Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities

Abstract

Recent research using repeat photography, long-term ecological monitoring and dendrochronology has documented shrub expansion in arctic, high-latitude and alpine tundra 1 1748-9326/11/045509+15$33.00 c 2011 IOP Publishing Ltd Printed in the UK Environ. Res. Lett. 6 (2011) 045509 I H Myers-Smith et al ecosystems.Here, we (1) synthesize these findings, (2) present a conceptual framework that identifies mechanisms and constraints on shrub increase, (3) explore causes, feedbacks and implications of the increased shrub cover in tundra ecosystems, and (4) address potential lines of investigation for future research. Satellite observations from around the circumpolar Arctic, showing increased productivity, measured as changes in 'greenness', have coincided with a general rise in high-latitude air temperatures and have been partly attributed to increases in shrub cover. Studies indicate that warming temperatures, changes in snow cover, altered disturbance regimes as a result of permafrost thaw, tundra fires, and anthropogenic activities or changes in herbivory intensity are all contributing to observed changes in shrub abundance. A large-scale increase in shrub cover will change the structure of tundra ecosystems and alter energy fluxes, regional climate, soil-atmosphere exchange of water, carbon and nutrients, and ecological interactions between species. In order to project future rates of shrub expansion and understand the feedbacks to ecosystem and climate processes, future research should investigate the species or trait-specific responses of shrubs to climate change including: (1) the temperature sensitivity of shrub growth, (2) factors controlling the recruitment of new individuals, and (3) the relative influence of the positive and negative feedbacks involved in shrub expansion.

Projected changes in diverse ecosystems from climate warming and biophysical drivers in northwest Alaska

“…Slow forest and shrub migration into new areas (Supplemental Material, Fig. 1), altitudinal increases in treeline, and shifts in dominance within plant communities have altered canopy dominance and understory composition (Suarez et al 1999;Sturm et al 2001;Myers-Smith et al 2011). Topographic barriers are important in constraining this expansion (Rupp et al 2001).…”

New insights into the 21 November 2000 tsunami in West Greenland from analyses of the tree−ring structure of Salix glauca

“…willow (Salix spp. ), which form annual growth rings that can be used for dating purposes (Schweingruber and Poschlod 2005;Myers−Smith et al 2011b;Schweingruber et al 2013;Myers−Smith et al 2015). The potential of the shrub Salix spp.…”

Detection and Attribution of Observed Impacts

“…Climate change impacts have been related to permafrost changes, including an increase of flow speed of rock glaciers and debris lobes in the European Alps and Alaska (high confidence), resulting in rockfall, debris flows, and potential hazards to transport and energy systems (Kääb et al, 2007;Delaloye et al, 2010;Daanen et al, 2012), expansion, deepening and higher dynamics of thermokarst lakes and ponds in the Arctic (Rowland et al, 2010), and a doubled erosion rate of Alaska's northern coastline over the past 50 years (high confidence; Section 18.3.3.1, Table 18-8; Mars and Houseknecht, 2007;Karl et al, 2009;Forbes, 2011). Expansion of channel networks (Toniolo et al, 2009), increased river bank erosion (Costard et al, 2007), and an increase in hillslope erosion and landsliding in northern Alaska since the 1980s (Gooseff et al, 2009) have all been related to climate.…”

“…Field and satellite measurements indicate substantial changes in freshwater and terrestrial ecosystems (often linked to permafrost thawing) in many areas of the Arctic tundra (high confidence; Hinzman et al, 2005;Axford et al, 2009;Jia et al, 2009;Post et al, 2009;Prowse and Brown, 2010;Myers-Smith et al, 2011;Walker et al, 2012). Vegetation productivity has systematically increased over the past few decades in both North America and northern Eurasia (Goetz et al, 2007;Jia et al, 2009;Elmendorf et al, 2012).…”

“…While processes related to climate change, such as rising mean sea levels (Leatherman et al, 2000;Ranasinghe and Stive, 2009), more frequent extreme sea levels (Woodworth et al, 2011), or permafrost degradation and sea ice retreat (Forbes, 2011) can be expected to enhance global erosion, there are multiple drivers involved in shoreline erosion that are unrelated to climate change including long shore sediment transport; the diversion of sediments by dams; and subsidence due to resource extraction, mining, and coastal engineering and development (see also Mars and Houseknecht, 2007;Forbes, 2011).…”