Until now, the Arctic tundra has been the domain of low-growing grasses and dwarf shrubs. Defying the harsh conditions, these plants huddle close to the ground and often grow only a few centimeters high. But new, taller plant species have been slowly taking over this chilly neighborhood, report an international group of nearly 130 biologists in Nature. This has led to an overall increase in the height of tundra plant communities over the past three decades.

The study analyzed the most comprehensive data set on
plants in the Arctic tundra available. The study encompassed almost 120 tundra
sites, most of them located in Arctic regions of Alaska, Canada, Iceland,
Scandinavia and Siberia.

“The increase in height we saw was
not just in a few sites but nearly everywhere,” says lead author Dr. Anne
Bjorkman, who now works at the Senckenberg Biodiversity and Climate Research Centre
and who conducted the study at the iDiv research centre, the University of
Edinburgh, and Aarhus University.

The researchers identify
climate warming as the underlying cause. Temperatures in the Arctic have risen by
about 1 degree Celsius in summer and 1.5 degrees in winter over the three decades
covered by the study, some of the fastest rates of warming on the planet.

A detailed analysis showed that not only do individual plants grow taller
with warmer temperatures, but that the plant community itself has also shifted.
“Taller plant species, either from warmer pockets within the tundra or from southern
or lower elevation areas, have spread across the tundra”, says Dr. Nadja Rüger, a
scientist at the German Centre forIntegrative Biodiversity Research (iDiv) and at
Leipzig University and a co-author of the study.

This move is far
from over, as Bjorkman points out: “If taller plants continue to spread at the
current rate, the plant community height could increase by 20 to 60% by the end of
the century.” Surprisingly, the researchers found no evidence that this “invasion”
of taller species is currently leading to a decline in shorter species.

"ArcticTundra_AnneBjörkman_www.jpg"
Photo
credits: Anne Björkman

Arctic regions have long been a
focus for climate change research, as the permafrost underlying tundra vegetation
contains one-third to half of the world’s soil carbon. When the permafrost thaws,
greenhouse gases could thus be released.

An increase in taller
plants could speed up this process as taller plants trap more snow in winter, which
insulates the underlying soil and prevents it from freezing quickly and deeply in
winter.

“Although there are still many uncertainties, taller
tundra plants could fuel climate change, both in the Arctic and for the planet as a
whole”, Bjorkman concludes.

In contrast to plant height,
researchers found that six other measures, such as the size of leaves and their
nitrogen content, showed no consistent change over the last thirty years. These
other plant characteristics were strongly influenced by moisture levels in addition
to temperature.

The researchers conclude that the response of the
plant community as a whole to climate warming will depend on whether the tundra
becomes wetter or drier over time. Rüger says: “In order to predict how the plant
community in the tundra will react in the future, it is necessary to not only take
into account alterations in temperature, but also in water availability. If
precipitation or the water cycle change, or if the timing of snowmelt shifts, this
may have severe effects on the tundra vegetation.”

More information:

Bjorkman, A. et al. (2018): Plant functional trait change across a warming
tundra biome. Nature, doi: doi.org/10.1038/s41586-018-0563-7

Research Professor Bruce Forbes
Arctic Centre,
University of Lapland
+358408479 202, bruce.forbes(at)ulapland.fi

Dr. Anne Bjorkman
Senckenberg Biodiversity and
Climate Research Centre
+49 (0)69 7542 1914,
anne.bjorkman(at)senckenberg.de

Dr. Nadja Rüger
German Centre for Integrative Biodiversity Research (iDiv)
Leipzig
University
+49 (0)341 9733168, nadja.rueger(at)idiv.de