Boosting beaver populations could have toxic consequences

 

 

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CLIFFORD ADAMCHAK'S BOAT WITH SAMPLING EQUIPMENT IN A BEAVER POND IN CRESTED BUTTE, COLORADO. 

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CREDIT: CLIFFORD ADAMCHAK/CU BOULDER

Beavers are influential animals in ecosystems. These dam-building, tree-chewing rodents change streamflow with their wooden barriers and create rich wetland habitats by diverting water into soils near rivers. They help conserve water and improve biodiversity. 

But a preliminary study by CU Boulder researchers suggests that beaver activities in the Western U.S. may exacerbate the spread of mercury-containing toxins in rivers and the surrounding habitats. Clifford Adamchak, a Ph.D. student in the Department of Ecology and Evolutionary Biology presented the team’s findings Tuesday at the 2023 meeting of the American Geophysical Union in San Francisco.

“In a world where beavers are increasingly being seen as an effective means to achieve various conservation and restoration goals, there is a possibility that we would see an abnormally large flush of methylmercury if we were to reintroduce beavers in the Western U.S. on a larger scale,” said Adamchak.  “So it is important to better understand the impacts of their activities.”   

Beavers were once ubiquitous in North American streams before Europeans arrived in the region. The animal’s population then plummeted because of hunting and habitat loss. 

Research has shown that beavers change the environment significantly, especially over longer timescales, and can provide various environmental benefits. By building dams and trapping water in their ponds, they help to replenish groundwater supplies and maintain wetland habitats for other species. Beaver ponds also help cool the water and mitigate the spread of wildfires, some increasingly significant benefits as climate change heats up the planet and intensifies wildfires in the Western U.S. As a result, several states, including California, Colorado and Oregon are exploring the idea of releasing more beavers to boost populations.

But beaver ponds, because they lack oxygen, are a hot spot for bacteria that can generate mercury-containing neurotoxins. 

“A stream that flows smoothly with nothing stopping it would have very different biological chemical and geological processes than a stream that has cascading beaver dams and ponds,” said Adamchak. “Beaver activities also impact the surrounding landscape, because the animals forage for woody vegetation on land.” 

Human activities, including coal burning and mining, emit mercury into the atmosphere. The mineral then gets into lakes and streams through rain and snow. In water, chemical reactions and certain bacteria transform the mineral into methylmercury, a toxic organic compound that can build up in organisms and travel down the food chain. For example, when a bear eats a fish containing methylmercury, the neurotoxin will accumulate in the bear’s body. Studies have shown consuming large amounts of methylmercury-containing food can lead to mercury poisoning and nervous system damage in humans. 

While atmospheric mercury levels in the Eastern U.S. have decreased over the years because of emission reduction efforts, the levels in the Western U.S., have remained constant or even slightly elevated. 

Adamchak and the team set off to investigate whether increased beaver activities—partly due to reintroduction efforts—have led to a rise in methylmercury levels in the Western U.S. water. 

Over the past summer, Adamchak visited several beaver ponds in California and Colorado, taking more than 300 samples of water and sediment from the ponds and their surrounding environment. He found that the methylmercury levels in the water of beaver ponds were very low, whereas the levels in the sediment— the soil and sand at the bottom and around the ponds—were very high. This suggests that the toxins might be accumulating in the sediment, rather than the water. 

In addition, Adamchak found that the sediment around the ponds, where water periodically submerges, had the highest methylmercury levels. This implies that beavers could spread the mercury-containing neurotoxin in the surrounding landscape. 

The research is still in its early stages, and Adamchak said it’s unclear to what degree methylmercury can affect the wetland ecosystem as a result of beaver activities. But researchers are concerned that as beavers move around the river corridor across their lifespans and abandon old ponds, more vegetation may grow in areas with high methylmercury concentrations in the soil and get passed on to organisms that feed on them.  

Fortunately, previous studies have shown beaver ponds tend to have higher methylmercury concentrations when they are new, and the levels decrease significantly with age. “That suggests beavers probably don’t have overwhelmingly negative effects on the ecosystem. But at this point it’s very hard to say if more beaver activities are good or bad in terms of mercury levels,” Adamchak said.

Adamchak planned to revisit these ponds next year to collect more data. He will also investigate if the age of the ponds or seasons influence the methylmercury levels in the ponds.
 

The return of the grey wolf (Canis lupus) to Germany,

The return of the grey wolf (Canis lupus) to Germany, which began 23 years ago in the region of Lusatia in Eastern Germany, is a process of great ecological and social significance. Therefore, a precise understanding of the recolonisation of the original habitat by the grey wolf and a reliable prediction of its future potential distribution are highly valuable. A detailed comparison of different approaches to spatial modelling using 20 years of distribution data now unravelled the complexity of the recolonisation process. A team led by scientists from the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) shows in a paper in the scientific journal Diversity and Distributions that grey wolf habitat selection changed from the early (when they cherry-pick the finest locations) to late phases of recolonisation (when they are much less selective) in a particular area. These results are a refinement of the team’s earlier habitat modelling from 2020, originally published by the Federal Agency for Nature Conservation.

Grey wolves prefer habitats with plenty of cover at a substantial distance from people, their settlements and roads. These preferences were demonstrated during their return to Germany in the 21st century, when they recolonised the habitat from which they had been extinguished 200 years earlier. Knowledge of such habitat requirements and associated preferences also allows predicting the further expansion of their current range in Germany in the future. In 2020, the Federal Agency for Nature Conservation (BfN), in collaboration with a scientific team from the Department of Ecological Dynamics at the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW), published a study on modelling suitable habitats.  In this study, the team calculated that there could potentially be space for around 700 to 1,400 wolf territories in Germany's natural areas. The scientists have now taken a closer look and tested a variety of approaches to spatio-temporal modelling with regard to different phases of recolonisation.

“There is reason to believe that the recolonisation of Germany by the grey wolf is not a so-called stationary process, but is characterised by changing framework conditions”, explains Prof Stephanie Kramer-Schadt, Head of the Department of Ecological Dynamics at the Leibniz-IZW. “Stationary processes in this case would mean that the wolves find the same or very similar environmental conditions in the regions into which they newly enter – and that they respond to the environmental conditions in the same way during all phases of the process.” Both assumptions appeared to be doubtful in the case of the recolonisation of Germany by the grey wolf. On the one hand, eastern Germany and the Rhine-Ruhr area in the west, for example, considerably differ in terms of the density of human infrastructure. On the other hand, wolves may show different or varying degrees of habitat preferences depending on whether they move in during the early, first phase or during the late, saturation phase of recolonisation.

“These questions are highly relevant for the quality of the predictions”, says first author Dr Aimara Planillo, a scientist at Kramer-Schadt's department at the IZW. “If models are developed on the basis of the specific environmental conditions of a particular region, they could underestimate the suitability of another, very different region to which such a model might be applied. At the same time, models created with data from early recolonisation phases may underestimate the suitability of habitats during the late phases – because the wolves during the early phase have a free choice to cherry-pick particular places and habitats and thus appear to be considerably more selective than they will be during the later phases. The reverse is also true: data from late recolonisation phases might suggest that wolves appear to be less selective, which is why the selectivity of their choice and use of habitats in newly colonised areas would probably be underestimated.”

This investigation was conducted by a team led by Dr Planillo and Prof Kramer-Schadt, in collaboration with scientists from LUPUS – the German Institute for Wolf Monitoring and Research –, the Eberswalde University for Sustainable Development, the Technical Universities of Dresden and Berlin, the Humboldt University Berlin, the Federal Agency for Nature Conservation and the University of Veterinary Medicine Vienna. They tested a variety of modern modelling methods and algorithms with data from more than 20 years of wolf monitoring in Germany with particular attention to the potential pitfalls arising from the actual dynamics of the recolonization process. They developed the models on the basis of a combination of radio telemetry and observation data and tested how well they could predict subsequent phases of the colonisation process. “The new models confirmed our previous work in two ways”, conclude Planillo and Kramer-Schadt. “On the one hand, our projections from 2020 were proven to be largely accurate. Secondly, the sometimes significant differences to model forecasts of the various spatial phases of the process show that it is indeed non-stationary”, say the authors. “When recolonising an area, wolves always secure the best habitats first. It therefore appears that they are considerably more sensitive to environmental variables. Neighbouring second class sites are colonised just as reliably in later phases, as we were able to demonstrate in many regions of eastern Germany.” The team was thus able to validate their predictions and refine them in a more differentiated manner. “Spatio-temporal projections of habitats of expanding species should be carried out with great caution”, they conclude.

The most important factors for habitats to be suitable for wolves are close proximity to forests or cover-rich areas and a large distance from roads. The best habitats for wolves are found in the north and northeast as well as in the south of Germany, whereas habitats of lower quality tend to be found in the west. In the south of Bavaria and in some forest areas of central Germany (in the Harz Mountains as well as in the Spessart, Odenwald and Rhön), larger habitats of high quality are still unoccupied by wolves at the time the team ran the analysis. It is likely that the first wolves to arrive there will first settle in prime locations – which by now has already happened according to the most recent data – and colonise medium-quality locations over time. “With regards to our latest modelling and similar experiences from other European countries, where habitats of lower quality are also used permanently when wolf densities are high, previous habitat modelling tends to be too conservative”, says Kramer-Schadt. “However, they provide a good spatial forecast for the initial colonisation of new habitats.”

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JOURNAL

Diversity and Distributions

DOI

10.1111/ddi.13789 

Wolves hunting and killing sea otters and harbor seals on Alaska’s Katmai coast

Peer-Reviewed Publication

OREGON STATE UNIVERSITY

 

IMAGE: 

WOLF WITH A SEA OTTER ON ALASKA'S KATMAI COAST.

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CREDIT: KELSEY GRIFFIN

CORVALLIS, Ore. – Firsthand observations of a wolf hunting and killing a harbor seal and a group of wolves hunting and consuming a sea otter on Alaska’s Katmai coast have led scientists to reconsider assumptions about wolf hunting behavior.

Wolves have previously been observed consuming sea otter carcasses, but how they obtain these and the frequency of scavenging versus hunting marine prey is largely unknown. Scientists at Oregon State University, the National Park Service and Alaska Department of Fish and Game are beginning to change that with a paper just published in Ecology.

In the paper, they describe several incidents they observed involving wolves and marine mammals in Katmai National Park that they believe haven’t been previously documented:

• In 2016 the researchers witnessed a male wolf hunt and kill a harbor seal. The wolf was positioned near the mouth of a creek when it charged into the water, grabbing the tail of the harbor seal. The wolf continued to tear into the flesh of the seal’s tail and after an approximate 30-minute struggle, the seal appeared to tire, straining to lift its head above water. The wolf dragged the seal onto the exposed sandbar and began to tear into the existing wound and consume the tail.
• On three separate days in 2016, 2018 and 2019 the scientists and others observed wolves carrying sea otter carcasses.
• In 2021, the researchers watched three wolves hunt and eat an adult sea otter on an island during a low tide. They watched the wolves travel to the island, then lost sight of them for about one minute and then saw them reappear carrying a limp sea otter. They fed on the carcass for about 60 minutes. Once the wolves left, the researchers examined the kill site and found an area of concentrated blood where the sea otter was likely killed. The presence of blood indicates the sea otter had been alive when ambushed by the wolves, as opposed to being scavenged, the researchers note. 

“This is really exciting documentation of behaviors we believe have never been directly observed by scientists,” said Ellen Dymit, a doctoral student at Oregon State. “It kind of forces us to reconsider the assumptions that underlie a lot of our management decisions and modeling around wolf populations and populations of their prey, which often assume that wolves depend on ungulates, like moose and elk.”

The research project originated in 2016 when Kelsey Griffin, a National Park Service biologist, and some of her colleagues stopped for lunch on the beach during a day of conducting marine debris and bird mortality surveys at Katmai National Park.

“Seemingly out of nowhere, we are sitting there, we just see this white wolf carrying an otter just trotting by,” Griffin said. “What? I was just blown away. I have never seen anything like that before.

“Then I was asking my co-workers: ‘Has anyone seen this before? Do wolves often eat sea otters?’ I was just asking a bunch of questions about the wolves and it just seemed like there was not a whole lot of information about them. That was the initial observation. I just got lucky. Wolves on the Katmai coast have never been studied and our research highlights the unique role wolves play in nearshore ecosystems in Alaska” 

Griffin connected with Gretchen Roffler, a biologist with Alaska Department of Fish and Game, who introduced Griffin to Taal Levi, a professor at Oregon State and Dymit’s advisor.

The project builds on work by Roffler, Levi and others on wolves and sea otters on Pleasant Island, an island landscape adjacent to Glacier Bay about 40 miles west of Juneau and hundreds of miles east of Katmai across the Gulf of Alaska.

In a paper published earlier this year, they found wolves on Pleasant Island caused a deer population to plummet and switched to primarily eating sea otters in just a few years. They believe this is the first case of sea otters becoming the primary food source for a land-based predator.

Future papers will include analysis of wolves and sea otters from Lake Clark National Park, Glacier Bay National Park and Kenai Fjords National Park, in addition to Katmai. The research team plans to look at how sea otter density impacts the diets of wolves and variations of wolf diet on a pack level versus and individual level.

Study reveals the most important considerations for grizzly bear conservation

 

Humans negatively impact the health of grizzly bear populations through top-down influences like direct mortality associated with forestry roads (from conflict or illegal killings) and displacement from high quality habitats, and through bottom-up influences like reducing availability of food resources. Research published in Wildlife Monographs reveals the relationship between these forces, informing a strategic conservation program.

Investigators radio-collared and followed numerous grizzly bears over multiple years in southeastern British Columbia. They found an interesting interplay between the most important bottom-up factor, huckleberry patches, and mortality risk from forestry roads (road density and the amount of secure habitat away from roads). Top-down influences were not only associated with mortality risk, but they limited contributions of critical food resources, reducing female grizzly fitness and density, in essence having a similar effect as habitat loss. This doubly negative effect likely contributes to the ubiquitous detriment that high forestry road density confers to grizzly bear populations in western North America.

The findings highlight the importance of considering both bottom-up and top-down influences affecting wildlife populations. “The securing of important food resources to make them accessible to bears is accomplished through some degree of restriction of human access,” said lead author Michael Proctor, PhD, of Birchdale Ecological Ltd. “Our results suggest that benefits of critical bear foods are not satisfactorily realized unless human access to nearby roads is reduced.”

URL upon publication: https://onlinelibrary.wiley.com/doi/10.1002/wmon.1078

Broken by bison, aspen saplings having a tough time in northern Yellowstone

 

 

IMAGE: A BISON BULL BREAKING ASPEN SAPLINGS AND EATING ASPEN IN THE LAMAR VALLEY IN NORTHERN YELLOWSTONE NATIONAL PARK. OVERSTORY ASPEN TREES HAVE DIED AND FALLEN TO THE GROUND AS SEEN IN THE PHOTO, AND TALL SAPLINGS HAVE GROWN SINCE THE EARLY 2000S. BROKEN STEMS OF ASPEN SAPLINGS ARE VISIBLE IN THE FOREGROUND, AND SILHOUETTED AGAINST THE BODY OF THE BISON (PHOTO BY LUKE PAINTER, 2020). THESE BROKEN STUMPS SHOW THAT SAPLINGS RECENTLY COVERED MUCH MORE OF THE STAND AREA, BUT THEY HAVE BEEN BROKEN AND KILLED BY BISON, AND BISON CONTINUE TO BREAK THE REMAINING SAPLINGS. THESE SAPLINGS WERE TALLER THAN 4 METERS, NO LONGER VULNERABLE TO SUPPRESSION BY ELK OR BISON EATING THEIR TOP BRANCHES, BUT BISON BROKE THEM OFF AT A LOW HEIGHT. view more 

CREDIT: A BISON BULL BREAKING ASPEN SAPLINGS AND EATING ASPEN IN THE LAMAR VALLEY IN NORTHERN YELLOWSTONE NATIONAL PARK. OVERSTORY ASPEN TREES HAVE DIED AND FALLEN TO THE GROUND AS SEEN IN THE PHOTO, AND TALL SAPLINGS HAVE GROWN SINCE THE EARLY 2000S. BROKEN STEMS OF ASPEN SAPLINGS ARE VISIBLE IN THE FOREGROUND, AND SILHOUETTED AGAINST THE BODY OF THE BISON (PHOTO BY LUKE PAINTER, 2020). THESE BROKEN STUMPS SHOW THAT SAPLINGS RECENTLY COVERED MUCH MORE OF THE STAND AREA, BUT THEY HAVE BEEN BROKEN AND KILLED BY BISON, AND BISON CONTINUE TO BREAK THE REMAINING SAPLINGS. THESE SAPLINGS WERE TALLER THAN 4 METERS, NO LONGER VULNERABLE TO SUPPRESSION BY ELK OR BISON EATING THEIR TOP BRANCHES, BUT BISON BROKE THEM OFF AT A LOW HEIGHT.

CORVALLIS, Ore. – In northern Yellowstone National Park, saplings of quaking aspen, an ecologically important tree in the American West, are being broken by a historically large bison herd, affecting the comeback of aspen from decades of over-browsing by elk.

Findings of the research led by Luke Painter of Oregon State University were published today in Ecology and Evolution.

The study comes five years after Painter, who teaches ecology and conservation in the OSU College of Agricultural Sciences, published a paper in Ecosphere showing that wolf reintroduction in Yellowstone had been a catalyst for aspen recovery both outside and inside park boundaries.

“I’ve studied the response of aspen in northern Yellowstone to the reduction in elk after the wolves were brought back and found that during this time, bison increased and have begun to affect aspen,” Painter said. “Now we’re showing strong evidence of a previously unreported behavior of bison bulls breaking aspen saplings.”

The saplings were tall enough to escape most browsing by elk and thus likely to grow into trees, but bison broke them off at a low height, he said. Other saplings were killed when bison scraped off the bark with their horns.

Quaking aspen largely reproduces by root sprouts, a process known as suckering, and stands of aspen are often a single organism connected by the trees’ common root system. Fire stimulates aspen reproduction from both roots and seeds.

For much of the 20th century, Painter said, aspen sprouts were unable to grow into trees because they were eaten by elk during winter. But at the end of the century, when wolves were reintroduced and the numbers of other large predators such as grizzly bears and cougars increased, elk numbers in the northern part of Yellowstone went down, bringing relief to the aspen.

“Some young aspen began growing into saplings – young trees taller than 2 meters – which was an indication they were no longer being consumed by elk and were likely to grow into mature trees,” Painter said. “It was a trophic cascade that changed the Yellowstone ecosystem, creating conditions that could bring it closer to what it was historically, with more aspen, willow and beaver, which depend on these plants. But the tremendous increase in bison over the last two decades has added a new turn to the story.”

Bison have long been known to have strong effects on their environment, Painter said. Among those is removing and suppressing shrubs and trees by eating, trampling and breaking them – and as bison numbers have greatly risen in northern Yellowstone in the last two decades, their effects on plants have also increased.

In places where bison are present in large numbers, like Yellowstone’s iconic Lamar Valley, they are hindering some aspen stands from replacing their dying trees, he said.

The Yellowstone bison herd is divided into central and northern herds, and this study was in the range of the northern herd. The northern herd’s numbers were generally less than 1,000 until 2005 and then increased, for reasons that aren’t fully understood, to about 4,000 during the last decade, Painter said.

Painter and OSU College of Forestry collaborators Robert Beschta and William Ripple examined a random sampling of plots in 87 randomly selected aspen stands, and 18% of saplings had been broken. They may resprout from their base, but the sapling height has been lost and new sprouts are vulnerable to being eaten by bison or other herbivores, the researchers note.

Multiple lines of evidence support attributing the breakage to bison, Painter said.

“Most broken saplings were in areas of high bison density and low elk density, and they were broken in summer when elk wouldn’t have been foraging on them,” he said. “Plus we directly observed bison breaking aspen saplings. The purpose of the behavior doesn’t seem to be about accessing food, and we observed only bulls engaging in this behavior, so it may be related to displays of aggression.”

Painter noted that Yellowstone bison are managed under an agreement with the state of Montana that requires them to remain in or very near the park – those that stray are killed, captured or hazed back into the park, in large part because they can carry bacteria that cause brucellosis, a threat to Montana’s cattle industry.

Elk also carry brucellosis and have passed it to cattle, but the same restrictions are not applied to them. Thus, unlike other wildlife bison are not allowed to disperse to other areas as their numbers and density increase.

The conservation of bison in Yellowstone, whose numbers plummeted nationally from over-hunting in the 1800s, is a big success story, Painter noted – and so is the recovery of aspen and other deciduous woody plants that began when the park’s large predators made their comeback.

“Thus, one important conservation goal is affecting another important conservation goal,” he said. “Researchers are only beginning to understand how these conservation goals have overlapped and affected each other. We reported a piece of this complex puzzle, describing and quantifying one way that bison shape their habitat by suppressing trees.”

The study was supported in part by the National Science Foundation and the Ecosystem Restoration Research Fund of the Oregon State University Foundation.

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JOURNAL

Ecology and Evolution

DOI

10.1002/ece3.10369 

Gray wolf recovery is a success—is that a problem?

 

Peer-Reviewed Publication

AMERICAN INSTITUTE OF BIOLOGICAL SCIENCES

Over the past 30 years, efforts to recover gray wolf populations in the United States have been broadly successful, with many regions now sporting robust populations of the charismatic carnivore. Writing in BioScience, wolf experts David E. Ausband and L. David Mech describe the conservation landscape and also the obstacles that wolves face as their populations expand into their historical ranges.

                "Remarkable wolf conservation success yields remarkable challenges," say the authors, as 6000 wolves now occupy habitat across 11 states. These growing populations now face significant threats as they attempt to colonize human-dominated areas, among them "fragmented habitats and barriers to dispersal, as well as increased encounters with humans, pets, and livestock."

                In response to those concerned about wolves’ potential impacts to prey populations and domestic livestock production, many jurisdictions have ramped up wolf efforts. For instance, in Wisconsin, "the legislature requires a public hunting or trapping season whenever wolves are delisted from the US Fish and Wildlife Service’s (USFWS) list of Endangered species." In contrast, wolves are seen as desirable in other areas, such as Colorado, where voters recently passed a ballot initiative to reintroduce them in the state. The authors caution that such pro-reintroduction initiatives, which may seem initially promising for wolves, could have the unintended consequence of setting precedent for laws barring reintroduction and thus complicate management. An uncertain regulatory regime, say Ausband and Mech, could cause major fluctuations in wolf populations, with dire consequences for conservation efforts.

                The answer to this quandary, the authors suggest, is thoughtful management that carefully considers the needs of diverse stakeholders: "Future wolf conservation in the United States will be affected by the ability of managers to predict colonization and dispersal dynamics, to reduce hybridization and disease transmission, to mitigate and deter wolf–livestock conflicts, to harvest wolves sustainably while satisfying diverse stakeholders, to avert a reduction in tolerance for wolves due to a disinterest in nature, and to engage diverse stakeholders in wolf conservation to avoid management by ballot initiative or legislative and judicial decrees." Only through such science-informed management, argue Ausband and Mech, can the present success of wolf conservation be built on in the future.

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David E. Ausband is affiliated with the US Geological Survey’s Idaho Cooperative Fish and Wildlife Research Unit, at the University of Idaho, in Moscow, Idaho, and L. David Mech is affiliated with the US Geological Survey’s Northern Prairie Wildlife Research Center, in Jamestown, North Dakota, and with the University of Minnesota in St. Paul.

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JOURNAL

BioScience

DOI

10.1093/biosci/biad053 

Moose can play a big role in global warming

Peer-Reviewed Publication

NORWEGIAN UNIVERSITY OF SCIENCE AND TECHNOLOGY

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IMAGE: THIS BIG BOY CAN BE RESPONSIBLE FOR HUGE AMOUNTS OF CARBON EMISSIONS, SIMPLY BY EATING YOUNG VEGETATION THAT SPROUTS AFTER A CLEARCUT AND THAT IF LEFT ALONE, WOULD GROW UP AND STORE CARBON. view more 

CREDIT: PHOTO: ENDRE GRÜNER OFSTAD

One of the biggest potential single sources of carbon emissions from wooded parts of Norway has four legs, weighs as much as 400-550 kg and has antlers.

That’s right — moose can reduce carbon storage in clearcut sites equivalent to as much as 60 per cent of the annual fossil fuel carbon emissions from a region, a new study shows.

“Moose are an ecosystem engineer in the forest ecosystem, and strongly impact everything from the species composition and nutrient availability in the forest,” said Gunnar Austrheim, an ecologist at the NTNU University Museum who was one of the study’s co-authors. “A grown animal can eat 50 kilograms of biomass each day during summer.”

That consumption represents roughly 10 per cent of what the Norwegian forest industry itself harvests, he said.

And therein lies the reason why moose can be responsible for such a large additional amount of carbon emissions, said Francesco Cherubini, director of NTNU’s Industrial Ecology (IndEcol) Programme, and co-author of the paper.

Moose influence vegetation growth and more

Moose like to eat young deciduous trees, like birch, rowan and willow. So the young saplings that would normally sprout in the forest after a timber company clearcuts an area never get the chance to grow.

When saplings grow into mature trees, they bind up CO2 in their trunks, leaves and roots. Moose essentially gobble up that possible source of carbon storage.

“It was really a surprise to see how much moose can influence vegetation growth, the carbon cycle and the climate system,” said Xiangping Hu, a researcher at IndEcol and co-author of the study.

Scientists have known that browsing by large animals like moose could be an unaccounted-for source of additional carbon emissions, but there are very few studies with actual numbers to say precisely how much, Hu said.

Filling in the unknowns in climate modelling

Researchers use computer models to try to predict future climate scenarios, based on current and expected emissions of carbon dioxide and other greenhouse gasses.

That’s basically the information we get from the Intergovernmental Panel on Climate Change, or IPCC.

Most recently, the IPCC said humanity is on track to raise the Earth’s average temperate by 2.4 C, which is quite a bit higher than the 1.5 C goal that scientists agree we should aim for.

The challenge is that climate modelling is imperfect. It’s getting better, but there are areas where researchers simply don’t have enough information yet.

They know there are factors that should be in their climate models, but they simply don’t have enough data to include those factors in a realistic way.

The effects of large animals are one of those factors, Cherubini said.

“One of the biggest unknowns that we have in our understanding of the climate system and the carbon cycle is potentially the effect of larger animals, and how they interact with carbon storage in vegetation,” he said.

“This study gave us a great opportunity to quantify this effect,” he said. “We have some numbers that we can relate to the regional carbon budget, and which actually show the importance of large animals like the moose.”

Good for the forest industry, maybe not so good for the climate

The researchers were able to discover the importance of moose on climate as a result of a different, but related study that began in 2008.

At that time, researchers at NTNU and NINA ( the Norwegian Institute for Nature Research) wanted to know what effect moose had on the forest ecosystem after an area had been clearcut. They looked at vegetation regrowth, species diversity and soil nutrient dynamics. Clearcutting is a process where essentially all trees are harvested from an area.

So the researchers set up 47 paired plots in areas that had been clearcut in the previous three years. One of the plot pairs was fenced off so that moose couldn’t browse on the tasty new saplings that naturally spring up after an area has been cut.

The second, nearby plot pair, was open to moose but marked so that researchers could go back year after year to see what happened to tree regrowth and other ecosystem metrics as moose feasted on the vegetation.

What they found was that moose were doing Norway’s forest industry a huge favour, Cherubini said.

“So the forest industry prefers coniferous species, they prefer pine, they prefer spruce. So moose to some extent, are helping them because they’re reducing competition,” by thinning out the deciduous trees and partly pine, leaving the spruce, he said.

Win for the climate, biodiversity and forest management?

The researchers realized they could revisit the plots to study effects on carbon emissions by calculating the differences in aboveground carbon content between browsed and unbrowsed plots.

That enabled them to see potential additional carbon emissions that moose caused by eating deciduous saplings.

Birch and other highly selected deciduous species such as rowan, willow and aspen may also help contribute to the biodiversity of an area, Austrheim said, which moose also affect by removing those species.

So while moose were relatively good for the forest industry, they aren’t necessarily that good for the climate or biodiversity.

But there’s good news.

Finding a balance

Almost all of Norway’s productive forests are harvested using clearcuts.

“These clearcuts provide a lot of good food for moose,” Austrheim said.  Moose are also very heavily managed in Norway, he said.

“We don’t only regulate the amount of animals, we very carefully regulate the proportion of females, males and calves. So there’s a  stronger management for moose than for most livestock in Norway,” he said.

That means it should be possible to find the right balance between moose numbers and how forested lands are managed. That, in turn, could make it possible to limit excess carbon emissions, boost biodiversity and increase forest productivity, the researchers said.

“I think as we get more of an understanding of how all these different things are interrelated, land managers could come up with an optimal plan,” Cherubini said. “That could be a much needed win-win solution for climate, for biodiversity and for timber value.”

Reference: Salisbury, J., Hu, X., Speed, J. D. M., Iordan, C. M., Austrheim, G., & Cherubini, F. (2023). Net climate effects of moose browsing in early successional boreal forests by integrating carbon and albedo dynamics. Journal of Geophysical Research: Biogeosciences, 128, e2022JG007279. https://doi.org/10.1029/2022JG007279

 

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JOURNAL

Journal of Geophysical Research Biogeosciences

DOI

10.1029/2022JG007279 

New study identifies key success factors for large carnivore rewilding efforts

 

• The findings are based on data from almost 300 relocations of large carnivores, from wolves to bears;
• Relocations showed a high overall success rate, and a significant increase over recent years;
• Key factors that boosted survival of relocated animals included using younger animals, using wild-born animals, and including an acclimatisation period;
• Low mating success of relocated animals indicates ongoing challenges for rewilding programmes.

New research published today has identified the top factors that determine whether efforts to relocate large carnivores to different areas are successful or not. The findings could support global rewilding efforts, from lynx reintroductions in the UK to efforts to restore logged tropical forests.

 As apex predators, large carnivores play crucial roles in ecosystems, however their numbers have plummeted over recent decades. Relocating large carnivores can support their conservation, for instance to reintroduce a species to an area where it has been exterminated, or to reinforce an existing population to increase its viability. But to date, there has been little information about what factors determine whether these (often costly) efforts are successful or not.

The study was carried out by an international team led by researchers at the University of Oxford’s Department of Biology, Wildlife Conservation Research Unit (WildCRU), and School of Geography and the Environment. The group analysed data from almost 300 animal relocations which took place between 2007 and 2021. These spanned 22 countries in five continents, and involved 18 different carnivore species, including bears, hyaenas, big cats, and wild dogs.

Key findings:

• Overall, two thirds (66%) of the relocations were successful (where the animal survived in the wild for over 6 months).
• Success rates for large carnivore relocations have increased significantly since before 2007. For wild-born carnivores, success rates increased from 53% pre-2007 to 70%; and for captive-born animals, success rates doubled from 32% in pre-2007 to 64%.
• The species with the highest success rates included maned wolves, pumas, and ocelots which had a 100% success rate. The species with the lowest success rates (around 50%) were African lions, brown hyenas, cheetahs, Iberian lynx, and wolves.
• Overall, using a ‘soft release’ increased the odds of success by 2.5-fold. This involves acclimatising the animal to the new environment before it is fully released.
• Releasing younger animals (particularly 1 -2 year olds), also increased success rates. This may be because younger animals have greater behavioural plasticity to adapt to new environments, and they are less likely to have developed homing behaviours.
• For animals born in captivity, the success rate decreased by 1.5-fold, compared with animals born in the wild.
• However, just over a third (37%) of the relocated animals were observed to find a mate and/or raise a cub in their new habitat.

Although the fact that most relocated animals survived is encouraging, the authors say that the low mating success shows the ongoing challenges facing rewilding efforts and, crucially, the importance of protecting habitats that already exist.

Lead author Seth Thomas (Department of Biology, University of Oxford) remarked: ‘In the last 15 years we have become more successful at translocating and reintroducing large carnivores. This allows us to be optimistic for the future of rebuilding damaged ecosystems around the globe, but we must remember that it is always more important to protect large carnivore populations where they are now before we lose them. Even as we have grown to be more successful, 34% of individual translocations fail and they cannot be seen as a replacement for immediate conservation action to save these populations.’

In the near future, relocating large carnivores may become increasingly necessary as habitats become altered due to climate change, and if land use changes increase conflict between humans and animals.

In the UK, one of the most nature-deprived countries in the world, there have been calls to reintroduce formerly native apex predators, such as wolves and the Eurasian lynx.

Professor David Macdonald (WildCRU, Department of Biology, University of Oxford), a co-author for the study, said: ‘As the UN decade of ecosystem restoration gets underway, the ecological need and political appetite for relocations of large carnivores has never been greater, and they have the potential to contribute more now than ever before to biodiversity conservation. By scrutinising the most geographically comprehensive sample of relocated large carnivores to date, our study makes plain to conservationists and policy makers the urgency of improving rewilding efforts.’

Professor Alastair Driver, the Director of the charity Rewilding Britain (who were not directly involved in the study) said: ‘This study could not come at a better time here in the UK, with the devolved governments at last consulting positively on the merits of species reintroductions and various groups working hard on the feasibility of reintroducing species such as the European Wildcat and Eurasian Lynx. We still have a long way to go to overcome the misconceptions which dominate societal concerns around sharing our human-dominated landscape with other apex predators, but this report and the successes which it documents, will be hugely valuable in securing a more "grown-up" discussion on the subject. I have no doubt that this will, in turn, lead to well-planned and implemented carnivore reintroductions which only 10 years ago, I would have thought inconceivable in my lifetime.’

Dr. Miha Krofel (University of Ljubljana), a co-author who worked on lynx reintroductions included in the study said: ‘The main reason that allowed us to quantify the higher rate of success is the wider applicability of tracking technology compared to 15 years ago. Nowadays, many practitioners and scientists fit animals with tracking tags for better post-release monitoring of the translocated individuals. This allows us to learn from past releases to improve our interventions in the future.’

Caribou have been using same Arctic calving grounds for 3,000 years

 

IMAGE: ALASKA'S BARREN-GROUND CARIBOU HAVE BEEN USING THE SAME PARTS OF THE ARCTIC NATIONAL WILDLIFE REFUGE TO GIVE BIRTH TO THEIR CALVES FOR AT LEAST 3,000 YEARS, ACCORDING TO RESEARCHERS. view more 

CREDIT: MICHAEL MILLER

Caribou have been using the same Arctic calving grounds for more than 3,000 years, according to a new study by the University of Cincinnati.

Female caribou shed their antlers within days of giving birth, leaving behind a record of their annual travels across Alaska and Canada’s Yukon that persists on the cold tundra for hundreds or even thousands of years. Researchers recovered antlers that have sat undisturbed on the arctic tundra since the Bronze Age.

“To walk around the landscape and pick up something that’s 3,000 years old is truly amazing,” said Joshua Miller, an assistant professor of geosciences at the University of Cincinnati.

He has been leading summer expeditions to the Arctic National Wildlife Refuge since 2010, using rafts to navigate remote rivers to search for caribou antlers exposed on the tundra.

“We think about having to dig down into the soil to find that kind of ecological history, but on the Coastal Plain, the vegetation grows extremely slowly,” Miller said. “Bones dropped by animals that lived dozens or even hundreds of generations in the past can provide really meaningful information.”

The study demonstrates how important the area is for an animal that native Alaskans and Candians still depend on for sustenance, even as energy companies seek to exploit oil and gas resources in this protected area.

The Biden Administration in 2021 suspended drilling leases in the Arctic National Wildlife Refuge, the largest tract of undeveloped wilderness in the United States. 

“We know this region of the Arctic National Wildlife Refuge has been an important area for caribou for millennia,” Miller said. “That should give us pause on how we think about those landscapes.”

The study was published in the journal Frontiers in Ecology and Evolution.

Barren ground caribou undertake nature’s longest overland migration, traveling as far as 800 miles each year to reach their spring calving grounds in the Arctic National Wildlife Refuge and Canada’s Ivvavik National Park. The largest herd in this area, named for the Porcupine River, numbers in the hundreds of thousands of animals.

Scientists think caribou use these areas because they have fewer predators and offer seasonal vegetation near places where they can avoid the worst of the mosquitoes.

“The mosquitoes are horrible,” Miller said. “You get swarmed — literally covered in them. They can do significant damage to a young calf.”

Whatever the reason, the antlers they leave behind provide a physical record of their epic yearly travels that researchers can unlock through isotopic analysis. 

Caribou antlers, like those of elk, deer and moose, are made of fast-growing bone that the animals shed each year and regrow the following year.

“It is amazing to think that the oldest of the antlers found in our study were growing approximately the same time Homer was penning ‘the Iliad’ and ‘the Odyssey,’” study co-author Patrick Druckenmiller said.

He is director of the University of Alaska Museum and professor of the Department of Geology and Geophysics at the University of Alaska Fairbanks. Eric Wald from the U.S. Fish and Wildlife Service also co-authored the study.

The antler surveys in the vast expanse of the Arctic refuge require meticulous logistical planning, Miller said. Small planes deposit researchers and their gear deep in the interior, where they have to be watchful for grizzly and polar bears. They pilot rafts to the Beaufort Sea, conducting a  grid search of suitable caribou habitat identified in advance using aerial photography.

“We search for antlers along old river terraces, walking back and forth, covering every inch of habitat to find those ancient treasures,” Miller said. 

While male caribou antlers span four feet and weigh more than 20 pounds, female caribou antlers are much smaller. The antlers contain nutrients such as phosphorus and calcium that are important to plants and animals.

The dropped antlers create “nutrient sinks,” which could have a profound effect on the area’s vegetation. Miller said the caribou’s migration serves as a nutrient “conveyor belt” that might even draw caribou back to reap the benefits of this fertilizer in a reinforcement loop.

Caribou and other mammals are known to chew on dropped antlers for their valuable minerals. This could be an important dietary supplement for new caribou moms.

“We’d like to know to what degree this conveyor belt influences why caribou are going there in the first place,” Miller said.
The study was supported by the U.S. Fish and Wildlife Service, the National Geographic Society, the National Science Foundation, the Wildlife Society and the UC Office of Research.

Miller said the Arctic is warming faster than other parts of the globe. Parts of the Arctic that were once barren tundra are sprouting new spruce forests.

“We were in Arctic Village this summer, just south of the calving grounds, talking to elders about the changes they have seen,” Miller said. “Where once it was open tundra, large stretches of this barren ground are now full of trees everywhere. What will happen to the barren ground caribou as this habitat gets converted into forest?”

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JOURNAL

Frontiers in Ecology and Evolution

DOI

10.3389/fevo.2022.1059456