Somewhere near the precipice of the Brooks Range, as the land makes a last gasp for altitude before its slow decline towards the Beaufort Sea, lies treeline. Global treeline, that is. The trees here are the farthest north in the world, stands of white spruce and poplar eking out a living before the inhospitable climate of the North Slope, home of the Arctic LTER.
At the third of his sampling sites here, Kevin Griffin, lead PI of the Arctic LTER, looks uphill. “That sure wasn’t there last year,” he says, and points. A stripe of upturned soil scars the otherwise unblemished hillside. The depression appears to ooze downhill, and lo and behold, one of his trees sits in the trail of gray gloop. “That tree used to be totally in hummocky ground, and now it’s totally in mud.”
The mudslide is better known as a thermokarst, an area where the permafrost that underlies much of the tundra has thawed. The water leaches out, the land sinks underneath, and the tundra, once green with plant life, is replaced with mud.
Kevin is just mildly surprised. He first traveled to the Arctic in 2000 to study the plant life north of treeline. The area is warming four times faster than anywhere else on the planet. It’s rife with change, change that he has personally witnessed. The tundra, though still dominated by diminutive but hardy plants, is slowly turning into bigger shrubs. Heatwaves are now common. The short growing season is just a bit longer. Sometimes, large swaths of tundra catch fire—a shock in a landscape with continuous standing water and dominated by plants that barely reach up to one’s calf. And, of course, the ground is sinking as the tundra melts.
Capturing change
Griffin’s sites in the Brooks Range are part of a broader project exploring the slow migration of trees beyond treeline. In the last thirty or so years, seedlings have taken root in places they haven’t been seen in millenia (millions of years ago, trees covered much of the Arctic). Now, these balsam poplar and white spruce saplings edge into maturity, becoming fully fledged trees (the most common definition of “tree” is a woody plant with a 10cm diameter at breast height; the slow growing saplings in the Arctic might be thirty years old or older if they ever hit this point).
Why are these trees suddenly able to exist where they haven’t previously? The answer, Griffin tells me, is clearly climate related—but it’s not clear whether the culprit is a longer snow free season, or warmer temperatures, or increased soil depth from melting permafrost, or something else. Griffin hopes that comparing environmental conditions at this new stand of poplars will help him figure out what, exactly, allowed them to grow into mature trees.
The presence of trees has an effect on the ecosystem, too. Trees cycle nutrients differently than tundra, for example, and different birds prefer the cover of trees to the wide open tundra. If trees continue to encroach across the landscape, which Griffin tells me is an expected consequence of further climate change, the Arctic as a whole might cycle carbon differently than before, or be able to support new species that previously weren’t found that far north. So, in addition to climate sensors, Griffin and his collaborators also record bird songs near the trees and take a whole host of biogeochemical and physiological samples to identify just how this new ecosystem might look.
Change from the beginning
Griffin’s inquiry into trees is representative of research as a whole at the LTER site. For one, the ecosystem functions unlike any other on the planet: water skates through a thin layer of soil atop permafrost, plants lie dormant except for a few months of vibrant growth in the endless daylight of summer. Researchers are continually trying to figure out just how things up here work.
The Arctic is also changing faster than pretty much anywhere on the earth, experiencing warming nearly four times faster than average. That rapid change was already apparent when researchers first started studying in the area in the 1970s. By 1987, when the LTER was initially funded, Toolik Lake had already warmed nearly 2ºC. In response, researchers have always tried to understand how the ecosystem will look a few decades from now, in a new climate.
When the sun gets low behind the Brooks Range (around midnight when I’m there, as the sun never sets), it catches the tops of several structures on the hill behind camp, illuminating the plastic tents like lanterns. These greenhouses mark the latest iteration of an experiment designed to simulate these climate induced changes on the tundra.
Early LTER researchers predicted that warming would affect the tundra in two ways: first, by physically warming the landscape, and second, by causing a series of events that would flood the ecosystem with new nutrients. To simulate the effects of this on tundra plant communities, researchers fertilized some plots of tundra with nitrogen and placed greenhouses over others. Then, three decades went by.
Walking around the hill, the results of these experiments are dramatic, even to my untrained eye: many plots are overtaken by woody shrubs, and some plots are full of dead vegetation. The neighboring tundra looks, well, like tundra should: the vegetation low, mosses and lichen abound, tussocks taunt a visitor’s surefootedness.
Both added nutrients and warmer soil spurred shrubification of the tundra—the conversion of tundra to bigger woody plants. Shrubification has consequences. A recent study from the site showed that shrubby areas are more often a source of carbon than their tundra counterparts. Another implicated the nutrients released from melting permafrost in shrub expansion.
Rich water
Similar experiments are scattered across the LTER, and they are designed to understand how the effects of climate change will affect the rivers, lakes, and tundra now and far into the future. From the Toolik Field Station, this kind of Arctic LTER research stretches out across the tundra in a circle miles wide.
I have butterflies in my stomach when the helicopter takes off—for one, because it’s my first helicopter flight; for another, because I’m in here with Griffin and George Kling, two expert Arctic researchers who decide to give me an in-depth tour of the LTER site from the air. We have the door open so I can shoot video out the helicopter window. The Brooks Range remains a steady backdrop as the chopper darts across the landscape.
“And that river there, we actually fertilized the whole thing,” says Kling through his headset, pointing down at the Kuparuk River, which, from above, forms immaculate bowknots as it winds down a shallow valley.
I ask him to elaborate. This river experiment, it turns out, mirrored the nutrient addition experiments on the tundra. Researchers predicted that nutrients would flood the watershed in a warmer climate. The Kuparuk was strongly nutrient limited; the additional nutrients would, researchers predicted, cause severe changes to the system. So, researchers started to add phosphorus to the stream each summer.
The additional phosphorus initially stimulated diatoms; for the first decade, these organisms, which were already abundant in the stream, proliferated. But then, suddenly, everything changed. Moss encroached. It began to outcompete the diatoms. Before long, the stream was a thick bryophytic mess.
Kling lights up when describing the experiment. For him, the stream trajectory is a quintessential argument for the value of long-term studies. The Kuparuk only converted to its moss-dominated state after eight years of nutrient addition. Had the experiment run shorter, researchers would have missed the transition. That error could have been costly—incorporating just the diatom state into models might lead to incorrect predictions for carbon stored in the region.
Convergence
An experiment at treeline, one on the tundra, one in the Kuparuk. Each has provided researchers with valuable truths about how each system responds to change. But from the helicopter, tundra rolls softly as far as the eye can see, a camouflage patchwork of different types of tundra, cut by rivers and shrubs in the lowlands. Each environment—forest, river, tundra, shrub—isn’t as siloed as the Arctic LTER’s past experimental design might lead one to believe. Water flows easily through tundra to the streams. Plant communities blend into one another, blank ground becoming tundra, tundra slowly turning to shrubland.
These poorly defined boundaries between systems are the future of Arctic LTER research, Rose Cory tells me over dinner. She’s a hydrologist who studies how water moves through the Arctic and a co-PI on the grant. “This approach is challenging,” she adds, noting that refined methods exist for studying lakes or tundra hydrology, for example, but fewer tools exist to study the interface between the two.
“The old approach [where teams were split] led to great science,” she adds, noting that leaving each team to ask their own questions facilitated quick results. But, she admits, the most pressing questions in a changing Arctic really require understanding the whole system, including how nutrients or carbon or water crosses these imaginary ecosystem boundaries.
Dinner continues, and Cory and I are joined by Kling, who studies lakes and streams, and Griffin, a plant physiologist. The three float hypotheses by each other. At times, a few other researchers stop by and are sucked into the conversation: microbial ecologists and pollinator specialists and soil experts all lend their opinion. With such enthusiastic collaboration present at dinner on a random Tuesday evening, it’s hard to imagine those boundaries will remain for long.
by Gabriel De La Rosa
