Wednesday, June 6, 2012

813. Climate Change: Warming Arctic Tundra Producing Pop-Up Forests

By Andrew C. Revkin, The New York Times, June 3, 2012
Arctic forests
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 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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