Conserving and managing the subnivium

Abstract

In regions where snowfall historically has been a defining seasonal characteristic of the landscape, warming winters have reduced the depth, duration, and extent of snowpack. However, most management and conservation has focused on how aboveground wildlife will be affected by altered snow conditions, even though the majority of species that persist through the winter do so under the snowpack in a thermally stable refugium: the subnivium. Shortened winters, forest management practices, and winter recreation can alter subnivium conditions by increasing snow compaction and compromising thermal stability at the soil-snow interface. To help slow the loss of the subnivium in the face of rapidly changing winter conditions, we suggest managers adopt regional conservation plans for identifying threatened snow-covered environments; measure and predict the effects land cover and habitat management has on local subnivium conditions; and control the timing and distribution of activities that disturb and compact snow cover (e.g., silvicultural practices, snow recreation, and road and trail maintenance). As a case study, we developed a spatially explicit model of subnivium presence in a working landscape of the Chequamegon National Forest, Wisconsin. We identified landscapes where winter recreation and management practices could threaten potentially important areas for subnivium persistence. Similar modeling approaches could inform management decisions related to subnivium conservation. Current climate projections predict that snow seasons will change rapidly in many regions, and as result, we advocate for the immediate recognition, conservation, and management of the subnivium and its dependent species.

Seedling responses to decreased snow depend on canopy composition and small‐mammal herbivore presence

“…Our data show that the effects of winter climate change on soil temperatures, and consequently seedling dynamics, will likely vary across regional landscapes, and that snow depth may play an underappreciated role in shaping winter herbivory by small mammals. Additionally, variation in canopy composition may provide land managers with a means of predicting the effects of reduced snow on winter soil temperatures, and consequently seedling survival, across large spatial scales (Zuckerberg and Pauli 2018). We show that snow cover and small-mammal herbivory can interact to decrease seedling survival in a relatively small sample of seedlings, but small-mammal foraging may change as a function of seedling density (Manson et al 1998).…”

“…Snow-removal studies that also manipulate seedling density could help us understand the importance of snow for small-mammal herbivory and seedling survival following high-mast versus low-mast years. Additionally, variation in canopy composition may provide land managers with a means of predicting the effects of reduced snow on winter soil temperatures, and consequently seedling survival, across large spatial scales (Zuckerberg and Pauli 2018). While ecologists grapple with the challenge of predicting species distributions and abundances in a rapidly changing world, understanding the intricate links between winter and summer processes could provide an important perspective in predicting the future composition of northern temperate forests.…”

Future winters present a complex energetic landscape of decreased costs and reduced risk for a freeze‐tolerant amphibian, the Wood Frog (Lithobates sylvaticus)

“…The subnivium exists at the soil–snow interface and acts as a stable thermal environment sheltering plants and small animals attempting to survive a period of resource deprivation and inclement weather to emerge in the spring and begin their annual reproductive processes (Pauli et al., 2013). A wide‐ranging microhabitat, the subnivium extends throughout much of the cryosphere, but winter warming and diminishing snow cover threaten the extent, timing, and stability of the subnivium and its dependent species (Thompson et al, 2018; Zuckerberg & Pauli, 2018). Decreases in snow cover extent, duration, and thermal insulation capacity (arising from reduced depth and increased density) disrupt a diversity of ecological processes ranging from nutrient cycling and hydrology to community composition and biotic interactions (Campbell, Mitchell, Groffman, Christenson, & Hardy, 2005; Contosta et al., 2017; Kreyling, Haei, & Laudon, 2012; Martz, Vuosku, Ovaskainen, Stark, & Rautio, 2016).…”

The decline of a hidden and expansive microhabitat: the subnivium

“…Maintenance of this seasonal habitat depends on a balance between air temperature, snow depth, and snow density, with stable subnivium conditions developing at below-freezing temperatures, under deep snow and low snow densities (Thompson et al 2018). Shallower and denser snowpacks due to warming winters reduce the insulating capacity of the snow cover (Zuckerberg and Pauli 2018), leading to paradoxically colder ground temperatures (Brown and DeGaetano 2011). Despite a mechanistic understanding of how these drivers impact the subnivium (Thompson et al 2018), the effects of warmer winter temperatures on this microhabitat will likely be geographically complex and challenging to predict across regional scales because the subnivium is influenced by variations in land cover and broad-scale differences in the timing of snowfall (Petty et al 2015;Thompson et al 2018).…”