Arctic grazers secretly shape plant growth and survival

We often hear about the insidious creep of climate change and the warming that’s altering landscapes around the world. Well, the Arctic and its plants aren’t immune to this silent invasion.

New evidence suggests that it’s not just the temperature change we should be monitoring, but also our hoofed friends out on the tundra. Arctic greening, as it is often called, might be more about caribou and muskoxen than we ever realized.

Greening of the Arctic landscape

Research released from the University of California, Davis (UC Davis) indicates that the large grazers of the Arctic landscape – the caribou and muskoxen – have a direct effect on the timing and abundance of Arctic plants.

This correlation reveals significant implications for the overall Arctic ecosystem.

The findings were recently detailed in a study published in the journal PNAS Nexus and illuminate the vital role that these large herbivores play in our understanding of the Arctic ecosystem.

The focus of the narrative so far has been climate change and the increasing temperatures, but there seems to be more to it than that.

Plants emerging in the Arctic

To fully appreciate the impact of this discovery, it’s essential that we first understand phenology- the study of timing and patterns in nature.

It’s what alerts us when birds are migrating, or when a plant first bursts to life or bursts into bloom. Within the context of a rapidly warming Arctic, understanding these patterns becomes critical.

“Caribou and muskoxen play a key role in how soon plants emerge and this translates to how abundant they become,” said lead author Eric Post, a professor and arctic ecologist in the UC Davis Department of Wildlife, Fish and Conservation Biology.

“This is an important, and overlooked, factor we need to consider as we seek to more fully understand climate change impacts on tundra vegetation in the Arctic.”

Herbivores and plant growth

The research that led to these insights was conducted over a period of 22 years near Kangerlussuaq, Greenland. Here, Post and his team designed an exclusion experiment to understand the effect of herbivores on the timing of plant growth and abundance.

The researchers compared the timing of spring green-up of nine plant species with and without the grazing animals, from 2009 to 2017.

The overall conclusion was that plants where caribou or muskoxen were present underwent earlier green-up and enjoyed greater abundance later into the growing season.

However, not all plants responded equally to the grazing. While about two-thirds of plants greened up earlier, and three-quarters thrived more effectively later in the season with grazing animals present, some species such as dwarf birch and harebell emerged later when grazers were present.

Impact of herbivore grazing

While it’s still unclear why Arctic plants respond this way to the presence of grazers, what is clear is that there is a connection.

“We’re used to thinking of the timing of plant availability as impacting the productivity of grazing animals, but not the reverse,” Post said. “The absence or presence of herbivores can also impact the timing of plant growth and their productivity.”

This understanding becomes increasingly important in light of the current decline of many caribou populations in the Arctic. According to the IUCN Red List, migratory tundra caribou are now considered vulnerable, having lost more than half of their total abundance since the 1990s.

Planting trees in the Arctic

In a related study, Post suggested that supporting sustainable populations of herbivores in the Arctic could be a more effective nature-based solution to climate change in the region than planting trees there. The findings of the PNAS Nexus study lend credence to this suggestion.

We now have a better understanding of the crucial role our hoofed friends play in the Arctic ecosystem, but it is clear that more research is needed.

The challenge is enormous, yet with every bit of new knowledge, we get one step closer to a comprehensive understanding of the Arctic ecosystem and how we can best protect it against the backdrop of climate change.

The study is published in the journal PNAS Nexus.

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