Multi-Decadal Changes in Tundra Environments and Ecosystems: Synthesis of the International Polar Year-Back to the Future Project (IPY-BTF)

Abstract

Understanding the responses of tundra systems to global change has global implications. Most tundra regions lack sustained environmental monitoring and one of the only ways to document multi-decadal change is to resample historic research sites. The International Polar Year (IPY) provided a unique opportunity for such research through the Back to the Future (BTF) project (IPY project #512). This article synthesizes the results from 13 papers within this Ambio Special Issue. Abiotic changes include glacial recession in the Altai Mountains, Russia; increased snow depth and hardness, permafrost warming, and increased growing season length in sub-arctic Sweden; drying of ponds in Greenland; increased nutrient availability in Alaskan tundra ponds, and warming at most locations studied. Biotic changes ranged from relatively minor plant community change at two sites in Greenland to moderate change in the Yukon, and to dramatic increases in shrub and tree density on Herschel Island, and in subarctic Sweden. The population of geese tripled at one site in northeast Greenland where biomass in non-grazed plots doubled. A model parameterized using results from a BTF study forecasts substantial declines in all snowbeds and increases in shrub tundra on Niwot Ridge, Colorado over the next century. In general, results support and provide improved capacities for validating experimental manipulation, remote sensing, and modeling studies.

Modelling Tundra Vegetation Response to Recent Arctic Warming

“…The Arctic version of LPJ-GUESS employed in this study is being developed for this purpose. Callaghan et al (2011) challenged modellers to test the ability of their tools to reproduce trends and variations in tundra ecosystems seen in monitoring studies. We have accepted the challenge, and to some extent LPJ-GUESS proved successful in simulating the enhanced productivity and increased woody component in vegetation, apparent in many observational studies, and attributable at least in part to a positive temperature trend over the Arctic since the 1970s (see discussion and references above).…”

“…A further issue concerns the heterogeneity of responses seen in different studies and in different parts of the Arctic (e.g. Callaghan et al 2011;Elmendorf et al 2012). While temperature regimes are obviously a major driver of ecosystem structure and function in polar regions, other factors such as water balance, geology, soil type, trophic interactions, as well as anthropogenic management and land use also play an important role, and in some situations the combination of several drivers may lead to 'counterintuitive' changes, even over a period when temperatures are rising consistently and markedly.…”

“…Important lines of evidence include positive trends in surface greenness and photosynthetic activity inferred from satellite data (Tucker et al 2001;Bunn and Goetz 2006;Bhatt et al 2010;Beck and Goetz 2011), advancement of elevational and latitudinal treelines (Sonesson and Hoogesteger 1983;Kullman 2002;Harsch et al 2009;Van Bogaert et al 2010, 2011, and an increased cover, abundance and stature of shrubs in tundra areas (Kullman 2002;Jia et al 2003;Tømmervik et al 2004;Tape et al 2006;Hedenås et al 2011;Rundqvist et al 2011). Despite numerous local exceptions, the weight of evidence from observational studies suggests that, in general, Arctic vegetation is responding to rising temperatures through increases in productivity, density, cover and stature of vegetation and, in many areas, an increase in woody biomass and the representation of trees and shrubs (Post et al 2009;Callaghan et al 2011;Elmendorf et al 2012). These findings are qualitatively consistent with expectations based on the results of tundra warming experiments (Chapin et al 1995;Michelsen et al 1996;Arft et al 1999;Graglia et al 2001;Walker et al 2006;Olsrud et al 2010), and simulations using vegetation models (Kaplan et al 2003;Smith et al 2008a;Wolf et al 2008a;Wramneby et al 2010).…”

“…Synthesising findings from studies that have tracked changes in Arctic tundra vegetation over recent decades, Callaghan et al (2011) challenged modellers to use the findings to validate-and improve-the models. Here, we take on this challenge, applying a customised, Arctic version of the LPJ-GUESS dynamic vegetation model (Smith et al 2001) across the Arctic, forced by climate data for the past three decades, during which the region has experienced a net warming of [1°C.…”

Using Available Information to Assess the Potential Effects of Climate Change on Vegetation in the High Arctic: North Billjefjorden, Central Spitsbergen (Svalbard)

“…Although the list of references recording the impact of climate changes on biota in the Arctic is enormous (Parmesan 2006;Thuiller et al 2008), reports are rare from conditions which were not experimentally manipulated and for which comparative data describing past vegetation composition, biomass production or plant distribution are available, and methods of assessment are repeatable (Callaghan et al 2011). As a consequence, determining how the vegetation has changed over decades at specific locations is difficult.…”