northern grasses punching above their weight

By Jerome Stueart, courtesy of the Arctic Institute of North America's Kluane Lake Research Station High on the side of a hill overlooking Christmas Bay on Kluane Lake, Jennie McLaren enters her office.

By Jerome Stueart,

courtesy of the Arctic Institute of North America’s Kluane Lake Research Station

High on the side of a hill overlooking Christmas Bay on Kluane Lake, Jennie McLaren enters her office. It is a plot of land surrounded by electrical fence to keep away wandering horses or straying bison.

The views are stunning – both the overlook towards Kluane Lake and Kluane National Park in the distance and the view from a metre above tiny sections of her plot, where she observes how plants in a northern landscape interact.

We duck inside the electrical fence, and walk around square experimental patches where McLaren, a graduate student at the University of British Columbia, has been systematically removing one of three kinds of plants and measuring the results. Mosquitoes are everywhere but McLaren doesn’t seem to notice as she bends down to show us her work.

Placing a grid made from string and PVC pipe above the small plots, she looks down through the string outlines, where she’s mapped out what plants are in each tiny section. In most of the plots, she has removed either grasses, legumes or forbs.

“I had to paint on the herbicide with a very fine brush to take out only the plants I wanted to take out,” she says.

She wanted to see what other plants might do if suddenly there were more space. Which plants might be most active in that kind of situation? How would the ecosystem recover from the loss of a specific group of plants? And, more specifically, will climate change make it more difficult for certain plants to survive?

While some theories suggest that a plant’s abundance determines its importance in an ecosystem, McLaren is discovering that grasses, with a small biomass, play a larger-than-expected role in one northern landscape. Seven years into her biodiversity and grassland study, she’s been surprised at the results.

“I understood that biodiversity loss might affect ecosystems in general – but I wanted to know the loss of which plants would have the biggest effect,” McLaren says.

“It sounds simple to say that different plants do different things, but it’s important when you apply it to species extinctions (or biodiversity loss). Some plants are more essential to their ecosystems – they control how the ecosystem works.”

McLaren’s way of experimenting with the landscape is unusual. “Most grassland studies are done with artificially assembled communities and have the plants at unnatural abundances,” she says.

Instead, she starts with a natural community and uses a technique borrowed from gene research. When a researcher wants to know the role of a gene in a genome sequence, she turns off that gene in the genome, or “knocks it out.” Whatever happens to the organism reflects the role that gene played in the organism.

McLaren believed she could understand the roles of plants in a northern ecosystem by knocking out different plants and measuring the effects on the landscape. By knocking out one group at a time, she is asking what role that group plays – both below ground and above ground.

“Sometimes the processes hidden in the soil are more important. Who regulates the amount of moisture in the soil, amount of available nutrients, the rate of decomposition? How are nutrients recycled? How do the living affect the dead, and how do the dead affect the living?” she says.

“How do the other members of a community react to the loss of one of the members? When you know the reaction, you know the role of the lost member.”

When grasses were knocked out, she noticed major changes. She discovered that grasses made nutrients available to other plants, intercepted more light than other plants – despite a smaller biomass – and reclaimed land faster than other plants did. When the grasses weren’t present, the other plants didn’t reclaim the land.

“In fact they didn’t do anything.”

And that was strange to her. She had expected other plants to thrive more when the grasses were taken out, but they didn’t increase or decrease. Only grasses changed when given the opportunity to reclaim land.

“But what really interested me was what grasses did to the dead community.”

Grasses promote decomposition both while they are living and when they are dead. Plants simply break down faster in their presence. However, with no live grasses and no dead grasses to be recycled into the soil, the rate of decomposition is slower, resulting in a build up of dead plants that don’t turn into new soil.

McLaren realizes her study might seem to contradict aspects of major grassland studies done elsewhere. She suspects that grasses in the north, with their more upright stature, intercept light effectively from a sun that is at a lower angle than it is further south. This allows a plant of small biomass to have a relatively large effect on the landscape.

Since northern grasses control so much of their environment, they “punch above their weight.” McLaren believes this makes them extremely important to the northern ecosystem. She says their loss would be more devastating than the loss of other kinds of plants.

“Biodiversity is important to functioning well in ecosystem. We’re not only worried about the loss of the numbers of plants – but also who is lost through climate change. In climate change models we’ve only been looking at plants as one homogeneous category – as in, in the future, are there plants or not? It matters which ones are left.”

For more information about Jennie McLaren’s research, contact her at jennie.mclaren@gmail.com. For information about research at Kluane Lake Research Station, contact Andy Williams at (867) 841-4561.

This column is coordinated by the Northern Research Institute at Yukon College with financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon.