for most physiological processes in alpine plants (Körner 2003), however, while
snow is lying on the ground, warm atmospheric temperatures are of little effect on
the plants below the snow (but see Starr and Oberbauer 2003; Palacio et al. 2015).
Furthermore, there is evidence that with climate warming precipitation in the form
of snow can actually increase and subsequently delay the timing of snowmelt and
hence shorten the vegetation period (Bjorkman et al. 2015). Hence, to understand
climate effects on alpine vegetation, we need to know summer temperatures and the
timing of snowmelt.
Unfortunately, detailed snow information with high temporal and spatial resolution is often not easy to obtain. One possible approach is to use information of
climate stations that not only record temperature but also snow cover below the
stations. This approach has been used in the Swiss Alps where more than 100 metro
stations have been employed since 1998 (Jonas et al. 2008; Rammig et al. 2010;
Fontana et al. 2008). Plant phenology and productivity were analysed between
stations and between years, and variables related to precipitation and snowmelt
explained as much variance or more than temperature variables (Jonas et al. 2008).
Also, vegetation change on Piz Linard (see above, Wipf et al. 2013b) and on
Scandinavian mountains (Grytnes et al. 2014) seemed to be partly driven by the
snow distribution on the summit. Furthermore, the small-scale distribution of snow
in complex alpine terrain is extremely important for the distribution of plants:
within the same elevation, the date of snowmelt can differ by more than a month
within a few metres depending on topography (Rixen et al. 2010), which influences
vegetation and plant populations considerably (for studies on the snowbed species
Salix herbacea see Wheeler et al. 2015; Sedlacek et al. 2015; Cortes et al. 2014).
Hence, future efforts should clearly focus on not only explaining vegetation
changes by temperature but by a combination of temperature and
precipitation/snow cover.
Apart from temperatures and precipitation, also factors such as nutrient input,
elevated atmospheric CO 2 , extreme events, land use, grazing, etc. need to be taken
into consideration as drivers of vegetation change. Although nitrogen input is
usually smaller (Hiltbrunner et al. 2005) and land-use less intensive at high elevation compared to lowlands, they are by no means negligible (Boutin et al. 2015).
There is evidence that nitrogen deposition could affect alpine plants more than
climate warming (Bobbink et al. 2010). Grazing by sheep can be observed up to the
highest alpine grasslands e.g. in the Alps or the Pyrenees, and might over the long
term have changed alpine vegetation composition profoundly. Abandonment of
remote or steep areas, which is common e.g. in the Pyrenees and the Alps, is hence
likely to change vegetation again, but in combination with climate change it is
unlikely that vegetation will change back to its previous composition. Elevated
atmospheric CO 2 concentrations did not enhance plant growth in alpine grasslands
(Inauen et al. 2012; Korner et al. 1997) but in shrub communities at treeline
(Anadon-Rosell et al. 2014; Dawes et al. 2013, 2014) where the bilberry
(Vaccinium myrtillus) showed more growth, possibly at the cost of smaller or less
responsive plant species.
12 Non-equilibrium in Alpine Plant Assemblages …
293
snow is lying on the ground, warm atmospheric temperatures are of little effect on
the plants below the snow (but see Starr and Oberbauer 2003; Palacio et al. 2015).
Furthermore, there is evidence that with climate warming precipitation in the form
of snow can actually increase and subsequently delay the timing of snowmelt and
hence shorten the vegetation period (Bjorkman et al. 2015). Hence, to understand
climate effects on alpine vegetation, we need to know summer temperatures and the
timing of snowmelt.
Unfortunately, detailed snow information with high temporal and spatial resolution is often not easy to obtain. One possible approach is to use information of
climate stations that not only record temperature but also snow cover below the
stations. This approach has been used in the Swiss Alps where more than 100 metro
stations have been employed since 1998 (Jonas et al. 2008; Rammig et al. 2010;
Fontana et al. 2008). Plant phenology and productivity were analysed between
stations and between years, and variables related to precipitation and snowmelt
explained as much variance or more than temperature variables (Jonas et al. 2008).
Also, vegetation change on Piz Linard (see above, Wipf et al. 2013b) and on
Scandinavian mountains (Grytnes et al. 2014) seemed to be partly driven by the
snow distribution on the summit. Furthermore, the small-scale distribution of snow
in complex alpine terrain is extremely important for the distribution of plants:
within the same elevation, the date of snowmelt can differ by more than a month
within a few metres depending on topography (Rixen et al. 2010), which influences
vegetation and plant populations considerably (for studies on the snowbed species
Salix herbacea see Wheeler et al. 2015; Sedlacek et al. 2015; Cortes et al. 2014).
Hence, future efforts should clearly focus on not only explaining vegetation
changes by temperature but by a combination of temperature and
precipitation/snow cover.
Apart from temperatures and precipitation, also factors such as nutrient input,
elevated atmospheric CO 2 , extreme events, land use, grazing, etc. need to be taken
into consideration as drivers of vegetation change. Although nitrogen input is
usually smaller (Hiltbrunner et al. 2005) and land-use less intensive at high elevation compared to lowlands, they are by no means negligible (Boutin et al. 2015).
There is evidence that nitrogen deposition could affect alpine plants more than
climate warming (Bobbink et al. 2010). Grazing by sheep can be observed up to the
highest alpine grasslands e.g. in the Alps or the Pyrenees, and might over the long
term have changed alpine vegetation composition profoundly. Abandonment of
remote or steep areas, which is common e.g. in the Pyrenees and the Alps, is hence
likely to change vegetation again, but in combination with climate change it is
unlikely that vegetation will change back to its previous composition. Elevated
atmospheric CO 2 concentrations did not enhance plant growth in alpine grasslands
(Inauen et al. 2012; Korner et al. 1997) but in shrub communities at treeline
(Anadon-Rosell et al. 2014; Dawes et al. 2013, 2014) where the bilberry
(Vaccinium myrtillus) showed more growth, possibly at the cost of smaller or less
responsive plant species.
12 Non-equilibrium in Alpine Plant Assemblages …
293