Large herbivores slow climate impacts on tundra, study says

Diversity in tundra vegetation has declined in recent years with rising temperatures and shrinking sea ice, according to a new study conducted in southwestern Greenland.

But large herbivores such as caribou and muskox slow this loss of diversity, the same study found, suggesting that efforts to conserve or reintroduce large herbivores, like rewilding, may help mitigate climate impacts.

Rapid warming is driving massive changes in the Arctic, including thawing permafrost, dwindling sea ice and the encroachment of shrubs into the tundra.

Some scientists have suggested that restoring populations of wild animals to promote healthy food webs and ecosystems, known as trophic rewilding, might help lessen the negative impacts of warming.

Most famously (and controversially), the concept is being put to the test in Siberia’s Pleistocene Park, a 14,000-hectare reserve that scientists are trying to repopulate with millions of large herbivores to recreate an ecosystem that dominated in the time of the woolly mammoth. The idea is that, by suppressing shrubs and trampling snow, the animals may help preserve permafrost, averting the release of carbon stored in the frozen ground.

Large herbivores are known to eat some types of vegetation more than others, according to Jeffrey Kerby, an ecologist and postdoctoral fellow at Aarhus University in Denmark, who co-authored the new study.

As a result, they can limit the expansion of shrubs, providing space for greater plant diversity, which has been shown to have knock-on effects on permafrost thaw and the carbon cycle, he said.

“Decades of scientific research demonstrate how important herbivores can be to ecosystem function and resilience,” Kerby told Cabin Radio via email.

He added that few studies have examined how these processes play out in a rapidly changing Arctic, however.

The new study, which appeared last month in the journal Science, is one of the first to explore these dynamics by combining long-term experimentation with background changes in climate and wildlife, Kerby said.

Halving the rate of diversity loss

To examine how warming and herbivores interact to affect tundra vegetation, the research team began an experiment in 2002.

They set up six 800-square-metre areas near Kangerlussuaq, Greenland. Three of these areas were fenced to keep muskox and caribou out.

Every summer for 15 years, the team assessed the number of plants, fungi and lichen on plots within each area. Half of the plots were artificially warmed with passive warming chambers, which act like little greenhouses.

Between 2002 and 2017, the diversity of tundra vegetation declined on all the plots, the team reported.

Diminishing diversity is tied to rising temperatures during the growing season and the loss of sea ice, they found. Their analysis also revealed that diversity loss was largely explained by increasing shrubs.

Foraging by muskox and caribou had a substantial impact on the diversity of vegetation, however. Diversity declined at nearly twice the rate on plots that were fenced compared to those that weren’t, the researchers reported.

These findings suggest that herbivores can help curtail biodiversity loss associated with climate change, Christian John, a postdoctoral researcher at the University of California, Santa Barbara, told Cabin Radio via email. John was involved in the study while working in Eric Post’s lab at the University of California, Davis.

In addition, the team found that caribou and muskox had differing effects on tundra diversity, and that vegetation diversity was more strongly linked to herbivore diversity than either animal’s abundance.

According to John, this may be explained by the fact that the two species eat different plants at different times of the year, resulting in a variety of impacts on vegetation.

Overall, the findings speak to the role that thriving large herbivore populations can play in maintaining tundra diversity under climate change, said Jens-Christian Svenning, professor of ecology at Aarhus University, who provided comments on the manuscript but was not involved in the work.

“It fits the expectation, but it’s nice to see it,” he said, adding that the study may be the first to quantify the effects of climate and herbivores on tundra vegetation.

Given that diversity declined across all plots, Svenning said the research also speaks to the need to limit warming as much as possible.

While Svenning thinks the study is solid, he said one limitation is that the research was conducted within small areas, which may not be subject to all the same ecological dynamics as the larger landscape.

Kerby also pointed out that the findings are local to western Greenland. At the moment, he said, it’s difficult to generalize the results to other areas with different ecological contexts, such as the Northwest Territories. He also noted that management decisions have to balance ecological, societal, ethical and cultural factors.

Nonetheless, Kerby thinks the results encourage further research on the topic. He said studies elsewhere in the Arctic could shed light on how similar dynamics play out in other contexts.