Hot Topics in Ecology

Climate change: Alpine shrubs as ecosystem engineers

Climate warming promotes shrub cover and range expansion via landscape flammability, snow accumulation and nutrient cycling feedbacks
Susanna Venn (Australian National University), Isla Myers-Smith (University of Edinburgh), James Camac (University of Melbourne), Adrienne Nicotra (Australian National University)
  • Alpine shrub cover is increasing in response to a warming climate.
  • Shrub increases are enhanced by positive feedbacks involving fire responses, snow-drifting patterns, leaf litter decomposition and soil nutrient cycling.
  • Critical knowledge gaps surround the rate of shrub range-expansion, the effect of shrubs on local extinctions and the future of mountain catchment water yields.
Alpine shrub, Orites lancifolia, effectively creates a snowdrift in its lee, which can promote soil nutrient cycling feedbacks

Worldwide, shrub cover is increasing across alpine tundra. In Australia, alpine shrub increases match a trend spanning four decades of rising temperatures and declining snowpack. Repeat photography, long-term monitoring, field warming experiments and dendrochronology have revealed that alpine shrubs are responding by encroaching into otherwise non-shrubby communities, such as alpine herbfields and grasslands.

Alpine shrubs readily restrict the growth of other plants via shading and smothering with leaf litter, and they can alter wildlife habitats. Warmer conditions may also exacerbate a feedback between shrubs and fire, whereby increased fire activity due to highly flammable foliage and leaf litter, stimulate vigorous re-sprouting and seeding, resulting in further increases in shrub cover.

Some shrub growth forms interact with winter processes; they can accumulate snow in their lee, thereby insulating soils from extreme winter temperatures. These effects may also promote a second feedback whereby deeper snowpack, warmer soils and higher soil moisture, coupled with leaf litter under shrub canopies, increases microbial activity. These effects in turn, can enhance soil nutrient cycling and ultimately promote shrub growth. Deeper snowpack around shrubs also contributes to winter and spring water yields in mountain catchments.

Given that alpine shrub range-expansion has the potential to significantly modify existing landscape flammability, winter processes and ecosystem function, alpine shrubs effectively act as ecosystem engineers. There is an urgent need for land managers to monitor changes in shrub abundance, and for stakeholders to understand these processes in order to determine whether increases in shrub cover and shrub encroachment will result in alternate stable states in alpine vegetation, local plant and/or animal extinctions, and whether an overall declining snowpack will mitigate or exacerbate these processes.

Hot Topic Lead Author: 
Name: Dr Susanna Venn
Phone: (03) 9479 2327

ID Title Location Type
8629 Boelman et al. (2015) Greater shrub dominance alters breeding habitat and food resources for migratory songbirds in Alaskan arctic tundra. Global Change Biology 21, 1508-20. Brooks Mountain Range, Alaska. Simulation, natural contrasts.
8593 Buckeridge K. M. & Grogan P. (2008) Deepened snow alters soil microbial nutrient limitations in arctic birch hummock tundra. Applied Soil Ecology 39, 210-22. Canadian low Arctic. manipulative experiment.
8594 Buckeridge K. M., Zufelt E., Chu H. & Grogan P. (2010) Soil nitrogen cycling rates in low arctic shrub tundra are enhanced by litter feedbacks. Plant and Soil 330, 407-21. Low Canadian Arctic. pre-existing gradient.
8595 Camac J. S., Williams R. J., Wahren C.-H., Hoffmann A. A. & Vesk P. A. (2016) Climatic warming strengthens a positive feedback between alpine shrubs and fire. bioRxiv, 043919. Bogong High Plains, SE Australia. Field surveys, experimental manipulations.
8596 Camac J. S., Williams R. J., Wahren C.-H., Jarrad F., Hoffmann A. A. & Vesk P. A. (2015) Modeling rates of life form cover change in burned and unburned alpine heathland subject to experimental warming. Oecologia 178, 615-28. Bogong High Plains, SE Australia. Manipulative experiment.
8597 Camac J. S., Williams R. J., Wahren C. H., Morris W. K. & Morgan J. W. (2013) Post‐fire regeneration in alpine heathland: Does fire severity matter? Austral Ecology 38, 199-207. Bogong High Plains, SE Australia. Pre-existing contrasts, simulation.
8598 Cannone N., Sgorbati S. & Guglielmin M. (2007) Unexpected impacts of climate change on alpine vegetation. Frontiers in Ecology and the Environment 5, 360-4. Itialian Alps. pre-existing gradient.
8599 Chu H. & Grogan P. (2010) Soil microbial biomass, nutrient availability and nitrogen mineralization potential among vegetation-types in a low arctic tundra landscape. Plant and Soil 329, 411-20. Canadian low arctic. pre-existing contrasts.
8600 Essery R. & Pomeroy J. (2004) Vegetation and topographic control of wind-blown snow distributions in distributed and aggregated simulations for an Arctic tundra basin. Journal of Hydrometeorology 5, 735-44. Canadian low Arctic. Simulation.
8601 Fiddes S. L., Pezza A. B. & Barras V. (2015) A new perspective on Australian snow. Atmospheric Science Letters 16, 246-52. Australian Alps. Pre-existing gradient, simulation.
8602 Liston G. E., Mcfadden J. P., Sturm M. & Pielke R. A. (2002) Modelled changes in arctic tundra snow, energy and moisture fluxes due to increased shrubs. Global Change Biology 8, 17-32. Alaskan Arctic Tundra. Simulation.
8603 Maestre F. T., Eldridge D. J. & Soliveres S. (2016) A multifaceted view on the impacts of shrub encroachment. Applied Vegetation Science 19, 369-70. NA Review / Commentary.
8604 McDougall K. L. (2003) Aerial photographic interpretation of vegetation changes on the Bogong High Plains, Victoria, between 1936 and 1980. Australian Journal of Botany 51, 251-256. Bogong High Plains, SE Australia. Natural experiment.
8605 Myers-Smith I. H., Elmendorf S. C., Beck P. S., Wilmking M., Hallinger M., Blok D., Tape K. D., Rayback S. A., Macias-Fauria M. & Forbes B. C. (2015) Climate sensitivity of shrub growth across the tundra biome. Nature Climate Change 5, 887-91. Circumpolar Arctic. Correlation.
8606 Myers-Smith et al. (2011) Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities. Environmental Research Letters 6, 045509 Global. Data synthesis / Review.
8607 Myers‐Smith I. H. & Hik D. S. (2013) Shrub canopies influence soil temperatures but not nutrient dynamics: an experimental test of tundra snow–shrub interactions. Ecology and evolution 3, 3683-700. Kluane Region, sothwest Yukon Territory, Canada. Manipulative experiment.
8608 Scherrer P. & Pickering C. M. (2005) Recover of alpine vegetation from grazing and drought: data from long-term photoquadrats in Kosciuszko National Park, Australia. Arctic, Antarctic and Alpine Research 37, 574-84. Snowy Mountains, SE Australia. Pre-existing contrasts.
8609 Sturm M., Holmgren J., McFadden J. P., Liston G. E., Chapin III F. S. & Racine C. H. (2001a) Snow-shrub interactions in Arctic tundra: a hypothesis with climatic implications. Journal of Climate 14, 336-344. Alaskan Arctic Tundra. Field surveys, correlations.
8610 Sturm M., Racine C. & Tape K. (2001b) Climate change: increasing shrub abundance in the Arctic. Nature 411, 546-7. Between the Brooks Range and the Arctic coast. Correlations.
8611 Sturm M., Schimel J., Michaelson G., Welker J. M., Oberbauer S. F., Liston G. E., Fahnestock J. & Romanovsky V. E. (2005) Winter biological processes could help convert arctic tundra to shrubland. Bioscience 55, 17-26. Alaskan Arctic Tundra. Correlations, simulations, natural experiment, anecdotes.
8612 Vankoughnett M. R. & Grogan P. (2016) Plant production and nitrogen accumulation above-and belowground in low and tall birch tundra communities: the influence of snow and litter. Plant and Soil, 1-16. Canadian North West Territories. Manipulative experiment.
8613 Venn S., Pickering C. & Green K. (2014) Spatial and temporal functional changes in alpine summit vegetation are driven by increases in shrubs and graminoids. AoB plants 6, plu008. Snowy Mountains, SE Australia. Natural gradient.
8614 Venn S. E., Pickering C. M. & Green K. (2012) Short-term variation in species richness across an altitudinal gradient of alpine summits. Biodiversity and Conservation 21, 3157-3186. Snowy Mountains, SE Australia. Natural gradient.

Further information about this topic contact:

Dr Susanna Venn
(03) 9479 2327

Chair, Hot Topics Editorial Board
Dr Brett Murphy