Increase in species richness on Swiss Alpine mountain summits in 20th century

Note: Endemic, coldadapted species are declining as pioneer species drive them out of their characteristic niches due warming conditions

Data source:

Walther, G-R.; Berger, S. and Sykes, M. T., 2005. An ecological 'footprint'; of climate change. Proceedings of the Royal Society of London Series B Biological Sciences 272: 14271432.

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Projected changes in number of plant species in 2050

Note: Results for stable area per grid cell, using the EuroMove model with HadCM2 A2 climate scenario.

Data source:

Bakkenes, M.; Eickhout, B. and Alkemade, R., 2006. Impacts of different climate stabilisation scenarios on plants species in Europe. Global Environmental Change 16: 2006.

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Past trends

Warmer temperatures in the past 30 years have significantly influenced seasonal patterns across Europe. As evidenced during glacial and inter-glacial periods, the predominant adaptive response of temperature-sensitive plant species has been to shift distributions, resulting in northward and altitudinal movements. One such climate-limited species is holly (Ilex aquifolium), which has expanded in southern Scandinavia in a manner consistent and synchronous with recorded regional climate changes, linked in particular with increasing winter temperatures (Walther et al., 2005).
Mountain ecosystems are particularly vulnerable to climate change (IPCC, 2007). There has been a general increase in mountain summit species in Europe since the Little Ice Age in the 18th century. In Switzerland, for example, the uphill shift of Alpine plants showed an accelerating trend towards the end of the 20th century that is likely to be linked with the extraordinarily warm conditions of the 1990s (Walther et al., 2005) (Figure 1). Evidence also emerged of declines in cold-adapted species as warming conditions and pioneer species drove these from their characteristic niches. Similar observations are expected from current European monitoring programs (e.g. GLORIA) for which results will be available by the end of 2008. In the Swedish Scandes, the tree line of the Scots pine (Pinus sylvestris) rose by 150-200 metres as warmer winters significantly lowered mortality and increased rates of establishment. Observations from other continents show that uphill tree line migration is a global phenomenon that could become a major threat to biodiversity in high mountains (Kullman, 2006; 2007; Pauli et al., 2007).

Projections

Projections indicate that, by the late 21st century, the potential range of many European plant species may shift several hundred kilometres in a northerly direction. This is several times faster than past rates as estimated from the Quaternary record or from historic data (Huntley, 2007). The distribution of tree species is also likely change significantly, with forests expanding in the north and contracting in the south, and broadleaved species replacing native coniferous species in western and central Europe (IPCC, 2007).
Modelling of late 21st century distributions of 1 350 European plant species under a range of scenarios led to the conclusion that more than half will be at the edge of their geographic and altitudinal ranges and could become threatened by 2080, with high risks of extinction (Thuiller et al., 2005). The greatest changes are projected for endemic plant species in Mediterranean, Euro-Siberian and many mountain regions. Mountain communities may face up to a 60 % loss of plant species under high emission scenarios, reversing the 20th century trend outlined above (Thuiller et al., 2005; IPCC, 2007).
Bakkenes et al. (2006) obtained similar results from modelling stable areas of plant species distribution for this century under different climate change scenarios (Figure 2). This study suggests that 10-50 % of plant species in European countries are likely to disappear by 2100 from their current location in the absence of climate change mitigation. Again, species in southeast and southwest Europe are likely to be worst affected. This number will be higher if migration is restricted due to continuing fragmentation or if there is competition with invasive species.