12.6 Alpine Plants on the Verge to Extinction or Safe
in Cold Microhabitats?
Although most studies demonstrate an impressive increase in species numbers and
local colonisations, only relatively little local extinction, and no particular traits or
species groups that were mainly affected by local extinctions, were found in
long-term vegetation surveys in European alpine ecosystems (Hofer 1992; Walther
et al. 2005; Wipf et al. 2013b; Grabherr et al. 2001; Matteodo et al. 2013).
Moreover, the summit flora has been found to become more similar in composition
over time, and there is evidence that many high-alpine species that were already
present on few summits have meanwhile also colonised further summits (Kammer
et al. 2007; Jurasinski and Kreyling 2007). Thus, up to now, we see many winners,
but few losers on Europe’s mountain summits even after several decades of ongoing
climate warming.
Species distribution models recently predicted mountain flora to be threatened
unequally across Europe in the twenty-first century (Engler et al. 2011).
Specifically, temperature increase and precipitation decrease are expected to be
more pronounced in e.g. the Alps and the Pyrenees than, e.g. in the Norwegian
Scandes (Engler et al. 2011), which can be seen, in part, already in the temperature
changes occurred in the recent past (Gottfried et al. 2012). Short-term floristic
changes on European summits analysed by the GLORIA initiative indeed indicate a
signal towards an increased prevalence of species with higher temperature preferences over 8 years that correlates with the magnitude of recent warming (see above,
Gottfried et al. 2012).
While most studies agree that species upwards shifts are already happening,
there is little consensus on potential losses of alpine biota due to future climate
change. At first glance, the modelled projections of massive extinction rates in
high-alpine species, and the observational findings of strong increase in summits
species numbers even contradict each other. However, as the expected local
extinctions are thought to be driven by competition through species rising to higher
altitudes, it could be expected that an initial enrichment with new colonisers will be
followed by an extinction of the formerly local species after a certain time lag
(Dullinger et al. 2012; Engler et al. 2009). On the other hand, evidence for competitive replacement of high-alpine species is, at best, weak, even after decades of
ongoing climate warming. Also, species in cold habitats are assumed to be less
affected by competition (Pellissier et al. 2013) and their niches to be more closely
related to their physiological limits (Normand et al. 2009). However, these studies
do not take into account that some alpine species are true cold species, i.e. that they
are not able to adapt their physiology (dark respiration) to a warmer temperature
(Larigauderie and Körner 1995).
In contrast to the massive range contractions and high extinction rates among
high-alpine plants predicted by species distribution models, recent micrometeorological studies show that due to the large variety of different microhabitats on a
small spatial scale, the alpine belt offers a large number of small-scale “refugia” that
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C. Rixen and S. Wipf
in Cold Microhabitats?
Although most studies demonstrate an impressive increase in species numbers and
local colonisations, only relatively little local extinction, and no particular traits or
species groups that were mainly affected by local extinctions, were found in
long-term vegetation surveys in European alpine ecosystems (Hofer 1992; Walther
et al. 2005; Wipf et al. 2013b; Grabherr et al. 2001; Matteodo et al. 2013).
Moreover, the summit flora has been found to become more similar in composition
over time, and there is evidence that many high-alpine species that were already
present on few summits have meanwhile also colonised further summits (Kammer
et al. 2007; Jurasinski and Kreyling 2007). Thus, up to now, we see many winners,
but few losers on Europe’s mountain summits even after several decades of ongoing
climate warming.
Species distribution models recently predicted mountain flora to be threatened
unequally across Europe in the twenty-first century (Engler et al. 2011).
Specifically, temperature increase and precipitation decrease are expected to be
more pronounced in e.g. the Alps and the Pyrenees than, e.g. in the Norwegian
Scandes (Engler et al. 2011), which can be seen, in part, already in the temperature
changes occurred in the recent past (Gottfried et al. 2012). Short-term floristic
changes on European summits analysed by the GLORIA initiative indeed indicate a
signal towards an increased prevalence of species with higher temperature preferences over 8 years that correlates with the magnitude of recent warming (see above,
Gottfried et al. 2012).
While most studies agree that species upwards shifts are already happening,
there is little consensus on potential losses of alpine biota due to future climate
change. At first glance, the modelled projections of massive extinction rates in
high-alpine species, and the observational findings of strong increase in summits
species numbers even contradict each other. However, as the expected local
extinctions are thought to be driven by competition through species rising to higher
altitudes, it could be expected that an initial enrichment with new colonisers will be
followed by an extinction of the formerly local species after a certain time lag
(Dullinger et al. 2012; Engler et al. 2009). On the other hand, evidence for competitive replacement of high-alpine species is, at best, weak, even after decades of
ongoing climate warming. Also, species in cold habitats are assumed to be less
affected by competition (Pellissier et al. 2013) and their niches to be more closely
related to their physiological limits (Normand et al. 2009). However, these studies
do not take into account that some alpine species are true cold species, i.e. that they
are not able to adapt their physiology (dark respiration) to a warmer temperature
(Larigauderie and Körner 1995).
In contrast to the massive range contractions and high extinction rates among
high-alpine plants predicted by species distribution models, recent micrometeorological studies show that due to the large variety of different microhabitats on a
small spatial scale, the alpine belt offers a large number of small-scale “refugia” that
294
C. Rixen and S. Wipf