Geography Compass 4/8 (2010): 1133–1153, 10.1111/j.1749-8198.2010.00356.x Climate Change Impacts in Alpine Environments Georg Grabherr1*, Michael Gottfried1 and Harald Pauli2 1Department of Conservation Biology, Vegetation and Landscape Ecology, University of Vienna, Vienna, Austria 2Institute of Mountain Research: Man and Environment, Austrian Academy of Sciences, Vienna, Austria Abstract Alpine ecosystems (alpine tundra) occur at a range of air density, water availability and seasonality worldwide on the treeless high terrain of mountains. They vary along geographic scales: boreal dwarf-shrub heaths, temperate sedge heaths, subtropical dwarf shrubs and tussock grasslands, and tropical giant forblands. Along local topographic gradients plant cover changes from windswept dwarf-shrub heath, to dense grass-sedge heath, to snowbank vegetation. These cold and relatively little exploited alpine ecosystems, nonetheless, are among those where climate warming impacts are forecast to be pronounced and detectable early on. We first review alpine life conditions and organism traits as a background to understanding climate impact related processes. Next, we pro- vide an account of how alpine flora and vegetation have been impacted by recently observed climate change. Finally, a global network for long-term monitoring of climate-induced changes of vegetation and biodiversity in alpine environments is described. Alpine Environments – Definition, Distribution, Elevation, Zonation Alpine environments (Figure 1), occur in a low temperature climate where growing season means in general do not exceed 6–8 °C; this temperature limit marks the lower distribution limit of the alpine zone worldwide (Ko¨rner and Paulsen 2004). However, there is a large variability with respect to altitude (air density), water availability, and sea- sonality across the globe (Figure 2). Accordingly, alpine is a rather broad term that encompasses a number of designations biogeographers have proposed (Nagy and Grabherr 2009, Table 1.1). Nonetheless ‘alpine’ is commonly used in a broad sense for the treeless areas above a low-temperature determined treeline in the high reaches of mountains (Grabherr et al. 2003; Ko¨rner 1995, 2003; Nagy and Grabherr 2009; Wielgolaski 1997). This area can be divided into at least two zones: alpine sensu stricto and nival. The alpine zone (or alpine tundra) may extend over an elevation interval of 1000 m (Grabherr et al. 1995) where species-rich closed plant communities dominate the landscape (e.g. heath, fell-fields, grasslands, pa´ramo, puna; Figure 3). These zonal communities form a landscape matrix (Figure 5a) that might be interspersed to varying degrees with specialist habitats, such as rock faces, screes, glaciers, snowbeds, and marshes. At the upper limit of the alpine zone, vegetation becomes open (Figure 4a); nonetheless many plant and animal species live in favourable niches at higher altitudes. It is the so-called nival zone (Fig- ure 4), expanding another c. 1000 m of elevation to the limit of higher plant life. The highest growing vascular plants have been found above 6000 m in the Himalayas (Miehe 1997, 2004; Webster 1961), and lichens at 7400 m (Miehe 2004). Bryophyte-dominated ecosystems around steam vents near the top of Volcan Socompa (6060 m) in the Andes ª 2010 The Authors Journal Compilation ª 2010 Blackwell Publishing Ltd 1134 Climate change impacts in alpine environments Fig. 1. Piz Linard (3411 m), Switzerland, shows impressively the elevational zonation of a mountain, where the zone beyond the treeline is considered as ‘‘alpine’’ throughout the globe. Major subdivisions are alpine sensu stricto for the vegetated but treeless zone, nival for the region of rock, scree and snow that still hosts vascular plants, and aeolian above where only a few organisms of microbes, lichens, or arthropods exist (not occurring at Piz Linard with thirteen vascular plant species at the very top). Fig. 2. The main environmental factors that differentiate mountains in an ecological perspective. Examples are: Ruwenzoris (aseasonal wet tropics), Cordillera Blanca (seasonal tropical), Tibesti (dry subtropical), Alborz (Mediterra- nean), Hohe Tauern (Alps; temperate), Franz Joseph Land (polar region). (modified after Nagy and Grabherr 2009). represent an extreme outpost for a complex biotic community (Halloy 1991), in an otherwise bare desert environment. Thirty-six taxa of mosses and lichens, some insects, a small rodent (Phyllotis darwinii rupestris) and a bird (Sicalis olivaceus) form isolated ‘islands of ª 2010 The Authors Geography Compass 4/8 (2010): 1133–1153, 10.1111/j.1749-8198.2010.00356.x Journal Compilation ª 2010 Blackwell Publishing Ltd Climate change impacts in alpine environments 1135 (a) (b) (c) (d) Fig. 3. The main zonal alpine biota worldwide: (a) Giant rosette formation (pa´ ramo, giant forb lands) of tropical humid mountains (Lobelia rhynchopetala; Bale Mts., Ethiopia). (b) Tussock grasslands of the seasonal tropical puna region (Cordillera Blanca, Peru). (c) Spiny cushion formation of Mediterranean mountains (Alyssum spinosum; Atlas, Morocco). (d) Northern hemisphere mountain grasslands (Kobresia ⁄ Carex community; alpine tundra, alpine steppe; Tienshan, Kyrgyzstan). (a) (b) (c) (d) Fig. 4. Nival biota and their plant life forms: (a) Assemblage of nival plants from the Austrian Alps (3100 m). (b) Cushion, a ‘‘heat collecting’’ growth form (Androsace alpina, Austrian Alps). (c) Mesophytic forb Ranunculus glacialis can survive 33 months under snow (Austrian Alps). (d) Grass Poa ruwenzorensis stays frozen every night (5100 m, Ruwenzori, Uganda). ª 2010 The Authors Geography Compass 4/8 (2010): 1133–1153, 10.1111/j.1749-8198.2010.00356.x Journal Compilation ª 2010 Blackwell Publishing Ltd 1136 Climate change impacts in alpine environments (a) (b) (c) (d) Fig. 5. Typical alpine landscape of the Central Alps and life strategy of the dominant Carex curvula: (a) The ele- ments of alpine environments sensu stricto: zonal grassland, glacier forefields, rocks, snowbeds; note that leaf tips are withering which is obligatory in this species. A leaf grows for about 3 years from the base and withers from the end. (b) Individual of Carex curvula, about 30-years-old. (c) Fairy ring of a 60-year-old individual. (d) Clonal pop- ulation of Carex curvula in late successional state. The chaotic pattern suggests that the ramets belong to a few genets germinated some hundreds years ago if not more. A fairy ring of about 40 years is visible as a computer simulation suggests (right above). Circles: tillers with leafs; Dots: without leafs (modified after Grabherr 1997). life in the sky’ (Halloy 1991). In temperate mountains such as the Alps, or the Rocky Mountains, the limit of higher plant life lies at around 3000–4000 m; in boreal and arctic mountains it drops below 2000 m, and to 1000 m, respectively. Above lies the aeolian zone with barren rocks, debris, ice and snow. Small animals and microbes characterize the aeolian zone (Swan 1992) where organic material (detritus, wind-blown organisms originating from lower altitudes), deposited by wind, provides most of the food for scav- enging and predatory animals. Variability of Alpine Environments Altitude (air density), water availability, and seasonality (Figure 2) are specific to each mountain region. These factors determine, besides the available flora and fauna, the altitu- dinal zonation, the structure and functioning of the ecosystems. No two mountain systems are identical. EFFECTS RELATED TO CHANGING ELEVATION (TEMPERATURE, AIR DENSITY DECREASE) Mountains with an alpine zone occur at all latitudes, from the wet tropics to the polar regions (Figures 3 and 12). Apart from a steady decrease of temperature with increasing ele- vation at an average rate of 0.60 °C⁄100 m (Nagy and Grabherr 2009, p. 23), air pressure also decreases. The latter becomes particularly relevant in mountains such as the Himalayas where the highest peaks reach beyond 8000 m. Low oxygen might be one of the causes for the absence of many animal groups from the high grounds or their generally low diversity ª 2010 The Authors Geography Compass 4/8 (2010): 1133–1153, 10.1111/j.1749-8198.2010.00356.x Journal Compilation ª 2010 Blackwell Publishing Ltd Climate change impacts in alpine environments 1137 compared to the lowlands (Nagy and Grabherr 2009, p. 59). Contrarily, low carbon dioxide pressure seems to have no limiting effect on plants; other factors such as low temperatures set the limits (Ko¨rner 2003.) EFFECTS RELATED TO SEASONALITY The macroclimate of the life zone to which a mountain region belongs to determines the climatic conditions in its alpine zone, e.g. the aseasonal climate regime of the wet tropics is also evident at high altitudes. Plants are permanently in an active state in the tropics, such as the Lobelia spp. and Dendrosenecio spp. in Africa, and the Espeletia spp. in tropical South America (Beck et al. 1982; Squeo et al. 1991; Figure 3a), whereas alpine and nival plants (Figures 4 and 5) under seasonal climates undergo winter dormancy and survive long winters under snow protection, or are frost resistant. Plants such as Saxifraga oppositi- folia or Silene acaulis can tolerate extreme temperatures in winter (e.g. both species survived immersion into liquid nitrogen at )196 °C; Kainmu¨ller 1975). Species that are sensitive to frost require permanent snow protection, and as a result, have developed a remarkable snow tolerance. For example the nival zone Ranunculus glacialis (Figure 4c) in the Alps is known to be able to survive up to 33 months permanently under snow (Moser et al. 1977). Animals on the high grounds may overwinter either by hibernating (e.g. Marmota spp.), or they may stay active under deep snow cover (e.g. Thomomys spp., Ochotona spp.). Some alpine animal traits, especially of insects, such as reduced body size, melanism, increased pubescence, prolonged life cycle, thermoregulation, or freezing toler- ance may be related to adaptation to low temperatures (Sømme 1997). Life Forms, Life Cycles The diversity of alpine climates might be one reason that no specific single alpine life strategy exists (Ko¨rner 1995).