The increased snow cover that is predicted in some More frequent winter thaws can also affect ecosystems.
northern areas as temperatures rise will affect both eco- Thawing changes the mechanical properties of snow
system structure and function. Long-term experimental dramatically. This can reduce the insulating properties
increases in snow cover affected species abundance, of the snow cover, with increased potential for frost pen-
height of the vegetation, and diversity of plant functional etration into the soil and root damage to certain plant
types in the Alaskan tundra
40
. The increase in snow cov- species. During the brief thaw, soil microbial activ-
er had a greater impact on vegetation than experimen- ity may also release greenhouse gases. This occurs at a
tal summer warming, partly because insulation by in- time when plant uptake of carbon, which could offset
creased snow in winter caused higher soil warming than the increase in atmospheric carbon, is not possible, and
increased air temperatures. In the subarctic, an experi- adds to atmospheric concentrations of greenhouse gas-
mental doubling of winter snow cover on a peat moss es. In addition, re-freezing occurs after thawing, which
bog increased air and soil temperatures and strongly forms ice layers that can be on the surface, throughout
increased moss growth
41
. This increase in moss growth the snow cover or, if snow falls after a thawing event,
could increase the carbon sink effectiveness of northern under the snow in contact with the ground. Ice layers
peat lands in areas where snow depth increases. can act as a mechanical barrier, preventing herbivores
such as musk oxen
66
and reindeer from digging through
the snow to reach critical lichens and other forage (see
box on the snow-loving deer of the Arctic). This greatly
affects their health in winter and can determine their
survival
67
. Ice layers may also inhibit the diffusion of
organic compounds that reindeer possibly use to detect
food
68
. Presence of ice layers affects the survival of other
animals such as voles as well
69
. Ice layers can act as a
barrier to small mammals accessing shelter, food, nests
and protection from predators.
Snow cover in mountain regions is a critical source of
freshwater; changes in snow cover could have indirect
effects on ecosystems due to changes in availability of
Figure 4.8: The duration of snow cover is a major determinant
these water resources. One potential effect is increased
of the length of the growing season for plants. Shown here is
intensity and size of wildfires because of moisture
a persistent snow patch in western Greenland. With increasing
stress on mountain forests. There could also be im-
distance from the centre of the snow patch, the growing season
becomes longer, and thus plant communities become more de-
pacts on anadramous fish, which require high stream
veloped and productivity increases.
flow for their migration to the ocean after hatching in
Photo: Terry Callaghan fresh water.
CHAPTER 4 SNOW 51