por_035.fm 96 Polar Research 26 2007 96–103 © 2007 The Author FROM THE CONFERENCE MELT ING ICE—A HOT TOPIC? Climate change and biodiversity in the Arctic—Nordic perspectives Philip A. Wookey School of Biological and Environmental Sciences, University of Stirling, Stirling, FK9 4LA, UK. E-mail: philip.wookey@stir.ac.uk This paper is based upon a presentation given on United Nations Environment Programme (UNEP) World Envi- ronment Day, 5 June 2007, as part of the Nordic Perspec- tives session of the climate change conference Melting Ice—A Hot Topic? The broad aims of this paper are to define biodiversity and ecosystem services, to set the biodiversity of the Arctic terrestrial realm into its global context, and, through the use of case studies, to illustrate how environ- mental change can influence biodiversity and ecosystems, and to explore what the implications of these changes might be. A comprehensive treatment of the topic is well beyond the scope of both the presentation and this paper, but the reader is directed to the CAFF (2001) and ACIA (2005) reports for reviews and synthesis. Biodiversity and ecosystem services Biodiversity is defined as The variability among living organisms from all sources including, inter alia , terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are a part; this includes diversity within species, between species and of ecosystems. (Article 2, Convention on Biological Diversity 1992) This presentation focuses upon terrestrial biodiversity, but a key point to emphasize in the definition is that biodiversity includes “diversity within species” and “of ecosystems”. So biodiversity cannot be used interchange- ably with “species richness” (numbers of species). In the Arctic the diversity within species can be very great, and CAFF (2001: 49) notes that “genetic, morphological and behavioural diversity may be especially significant com- ponents of biodiversity”; this assumes even greater signif- icance in the Arctic, where species richness is often low compared with communities and ecosystems from tem- perate and tropical environments. Biodiversity is fundamental to the provision of “ecosys- tem services”, and these are defined by the Food and Agriculture Organization (FAO) as The conditions and processes through which natural ecosystems, and the species that make them up, sustain and fulfil human life. Examples include provision of clean water, maintenance of liveable climates (carbon sequestration), pollination of crops and native vegeta- tion, and fulfilment of people’s cultural, spiritual, intellectual needs. (FAO 2005) Note that the term “ecosystem services” is anthropocen- tric, and refers to services to Humankind. So, in essence, when we talk of ecosystem services this is a utilitarian view of life on Earth, but it does provide a basic foundation for an assessment of the value of biodiversity to people, and as such has some worth. In the context of the Arctic terrestrial realm, ecosystem services that are straightfor- ward to recognize include (i) the provision of food and fodder (e.g., for reindeer herders and their animals in the Nordic and Russian contexts), (ii) fuel and fibre (the latter including animal and plant products), (iii) a sense of cultural and spiritual identity, (iv) the maintenance of fundamental ecosystem services (such as photosynthesis, decomposition and nutrient recycling), (v) a clear link to the global climate system and biogeochemical cycles, (vi) the provision of genetic resources and (vii) a clear link with service industries such as the tourism sector. In relation to (v), the Arctic is profoundly important in the global energy budget (with snow cover, and the forest– tundra ecotone, assuming great importance in terms of albedo and surface roughness effects). In terms of genetic resources (vi), cold-adapted organisms (particularly micro-organisms) are likely to have major potential for development of therapeutic or pharmaceutical products, and soils and sediments undoubtedly represent major reservoirs of genetic diversity in the Arctic terrestrial realm (as indicated by the work of Torsvik et al. 2002). doi:10.1111/j.1751-8369.2007.00035.x P. A. Wookey Climate change and biodiversity in the Arctic Polar Research 26 2007 96–103 © 2007 The Author 97 Arctic terrestrial biodiversity in context Set against this background of the role of biodiversity for ecosystem services in the Arctic, and emphasizing the point that biodiversity includes within-species and among-ecosystem diversity, a tacit generalization can be made that biodiversity is low in the Arctic (at least among higher plants and vertebrates: see Table 1). The results of Rannie (1986), Chernov (1989, 1995) and Matveyeva & Chernov (2000) show a clear inverse rela- tionship, for example, between mean July temperature and the biodiversity of vascular plant species, nesting birds, ground beetles and day butterflies across transects in Canada and Russia. The logical conclusion from this is that warming should increase biodiversity (at least in the long term). But this is likely to be a gross oversimplifica- tion, particularly bearing in mind the predicted rapid rates of climate change (especially for the Arctic land- masses), and the other drivers of change superimposed upon climate; this is an issue that will be raised again in due course. Some specialist “Arctic” species may, how- ever, be lost (e.g., of the plants, some “euarctic” compo- nents, currently widespread in the northern part of the Arctic tundra zone, and hyperarctic species of the north- ern tundra, polar deserts and semi-deserts, may be espe- cially vulnerable; see Callaghan et al. 2005). This partly reflects the likely northern shift in life zones, and an overall contraction of the tundra biome. Plants, animals and microorganisms are also likely to respond differen- tially to change (because of contrasting life histories, generation times and dispersal mechanisms), resulting in the advent of “novel” communities for which there are no contemporary analogues. Although interspecific diversity is generally low in the Arctic, some taxa are proportionally well-represented in the Arctic terrestrial biota (Table 1), in particular in the cryptogams (spore-producing plants; specifically the algae, lichens and mosses) and soil invertebrates such as the collembola (springtails) (CAFF 2001; ACIA 2005). The diversity of soil microorganisms in Norwe- gian tundra and Arctic desert (Svalbard) soils also com- pares favourably with arable and pasture soils (Torsvik et al. 2002). Indeed for Arctic terrestrial ecosystems the soil is undoubtedly the largest reservoir of biodiversity and genetic capital, although this situation is unlikely to be unique among terrestrial ecosystems. Soil biodiver- sity is, in ecosystem terms, as important as plant biodi- versity, and in terms of energy flows and material recycling there are internal recycling processes (where Fig. 1 A general model of a terrestrial ecosystem. The three component subsystems (plant, herbivore and decomposer) are shown, together with their component parts. The major transfers of material are denoted by arrows, whereas organic matter pools are shown within rectangles, and inorganic pools are shown within “clouds”. Note, in particular, that a key raw material for photosynthesis (carbon dioxide [CO 2 ]) is returned to the atmosphere principally by the decomposer organisms (this is certainly the case in the Arctic), and that “mineral” nutrients are also made available to plants by the decomposers (although there is growing evidence that plants may “bypass” this process and take up amino acids, for example, directly from the soil, or via mycorrhizas). Note, also, the internal recycling within the decomposition subsystem: this is an aspect of internal biocom- plexity that is not matched directly within the plant and herbivore sub- systems. Furthermore, we know very little indeed of soil biodiversity in most Arctic terrestrial ecosystems, in spite of the significance of the decomposition subsystem to ecosystem processes and properties (including carbon sequestration in soil organic matter and permafrost). Figure redrawn from Swift et al. (1979). Carnivore 2Carnivore 1Herbivore Detritus Decomposers CO2 Inorganic nutrients Plant subsystem Herbivore subsystem Decomposition subsystem Recycling Table 1 Biodiversity estimates in terms of species richness (numbers of species) within selected groups for the Arctic terrestrial realm north of the latitudinal treeline, and their percentage of the terrestrial total globally. Modified from CAFF (2001) and ACIA (2005). “Other groups” includes amphibians and reptiles (seven species), centipedes (10 species), terres- trial molluscs (three species), oligochaetes (earthworms and enchytraeid worms; 70 species) and nematodes (ca. 500 species). Group Arctic species numbers Arctic % of total Insects 3300 0.4 Mites 700 1.9 Springtails 400 6.0 Spiders 300 1.7 Birds 240 2.9 Mammals 75 1.7 Other groups 600 – Fungi 2500 2.3 Lichens 2000 11.0 Flowering plants 1735 0.7 Algae 1200 3.3 Mosses 600 4.1 Liverworts 250 2.5 Ferns 62 0.6 Conifers 12 1.6 98 Polar Research 26 2007 96–103 © 2007 The Author Climate change and biodiversity in the Arctic P. A. Wookey Fig. 2 Schematic diagram of the annual pattern of environmental variables and net photosynthesis at Barrow, Alaska. Barrow has a climate classified as just within the High Arctic zone. The period of net photosynthesis is highlighted by the dashed box. Notice how snow cover lasts through until June, at a time when solar radiation inputs are at a peak and are soon to decline. Earlier snowmelt is likely to increase phytomass and accelerate plant reproductive phenology. Later senescence may result from later autumn freeze-up, although light may be limiting, and senescence may be triggered by changes in light quality (From Chapin and Shaver, 1985 reprinted with permission from Kluwer Academic Publishers and from the author.) Fig. 3 A schematic diagram showing a mesotopographic gradient for the Arctic that includes five habitats: dry, mesic (zonal), wetland, snowbed and streamside vegetation. The landscape heterogeneity here, associ- ated with the presence of a snowbed, increases habitat diversity and thus biodiversity. Asynchronous melting of snowbeds through the thaw period maintains the availability of newly-emerged high-quality food for herbi- vores over space and time. Earlier thawing of snowbeds has the potential to reduce habitat diversity. Redrawn from Walker (2000). 2 2 1 4a 3 4b 55 Late-melting Snow drift Prevailing wind 1. Dry exposed ridges 2. Mesic zonal sites 3. Wet meadows 4. Snowbeds a. well-drained, early -melting b. poorly -drained, late-melting 5. Streamside sites decomposer organisms themselves die, and are decom- posed in turn by others) which confer a complexity to the decomposer subsystem that is frequently over- looked in discussions of biodiversity and environmental change (Fig. 1). Environmental change in the Arctic is multifaceted Environmental change in the Arctic is multifaceted, and organisms respond both directly and indirectly to these changes. Climate change is just one of several environ- mental change “drivers”, alongside the ongoing changes in atmospheric composition themselves (e.g., increasing CO 2 concentrations; increasing deposition of airborne N- and S-containing contaminants; and stratospheric ozone depletion resulting in greater UVB fluxes at the surface), and direct anthropogenic disturbance (e.g., for transport infrastructure, fossil fuel and mineral extraction, forestry, tourism and hydropower generation). Because environmental changes of contrasting rate, magnitude and geographical extent are all occurring simultaneously in the Arctic, and organisms will respond differentially to these changes, there are serious chal- lenges involved in attempting to predict how biodiversity, communities and ecosystems will respond to change. And we cannot always rely with confidence on the lessons of history (“the past as a key to the future”; see Adams & Woodward 1992) because changes are occurring for which there are no analogues in the palaeoenvironmen- tal or palaeoecological records. P. A. Wookey Climate change and biodiversity in the Arctic Polar Research 26 2007 96–103 © 2007 The Author 99 But what are the effects of warming? However, setting this issue aside, even in the case of climate warming it is by no means straightforward to predict the impacts on terrestrial ecosystems. In an Arctic context, landscape heterogeneity and the role of the cryosphere are potentially significant “modifiers” of the effects of warming on ecosystems. Figure 2, for example, shows the potential for earlier snowmelt in tundra regions to have a major impact on plant phenology and photosynthesis resulting from the availability of substan- tial fluxes of photosynthetically active radiation (PAR) around the summer solstice (when solar elevations are high). Later autumn freeze-up may also result in delayed plant senescence. But earlier snowmelt may also have negative, or coun- terintuitive, consequences. In complex landscapes, where snow is redistributed from wind-exposed areas to hollows and depressions, early snowmelt may cause a reduction of habitat heterogeneity caused by the loss of snowbeds. Snowbed “specialists” (e.g., the moss Kiaeria starkei ) may not be able to survive the change in physical environ- mental conditions, or increased competition. Further- more, earlier melting of snowbeds may also have negative consequences for herbivores if it means that the availability of high-quality forage (associated with new growth) is temporally “compressed” earlier into the sum- mer; in this respect, complex landscapes, with a mosaic of vegetation communities and late-melting snowbeds, might offer newly-emerged high-quality food for herbi- vores throughout a growing season (Fig. 3) (Björk & Molau 2007). The effects of experimental warming on both Arctic and alpine tundra ecosystems has been investigated by the team of scientists from ITEX (the International Tun- dra Experiment). This experiment was launched, in con- cept, in 1990, and soon after was established at 28 sites in the tundra biome. The broad geographical coverage and international participation were seen as important com- ponents of the original set-up, in recognition that plants in contrasting parts of their geographical range might respond differently to the same change in temperature (Fig. 4). Initially, ITEX focused upon the phenological and growth responses of a set of broadly circumpolar Arctic and alpine vascular plant species (see e.g., Fig. 5) to experimental warming (achieved by using small hexago- nal open-topped chambers [OTCs]), designed to simulate the greenhouse effect. The OTCs generally produced a near-surface warming of around 1–3 ° C above the ambi- ent temperatures for control (unwarmed) plots. After several years (up to four) of the experiment, the data from 13 of the sites was subjected to meta-analysis to test whether any generalizations could be made regarding geographical contrasts in responses to warming, as well as contrasts relating to plant functional type (e.g., deciduous vs. evergreen dwarf shrubs, forbs and graminoids). This meta-analysis (Arft et al. 1999) demonstrated the sensi- tivity of tundra plants to warming, and identified differ- ential responses among contrasting growth forms and among contrasting regions (High Arctic; Low Arctic; alpine). With regards to the current presentation, how- ever, the subsequent ITEX work on community (as opposed to individual plant) responses to warming (Walker et al. 2006) provides data to suggest that some plant growth forms (specifically lichens and bryophytes) do badly in warmer conditions (Figs. 6, 7). This may be the result of shading by plant functional types that respond particularly vigorously to warming (e.g., decidu- ous dwarf shrubs such as the dwarf birch [ Betula nana ]), or to competition for nutrients, or to factors such as surface drying (a possible artefact of the OTCs). Diversity and evenness indices all decreased significantly with Fig. 4 This schematic diagram illustrates the performance of a plant spe- cies (in terms of net primary productivity [NPP]) across a gradient of tem- perature (which could be expressed as mean temperatures over a growing season, or as some other metric of thermal energy availability, e.g., grow- ing degree days, or in the case of tundra plants thawing degree days, representing accumulated “thermal time”). Increasing temperature in tun- dra ecosystems will co-vary with other abiotic factors (e.g., precipitation or depth of the active layer) and also with biotic factors, such as intensity of competition or herbivory. Intensity of competition (e.g., for light or soil nutrients) is likely to increase from the extreme polar deserts and alpine fellfields to the more closed tundras of the Low Arctic and mid- to low alpine (perhaps leading to a skewed NPP curve, with values dropping more steeply at the warmer end of the distribution as a result of competition interactions). Note that, according to this scheme, a given temperature increase ( ∆ T ) could produce quite different outcomes depending on where in the species’ range the warming occurs. Thus, warming at the colder end of the distribution could markedly improve plant performance, whereas towards the warmer end of the distribution increased respiratory demands, or intensity of competition, could reduce NPP to the extent that the species dies out, or is forced out, of the community. Temperature/position in range P ro ce ss r a te North South NPP Intensity of competition/ Influence of ‘invasive’ species 100 Polar Research 26 2007 96–103 © 2007 The Author Climate change and biodiversity in the Arctic P. A. Wookey Fig. 5 Some of the vascular plant species stud- ied as part of ITEX (Arft et al. 1999; Walker et al. 2006). (a) Saxifraga oppositifolia (purple saxi- frage), (b) Silene acaulis (moss campion), (c) Dryas octopetala ssp. octopetala (mountain aven) and (d) Cassiope tetragona (Arctic bell heather). (d) (c) (a) (b) Fig. 7 Response of tundra plant community variables to experimental warming in ITEX. The symbols represent the mean effect size based on the meta-statistic “Hedges D ” (the normalized difference between experimen- tal and control means adjusted for sample size), and the lines give 95% confidence intervals. The effect sizes for canopy height, ordination scores and diversity indices were all considered “moderate” by meta-analysis convention. Note the general increase in height of vascular plants (trian- gles), the significant increases in shrubs, deciduous shrubs and litter cover, and the decreases in both lichen and bryophyte cover (circles) and diversity indices (diamonds). (From Walker et al. 2006; reprinted with per- mission from the authors, copyright 2006 National Academy of Sciences, U.S.A.) Fig. 6 ITEX sites contributing to the Walker et al. (2006) meta-analysis of plant community responses to experimental warming. (From Walker et al. 2006; reprinted with permission from the authors, copyright 2006 National Academy of Sciences, U.S.A.) P. A. Wookey Climate change and biodiversity in the Arctic Polar Research 26 2007 96–103 © 2007 The Author 101 Fig. 8 Environs of the Agricultural Research Institute research station near Akureyri, north Iceland, with ice-layer formation in the foreground. Damage to perennial grasses resulting from anoxia beneath the ice cover can be very severe during “mild” winters. (Photograph by permission of Bjarni E. Gu leifsson.)ð warming, and the results strongly suggest that biodiver- sity might decrease (at least in the short term) in response to warming. The other notable results were that tundra plant communities exhibited detectable responses to warming over time periods of only three to four years, and the significant “winners” were the deciduous shrubs, with increases both in percentage cover and in height (Fig. 7) (see also Sturm, Racine & Tape (2001). The observation that lichens are adversely affected by experi- mental manipulations simulating climate change impacts (including the addition of mineral nutrients to simulate more rapid decomposition processes) has also been observed by Cornelissen et al. (2001), so this result seems robust and consistent. So, the effects of climate warming on tundra ecosys- tems are by no means straightforward to predict, and a criticism that has been levelled at programmes such as ITEX is that it might have placed too much weight on summer warming effects (whereas the general circulation models of the Earth’s climate suggest that winter warm- ing will be of much greater magnitude in the polar regions). Warmer winters in a cold environment might be expected to be beneficial for the biota, but again there are data from the Arctic suggesting the converse. Aanes et al. (2000) and Yoccoz & Imms (1999) have data from Sval- bard showing that both Svalbard reindeer ( Rangifer tarandus platyrhynchus ) and sibling voles ( Microtus rossiae- meridionalis ) have undergone population crashes during winters with freezing rain. This is likely to result from the formation of ice layers in the snowpack (which reindeer cannot penetrate for foraging), or the collapse of the subnivean space beneath the snowpack. Such examples are not restricted to Svalbard. Indeed in the Nordic context, milder winters with increased incidence of freez- ing and thawing cycles may have serious implications for summer pasture systems with perennial grasses (Fig. 8), as well as for natural ecosystems (see, for example, Robinson et al. 1998). The Arctic is not isolated In contrast to the views of many people living in industri- alized regions to the south, the Arctic is not isolated neither, biologically, climatically nor socio-economically. Migratory animals provide clear examples of the linkages between the Arctic and lower latitudes, and strong cli- matic teleconnections (e.g., between the North Atlantic Oscillation, Arctic Oscillation and the El Niño–Southern Oscillation) are evident, as are their biological conse- quences (e.g., Aanes et al. 2002; Post & Forchhammer 2004; Forchhammer et al. 2005). Events and policy out- side the Arctic often have a clear impact within the Arctic, even if this was unintentional. The European Union FRAGILE project (Fragility of Arctic goose habitat: impacts of land use, conservation, and elevated tempera- ture) highlights this, as does the example of snow geese in North America. The numbers of several species of goose that breed in Svalbard in the summer, but that migrate to western Europe to overwinter, have increased dramati- cally in the last 40 years (with a 30-fold increase in barnacle geese [ Branta leucopsis ] and a fourfold increase in pink-footed geese [ Anser brachyrhynchus ]). Changes in land use and hunting practice in the overwintering areas (both linked with socio-economic and/or political deci- sions) have resulted in rapid increases in winter survivor- ship, whereas earlier melt-out in the breeding areas may be responsible for increased breeding success (Cooper et al. 2004). Research to determine the impacts of the increased grazing intensity and climate change on the vegetation communities and ecosystem processes of the breeding areas in Svalbard is ongoing. This interplay between climate change drivers and socio-economic/ political drivers of change demonstrates clearly the link- ages between climate, wildlife and society, and these link- ages extend across thousands of kilometres. Conclusions • The Arctic biota has been subject to dramatic environ- mental change during the last 2.5 million years, but ongoing and predicted change is rapid and very different. • Conventional wisdom suggests that biodiversity should increase with warming in the medium to long term, but the tundra biome is increasingly “compressed” between the Boreal zone and the Arctic Ocean. 102 Polar Research 26 2007 96–103 © 2007 The Author Climate change and biodiversity in the Arctic P. A. Wookey • Many species and habitats in the Arctic are potentially highly vulnerable to change. • Rates of change are so rapid that “novel” assemblages of organisms will develop, and we know very little of how these will function, or of the possible role of “invasive” species. • Like it or not, the Arctic and its organisms and commu- nities are set to provide an early detection system of the impacts of environmental change on planet Earth. Acknowledgements Many thanks to the Norwegian Polar Institute, the Nordic Council of Ministers and the United Nations Environ- ment Programme for the opportunity to speak on World Environment Day. I would also like to thank my col- leagues in the International Tundra Experiment (ITEX) and the Circum-Arctic Terrestrial Biodiversity Initiative (CAT-B; supported by the International Arctic Science Committee) for their insights, enthusiasm and support over the years. References Aanes R., Sæther B.-E. & Øritsland N.A. 2000. 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