Soil Organisms (Aug 2011)
Invertebrate activity under snow in a South-Norwegian spruce forest
Abstract
The activity of invertebrates under snow was studied by pitfall traps during two winter seasons in a high altitude spruce forest in southern Norway. With a snow layer varying between about 30 and 150 cm during the sampling periods, the temperature in the subnivean air space stayed close to 0 oC. Traps were emptied and replaced at least once a month during the snow-covered period, from October/November to April/May. For phenological purposes, some trapping was also performed just before or after the snow period. Most invertebrate groups were identified to species level. Beneath a permanent snow cover, the most species-rich groups collected were Collembola (22 species), Acari (22 taxa), spiders (12 species) and beetles (13 species). Collembola and Acari (microarthropods) always dominated in numbers. Subnivean catches also included Opiliones, Pseudoscorpiones, Trichoceridae, Limoniidae, Brachycera, Mecoptera, Gastropoda, and Harpacticoidea (Copepoda). Beetle larvae of Cholevidae and Staphylinidae were quite common. Traps placed adjacent to natural cavities between stones etc. did not achieve higher catches than traps on flat ground with a narrow subnivean space, indicating general subnivean activity over the whole forest floor. Many Collembola and Oribatida species were actively feeding under snow, having a characteristic gut content of fungal hyphae and spores. Also the gut of Cholevidae larvae (Coleoptera) contained fungal hyphae and spores, but mixed with decaying plant material. Since fungal feeders perhaps do not need to move much, pitfall trapping may underestimate the extent of subnivean feeding. We hypothesize that certain fungi known to decompose litter beneath snow (snow molds) represent a valuable food source for winter-active Collembola, Acari and Cholevidae larvae. Some of these may be eaten by spiders. Spiders and beetle larvae are among the invertebrates known to be eaten by subnivean shrews, so we support the idea of subnivean food chains.
