In the Valley of the Wolves
Reintroduction of the Wolves

When the gray wolf was eradicated from Yellowstone National Park in the 1920s, more was lost than just the noble and fascinating predator. The park’s entire ecosystem changed. Now, nearly a dozen years since the wolves returned, the recovery of that system to its natural balance is well underway, say ecologists William Ripple and Robert Beschta of Oregon State University.

The researchers began studying the interaction of wolves with other parts of the ecosystem somewhat indirectly. “Back in 1997, I became aware that the aspen trees in Yellowstone were declining,” Ripple explains. “There was disagreement and confusion as to why these trees were disappearing, so I set out with graduate students to unravel this mystery.”

“We went out to the park and we cored the trees and studied the tree rings which show the annual growth, and we were able to age the trees that are still there,” Ripple says. The tree ring analysis indicated that the aspen, which usually regenerate themselves by sending off new shoots rather than by producing seeds, had stopped producing new trees during the first half of the 20th century.

Ripple and his colleagues looked at several possible variables that could be affecting the trees, from climate fluctuations to a changing natural forest fire regime. But the only factor that fit, Ripple says, was the browsing patterns of elk, which like to feed on the seedlings of aspen trees, and which are also a favored food of gray wolves: “The wolves were killed off from Yellowstone in the 1920s, which correlated with the start of the aspen decline. That led us to develop the hypothesis that the wolves were connected in some way to the aspen trees.” That connection, Ripple concluded, was mediated through elk: “We connected the dots: wolves affect elk; elk affect aspen; and therefore wolves affect aspen.”

Aspen grove (photo: NPS/J Schmidt; 1977)

Ripple and his colleagues subsequently discovered other changes. In some areas, willows — small, scrubby trees that grow in wet areas along stream beds — were starting to grow taller, because they were escaping predation by elk. In other areas, however, the willows continued to be heavily grazed upon. The same patchy changes were also seen with cottonwood trees, which also grow along streams.

“The more I looked at it the more I could see that what is going on may be an ecology of fear,” Ripple says. “The theory goes like this: the browser — in this case the elk — need to make behavioral decisions and tradeoffs as to how much time and energy to put into eating food versus how much time to be staying in safe places.” Those decisions affect where the animals concentrate their feeding efforts, and therefore the distribution of the vegetation they eat. “What we started noticing is that the plants were doing better where the terrain might favor the wolf a little bit more than the elk,” he says. For example, the elk might browse less in areas with poorer visibility (more dangerous to the elk because they can’t see if wolves are on the scene), or regions littered with heavy debris (a risk because it becomes an impediment to escape in the event of an attack).

Indeed, Ripple says, “we found that aspen were growing the tallest along streamside areas that had some downed woody debris or some downed logs nearby.”

Elk behavior and vegetation distribution aren’t the only factors impacted by the return of the Yellowstone’s wolves. Ripple suspects that the ripples of their recovery are reverberating throughout the entire ecosystem, in birds, fish, insects, as well as in other plants and animal species. Beavers, for example, are probably affected, he says. “The park service has been monitoring beaver since the wolves returned, and found that they have increased in numbers every year in the northern part of Yellowstone. Before the wolves returned, there really wasn’t much food for the beaver. But now with this growth of these plants — especially the willow — the beavers have more food, and they are also using the willows to build their lodges and their dams, which may be contributing to beaver population increases.”

“We are at the beginning of a grand ecological experiment,” Ripple says. “We were without wolves for seventy years, and we’ve just had them back in for 11 years, so we’re only just starting to see changes. It could take many decades for the ecosystem to recover.”

  • Beaver, Wolves and Water at Beside the Stream

    [...] because they’re more watchful and live in smaller herds.  And they browse less intensively, allowing cottonwood and aspen groves to replenish themselves for the first time since the 1920s when the wolves [...]

  • J. Igo

    What makes the ecosystem any the worse for lack of the wolves? Doesn’t it just make it DIFFERENT than it was before they were eradicated and today? It’s all relative to what’s a more valuable species to be keeping around. Is it any LESS beautiful to LOOK at? So, the beavers returned? They probably just migrated from other parts. People do the very same thing…migrate to where they can better survive. What if, like elk and other wild ungulants, we preferred to eat wolves, and if wolves kill off so many of them, maybe we should, ya think, make a delicacy of ‘em? We agree with our first conservation President, Teddy Roosevelt, who would have shot them all if he could have. [See his book, The Wilderness Hunter.] Yes, they are really fine looking animals, but so is the Great Pyrenees dog.

  • pcw

    Wolves and the greater balance of the ecosystem… all comes down to the survival of people and how people live. That includes the ranchers and farmers, their way of life and how they put food on the table for their families. What about them. The cattle, sheep, horses, and other livestock that the farmers and ranchers need to live. Keeping the wolf population in check is a must. That means hunting them.

  • greentangle

    I think it’s much more important to keep the human population in check, which we’ve failed miserably at. Ranchers and their domestic animals are an environmental disaster, but they consider themselves more important than the bigger picture. Fortunately the previous two posters and their opinions are as much a fading part of the past as the president one refers to.

  • rks

    What about everyone else that would like to keep their way of life? Most everyone is trying to put food on the table and a roof over their heads. I wouldn’t be surprised that the cow that gave me the milk I’m drinking today,I will be eating later.

  • firefly

    While at Bryce Canyon in Utah last year in July, it snowed, and leaving my two menfolk in the car, I got out to take pictures. Once home, I was shocked to see the face of a wolf in a stand of trees. Never saw him at the time. Thank goodness, I din’t become a delicious snack…But what a magnificent animal!

  • Wolf Boy

    According to a study, wolves as an attraction in Yellowstone could generate $19 million which is much more than the estimated amount of losses of livestock. In spite of ranchers’ concerns, the data thus far indicate that the wolves have remained largely within the reintroduction regions and have chosen to prey primarily on native deer and elk populations.

  • Nigel

    i think you are right wolf boy, thinking and seeing the bigger pictureis a must. Wolves however are not stupid and will go for an easy kill rather than on the hunt which they could get injured or killed on

  • Sportie

    i agree with pcw…wolves need to be kept in check and allowing them to deplete a rancher or a farmers lively hood by killing his income is not right, they need to be kept under control. But i dont agree that its the humans at fault, sure wolves go for any easy kill but they kill for sport, after they’ve eaten they kill and kill and just leave their prey.

  • laura

    Sportie: while some wolves may not kill when they they are necesarily hungry the food they do not eat does not go to waste. wolves are a huge help to the ecosystem. they will typically only eat 200 lbs from a 500 lbs kill. the foot that they do not eat is eaten by scavengers such as bears, ravens, foxes, cayotees, and magpies. so any food they dont eat somebody else will. also when a wolf kills a rancher’s livestock the rancher is compensated for their loss and paid the amount that the lost livestock is worth, so they are not totally left with nothing

  • WolfSaver

    I think that wolves will balance the ecosystem because they can control the population. Wolves will eat until they are completely full then the scavengers can eat the rest like bears, foxes, crows and coyotes. Yeah I agree with Laura that they will eat 200 lbs from a 500 lbs kill. That is still alot of meat they eat.

  • druid

    At Pcw the reason we do stuff is for humans but when you step back and look at the world as a whole you’ll see we are really messing things up. It’s true that no one will lay back and just let their family suffer but we need a better way to work with our environment. Also hunt down the wolves that cost about 2 million dollars to restore very, very bad idea. (Don’t even think about saying that was too much money to spend on them because they bring in about 20million annually)

    At Sportie let me ask you this. When you cook a whole chicken do you eat the whole thing? Meaning bones, liver, intestine, heart, lungs, etc. of course not! You eat the meat. So what do you do with the rest? You throw it out and let it rot in some land fill that is full of rats and vermin and all sorts of nasty stuff. All so humans are the only animals that kill for sport because we find enjoyment in it. A wolf kills because it is protecting a kill or it needs food that is it. What ever is not eaten gets eaten by another animal. Oh and fyi not to many animals eat the whole entire kill for the simple reason that is just to damn big. Also the federal government established a payment program to compensate ranchers for any loss of livestock. And due to the fact that the wolves that go after the livestock are typically lone wolves (that are either sick, dying, extremely old or a combination of all three) there have been relatively few cases where ranchers needed to be paid. In fact when paying greater than market value (3,500 per cow) for the losses the total cost for it was only about 60,000. So paying 3,500 for each cow lost that puts the total cows lost at a grand total of 17 cattle. (Even I was surprised at that number)

    Wolf populations are as necessary to American wild life as lions are Africa. They are natural predators which keep the ecosystem in check and by removing them we endanger not just that ecosystem but our world as well.

  • Amare Gizaw

    Wonderful program on PBS detailing the reintroduction of wolves. It is our desire that the wolves still be protected to maintain the desired wildlife balance in all areas. The government must assume the appropriate responsibility and actions toward this protection. Thank you

  • AsciiWolf

    RE: J. Igo,
    All I can say about you is that you are really stupid and know nothing about wolves…
    Also, Teddy Roosevelt was hunter who was doing it _for fun_ so obviously he wanted to “shot them all” (not only wolves).
    And there’s small difference between us and wolves – wolves hunt for food (and because they usually kill the weak ones, they are helping the ecosystem and biodiversity of the nature), we hunt for fun and our actions usually broke the ecosystem…

  • ElkBoy

    Wolf Boy, In general numbers can be manipulated to make thing look better than what they are! According to the Wyoming Wolf management plan the attendance to Yellowstone has if anything declined since the reintroduction of the wolves. I believe the “study” you are referring to was based a questionnaire that the park had attendees filled out on why they came to the park. Also, be aware that the total cost of the livestock losses is confirmed predation (paid for) and non confirmed (not paid) for. Some wolf biologist (who have an interest shedding good light on the wolf) say that only 75% of the actual wolf predation can be confirmed wolf. Other experts say it could be under 50% can be confirmed. Your last comment on wolves staying “largely within reintroduction region” is funny. Now that the Northern Yellowstone herd has dropped from 19000 to 5000, I’m sure the wolves are sticking around and eating the new aspen growth that has been generated by the lack of elk.

  • I_Dont_know,_only_speculate

    “Human management of species screws things up,” or that is what many of the pro-wolf introduction contributors(pwic) have more or less said. I have a hard time seeing where you pwic’s are coming from with this statement. If the wolves were no longer inhabiting Yellowstone in the 1920’s who are we to put them back 70 years later. Is that not human management? Outside of the ramblings of an ecologist, do really have any evidence that reintroducing wolves will increase the number of aspen or willows? They are truly majestic creatures, and we should not have driven them out of the park in the first place, none the less we are only as the ecologist said, doing an experiment. In all our infinite wisdom we think we can simply introduce them to “bring balance?” I guess it’s too late for any of that. If a wolf is in the park I have no problem letting it be, but I ever felt that they threatened my cattle (of which none I currently own) I really would have no problem shooting it. In fact it would make a fine trophy.

  • Steven Boyett

    Reading most of these pro-hunting, anti-wolf, let’s-favor-the-ranchers as if somehow that maintains a natural balance (as opposed to the artificial one maintained by humans in order to feed humans) at a great deal of ecological asymmetry, emotional, anecdotal, and utterly ignorant diatribes, it’s pretty clear to me that the value of intelligence as a survival tool is greatly exaggerated. You’d shoot the wolves because they supposedly harm (which they insignificantly do, by the way) a food crop that isn’t in the area naturally. You’d shoot the wolves because they reduce herd populations (which isn’t true; they weed out the culls), the most demonstrable harm of which is that it gives herd hunters less to shoot at.

    The hell with all of you.

  • bystander

    Steven Boyett wins.

  • thewholepicture

    Why is there a coyote pictured with the kill right under the title Reintroduction of the Wolves? How do we feed all these people? We’re doomed and to hell with you Mr. Boyett!

  • Antil Tree Hugger

    Werid Steven Boyett sounds like hes from california, and has never been to Yellowstone in his life. “they weed out the culls”? look up wolf kills on you tube they kill for the fun of it half of the time. They introduced a much larger grey wolf than was native to the Rocky Mountains. That in which is taking a Huge toll out of not only our elk and deer herds, but the Ranchers sheep and cattle herds. But its ok they only cull out the weak sheep, and cattle right Mr. Boyett?

  • Ryan

    You are aware that the picture at the beginning of the article is of a coyote and not a wolf?

    Most people couldn’t identify a wolf over a coyote to begin with. You guys just proved the fact.

  • person

    aloha homie

  • persona

    goodbye hommie G

  • Christelle

    we we we so excited, we so excited, we gonna have some fun today, tommorow is saturday and sunday comes afterwards…..I dont want this weekend to end!!!! Its Friday ,Friday, gotta get down on Friday!

  • person=)


  • persona

    No its over!!!

  • person=0


  • Christelle

    Hey, its all right! U have me Bella

  • person=0

    dont leave me alone=(

  • Enyaface

    Yeah that’s coyote in the picture somebody screwed up there……..Wow the comments posted are an unbelievably testosterone based pissing contest. You know everyone has a right to their own opinion. That’s what makes us unique as humans. The name calling is so unnecessary. We can agree to disagree and still have respect for one another. This issue will never be resolved, there are two sides: for and against. I am open to hear the pros and cons but only when the facts are presented. I try to read every article I can from the side of the environmentalist, biologist, activist, cattle/sheep rancher and government agency. So much information is out there that it’s mind boggling.
    But bottom line the wolf issue needs to be based on the science not politics.

  • Rachelle

    to J. Igo: I read Teddy Roosevelt’s book The Wilderness Hunter. There nothing in there that even suggests he would have ’shot all the wolves’… if he could. He was equal-opportunity HUNTER who also killed cougars, coyotes and anything else that he could. Does that mean we should exterminate those species as well? One man’s penchant for killing doesn’t and shouldn’t define the environmental policies of today. There are over 8 BILLION PEOPLE in the world, it time we all start learning how to share space and resources. Selfishness will spell disaster for us all. Wolves play a vital part of the eco-system and … I might add.. we there long before you & I set foot in THEIR land. The people who oppose a wolf presence in the wildlands are selfish despicable people who look out only for themselves.

  • Wolf

    Do you guys relize how stupid your sounding?!?! Has anyone considered that the gray wolf and the elk have lived together since the end of the ice age without ever going extinct, but since Eouropeans arrived many animals HAVE gone extinct. How about the sea mink? The caralina parekeet? The eastern couger? The labrador duck? What happened to them? Did the wolf kill them? NO! Humens did! Why? Becouse humans are the only animal that do not relize you can’t just take anything you want from nature without it disappering! Wolves relize this and don’t take take take from the envirment, disbite what all you morons think. Please stop making arguments for thing that you no nothing about and stop being so ignerant.

  • indonesian

    well who would want a wolf in their backyard… i guess no one…

    but its human who trespassed their backyard in the 20’s, and kill them out of prejudice
    yes human…

    well who (wolf) would want a human in their backyard… i guess no one..

    and i hate sport killing, if there isn’t any of it, i might still find tiger in the wild at least once in my lifetime…
    but sadly exterminated for fun by the colonials…

  • farmer1

    humans could have the same effect on elk by hunting them as wolves do, so why dont we just take care of it ourselves so the ecosystem could be protected and wolves wouldnt be introduced to areas that they can migrate from and hurt peoples property and complety destroy the smaller deer and elk popultions of the surrounding areas like where i live

  • Big Luigi

    “THEIR land.” Rachelle, When did wild animals, wolves included, get property rights? Can’t build that hospital ’cause the ground squirrels own that land. What a ridiculous idea. Rachelle where are you living? Probably some pissed off ants over the construction on their property! get a life.

  • shakira wannabe

    i think wolves are amazing. the bond between them and nature was broken, and it needs to be fixed. i am doin this for a science debate, and i like the comments and arguments i have read

  • wolf lover


  • jadebob

    poor wolves :(

  • Dog and wolf lover

    I love wolves and if we don’t let them live they will not be able to see the world to see daylight AGAIN

  • The Wolf Savior

    Many wolves have died by mans hands, for fur, for coats, meat, and even for sport. But wolves are just humans as canines. They are trying to reproduce, and hunt, so they can survive. They’re are more humans on this planet, than there were ever wolves. I ask you this, you hunters and poachers… WHY would you hunt them? WHY would you poach them? And WHY would you say such a thing, as to make them go extinct? Answer me… WHY?

  • Wolf lover

    Wolves played a major role in the ecosystem. If you can’t see what has happened, then you really are a moron. I like the previous comments and arguments. The ecosystem needs balance.

  • Blaidd

    Well we can’t exactly have it as was in the “wild” or back before we humans”invaded” their terroritory. I do however agree we should make a FAIR comprimise and keep the wolves somehow. But hey! Who the heck cares what I think.

Produced by THIRTEEN    ©2014 THIRTEEN Productions LLC. All rights reserved.

PBS is a 501(c)(3) not-for-profit organization.