4:10 - 4:30 pm
Study Results: Bison Use of Groomed Roads
Rick Wallen
Yellowstone Center for Resources

Transcript

Female Voice:  And now, because we couldn’t control ourselves, back to critters. (Laughter) And Glenn Plumb was going to give this talk but I understand that he is at a brucellosis meeting in Wyoming, how appropriate.  So Rick Wallen’s going to present a short, 20 minute presentation, short

Rick Wallen:  He told me it was an hour...

Female Voice:  No short!...on bison on groomed roads study.

Rick Wallen: Ok, yes...Glenn told me I had an hour or so to talk about this, so I’ll be brief. About a year ago Yellowstone National Park was having some judicial challenges with winter use, and we sat down and decided to contract with an unbiased party that would have some information and knowledge about ungulate and bison ecology in general, and try and find someone that could come here to Yellowstone, do an unbiased review of movement ecology of ungulates, specifically bison, and try and relate to our issues here on the landscape.

At that point in time we contracted with Dr. Cormack Gates up at the University of Calgary, in Canada.  Dr Gates solicited five colleagues to work with him, primarily Dr. Stelfox, who’s a systems modeler, runs a private consulting business, and has done this kind of work for many, many years. Yes, he used to work at the Teton Science School. And so, Cormack got together, hired one of his graduate students to be the data compiler, and went around and did a lot of data compiling. And then he’s hired a couple of people to do some review of their work done outside of the actual details of what they did in the field.

There were two issues that he was asked to look at. Primarily he was asked to look at road grooming and motorized winter use and how that influences bison movement patterns and bison dynamics and ecology here at Yellowstone National Park. And also take a look at how movement patterns and the controversial issues we deal with at the park boundary might relate to our management strategies that we’re conducting right now.

Like I said, we were under the guise of conflicting court judgments, and so the task at hand was to go out, look at the general literature review of ecology of movements of ungulates worldwide, and try and apply the concepts of dispersion and dispersal and migration, concepts of that nature, to our issues here at Yellowstone National Park.  And also to provide some recommendations on what sort of adaptive management procedures we could potentially implement to gain a better understanding of what we don’t know about relative to our two primary issues that deal with winter and bison.

Terms of reference that we were really looking for were that, you know, we were really trying to stay away from somebody that’s worked in the Yellowstone ecosystem, been involved in the, you know, reading the newspaper and understanding some of the political concerns.  We were really focused on an independent assessment from somebody that lives far away.  We funded the program completely. It was administered by the CESU up at the University of Montana, and the University of Calgary helped negotiate all of those financial arrangements for Dr. Gates and his crew.

The approach that we took was really this general literature review of movement ecology of ungulates in general. They looked at large systems in Africa. There’s not a lot of other large systems with big movements of ungulates on the landscape in North America, but there are a few, and Canada has a few of those examples.  They went about identifying key informants because there’s so many uncertainties. They went about interviewing people that had first hand information of how our winters lay out, the systems that play, and how they affect ungulates of all varieties. And then also some of the key informants were more focused on bison management in the Yellowstone area.  They developed a hypothesis, and they’ve diagrammed it and I’m going to take a stab at trying to present that to you guys today.  After they compiled all this information from interviews they came back and did some technical workshops and tried to develop some models of the system that we’re operating in here. And then in the end hopefully we’ll have a model that we can utilize to get through some of our environmental planning processes that we have ahead of us for the next couple of years.

The key informant interviews were really a rapid appraisal of bison ecology and management in our landscape here. It was really an exploration of various people’s insights about what they thought the system did and how it functioned. They went to National Park Service employees from all units of the Park Service, they went and interviewed other agency and academic research scientists that have come to Yellowstone and studied this system, and they also interviewed a couple of non- government organization groups. 

You can see the technical workshops were split up where they gathered all of the people they interviewed into five groups. They did that last October, so they put most of this information together in a very short period of time this winter. They concluded their technical  workshops by gathering the conservation community together in Livingston, gave a review of what they were trying to come up with as far as a way to describe the system having no information about the Yellowstone ecosystem, well, very little information about the details of the system before they came to do this project.

They came to some of the same conclusions that we’ve seen over time. I keyed in on the general movement patterns that occurred prehistorically. They looked at some of the population dynamics that I displayed and talked about earlier. They came up with this list of key questions that were probably the most important key questions to address in our modeling effort.  Probably the most important one is this is this No. 6, regarding how road grooming affects bison population dynamics, and what causes populations to expand and use new habitats over time.

The ecological setting was no surprise. They keyed right in on the issues that we deal with around Yellowstone very quickly.  One thing that I thought was very enlightening that I appreciate is the fact that we’ve had two previous analyses of similar subjects. And both of these were done by the National Academy of Sciences, produced great big books. And Cheville and his crew of scientists published in 1998 on brucellosis in the Greater Yellowstone area. They kind of cursorily looked at the issue that Gates and company looked at.  Klein and his crew of folks published just a couple years ago, they focused primarily on the northern range but they were looking at some of the same criteria. And in both of those previous evaluations of Yellowstone and our system here, they looked at Yellowstone bison as a single population, and really kind of ignored the differences in ecology and dynamics that occur between the northern range and the central part of the park. And Gates and company really keyed in on that, and I think they did a really good job of taking that into consideration.

Let’s see here, there was a little pointer here. These guys came to the conclusion after the key informant interviews that there were really five ranges within the park. There’s a boundary range here at the north, there’s a Lamar/Blacktail Deer Plateau range. He and company split the Pelican Range apart from the Mary Mountain Range of bison, and then they identified a boundary range at the western part of the park.  And then in between all of these locations there’s these movement corridors that they identified, including one movement corridor between the two components of the  Mary Mountain Range that connect the Hayden Valley and the Firehole River Basin.

So what he’s done here is he’s captured a whole lot of information. The red polygons show geothermal features on the landscape. The ranges, the colors that you see in his various ranges articulate snow water equivalency, which is a measure of probably both snow depth and snow hardness combined.  The whiter the color in these polygons the more snow water equivalency there is. And this is through empirical data that they’ve been able to gather from the logs at the ranger stations around the park as well as the snow pillows at some of the snow monitoring stations throughout the park. So they very eloquently showed that what I tried to talk about this morning, the difference between snow accumulation between the north and the central part of the park.

Ok, here’s the diagram for how they articulated their hypothesis.  They focused their whole effort on explaining inter-range winter movements during the middle of February, so they focused all of their effort on what you might expect the bison population to do in the middle of February. 

There are two kind of key drivers, one being the amount of food available for bison at that time of year, and the other being the ability for bison to move from range to range, and they term that permeability of the corridors.

And then there’s this sort of unknown that really has nothing to do with the density of the bison; this random walk is the concept that there’s some movements on the landscape that you just can’t explain. Bison do that, almost all animals do that.

There’s some features that we really have no control over. The geothermal features are where they are, and as large as they are. The topographic gates that they talk about in their report refers to canyons, much like the Firehole River Canyon and the Gibbon Canyon and places that there’s steep gradient, narrow corridors for movement through those canyons, and there’s no way to manipulate or change any of those kinds of things. There’s a set amount of habitat within each corridor, and each corridor has a defined length that affects this corridor permeability. 

And then the drivers that affect food availability are primarily the density of bison on the landscape, and the density of elk, and we have to consider both.  The amount of snow that falls during the wintertime affects both food availability as well as the ability for bison to travel. And then primary production is really the concept that only a certain amount of grass grows in the previous summer.

And the drivers on how much food is produced in the summertime is summer precipitation, but as far as how much food is available in the wintertime, also is affected by winter precip. Now that I look at this you probably should have one more arrow in there, but winter precipitation the previous winter influences the amount of forage that’s produced. And there’s been a number of studies done in Yellowstone National Park that talk about not only that the summer precip but the amount of moisture that’s carried into the summer from the previous snowpack, and the snow melting conditions affect that as well.

Some of the drivers behind snow cover are obviously winter precipitation. Snow crustiness, which is a term that we had to invent, that I tried to describe as the winter progresses we move from early winter, snow is easy to post hole around, ‘til it gets a little bit harder, and the skiers love the powder ski in the early part of winter and then it’s a completely different scenario in late winter due to this crustiness.  And it’s the metamorphosis of the snow that starts at the surface and works its way all the way to ground level, that as a driver behind snow cover and its effects on the system. And then grooming of the winter roads was another the key issue that Gates and company were looking at, and it affects snow cover, and it affects bison ability to move on the landscape. So that’s more of a management lever that we can choose to do or not do.

Bison density is affected by the amount of habitat within in the area that bison occupy as well as the size of the population at the time. And then primary production...we’ve already got that summer precip up there, I talked about that.  Let’s see, what else do we have coming up here...oh yeah.  The desire for animals to move on the landscape in the middle of the winter has some influence, or herd size has some influence on the desire of animals to need to move around. More of that will come out I think in the report,  but the ideas was that historically in the early part of the last century there was very little movement, whereas now that we have large populations that we see today, there’s a lot more propensity and need for bison to move on the landscape.

The culling rate as part of our management program affects herd size. And the hunting mortality is something that could be a lever to play with in the future. And then natural mortality and reproductive rates all affect the population size that we have in any given year.

So you can see the complexity of the system that they’ve identified. And just to add just a little bit more complexity, predator management on the landscape and vaccination are things that we don’t do much of but have the potential to be model participants in the future, depending on how we want to play out our “what if” scenarios for environmental planning.

I think...oh yeah, there’s a couple more arrows here. Winter precipitation also affects reproductive rate, the ability for animals to carry the pregnancy through the winter is affected by that. And natural mortality is also affected by winter precip. Sometimes animals just get stuck and can’t go any farther, and that’s nature’s role in Yellowstone.

So I think that’s all the complexity that they’ve added into their model, and they’ve developed this with the scenario where some of these things have empirical data to fill in, and we have a known entity that we can play with, and some of its guesses. 

So what they’ve done is gone and queried these interested parties and expert panels, and come up with a strategy where each of those different work groups identified the parameters that they thought were driving the various hypotheses that were thrown out in that previous diagram.. The conclusion of Gates et al was that there was so much similarity from group to group that they just put together a majority average model. They went through a series of ninety pages of  “what if” projections and I wanted to show this one as an interesting way to use the effort for how we might plan things and analyze our proposals in the future.

In a no grooming versus a grooming scenario on the landscape they took and ran five projections. And the reason these lines don’t show up the same each time, as the model reaches into the hat and  pulls out a random amount of precip that might occur in a previous summer and a random amount of snowfall that might occur during a given winter. We’ve plotted this across 100 years, an estimate of 100 years, and in 1970 they populate the model with the demographic features that we knew in 1970 and just ran all these projections.  In a no grooming scenario it takes longer to get up into this range of natural variability than in a grooming scenario, but both scenarios show up where we would expect our bison population to range between 2,500 and 5,000 animals for a hundred years at a time no matter how we manage for winter use, and that the primary cause for periodic die outs is associated mostly with food availability during the February time period.

So they haven’t completed the project report.  I perused and got some of the key findings that I think are not going to change between now and when the final project report comes out, and just wanted to share a few of the conclusions. 

Forage production availability is affected by random events of weather, and the variation in our grazer community on the landscape.  They focused on the fact that there’s a deep correlation between total ungulate abundance and not any kind of elk versus bison interaction.

Winter food availability is a key driver in why animals move from range to range.

The inter- range movements are generally not constrained by winter snowpack, under most winter conditions. But there’s going to be a winter that comes along about every 7 - 10 years that is definitely going to drive mortality rates in the populations and cause these key die outs.

And then one of the things that road grooming does relative to animal populations here, is it creates somewhat of a dampening effect, in that sources in mortality because of management is going to be more chronic over time and we’ll see fewer animals per year, but over the long run the total number of animals that we end up killing in our management operations is probably not going to be much different.

There were some uncertainties. I think the biggest uncertainty is knowing at what depth of snow does it stop bison from moving from area to area. We just don’t know...we’ve seen them move through some pretty deep areas of snow.  It’s different in the early part of winter than it is in the late part of winter. And that’s something that we can focus on, trying to describe better for the future and utilize that and using this model parameterization.

The relationship between winter food availability and bison over-wintering mortality is vague at best. And the relationship between winter food availability and the probability that animals are actually going to go somewhere is again a kind of guess work. The various workshop groups were very close in their estimates of what they thought these parameters did. Out of the five groups one group was quite different, and four groups were very similar.

The Pelican Valley is somewhat perplexing when you look at the empirical data that’s available.  It looks like Pelican Valley should be producing a whole lot more food and supporting a whole lot more bison in the wintertime, so there’s probably some data that we can look to gather over time to validate one way or another whether our estimates are right.

The group of Gates et al came down and provided a draft copy to the park about one month ago. Nine park employees spent a frantic week reading and editing and providing something like fifteen pages of comments in very small margins and  (???)  and a whole lot of thought for the crew to take look at before they finished their final report.  Dr. Gates and Dr. Stelfox showed up one week ago, gave a briefing to the superintendent, and they’re currently reviewing the written comments that we provided earlier in the month, and the superintendent, assistant superintendent’s comments from their briefings. And we hope to have final project report, I’m guessing by mid to late May, and there’ll be a lot more information we’ll be able to share with how this project has drawn conclusions. I think that at that point in time at least my shop, if not several of us at YCR are probably going to have to develop a series of interpretations of how we think the key findings will affect our management options in the future.  And then, I think the big benefit of this particular effort is a dynamic systems model that can help us play some “what if” scenarios and help us with some of our analyses for winter use planning in the future.

So that’s everything I know about this particular project, and I think I ran out of time.  (Applause)