Washburn and Gallatin ranges (Pierce 1961), at least as low as 6,600 feet elevation. The mean monthly air temperature in the Lake Yellowstone area averages 32.S'F «1 'C), and if Yellowstone's famous geothermal heat were ignored for this example, would mean that the Lake area is only 0.8'F from being pennafrost. In actuality, geothermal heat is fairly common around the lake so that the mean annual soil temperature at Fishing Bridge, for example, is 42.1°F (5.6°C) (Friedman and Norton 1981). Winter range soil temperatures are generally cool. Average annual soil temperatures taken for several years in the mid-1970s on the northern
Page 1: YELLOW"STONE'S NORTHERN RANGE COMPL
Page 4 and 5: .. •.
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
Page 16 and 17: L ~I , }! \,.'1. J 4 f ; " IF , , 1
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 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 50 and 51: THE NORTHERN RANGE 34 indicates the
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
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ange grazing issue, Yellowstone man
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ELK POPULATION ISSUES 71 ... Other
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ELK POPULATION ISSUES 73 1996d), so
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ELK POPULATION ISSUES 75 the northe
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ELK POPULATION ISSUES 77 It has evo
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4 , ~ 1 v " 'It , \ J~ ~""~ .:,~ ",
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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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, .. , , " , ! I ." ~, ~ " ,.\ ,•
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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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