Shrub canopies influence soil temperatures but not nutrient dynamics: An experimental test of tundra snow–shrub interactions

Abstract

Shrubs are the largest plant life form in tundra ecosystems; therefore, any changes in the abundance of shrubs will feedback to influence biodiversity, ecosystem function, and climate. The snow–shrub hypothesis asserts that shrub canopies trap snow and insulate soils in winter, increasing the rates of nutrient cycling to create a positive feedback to shrub expansion. However, previous work has not been able to separate the abiotic from the biotic influences of shrub canopies. We conducted a 3-year factorial experiment to determine the influences of canopies on soil temperatures and nutrient cycling parameters by removing ∼0.5 m high willow (Salix spp.) and birch (Betula glandulosa) shrubs, creating artificial shrub canopies and comparing these manipulations to nearby open tundra and shrub patches. Soil temperatures were 4–5°C warmer in January, and 2°C cooler in July under shrub cover. Natural shrub plots had 14–33 cm more snow in January than adjacent open tundra plots. Snow cover and soil temperatures were similar in the manipulated plots when compared with the respective unmanipulated treatments, indicating that shrub canopy cover was a dominant factor influencing the soil thermal regime. Conversely, we found no strong evidence of increased soil decomposition, CO2 fluxes, or nitrate or ammonia adsorbtion under artificial shrub canopy treatments when compared with unmanipulated open tundra. Our results suggest that the abiotic influences of shrub canopy cover alone on nutrient dynamics are weaker than previously asserted.

Active-layer thickness estimation from X-band SAR backscatter intensity

“…On the one hand shrubs have been said to have a cooling effect due to shading in the summer (Blok et al, 2010;Lawrence and Swenson, 2011;Pearson et al, 2013), leading to shallower ALT. In other publications (Domine et al, 2016;Myers-Smith and Hik, 2013) shrubs have been linked with ground warming due to the isolating effect of snow cover. Shrubs trap wind-blown snow and limit snow erosion by wind.…”

Shifted energy fluxes, increased Bowen ratios, and reduced thaw depths linked with drainage-induced changes in permafrost ecosystem structure

“…The increased abundance of shrubs in high-latitude regions has been studied extensively (e.g., Sturm et al, 2001b;Myers-Smith et al, 2011;DeMarco et al, 2014a), and numerous studies have identified links with factors such as snow cover (Sturm et al, 2001a;Pomeroy et al, 2006), radiation regime (Bewley et al, 2007), and nutrient cycling (Myers-Smith and Hik, 2013;DeMarco et al, 2014b). Regarding soil temperatures, the isolated assessment of shrub expansion indicates that the capture of drifting snow by shrubs increases snow depth and soil temperatures in winter, while shading decreases temperatures in summer (e.g., Sturm et al, 2001a).…”

Initial Stages of Tundra Shrub Litter Decomposition May Be Accelerated by Deeper Winter Snow But Slowed Down by Spring Warming

“…Shrubs might alter the microclimate during summer in contrasting ways: on one hand, shrubs might reduce the surface albedo and create atmospheric heating (Chapin and others 2005;Sturm and others 2005a), but on the other hand, they might also lead to summer soil cooling by shrub shading (Blok and others 2010;Myers-Smith and Hik 2013). These shrub-induced changes in summer air and soil temperatures might, however, also indirectly affect decomposition rates through changes in soil moisture, as microbial decomposer communities are water dependent (Robinson and others 1995;Hicks Pries and others 2013).…”