Caribou and muskoxen shape the past and future Arctic

In the rapidly warming Arctic, grasslands are shrinking and shrubs are spreading, speeding up permafrost thaw and global climate warming. As JEFF KERBY writes, some researchers wonder if one solution might lie with the tundra’s few remaining giants—caribou and muskoxen—whose grazing and trampling could help hold the line.

I spent my first summer in Greenland 15 years ago camped on a patch of grass overlooking a glacial lake rimmed by rocky ridges. Back then, as a student, I was tracking caribou and muskoxen demographics and noting how plants raced through their growth stages in the short Arctic summer.  

These days, when I return with students of my own, I can still find that campsite. But shrubs have grown to block the lake view, and years of warm, wet summers have turned the firm, grassy ground into a mossy patch that oozes brown water with every footstep. The spot I once knew is gone.

Satellite images over the past 40 years show similar changes across tundra regions of the rapidly warming Arctic. The question many researchers are now asking is: can large herbivores—like caribou and muskoxen—slow or even reverse what is being lost? 

Tundra, the verdant but treeless land north of the boreal forest, has always been shaped by large herbivores. Although only caribou and muskoxen remain today, dozens of species roamed its grasslands during the last ice age. These animals are also central to the human history of the Arctic, sustaining peoples who followed the retreating ice millennia ago and remaining today as pillars of northern cultures and economies.

Nature’s grazing guardians

For the past three decades, my colleagues and I have combined ecological observations and field experiments to study how herbivores are responding as warmer and wetter conditions that alter the timing and amount of plant growth in the tundra of West Greenland. We ask how animals might push back against vegetation change in the landscape—such as through grazing and altering snow and soil conditions.  

These simple questions have complex answers, but the emerging picture is clear: animals at this study site are slowing the shift from grasslands to shrublands—though at their current numbers, they don’t seem to be stopping it. 

When grasslands diminish, populations of caribou and muskoxen often decline, either by moving elsewhere or having fewer surviving offspring. The proliferation of tall shrubs also changes how the tundra functions in several ways. First, shrubs are darker than grasses, so they absorb more heat from the sun and accelerate permafrost thaw. They also trap more snow, which (perhaps counter-intuitively) keeps the ground warmer in winter by insulating it from air that drops below –40 °C. Shallower annual freezes allow microbes living in the Arctic soils to start breaking down the region’s immense stores of organic matter earlier in the summer, giving them more time to release greenhouse gases like carbon dioxide and methane that had been locked away in permafrost.  

All these changes promote a warmer Arctic and reinforce positive climate feedbacks that affect the entire planet. 

What could slow these patterns? Some researchers suggest the answer is simply more large herbivores—caribou and muskoxen, or even the animals that once roamed the north during the last ice ages (the Pleistocene), such as horses and bison. Collectively, the larger and more diverse the population, the more they buffer the area against shrub expansion and the accelerated climate warming this brings. This is because grazing keeps shrubs short and promotes grasses, trampling breaks up snow and compresses the soil so the ground stays colder and drier, and droppings can fertilize grasses—all influences that tip the balance toward grassier landscapes that reflect more sunlight and slow permafrost thaw.

Clues on the tundra 

In the 1960s, muskoxen were introduced to West Greenland, a place they had not lived for dozens of millennia, if ever. Since then, their numbers have grown to more than 10,000, and the animals have become a core component of the local economy and culture. They now coexist with caribou, much as they did 15,000 years ago across broad areas of the European, Asian and North American Arctic. In a time of rapid warming, we’ve found that their greater presence has slowed some of the shrubification under way in West Greenland. But we still don’t know by how much across the region, or where in the landscape their impacts are strongest.

Not everywhere is shrubifying. In West Greenland, when I walk the tundra, I see more caribou and muskoxen in areas that have more grass. Are they causing this? Or are they simply following the shifting landscapes to places where change is slower or more sensitive to herbivores? Or is it both?  

It’s a chicken and egg problem that needs study across larger areas than traditional field projects. New tools—such as satellites, tracking collars and drones—are just now making this feasible. The stakes are high, both for Arctic communities and people far away who may not even know what a muskox is, but stand to benefit from a slowdown in the pace of climate warming. 

Scientific research can raise questions about management choices, but it must also embrace a core truth: northern peoples did not cause the greenhouse gas emissions that are now reshaping their homelands. Any exploration of the role of herbivores in moderating Arctic change must align first with the interests and involvement of the people who live there. There is no other way. 

There is promise here—both in learning how herbivores might slow climate change, and in doing so through approaches led and coordinated by northern communities. Whether large herbivores like caribou are a solution to challenges at this scale is uncertain. But if explored responsibly, it offers a rare chance at a win for the Arctic environment, northern communities and the entire planet.