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

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.

[1]  Volker C. Radeloff,et al.  Regime shift on the roof of the world: alpine meadows converting to shrublands in the southern Himalayas. , 2013 .

[2]  Marc Macias-Fauria,et al.  Eurasian Arctic greening reveals teleconnections and the potential for structurally novel ecosystems , 2012 .

[3]  Steven F. Oberbauer,et al.  Plot-scale evidence of tundra vegetation change and links to recent summer warming. , 2012 .

[4]  J. Welker,et al.  Landscape Heterogeneity of Shrub Expansion in Arctic Alaska , 2012, Ecosystems.

[5]  S. Goetz,et al.  Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities , 2011, Environmental Research Letters.

[6]  M. Bertness,et al.  Interactions among Foundation Species and their Consequences for Community Organization, Biodiversity, and Conservation , 2011 .

[7]  P. Grogan,et al.  The Influence of Vegetation Type on the Dominant Soil Bacteria, Archaea, and Fungi in a Low Arctic Tundra Landscape , 2011 .

[8]  P. Templer,et al.  Carbon and Nitrogen Cycling in Snow‐Covered Environments , 2011 .

[9]  Dorothy Cooley,et al.  Expansion of Canopy-Forming Willows Over the Twentieth Century on Herschel Island, Yukon Territory, Canada , 2011, AMBIO.

[10]  David L. Verbyla,et al.  Carbon loss from an unprecedented Arctic tundra wildfire , 2011, Nature.

[11]  J. R. Mackay,et al.  A Century (1910–2008) of Change in a Collapsing Pingo, Parry Peninsula, Western Arctic Coast, Canada , 2011 .

[12]  M. Mack,et al.  The Effects of Snow, Soil Microenvironment, and Soil Organic Matter Quality on N Availability in Three Alaskan Arctic Plant Communities , 2011, Ecosystems.

[13]  D. Cairns,et al.  Patterns and processes of global shrub expansion , 2011 .

[14]  S. Goetz,et al.  Tundra vegetation effects on pan-Arctic albedo , 2011 .

[15]  F. Daniëls,et al.  Vegetation change in Southeast Greenland? Tasiilaq revisited after 40 years , 2011 .

[16]  I. Myers-Smith.  Shrub encroachment in arctic and alpine tundra: Patterns of expansion and ecosystem impacts. , 2011 .

[17]  Philip Marsh,et al.  Snowmelt energetics at a shrub tundra site in the western Canadian Arctic , 2010 .

[18]  R. Macdonald,et al.  The carbon budget of the northern cryosphere region , 2010 .

[19]  Sarah E. Gergel,et al.  Response of green alder (Alnus viridis subsp. fruticosa) patch dynamics and plant community composition to fire and regional temperature in north‐western Canada , 2010 .

[20]  Martin Hallinger,et al.  Establishing a missing link: warm summers and winter snow cover promote shrub expansion into alpine tundra in Scandinavia. , 2010, The New phytologist.

[21]  B. Forbes,et al.  Russian Arctic warming and ‘greening’ are closely tracked by tundra shrub willows , 2010 .

[22]  J. Melillo,et al.  Impacts of extreme winter warming events on litter decomposition in a sub-Arctic heathland , 2010 .

[23]  G. Schaepman‐Strub,et al.  Shrub expansion may reduce summer permafrost thaw in Siberian tundra , 2010 .

[24]  Kate M. Buckeridge,et al.  Deepened snow increases late thaw biogeochemical pulses in mesic low arctic tundra , 2010 .

[25]  Sonja Wipf,et al.  A review of snow manipulation experiments in Arctic and alpine tundra ecosystems , 2010 .

[26]  I. Hartley,et al.  The response of organic matter mineralisation to nutrient and substrate additions in sub-arctic soils , 2010 .

[27]  Kate M. Buckeridge,et al.  Soil nitrogen cycling rates in low arctic shrub tundra are enhanced by litter feedbacks , 2010, Plant and Soil.

[28]  P. Choler,et al.  Direct and indirect control by snow cover over decomposition in alpine tundra along a snowmelt gradient , 2010, Plant and Soil.

[29]  S. Brantley,et al.  Linking light attenuation, sunflecks, and canopy architecture in mesic shrub thickets , 2010, Plant Ecology.

[30]  R. Macdonald,et al.  Sensitivity of the carbon cycle in the Arctic to climate change , 2009 .

[31]  I. Stirling,et al.  Ecological Dynamics Across the Arctic Associated with Recent Climate Change , 2009, Science.

[32]  F. Stuart Chapin,et al.  The changing global carbon cycle: linking plant–soil carbon dynamics to global consequences , 2009 .

[33]  Sarah E. Gergel,et al.  Relative impacts of disturbance and temperature: persistent changes in microenvironment and vegetation in retrogressive thaw slumps , 2009 .

[34]  A. McGuire,et al.  Changes in vegetation in northern Alaska under scenarios of climate change, 2003-2100: implications for climate feedbacks. , 2009, Ecological applications : a publication of the Ecological Society of America.

[35]  T. E. Osterkamp,et al.  The effect of permafrost thaw on old carbon release and net carbon exchange from tundra , 2009, Nature.

[36]  O. W. Van Auken,et al.  Causes and consequences of woody plant encroachment into western North American grasslands. , 2009, Journal of environmental management.

[37]  S. Hagemann,et al.  Vulnerability of Permafrost Carbon to Climate Change: Implications for the Global Carbon Cycle , 2008 .

[38]  J. Cornelissen,et al.  Plant functional traits and soil carbon sequestration in contrasting biomes. , 2008, Ecology letters.

[39]  T. Lantz.  Relative influence of temperature and disturbance on vegetation dynamics in the Low Arctic : an investigation at multiple scales. , 2008 .

[40]  J. O H,et al.  Shrub encroachment in North American grasslands: shifts in growth form dominance rapidly alters control of ecosystem carbon inputs , 2008 .

[41]  Naoya Wada,et al.  Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes. , 2007, Ecology letters.

[42]  Paul Grogan,et al.  Deeper Snow Enhances Winter Respiration from Both Plant-associated and Bulk Soil Carbon Pools in Birch Hummock Tundra , 2007, Ecosystems.

[43]  David S. Hik,et al.  Variability, contingency and rapid change in recent subarctic alpine tree line dynamics , 2007 .

[44]  David S. Hik,et al.  Responses of white spruce (Picea glauca) to experimental warming at a subarctic alpine treeline , 2007 .

[45]  P. Grogan,et al.  Ecosystem CO2 production during winter in a Swedish subarctic region: the relative importance of climate and vegetation type , 2006 .

[46]  M. Sturm,et al.  The evidence for shrub expansion in Northern Alaska and the Pan‐Arctic , 2006 .

[47]  Timothy E. Link,et al.  Shrub tundra snowmelt , 2006 .

[48]  E. Davidson,et al.  Temperature sensitivity of soil carbon decomposition and feedbacks to climate change , 2006, Nature.

[49]  J. Webster,et al.  Loss of foundation species: consequences for the structure and dynamics of forested ecosystems , 2005 .

[50]  G. Liston,et al.  Changing snow and shrub conditions affect albedo with global implications , 2005 .

[51]  J. Schimel,et al.  Nitrogen Cycling and the Spread of Shrubs Control Changes in the Carbon Balance of Arctic Tundra Ecosystems , 2005 .

[52]  Per Capita,et al.  About the authors , 1995, Machine Vision and Applications.

[53]  J. Welker,et al.  Winter Biological Processes Could Help Convert Arctic Tundra to Shrubland , 2005 .

[54]  F. Chapin,et al.  Ecosystem carbon storage in arctic tundra reduced by long-term nutrient fertilization , 2004, Nature.

[55]  J. Schimel,et al.  Increased snow depth affects microbial activity and nitrogen mineralization in two Arctic tundra communities , 2004 .

[56]  R. Ruess,et al.  The role of lesser snow geese as nitrogen processors in a sub-arctic salt marsh , 1989, Oecologia.

[57]  Amy J. Symstad,et al.  Functional diversity revealed by removal experiments , 2003 .

[58]  J. Schimel,et al.  Interactions between Carbon and Nitrogen Mineralization and Soil Organic Matter Chemistry in Arctic Tundra Soils , 2002, Ecosystems.

[59]  C. Dormann,et al.  Climate change in the Arctic: using plant functional types in a meta‐analysis of field experiments , 2002 .

[60]  Roger A. Pielke,et al.  Modelled changes in arctic tundra snow, energy and moisture fluxes due to increased shrubs , 2002 .

[61]  C. Heyes.  Causes and consequences of imitation , 2001, Trends in Cognitive Sciences.

[62]  M. Sturm,et al.  Climate change: Increasing shrub abundance in the Arctic , 2001, Nature.

[63]  A. Watkinson,et al.  Dynamics of shrub encroachment in an African savanna: relative influences of fire, herbivory, rainfall and density dependence , 2001 .

[64]  Jon Holmgren,et al.  Snow-Shrub Interactions in Arctic Tundra: A Hypothesis with Climatic Implications , 2001 .

[65]  O. V. Auken.  Shrub Invasions of North American Semiarid Grasslands , 2000 .

[66]  C. Holzapfel,et al.  BIDIRECTIONAL FACILITATION AND INTERFERENCE BETWEEN SHRUBS AND ANNUALS IN THE MOJAVE DESERT , 1999 .

[67]  D. Wardle,et al.  Linking above-ground and below-ground interactions: How plant responses to foliar herbivory influence soil organisms , 1998 .

[68]  W. Cody,et al.  Flora of the Yukon Territory. , 1997 .

[69]  S. Hobbie.  Temperature and plant species control over litter decomposition in Alaskan tundra , 1996 .

[70]  D. Schimel,et al.  Mechanisms of shrubland expansion: land use, climate or CO2? , 1995 .

[71]  F. S. Chapin,et al.  Response to fertilization by various plant growth forms in an Alaskan tundra: nutrient accumulation and growth , 1980 .