Impact of Recreational Snow Compaction on Small Mammals in the Subnivean Space Derek Sweeney EBIO 4120 Spring 2008 Mountain Research Station University of Colorado, Boulder

Questions: Does recreational use of snow impact subnivean space characteristics? If so, what changes occur and what are the factors that control those changes? How do changes to the subnivean space impact small mammals that utilize that space?

Deer mouse Peromyscus maniculatus Home range: hectares Montane vole Microtus montanus Home range:.1 hectares Small mammals that utilize the subnivean space

S. red-backed vole Myodes gapperi Home range:.5 hectares.14 hectares in winter Masked shrew Sorus cinereus Home range: hectares Small mammals that utilize the subnivean space

HOME RANGES Most home range research for summer Very little research on effect of snow cover on home range and activity of small mammals (Sanecki, et al., 2006) Snowpack causes significant reduction in home ranges (Sanecki, et al., 2006) Snow limits access to food sources (Korslund, 2006) Snow affects ability to forage enough food

Predators that rely on subnivean animals Ermine Bobcat Coyote

Subnivean Space in Continental Snowpack

Small mammal use of subnivean space Small mammals depend on the development of the subnivean space between ground and snow to enable access to resources necessary for survival (Formozov 1946; Pruitt 1984; Halfpenny and Ozanne 1989) Protection from predators Insulation from low surface temperatures Constant temperature maintenance (0 o C) Ease of travel in low density, unconsolidated snow

Subnivean space due to depth hoar (average 16 cm)

Evidence of small mammal tunneling in subnivean space

Snow Compaction Due to Single Pass on Skis

Type of load force/area, ski, snowshoe, snowmobile Frequency of load number of times an area is compacted Snow depth how deep can compaction effect penetrate Possible factors affecting changes in the subnivean space

SITE Lodgepole pine forest Typical area of recreational use Open, uniform, undisturbed site Snow without melt/freeze crusts Compressed snow with skis Measured change in height of subnivean space and snow density First experiment: varied snow depth, held load and frequency constant Second experiment: varied frequency, held load and snow depth (65 cm) constant METHODS

Ski compaction of snowpack

RESULTS SUMMARY There are effects on the subnivean space Factors influencing subnivean change include snow depth, frequency of use, and type of load Height of the subnivean space and snow density affected With snowpack greater than 100 cm, compaction effects don’t extend to the subnivean space Compaction effect stabilizes after 3-5 passes

DISCUSSION Potential effects on small mammals(Sanecki et al. 2006) Loss of space Increased energy to travel Forced to surface Reduce/fragment home ranges/habitat reduced insulation/thermal stability Barriers to travel and access to food compaction may benefit some other mammals in the short term reduced transportation energy use for deer, elk, moose trails to increase coyote hunting range but also unexpected effects, lynx decline due to opening of range to coyotes

APPLICATION TO MANAGEMENT/PLANNING OF SNOW COVERED RECREATIONAL AREAS Be aware of the importance of the subnivean space Need more winter mammal surveys, home ranges Restrict early season travel on shallow snowpack Limit travel to designated trails in high use areas Make travel corridors narrower with more tree islands Suggestions to provide tunnels

REFERENCES Belk MC, Smith HD, Lawson Use and partitioning of montane habitat by small mammals. Journal of Mammalogy. 69:4, pp Formozov AN Snow cover as an integral factor of the environment and its importance in the ecology of mammals and birds. Boreal Institute: Edmonton. Hadley GL, Wilson KR Patterns of small mammal density and survival following ski-run development. Journal of Mammalogy. 85:1, pp Halfpenny JC and Ozanne RD Winter: an Ecological Handbook. Johnson Publishing Company: Boulder, CO. Korslund L, Steen H Small rodent winter survival: snow conditions limit access to food resources. Journal of Animal Ecology. 75:1, pp

REFERENCES Musser, G. G. and M. D. Carleton Superfamily Muroidea. Pp in Mammal Species of the World a Taxonomic and Geographic Reference. D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore. Pruitt, WO Jr Snow and small animals. In Winter Ecology of Small Mammals. Special publication No. 10. (Ed. J.F. Merritt) pp Carnegie Museum of Natural History: Pittsburgh, PA. Sanecki GM, Cowling A, Green K, et al Winter distribution of small mammals in relation to snow cover in the subalpine zone. Journal of Zoology. 269:1, pp Sanecki GM, Green K, Wood H, et al The implications of snow-based recreation for small mammals in the sub-nivean space. Biological Conservation. 129:4, pp Sanecki GM, Green K, Wood H, et al The influence of snow cover on home range and activity of the bush-rat (rattus fuscipes) and the dusky antechinus (Antechinus swainsonii). Wildlife Research. 33:6, pp

Deer mouse Masked shrew Southern red-backed vole Montane vole Small Mammals Utilizing the Subnivean Space