A tiny arctic shrub reveals secrets of plant growth on Svalbard

Counting tiny rings showed synchronous growth across an entire arctic archipelago

NORWEGIAN UNIVERSITY OF SCIENCE AND TECHNOLOGYSHARE PRINT E-MAIL

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IMAGE: THIS TINY ARCTIC WILLOW, SALIX POLARIS, IS ONE OF THE MOST IMPORTANT FOODS FOR REINDEER ON SVALBARD. WHILE REINDEER AND CARIBOU ELSEWHERE IN THE WORLD SUBSIST ON LICHEN, ON SVALBARD… view more CREDIT: LISA SANDAL, NTNU

The polar willow (Salix polaris) may not seem like much when you look at it — just a jumble of tiny green leaves in a dense mat that pokes out of the tundra.

But beyond its humble appearance, this little shrub plays an outsized role when it comes to the creatures living in the Arctic archipelago of Svalbard.

It’s not just that Svalbard’s reindeer depend on it for food. It’s also that how it grows reflects what happens with the growth of all other plants across the whole of Svalbard.

Now, researchers have found that the polar willow and other plants grow in synchrony across Svalbard, in direct response to July temperatures.

Mathilde Le Moullec, a postdoc at the Norwegian University of Science and Technology’s (NTNU) Centre for Biodiversity Dynamics, has spent much of her academic career investigating all of the interlocking puzzle pieces that make the Svalbard plant and animal community work.

She’s searched for reindeer for four summers as a way to get a highly accurate population estimate for the animals. She’s hunted for old reindeer antlers and bones during those years, so she could carbon date them.

All of that information combined allowed her to see where on Svalbard the animals formerly lived, and how their populations had changed over time. She used all this information to document how Svalbard’s reindeer population rebounded after being hunted down to very low numbers for centuries.

But Le Moullec realized she needed to look beyond just reindeer to have a deeper understanding of the whole ecosystem.

“Salix is an important part of their main diet, especially because there is almost no lichen on Svalbard,” she said. One study found that lichen makes up just 2 per cent of the diets of Svalbard reindeer, she said.

By studying what controls the growth of the polar willow across Svalbard, “you can also see how climate is affecting primary production in different places,” meaning growth of things like plants, which are at the base of the food chain, she said. “It also gives you a window on what different reindeer populations have to eat.”

Another advantage of studying something like the polar willow is that “you can go to one place, one time, dig up a willow, and come back with 40 years or more of data,” she said.

So that’s what she did. In 2015, when two friends offered the use of their sailboat Sillage to help her reach some of Svalbard’s more remote locations to count reindeer, she and her friend Morgen Bender, a PhD candidate from UiT — The Arctic University of Norway also set about digging up polar willows.

Thirty of their plants came from Semmeldalen, in south central Svalbard. The advantage of Semmeldalen was that René van der Wal, a professor at the University of Aberdeen and Swedish University of Agricultural Sciences, who worked with Le Moullec on other willow research, had established a long-term study of plants there starting in 1998.

But that was only the beginning.

Because then she and colleague Lisa Sandal, then a master’s student in the Department of Biology, had to count the microscopic growth rings in this miniature arctic shrub.

Even though some of the willows being studied were more than 40 years old — the oldest was 70 — the growth rings were teeny-tiny.

“The entire root is the thickness of the tip of a fork, it is just a few millimetres across,” Le Moullec said. “Each growth ring is just a few micrometres, so we cut cross sections that are a cell thickness of two micrometres.”

To put that in perspective, a strand of spider’s web silk is 3-8 micrometres in diameter.

The researchers also had to look at multiple cross sections from each plant.

That’s because some shrubs might not put on growth rings every year. Or the cross section might only have partial growth rings on one side that the researchers might not see, depending on where in the plant the cross section came from.

They put the cross sections under a powerful microscope and took photographs — as many as 70 for a cross section — so they could merge the pictures together to make a single stunningly beautiful photo with a great amount of detail.

“The lab part took almost two years,” Le Moullec said. “One person couldn’t do it alone. And with Lisa, we joked the whole time, if this research never becomes science, we can sell it as art. “

In fact, one of the images won the British Ecological Society’s 2018 Capturing Ecology photo competition in the Art of Ecology category.

“Fortunately, the art also became science!” Le Moullec said.

The shrub rings show distinctive patterns, year by year, based on how good or poor the growing conditions were. But the researchers wanted to know if one particular weather factor was more important than others in determining how well the plants would grow.

Certain years, called pointer years, are very good growth years for all plants. That makes the pointer year rings easy to find, making them like a time stamp in the rings of each willow. Using the pointer years enabled the researchers to figure out if some willows were missing growth years, or if the cross section they had might have had a ring that grew on only one side.

They needed to know this to know the year of formation for each growth ring for each shrub.

From there it was a matter of looking at weather data across Svalbard, and looking at five different weather-related factors to see which were best reflected in tree ring growth.

These factors were the onset of spring, amount of snowfall, rain-on-snow events, summer temperature and summer precipitation.

Of all these factors, July temperature was the most important for willows growing in all 8 sites. Yes, across a huge archipelago, July temperatures ruled for willow — and had an effect for all other vegetation there, causing vegetation to grow in lock-step. That also has significance for grazing animals, like reindeer.

Researchers have seen this kind of synchronous pattern before, in boreal or temperate forests, where summer temperatures have a coordinating effect on tree growth across large areas. But this is the first time this kind of research has been done in the Arctic, Le Moullec said, and in a tree where the largest structure — the root — is half the size of your pinkie finger.

Le Moullec and her colleagues did find another factor that negatively affected willow growth in some areas, and that was rain-on-snow events. These are exactly what they sound like — a weather event where rain falls on snow, and then the plants become covered in a thick layer of ice which seals them away from the air and essentially smothers them until the ice melts away.

In earlier research, Le Moullec’s supervisor, Brage Bremset Hansen, documented how rain-on-snow events could cause widespread problems for reindeer populations, ultimately causing a ripple effect for the other species that overwinter on Svalbard.

Researchers expect more rain-on-snow events on Svalbard as increasing climate change causes arctic temperatures to skyrocket.

As a result, the relative importance of seasons for growth patterns may change, Le Moullec said. Because the effect of rain-on-snow was so different in different parts of Svalbard, the synchronizing effect of July temperature on vegetation growth may be weakened over time, she said.

On one hand, that could be better for the overall health of the ecosystem, because when one area has a bad growth year, other areas may do fine. As a consequence, even though reindeer in areas with poor growth may have a hard time surviving, not all reindeer populations on the island will be equally affected.

On the other hand, if rain-on-snow become widespread all across Svalbard, all populations may have a hard time simultaneously.

Van der Wal, who has worked with Le Moullec although not on this study, said he was impressed by her “painstaking but elegant work.”

“We knew that warm summers allowed high arctic plants to grow well, but always believed that this was what happened above ground. For Mathilde to show that good years above ground also means good growth below ground, and for this to reflect the productivity of all higher plants together is a major step forward,” he said.

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Reference: Le Moullec, M., Sandal, L., Grøtan, V., Buchwal, A. and Hansen, B.B. (2020), Climate synchronises shrub growth across a high arctic archipelago: contrasting implications of summer and winter warming. Oikos. doi:10.1111/oik.07059

From EurekAlert!

39 thoughts on “A tiny arctic shrub reveals secrets of plant growth on Svalbard

  1. From Article:
    Now, researchers have found that the polar willow and other plants grow in synchrony across Svalbard, in direct response to July temperatures.

    Now, really, I’m surprised, I never would had thought that. Temperture dependend time of growing, wow !

    • This is actually hilarious:-

      Supposedly serious science ‘discovering’ the blindingly obvious and in the middle they suddenly start screaming ‘OMG EVERYTHING’S DOOMED BY CLIMATE CHANGE’ .

      “Researchers expect more rain-on-snow events on Svalbard as increasing climate change causes arctic temperatures to skyrocket.”

      Out of nowhere, that doesn’t sound like baseless crazy alarmist conjecture at all, no not at all………

      Then they mark their own homework as “painstaking/elegant/major step forward” 11/10.

    • I found the article pleasant and interesting reading, but the Eureka moments like growth across Svalbard remarkably occurred in July to their surprise was ‘silk purses from sows ears’. They also discovered that what was good for the above ground part also, remarkably was good for the roots! A little “protesteth too much” I guess can be expected in a tiny study like this.

  2. “Researchers expect more rain-on-snow events on Svalbard as increasing climate change causes arctic temperatures to skyrocket.”

    What researcher is expecting such nonsense? I’ll bet not one legitimate researcher was consulted to support that assertion. Hearsay doesn’t count in a court of law and it doesn’t count as supporting science either.

  3. Main question will be now, what was the exact grow-staring temperature ?
    Was it really the temperature ? It wasn’t the hight of the sun in the sky ? Or the day lenght ?

  4. Sounds like they all their “predictive bases” covered.

    “We knew that warm summers allowed high arctic plants to grow well, …”

    while…

    “Researchers expect more rain-on-snow events on Svalbard as increasing climate change causes arctic temperatures to skyrocket.”
    and…
    “Le Moullec’s supervisor, Brage Bremset Hansen, documented how rain-on-snow events could cause widespread problems for reindeer populations, …”

    So the take-away is, “If arctic plants do well in the coming decades… it’s b/c of Climate Change.” And conversely, “If arctic plants suffer from rain-on-snow and do poorly, it’s also because of climate change.” They’ve got both mutually exclusive outcomes covered with the same hypothesis of climate change.

    That folks is what Popper would call non-falsifiability and is the hallmark of pseudoscience.

    • “We knew that warm summers allowed high arctic plants to grow well, …”
      If I remember well, that’s not only so in the arctic, ok, not in summer, but in spring.

      • “We knew that warm summers allowed high arctic plants to grow well, …”
        So do increased CO2 levels which also helps them during the cooler summers. The benefits of CO2 are always there, the benefits of warmth are only there when it’s warm.

  5. Is this a joke or did I just miss something? Did they conclude that plants grow more when the weather is clement? Do they get paid for this?

  6. “Le Moullec and her colleagues did find another factor that negatively affected willow growth in some areas, and that was rain-on-snow events. These are exactly what they sound like — a weather event where rain falls on snow, and then the plants become covered in a thick layer of ice which seals them away from the air and essentially smothers them until the ice melts away.”

    My thoughts. These are based on my experience. I live in the subarctic. We have lots of tundra here. The upside of rain on snow events for tundra tree species is 1) they reduce blowing snow which is a major vertical growth inhibitor of trees (we see substantial colonization by trees in any area that provides wind eddies in the winter time this includes human structures and topographic variations in the tundra), 2) if the ice build up from rain is substantial enough it devastates the rodent population, as they lose access to subnivean spaces, and the fact that ice has a much lower thermal insulation value compared to snow. In my backyard, rodents harvest tubers and roots.

  7. Svalbard. Isn’t that where they built Earth for the white mice? Or was that the name of a character?

  8. If she really wanted to know about the reindeer, she should have just asked Rudolph The Red.

  9. This was the most interesting article I have read in a while. I regret that no photo was shown of the patterns referred to in the article. I also regret the obligatory obeisance to the global warming meme; on the one hand, we are told that the earth is still coming out of the most recent ice age, so warming is expected as temps rebound; on the other hand, we are told that all the “warming” is our fault, and it can be halted or reversed if we just STOP IT (using fossil fuels, driving cars, turning on electric lights, etc.). I can do without the stupidity, and I think any reference to “climate change” as a negative causative factor ought at least to be in red type and in italics, as a fraud warning. I do find it encouraging that the authors seem actually to have discovered something useful.

  10. They should measure the radioactivity of the isotopea Pb-210 and Po-210 in these Arctic willow leaves and flowers. If they’re anything like lichens, whose role as diet of the Caribou the willows replace on Svalbard, they will have tens to hundreds of thousands of Bq per kg, many orders of magnitude higher than most plants.

    That is why caribou themselves are radioactive. Seriously. Their bones, the organ containing most of the body’s Pb-210 and Po-210, contain 500-3000 Bq/kg, while the concentration of this natural pair of radionuclides (grandmother and granddaughter) at the end of the U-238 series, is about 1 Bq/kg. In humans at least. I measured caribou bones myself for alpha radioactivity of Po-210, with both solid state track detectors and semiconductor barrier detectors.

    Why all that radioactivity in lichens, and thus caribou also? These radionuclides arise as long-lived daughters of radon gas in the atmosphere. Lichens grow very slowly and live very long. The tundra soils in which they live are so nutrient-poor that the lichens absorb nutrients from air and rainwater also. In so doing they absorb whatever else is floating around in the air, such as Po-210 and Pb-210.

    That’s why it’s interesting to speculate about the radioactivity of the same Pb/Po-210 isotopes in the Arctic willow. If, like lichens, they grow very slowly, and live for 70 years or more, then it seems that they are living the same lifestyle and niche as the lichens. And like them, they probably concentrate airborne radionuclides in their tissues.

    So maybe this research team might be curious to try some alpha radiochemistry and measurement of Pb-210/Po-210 in the Arctic willow Salix polaris. They might be surprised what they find.

    https://www.tandfonline.com/doi/abs/10.1080/095530098142716

  11. I could not figure out if this was satire until it got to the bit about the future being grim because of ‘snow on ice’. Then I knew they were serious about finding that plants need temperatures above 0 to grow. Who would have thunk it??

  12. ““The entire root is the thickness of the tip of a fork, it is just a few millimetres across,” Le Moullec said. “Each growth ring is just a few micrometres, so we cut cross sections that are a cell thickness of two micrometres.”

    To put that in perspective, a strand of spider’s web silk is 3-8 micrometres in diameter.

    The researchers also had to look at multiple cross sections from each plant.

    That’s because some shrubs might not put on growth rings every year. Or the cross section might only have partial growth rings on one side that the researchers might not see, depending on where in the plant the cross section came from.

    They put the cross sections under a powerful microscope and took photographs — as many as 70 for a cross section — so they could merge the pictures together to make a single stunningly beautiful photo with a great amount of detail.”

    “Each growth ring is just a few micrometres, so we cut cross sections that are a cell thickness of two micrometres.”
    “researchers also had to look at multiple cross sections from each plant”
    “some shrubs might not put on growth rings every year”
    “They put the cross sections under a powerful microscope and took photographs — as many as 70 for a cross section”

    Missing growth rings, merging as many as 70 cross sections that are nearly as thick as they are wide?
    What can go wrong, besides everything?

  13. ”For Mathilde to show that good years above ground also means good growth below ground, and for this to reflect the productivity of all higher plants together is a major step forward,”

    Jeezuz!

  14. Rain-on-snow events are perfectly normal in Svalbard with (relatively) warm water to the west and sea-ice in the north and east. And it has always been a problem for the reindeer, occasional mass die-off are documented way back.

    And yes, woody growth in the Arctic is very closely correlated to growing-season temperatures, as anybody with the slightest interest in the subject knows.

    Typical “me too” research. It has two big advantages, it requires no real talent or originality, and it entails no risk of unwelcome results.

  15. There are a few points missing. Growing well is a misnomer as it may take 100 years for the willow to grow a foot long along the ground. There were not too many in the barren High Arctic islands when I was there in the 1970’s, so I hope there are more in Svalbard for them to eat.

  16. Why bother to do research on Svalbard? The researchers could have saved a lot of time by simply asking questions of the people who have commented on the article. After all, they know everything about Arctic shrubs, even if they couldn’t name any, don’t they?

  17. I seem to remember that it does not only require a rain-on-snow event to cause an ice blanket.

    Many years ago we had a couple of days of very heavy snow fall. Then, suddenly the sun appeared for a few hours and it was warm enough to melt the top inch or tow of snow. That night temperatures plummeted and the melted snow froze. The following days, temperatures never rose above 32 F and the ice cover last for more than a week. I do not remember if there was any more snow or any rain during that period. I do remember that because of a lack of snow ploughs many roads were impassible – not because of snow but because of ice.

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