Vulnerabilities - Terrestrial biodiversity

Mountain tops are smaller than the bases. Therefore, the upward shift of vegetation zones results in the present belts at high elevations occupying smaller and smaller areas. Thus, the corresponding species would have smaller populations and might become more vulnerable to genetic and environmental pressure (2). In the Alps, the main climatic space contraction and fragmentation of plant populations would be in the present alpine and nival belts, where rare and endemic species with low dispersal capacities could become extinct (1).

The calculated upward moving rates for nine typical nival plant species over the last 70-90 years (with a realized warming of approximately 0.7°C) were in most cases below 1.5 m per decade, but some species showed 4 m per decade (1).

A permanent plot study at the transition zone from alpine grassland to subnival vegetation on Schrankogel (Stubaier Alpen, Tyrol) showed that some pioneer species of alpine grassland has increased in cover, whereas all of the typical subnival species showed a decrease at their lower range margins (3); this is considered as a first signal of warming-induced species declines in the high Austrian Alps.

Climate change conditions of approximately 1°C warming and precipitation change of +/- 7% seem to characterize some kind of threshold beyond which the severity of potential adverse climate change impacts might increase substantially (4).

Given the information that in Austria 70% of its surface area is 500 m above the sea level and about 40% above 1,000 m together with the fact that ecosystems in mountainous regions are highly sensitive, it can be feared that Austria is particularly vulnerable to a climatic change (1). For Norway spruce in the Northern Limestone Alps (Germany and Austria), however, neither growth suppression at the lower elevation sites nor growth increase at higher elevation sites was observed in a dataset covering more than 150 years (until 2003), despite a sharp temperature increase of ~1°C since the 1990s (15). According to the authors, these findings reveal the ability of mountain forests to adapt to an unprecedented temperature shift, suggesting that adaptation to forthcoming climate changes might not require a shift in tree species composition in the Northern Limestone Alps (15).

In an accelerating climate warming regime the area losses for the subnival and nival zones above the alpine grassland belt may be drastic (5); typical subnival species already were observed to decline (3). Mountainous areas could be disproportionably sensitive to climate change with species losses of up to 60% (6).

The outstanding biological richness of mountain regions and the often spatially limited distribution range of their species make these areas particularly vulnerable to irretrievable biodiversity losses. All alpine areas in Europe that lie above the climatic treeline comprise around 3 % of the continent, but approximately 20 % of Europe’s native vascular plant species have the centre of distribution within this area (7). This includes many endemic species that are restricted to the higher altitudes of single mountain regions (3).

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) (11). 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) (12).

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 (12).

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 (12). 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 (13) and to the likely associated alterations in their biotic environments (14).

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 (12).

Vulnerabilities - Fresh water and wetlands biodiversity

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 (8). The rapid shrinking of glaciers results in a reduction in glacial meltwater contribution to river flow in many glacierized catchments (9). These changes potentially affect the biodiversity of specialized glacier-fed river communities (10).

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% (8). Extinction will probably greatly exceed the few known endemic species in glacier-fed rivers.

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 Austria.

1. Federal Ministry of Agriculture, Forestry, Environment and Water Management (2010)
2. Peters and Darling (1985); Hansen-Bristow et al. (1988); Bortenschlager (1993), in: Federal Ministry of Agriculture, Forestry, Environment and Water Management (2010)
3. Pauli et al. (2007), in: Federal Ministry of Agriculture, Forestry, Environment and Water Management (2010)
4. Lexer et al. (2000), in: Federal Ministry of Agriculture, Forestry, Environment and Water Management (2010)
5. Gottfried et al. (1999), in: Federal Ministry of Agriculture, Forestry, Environment and Water Management (2010)
6. Thuiller et al. (2005)
7. Väre et al. (2003), in: Federal Ministry of Agriculture, Forestry, Environment and Water Management (2010)
8. Jacobsen et al. (2012)
9. Barnett et al. (2005); Milner et al. (2009), both in: Jacobsen et al. (2012)
10. Brown et al. (2007), in: Jacobsen et al. (2012)
11. Thuiller et al. (2008), in: Dullinger et al. (2012)
12. Dullinger et al. (2012)
13. Bradshaw and Holzapfel (2006), in: Dullinger et al. (2012)
14. Brooker and Plant (2006), in: Dullinger et al. (2012)
15. Hartl-Meier et al. (2014)