Long-Term Experimental Manipulation of Winter Snow Regime
and Summer Temperature in Arctic and Alpine Tundra:
An Integrated Ecosystem Approach
M.D. Walker1, D.A. Walker1, J.M. Welker2,3, A.M. Arft1, T. Bardsley1,
P.D. Brooks4, J.T. Fahnestock3, M.H. Jones3, M. Losleben1, A.N. Parsons3,
T.R. Seastedt1, and P.L. Turner1
Three 60-m-long, 2.8-m-high snowfences have been erected to study long-term effects of changing
winter snow conditions on arctic alpine tundra. This paper describes the experimental design and
short-term effects of the manipulations. One fence has been placed at Niwot Ridge, Colorado, a
temperate high-altitude site in the Colorado Rockies (4003′N, 10536′W; 4085 masl), and two have
been placed at Toolik Lake, Alaska, a high-latitude site (6837′N, 14932′W; 700 masl). The fences
result in a drift that is about 3 m at its deepest and which tapers to low snow conditions at about 65 m
from the fences. Open-top fiberglass warming chambers are placed along the experimental snow
gradients and in control areas outside the fences; each warming plot is paired with an unwarmed plot.
The purpose of the experiment is to examine short- and long-term changes in the integrated physical-
biological systems under simultaneous changes of winter snow regime and summer temperature.
The studies are part of the Long-Term Ecological Research network and the International Tundra
Experiment. Initial results indicate that although experimental designs are essentially identical at the
arctic and alpine sites, experimental effects are different. The drift at Niwot Ridge lasts much longer
than do the Toolik Lake drifts, so that the Niwot Ridge fence affects both summer and winter condi-
tions, whereas the Toolik Kale fence affects primarily winter conditions. The temperature experi-
ment also differs between the sites. Although the average temperature increase at the two sites is very
similar, at Toolik Lake there is only minor diurnal variation, whereas at Niwot Ridge the daytime
increases are extreme on sunny days (as much as 710C), and minimum nighttime temperatures in
the chambers are often slightly cooler than ambient. The experimental drifts resulted in wintertime
changes in temperature and CO2 flux. Temperatures under the deep drifts were much more consis-
tent and warmer than in control areas, and at Niwot Ridge remained very close to 0C all winter.
These increased temperatures were likely responsible for observed increases in system carbon loss.
Initial changes to the aboveground biotic system included in increase in growth in response to both
snow and warming, despite a reduced growing season. This is expected to be a transient response
that will eventually be replaced by reduced growth. At least one species, Kobresia myosuroides, had
almost completely died at Niwot Ridge 3 years after fence construction, whereas other species were
increasing. We expect in both the short and long term to see the strongest effects of snow at the Niwot
Ridge site, and stronger effects of temperature at Toolik Lake.
1 Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309-0450 USA
2 Natural Resource Ecology Lab, Colorado State University, Fort Collins, Colorado 80523 USA
3 Department of Rangeland Ecology and Watershed Management, University of Wyoming, Laramie, Wyoming
USGS, Water Resources Division, Boulder, Colorado 80303 USA