Riparian willow, cottonwoods, and aspen along the Madison River in Yellowstone National Park on September 30, 1938 (from an early Kodachrome slide, Cushman Collection, Indiana University Archives P15797), and a mixed bison herd (bulls, cows, calves) along the river in c. 2000 (US National Parks Service YELL-16356).  A longer period of repeat photographs is available here.

Demise of Yellowstone’s Streamside Plant Communities

Widely travelled fur trader David Thompson described bison behavior in the mountains after passing through Howse Pass in 1808:

Near the head of the eastern defile we had the good fortune to kill two bison cows; these animals often frequent the gorges of the mountains for the fresh grass, water, and the free(dom) from flies; but are careful not to be shut in by impassable rocks; and on being hunted uniformly make for the open country; yet when found in a narrow place I have seen the Bisons take to the rocky hills and go up to places where they could barely stand, the bison is a headlong animal. ¹

Ideally, national parks should be scientific baselines for understanding the characteristic, long-term ecosystem states and processes that shaped the American landscape.² Unfortunately, past management practices, or current land uses may create situations where parks can no longer serve this role.  A classic case are riparian zones in Yellowstone National Park– impacted by chain reaction of removing indigenous hunters, predator control, then  as a result, high densities of elk, and now bison that eat and trample streamside vegetation. In 1995, the National Parks Service restored wolves to Yellowstone, and this appears to have sharply decreased the numbers of elk, their primary prey. Moreover, remaining elk may have altered their movements to avoid predation risk.³ However, humans, not wolves, are the main long-term predator of bison. Ironically, with reduced competition for forage from elk, bison numbers may have increased in Yellowstone due to the return of wolves.  The destruction of riparian vegetation, such the few remaining tiny willow, aspen, and poplar shoots along the edge of Madison River continues (click here for a longer time series of Madison River Seven-mile repeat photographs).

“Cows and Fish”

Even if Yellowstone valley bottoms can no longer serve as a scientific baseline for naturalness, is it possible still to restore riparian zones here? What is the process to evaluate vegetation condition and what management actions should be considered?  Fortunately, bison and domestic cattle are closely related members of the same evolutionary family—the Bovidae. In fact, archaeologists have great difficulty differentiating their bones within archaeological sites without genetic testing. Both species have similar foraging patterns, and show strong affinity for being near water, particularly in low predation-risk situations. So, one approach to considering Yellowstone’s riparian zones is to apply the decades of applied scientific research developed by the ranching industry to deal with effects of cattle near water. Hundreds of pages of government agency and professional handbook guidance exist for the numbers of cattle that can safely occupy these areas without damaging important natural states and processes, and management actions to correct impacts where they occur.⁴  An award winning program called “Cows and Fish” links cattle and domestic bison streamside impacts in the Alberta foothills with habitat for important native species such as bull and cutthroat trout. The “Cows and Fish” educational process stresses that public and rancher understanding of the importance of riparian zones is the foundation for successful monitoring, management and restoration of fisheries.⁵

What restoration actions might a program like “Cows and Fish” or guidelines from other professional, state, provincial, or federal agencies recommend for the Yellowstone scenario? Here’s a short list of potential research and management actions:

Understand long-term bison density patterns– Researchers propose alternate hypotheses for bison movements in this region of the Rocky Mountains. Bison researcher Cormack Gates and co-authors, quoting long-term Yellowstone bison researcher Mary Meagher state:

Prehistorically, YNP bison ranges were probably the “tips of the fingers” of seasonal migration from large source populations associated with expansive grasslands lying to the north, west and southwest around the Yellowstone Plateau (Interview with Mary Meagher, July 15, 2004).  The high mountains on the east side of YNP and discontinuous habitat would likely not have supported bison migration. Historical accounts indicate that interior ranges also supported resident bison populations.⁶

In contrast, United States national park researchers Paul Schullery and Lee Whittelsey reviewed a diversity of historical observations for the Greater Yellowstone area, and concluded that:

What the historical record does tell us is that bison were here, they were all over the place, they were abundant, and, if we may add a new and sadder meaning to Warren Ferris’s words, “nothing remains visible of the long black lines but dark clouds slowly sweeping over the distant plains.⁷

Moreover, Yellowstone researchers have estimated the number of bison that can be sustained by forage within in the park boundaries. These calculations suggest that over 5000 bison could exist within the park with minimal starvation, or out-of-park migration. However, the resulting condition of vegetation and streamsides was not evaluated in this assessment.⁸

As described above, detailed first person journal observations, traditional native American knowledge, wildlife movement process models, and the condition of riparian zones visible in historic photographs (see photograph series above) support Meagher’s “tips of the fingers” analogy for low bison numbers in the uplands and mountains of the Rocky Mountains.⁹ Long-term spatial and temporal variability in bison use of the montane valleys region of the western Cordillera was variable and complex, but still relatively predictable.¹⁰ This variation is related to interactions between biophysical and cultural factors relatively unique to this region that resulted in generally low and sporadic numbers of bison in the area of current-day Yellowstone National Park, in contrast to regions further north where bison were more routinely found some distance up mountain valleys.¹¹

Understand historic bison movement directions– Related to bison densities discussed above is a need to understand the direction of long-term bison movement patterns. The model currently used by the national parks service describes high numbers of bison on the uplands of the Yellowstone Plateau that would migrate down valley each winter.¹² The alternate model of higher numbers of bison at lower elevations suggests that bison movements to upper elevations might have been driven by communal hunting patterns, that human-killing rates might have been very high in narrow grassland valleys, and surviving bison in high elevation forests might be very wary, and possibly non-migratory.¹³ 

 Manage towards long-term bison densities and movement patterns– The understanding gained above can be used to refine population targets and herding strategies. With reference to the repeat photographs of the bison herd  in the fall season along the Madison River shown above, current agency managers are attempting to obtain an adequate amounts of winter range for bison to migrate down-valley out of the park. However, long-term communal human hunters would likely attempt to constrain the bison within the valley, or even move them up-valley into areas where constricted and steeper terrain and winter snows would facilitate hunting. We actually have a wonderful historical description of how this may have worked from the south eastern part of the Greater Yellowstone Ecosystem. On Wednesday, May 30, 1860 Jim Bridger guided a group led Captain William F. Raynolds of the United States Army up the Wind River to a point about 10 miles upstream of the current town of Dubois, Wyoming. They were accompanied by the famed scientist Ferdinand Hayden of the Geological Survey.  Their route across the mountains appeared blocked by the late-melting winter snow, so that evening Raynold and Ferdinand Hayden crossed the river, and scouted out a fork of the river that led northeast towards some interesting peaks. They were likely heading up the Du Noir valley towards Ramshorn Peak. In his journal, Raynolds recorded:

While passing in the valley and on the mountain sides Buffalo “Sign” as so plenty that it confirms the statement that I have heard that the Snake Indians kept the penned in the mountains last winter and killed them as they wanted them. Certain it is that it could be done and a camp where the Indian camp was would do it. ¹⁴

Thus, in times past, people would rarely have reasons to encourage bison movement down-valley onto broad plains where hunting was more difficult. Perhaps the wise elders would have advised:

“Only an idiot would chase the buffalo out of the mountains.”

Fencing and Planting Woody Plants– After over half a century of intensive grazing and browsing, and a high intensity mid-summer fire in 1988, possibly much of the valley bottom’s former riparian poplar forest and shrublands cannot recover without intensive help. Tree and shrub species may have lost the below ground root systems and nutrient reserves that would allow sucker regeneration if herbivory was reduced.  Surviving plants to provide seedlings may be distant. If this is the case, culturing and replanting of native woody species will be required.  Historically, dense shrubs and poplar forests likely may have allowed regeneration to occur in the presence of some bison and elk because these ungulates may have avoided cover that hid human hunters and other predators.¹⁵ But today’s open grassland does not provide this risk-sensitive protection for young suckers. Fencing may be the best solution to rebuild riparian zone structure. This is a common practice on cattle and bison ranches, Rocky Mountain National Park had built fences to recover riparian forests, and this has also been recommended for other streamside forests in Yellowstone.¹⁶ In some areas, streams may need to be dammed to raise the watertable to within reach of plant roots.¹⁷  

Map

Please click here for a map to this location, and for more repeat photographs. 

  Footnotes