Vulnerabilities - Terrestrial biodiversity

The Alps are one of the richest biodiversity hotspots in Europe with over 15,000 animal and 13,000 plant species (12). It is virtually certain that European mountain flora will undergo major changes due to climate change (1). Species in these regions are in general able to cope with a local warming of 1–2°C . Extinction of more than 90% of species is expected by temperature increases above 3°C (19)

A specific model application showed that a 1°C additional warming would result in the loss of 40% of the potential range of 62 endemic mountain species in the Alps, whereas a 4–5°C warming would imply a 90–97% loss (20). Endemic species suffer especially, because they will be unable to adapt to the changed environment, cannot migrate to more appropriate locations and cannot compete with immigrating (shrub and tree) species (19).

Three responses to climate change can be distinguished at the species level, namely genetic adaptations, biological invasions through species inter-competition, and species extinction. The treeline is predicted to shift upward by several hundred metres (2). There is evidence that this process has already begun in Scandinavia (3) and the Mediterranean (4). In fact, the upward shift of the tree line has also been found in Switzerland (13): typical alpine vascular plants have shifted their distribution in the uphill direction during the past few years. The number of plant species on alpine sample plots has increased. The upward moving species may compete with, and crowd out, species, which traditionally have occupied territories at higher altitudes (14).

Another major problem in many parts of the European Alps is that ecosystems have been so fragmented and the population density is so high, that many options for ecosy­stem conservation may be impossible to implement (5).Mountain ecosystems are among the most threatened in Europe (6).

Vast evidence of the impact of changing climatic conditions on plants stems from phenological observations. There are numerous indications for shifts in the phenological phases of plant development like the start of blossoming, flushing of leaves, length of the vegetation period and start of leaf fall in autumn (16). The shift is particularly marked since the 1980s when a significant upward trend in average temperatures was registered in Switzerland.

The 1990s were the warmest decade since the beginning of climate measurements. The extraordinary warm climatic conditions of the 1990s are reflected in the floristic composition of Alpine summit vegetation. Plant species richness of high alpine summit vegetation has increased during the last 100 years in the southeastern Swiss Alps; this increase has accelerated since 1985, consistent with a climate change explanation. An acceleration of the trend in the upward shift of alpine plants has also been shown (7).

Climatic changes affect plants beyond simply shifting the elevation belts upwards. Plants growing at higher elevations may benefit from warmer summer temperatures because their growth is primarily temperature-limited (9) whereas those growing at lower elevations may experience more droughty conditions than normal (10). Therefore, climatic changes and seasonal extremes must be evaluated in a biological context if we are to understand how these variations may affect photosynthesis, carbon sequestration and growth of natural vegetation (11).

In Switzerland, except for the southern part, a decrease in the number of species is particularly expected in low moors. This will become even stronger if precipitation decreases and the extension of these habitats decreases due to water shortage. With regard to this process, the upland moors in Switzerland are in a special position. The higher temperatures and the longer dry periods endanger the moss cover and enable species uncommon in upland moors to invade these habitats. This is unwanted because it represents an ecosystem modification and
species poverty represents a typical characteristic of upland moors. The displaced species are specialists that are unable to settle in any other habitat (21).

In the long term, the composition of many Swiss forests will change. This will be the combined result of changing climatic conditions and case-by-case human intervention induced by the impacts of climate change, e.g., afforestation with better adapted tree species after storm, fire, drought events or insect calamities. It is expected that the share of deciduous trees will increase and coniferous trees decrease. This will have consequences for the timber industry, which is mainly equipped for processing softwood (14).

Formerly absent species such as Mediterranean butterflies, dragonflies and bird species are now extending their habitat into Switzerland. … According to recent research, about 100 invasive alien insect species are established in European forests (15). Mostly, these were introduced via global trade but their subsequent establishment in forests is often the result of higher temperatures (14).

Climate change is expected to affect species composition, distribution, their cycles, synchronicity, the overall genetic diversity and the provision of ecosystem services. This will have a direct bearing on the future role of ecosystems for society in the areas of animal and plant species used for food production, genetic resources and biochemical substances for medical purposes, pollination, water purification, soil fertility and prevention of soil erosion, as well as landscape appearance for tourism (14).

Society draws on biodiversity as a vital resource. However, biodiversity is not given adequate recognition and ecosystems are often heavily exploited. Currently, projects addressing this issue are carried out globally and at the pan-European level, putting a monetary value on biodiversity and ecosystem services (The Economics of Biodiversity and Ecosystem Services) (14).

Overall, the number of species in Switzerland is increasing steadily in spite of increasing loss of species, since immigrations are considerably more numerous than cases of extinction. However, in the overall evaluation, the losses have to be given more weight because many of these species are becoming entirely extinct, that is worldwide, while the immigrating species often have their main distribution area in the Mediterranean, sometimes even on other continents (21).

Extinction debt of high-mountain plants

The extremes of possible climate-change-driven habitat range size reductions are commonly based on two assumptions: either species instantaneously adapt their ranges to any change in the distribution of suitable sites (`unlimited dispersal' scenario), or they are unable to move beyond the initially occupied sites (`no dispersal' scenario) (25). In addition to these static, niche-based model predictions, a so-called hybrid model was used that couples niche-based projections of geographical habitat shifts with mechanistic simulations of local demography and seed dispersal (based on regional circulation model projections and the A1B climate change scenario) (26).

Averaged across 150 species in the Alps, the hybrid model simulations indicate that by the end of the twenty-first century these high mountain plants will have lost 44-50% of their present alpine habitat ranges under high and low values of demographic and dispersal parameters, respectively (26).

The hybrid model indicates that the opposing effects of delayed local population extinctions and lagged migration rates will result in less severe twenty-first-century range reductions of alpine plants than expected from static, niche-based model predictions. However, these apparently `optimistic' forecasts include a large proportion of remnant populations under already unsuitable climatic conditions (26). The persistence of such remnant populations creates an extinction debt that will have to be paid later unless species manage to adapt phenotypically or genetically to the changing climate (27) and to the likely associated alterations in their biotic environments (28).

Most importantly, the hybrid model results consistently caution against drawing overoptimistic conclusions from relatively modest range contractions observed during the coming decades, as these are likely to mask more severe longer-term warming effects on mountain plant distribution (26).

Vulnerabilities - Fresh water and wetlands biodiversity

Since 1950, water temperatures in rivers and near the surface of lakes in Switzerland have in some cases increased by more than 2°C. In some lower-lying Swiss rivers, there is evidence suggesting that the maximum temperature that can be tolerated by local species of trout is now being exceeded (17).

Much of the long-term increase in water temperature in rivers and lakes at all depths is associated with the continued tendency for the North Atlantic Oscillation (NAO) to stay in its positive phase, resulting in warmer winters in much of Europe. Long-term winter warming also causes a reduction in the duration of ice cover in alpine lakes (18).

In summer 2003 central Europe suffered an unusually severe heat wave, with air temperatures similar to those predicted for an average summer during the late 21st century. From over half a century of lake data from two lakes in Switzerland, surface temperature and thermal stability in the summer of 2003 were shown to be the highest ever recorded, exceeding the long-term mean by more than 2.5 standard deviations. The extremely high degree of thermal stability resulted in extraordinarily strong hypolimnetic oxygen depletion (8).

Summer climate conditions equivalent to those expected to prevail near the end of the present century have an extreme physical impact on temperate lakes, resulting in an unprecedented intensification of thermal stratification with a concomitant increase in hypolimnetic oxygen depletion. … This provides a strong indication that the physical effect of climate warming on such lakes poses a potential threat to the largely successful long-term management efforts that have been undertaken to ameliorate the effects of anthropogenic eutrophication (8).

Glacier-fed rivers

As a result of the apparent `low' biodiversity, and minimal knowledge regarding the distribution of alpine aquatic species, glacier-fed rivers have received negligible attention from conservationists (22). The rapid shrinking of glaciers results in a reduction in glacial meltwater contribution to river flow in many glacierized catchments (23). These changes potentially affect the biodiversity of specialized glacier-fed river communities (24).

Research has shown that 11–38% of the regional species pools in study regions in Ecuador, the Alps and Alaska, including endemics, can be expected to be lost following complete disappearance of glaciers in a catchment, and steady shrinkage is likely to reduce local richness at downstream reaches where glacial cover in the catchment is less than 5–30% (22). Extinction will probably greatly exceed the few known endemic species in glacier-fed rivers.

Adaptation strategies

In September 2008, the Swiss parliament mandated the Federal Office for the Environment to develop a new and overarching national biodiversity strategy. This strategy will set the framework for biodiversity conservation over the next decades. Climate change is one of the pressures on biodiversity that the strategy will address, since even under the most modest climate change scenario, impacts on biodiversity in Switzerland are expected to increase (14).

Changes in ecosystem structure and functioning as well as unexpected interactions between species are likely to become more common. Given the role of climate in triggering shifts in the distribution of species and habitats, the national biodiversity strategy will place a particular focus on safeguarding the gene pool and habitat connectivity. By reinstating the connectivity of habitats the potential for adaptive changes in ecosystems shall be increased, the resilience of ecosystems safeguarded and thus the long-term provision of ecosystem services secured (14).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Switzerland.

1. Walther (2004), in: Bogatai (2007)
2. Alcamo et al. (2007)
3. Kullman (2002), in: Bogatai (2007)
4. Peñuelas and Boada (2003); Camarero and Gutiérrez (2004), both in: Bogatai (2007)
5. Bogatai (2007)
6. Schröter et al. (2005), in: Alcamo et al. (2007)
7. Walther et al. (2005)
8. Jankowski et al. (2006)
9. Körner and Paulsen (2004), in: Jolly et al. (2005)
10. Barr et al. (2002), in: Jolly et al. (2005)
11. Jolly et al. (2005)
12. Agrawala (2007)
13. Gehrig-Fasel et al. (2007), in: Federal Office for the Environment FOEN (Ed.) (2009)
14. Federal Office for the Environment FOEN (Ed.) (2009)
15. Mattson et al. (2007), in: Federal Office for the Environment FOEN (Ed.) (2009)
16. Defila and Clot (2001), in: Federal Office for the Environment FOEN (Ed.) (2009)
17. Hari et al. (2005), in: Federal Office for the Environment FOEN (Ed.) (2009)
18. Livingstone (1997b), in: Federal Office for the Environment FOEN (Ed.) (2009)
19. European Environment Agency (EEA) (2005)
20. Hare (2005); Pauli et al.(2001), in: European Environment Agency (EEA) (2005)
21. OcCC/ProClim- (2007)
22. Jacobsen et al. (2012)
23. Barnett et al. (2005); Milner et al. (2009), both in: Jacobsen et al. (2012)
24. Brown et al. (2007), in: Jacobsen et al. (2012)
25. Thuiller et al. (2008), in: Dullinger et al. (2012)
26. Dullinger et al. (2012)
27. Bradshaw and Holzapfel (2006), in: Dullinger et al. (2012)
28. Brooker and Plant (2006), in: Dullinger et al. (2012)