Field Notes: The Polar Field Services Newsletter

How climate change impacts Alaskan geese migration, plant growth, and ecosystems

An aerial view of the Yukon-Kuskokwim Delta in western Alaska. All photos: Karen Beard

An aerial view of the Yukon-Kuskokwim Delta in western Alaska. All photos: Karen Beard

The Yukon-Kuskokwim Delta in western Alaska is the stage for a three-year experiment to explore the connections between a changing climate, an advancing growing season, migratory geese and the chemical processes that impact the broader ecosystem.

Utah State University professor Karen Beard and a team of scientists and graduate students are beginning a National Science Foundation-supported project to try to answer the question of how the timing of the arrival of migratory geese to the region influences tundra vegetation, as well as carbon and nitrogen cycling in the ecosystem.

Plots set up on grazing lawn in the Yukon-Kuskokwim Delta.  There are exclosure plots and open-top chamber plots. The open-top chamber plots are there to warm up the ground and start the growing season early.

Plots set up on grazing lawn in the Yukon-Kuskokwim Delta. There are exclosure plots and open-top chamber plots. The open-top chamber plots are there to warm up the ground and start the growing season early.

Her project—Asynchrony in the timing of goose-vegetation interactions: implications for biogeochemical cycling in wet sedge tundra—kicks off this month with graduate students traveling to western Alaska to prepare for a summer field season filled with geese, soil sampling and experiments to simulate various herbivore-plant interaction scenarios.

“We are very interested in the arrival time of the geese relative to when the plants start growing. It’s that interaction that we are most interested in,” Beard explained.

The Migration of Thousands of Birds

As warmer temperatures give rise to an earlier growing season in the region, Beard is eager to uncover how the goose-vegetation interaction will impact biogeochemical processes, namely carbon and nitrogen cycling. Beard explained that the geese typically arrive in the Yukon-Kuskokwim Delta in mid-May. And with the arrival of some 500,000 geese in a few weeks, there’s bound to be an impact.

“We have some ideas about what the geese do in these systems—they change it from a landscape perspective. We know they change the vegetation from this sort of thick cover to something that looks like a grazing lawn. They change the chemistry of the plants, making them higher in nitrogen and lower in carbon. They also expose the soil to the atmosphere by reducing the shading and cover,” she said.

Beard has a few running hypotheses that will be put to the test this summer and over the next two field seasons. They are:

  1. If geese arrive when they typically do, relative to the growing season, plant productivity would be higher and ecosystem respiration would stay the same.
  2. If they come later relative to the start of the growing season, the geese might reduce plant productivity in the ecosystem.
Plots setup up on the grazing lawn and the licor chamber that measures CO2 flux.

Plots set up on the grazing lawn and the licor chamber that measures CO2 flux.

Studying an altered growing season

Beard’s team will soon begin a series of experiments to modify the start of the growing season and simulate various arrival times of geese. To mimic an early growing season, they’ll section off small plots of land and place Plexiglas, open-top chambers on the ground to heat the soil and encourage early plant development. The team will also keep twenty geese in captivity for the summer, moving them around the study area to graze under various controlled conditions.

“By doing this highly manipulative experiment, we are simulating scenarios like: what if the growing season starts early and the geese arrive early, or what if they don’t arrive early? We have all these different factorial combinations that we can test,” Beard said.

Metrics

“We are also measuring things like plant growth rate, changes in plant chemistry, nitrogen mineralization rates in soil and carbon flux. These measurements will help us model the carbon and nitrogen cycling in the study areas to get an idea about how carbon and nitrogen cycles will change if the interaction between the growing season and the timing of the geese arrival changes,” she explained.

Implications

The Yukon-Kuskokwim Delta is the perfect setting for Beard’s experiments. Scientists have long studied the biogeochemical processes of the region, giving Beard and her team a foundation of data on which to build. The delta is also a massive ecosystem with a wildlife reserve the size of Oregon, so the implications of what Beard’s study reveals will apply to a vast area.

With climate change rapidly affecting species and habitats, Beard’s work is timely and delves deeper into how a changing climate and its impact on a system’s plant-animal interactions may alter the fundamental chemical cycles of an ecosystem.

“Our understanding of what climate change is going to do and what kind of interactions are going to result is in its infancy. We are just starting to understand how species are responding to climate change, and more complex interactions—like the ones we are looking at—are not very well studied,” Beard said. “So this makes our research questions cutting edge because it’s not just about herbivore-plant interactions, but it’s also about the larger potential ecosystem consequences of that interaction.”

Click here to learn more about Karen Beard’s research. —Alicia Clarke

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