By Andrew C. Revkin, The New York Times, June 3, 2012
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| In the northernmost foothills of the Polar Ural mountains on the southern Yamal Peninsula in West Siberia, Russia, tundra shrubs are turning into small trees, with big implications. |
Even as insect infestations and other factors
accompanying warming have led to the “browning” of some stretches of boreal forest
between temperate regions and the Arctic tundra, the tundra appears to be
greening in a big way, various studies have shown. The newest such
work, focused on scrubby windswept regions along Russia’s northwest Arctic
coast, has found a particularly noteworthy shift is under way.
In this part of the Arctic, which could be a bellwether
for changes to come elsewhere with greenhouse-driven warming, what might be
called pop-up forests are forming. Low tundra shrubs, many of which are willow
and alder species, have rapidly grown into small trees over the last 50 years,
according to the study, led by scientists from the Biodiversity
Institute at the University of Oxford and the Arctic Center of the
University of Lapland. The researchers foresee a substantial additional local
warming influence from this change in landscapes, with the darker foliage
absorbing sunlight that would otherwise be reflected back to space. But the
fast-motion shift to forests will likely absorb carbon dioxide, as well.
A particularly interesting aspect of this work, to my
eye, is how it reveals the potential for fast-motion responses of ecosystems to
environmental change in the far north. In work I covered in 2007, botanists
found that Arctic plant species were extremely responsive
to fairly rapid climate shifts in the past.
The new study, published Sunday in Nature Climate Change, is significant in two
ways. It challenges a longstanding model of the Arctic ecological response to
global warming. The old notion was that forests in boreal regions ringing the
treeless tundra would slowly advance north.
The lead authors expound in the news release distributed by Oxford and the University of
Lapland:
“The
speed and magnitude of the observed change is far greater than we expected,”
said Prof. Bruce Forbes of the Arctic Center, University of
Lapland, corresponding author of the paper. Adds Dr. Marc Macias-Fauria from
Oxford University, lead author, “Previously people had thought that the tundra
would be colonized by trees from the boreal forest to the south as the Arctic climate
warms, a process that could potentially take centuries. But what we’ve found is
that the shrubs that are already there are transforming into trees in just a
few decades.”
This passage from the abstract pinpoints the
significance of the finding:
The processes
we report here … suggest a large-scale shift towards a structurally novel
ecosystem absent for millennia, which shares many characteristics with that
described for Beringia in the early Holocene epoch. This structurally complex
mosaic of open woodland characterized by thickets of tree-sized [taller than
six feet]
individuals of deciduous broad-leaved taxa has the potential of significantly
altering abiotic and biotic conditions within the Low Arctic….
This work is a snapshot from one region of the Arctic,
but Forbes told me that the findings fit well into the pan-Arctic trends
reported by a consortium of researchers that he’s part of. That work was well
summarized in an April study of trends in Arctic plants since 1982 in
Environmental Research Letters:
The
19.8% average increase in aboveground [Arctic tundra] biomass has major
implications for Arctic tundra ecosystems, including their hydrology,
permafrost and wildlife, and for how humans exploit Arctic landscapes. The
taller and denser vegetation uses up more carbon from the atmosphere, changes
the amount and composition of forage for grazing animals, and also alters the
partitioning and distribution of energy and heat at the land surface.
It’s vital to see that support for such work is
sustained, given the early stages of understanding and enormous significance of
these trends.
A very useful overview of forest trends in a
changing climate — exploring the full mix of factors, from fires and insects to
changes in precipitation and photosynthesis — is provided in the federal
report, “The Effects of Climate Change on Agriculture, Land
Resources, Water Resources, and Biodiversity.”
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