- What is the subnivian space and how does it form?
The subnivian space is a thin air layer found between the covering snow and the surface of the soil and its vegetative debris. This space forms especially well when the snow fall becomes established prior to the hard freezing of the soil and is particularly pronounced in complexly structured, "natural" soil-litter systems. Falling snow gathers on the surfaces of the irregular profile of the leaf litter and forms complex arches and domes over and above the dead plant materials. Heat from the unfrozen soil and also from the decomposition of the organic molecules in the leaf litter melts the contact snow layer which quickly re-freezes to form thin ice sheets which add to the structural strength and also to insulating potential of the forming snow pack. A winter with a continuous snow cover will allow a significant and continuous subnivian space to form.
- What animals might be found in the subnivian space (and why are they there)?
Within this space (which may be several mm's to a couple of cm's in thickness) a great variety of living organisms can be found. The micro-climatic conditions of the subnivia are sufficiently mild to allow temperature sensitive invertebrates (like beetles, collembola, mites and spiders) to continue their ecological activities of decomposition and predation throughout the winter season. Many small mammals (like voles, shrews and white footed mice) use the insulated subnivian space as shelter against the harsh surface conditions and also as a safe conduit between forage sites and their burrows. Within the subnivian space they are hidden from surface avian and mammalian predators like red foxes and over-wintering red tail hawks and owls. These predators can be observed in the winter standing very still on the snow surface using their keen senses of hearing rather than vision to detect these subnivian rodents. Track histories of red foxes in particular can be found reflecting the slow stalking, pausing and explosive digging through the snow cover in the foxes' search for their subnivian prey.