Snow–Shrub Interactions in Arctic Tundra: A Hypothesis with Climatic Implications

Abstract

In the Arctic, where wind transport of snow is common, the depth and insulative properties of the snow cover can be determined as much by the wind as by spatial variations in precipitation. Where shrubs are more abundant and larger, greater amounts of drifting snow are trapped and suffer less loss due to sublimation. The snow in shrub patches is both thicker and a better thermal insulator per unit thickness than the snow outside of shrub patches. As a consequence, winter soil surface temperatures are substantially higher, a condition that can promote greater winter decomposition and nutrient release, thereby providing a positive feedback that could enhance shrub growth. If the abundance, size, and coverage of arctic shrubs increases in response to climate warming, as is expected, snow-shrub interactions could cause a widespread increase (estimated 10%-25%) in the winter snow depth. This would increase spring runoff, winter soil temperatures, and probably winter CO 2 emissions. The balance between these winter effects and changes in the summer energy balance associated with the increase in shrubs probably depends on shrub density, with the threshold for winter snow trapping occurring at lower densities than the threshold for summer effects such as shading. It is suggested that snow-shrub interactions warrant further investigation as a possible factor contributing to the transition of the arctic land surface from moist graminoid tundra to shrub tundra in response to climatic warming.

The role of microbes in snowmelt and radiative forcing on an Alaskan icefield

“…Because algae remain on the surface over much of the melt season and perennially resurface across melt seasons, they compound their effects over time. Like arctic shrubs 35 , high-latitude microbes potentially drive a warming climate feedback if their radiative forcing at the regional scale increases the extent of near-freezing snowpack, their primary habitat. Given an upward-elevation shift with warming, algae will increase most rapidly across flat, snowcovered topography, such as Greenlandic and Antarctic ice sheets, regions with critical albedo effects on global climate 2,3,36 .…”

Nonlinear dynamics in ecosystem response to climatic change: Case studies and policy implications

“…Although the extensive invasion of low density white spruce into tundra can occur rather rapidly, the positive response of white spruce growth and stand infilling to a warmer climate may be of greater significance to natural resource managers. Infilling of spruce and/or shrubs will change ecosystem nutrient status, snowfall retention, and hydrology (Sturm et al, 2001). Such shifts will likely alter both above-and below-ground biodiversity (Kennedy et al, 2002;Porazinska et al, 2003;Heemsbergen et al, 2004).…”

Biome changes and their inferred climatic drivers in northern and eastern continental Asia at selected times since 40 cal ka bp

“…For example, 20th century warming caused shrub expansion ("arctic greening") in northern Siberia (Sturm et al 2001;Frost and Epstein 2014), whereas forest cover was reduced in central Yakutia from 1982 to 2005 due to permafrost degradation (Lloyd et al 2011). In the semi-arid forests of inner Asia, tree growth has declined since 1994 due to a temperature-induced reduction in effective moisture (Liu et al 2013).…”