of extinction risks will be too high, and models with finer scales end up with
strikingly lower losses of high-alpine species (Randin et al. 2009). Thus, in alpine
terrain with its high microsite diversity, coexistence between new colonisers and
persisting high-alpine species may be possible if they do not show any niche
overlap nor occupy the same microsites.
Even if species occupy the same microsite, they do not automatically out-compete
each other. Neighbour facilitation, whereby plant individuals benefit from the presence of their interspecific neighbours, is a widespread phenomenon, especially under
harsh environmental conditions (Brooker et al. 2008; Callaway et al. 2002; Choler
et al. 2001; Wipf et al. 2006). Positive neighbour interactions can affect alpine plant
diversity as much as climate (Cavieres et al. 2014). Neighbours can, e.g. ameliorate
the microclimatic, environmental, and soil conditions while competing for the same
resources at the same time (space, light, nutrients). If this facilitative force outbalances
the competition, then facilitation fosters the coexistence of plant species on a small
spatial scale (Kikvidze et al. 2001; Rixen and Mulder 2009) and could also play a
major role in the colonisation of new sites through species from lower altitudes. There
is even evidence that positive species interactions can extend species distributions into
otherwise unfavourable habitats (le Roux et al. 2012). Hence, it is conceivable that
facilitative neighbour interactions enable the coexistence of high-alpine species and
new colonisers on mountain summits, which could counterbalance projected
extinctions. Nevertheless, shifts in net interactions with environmental severity may
differ among indicators of severity, growth forms and scales (Dullinger et al. 2007).
Ongoing and future research will need to target at understanding if upward migration
of plant species will lead to a loss of high-alpine specialists, or if the mosaic of
microhabitats within one elevation range will provide enough buffer to prevent species loss, or if facilitation between neighbours enables the coexistence in the same
microhabitat.
12.7 From Knowledge to Action? Towards Conservation
of High Mountain Flora
Facing ongoing climate and vegetation change, the question remains if plants can
adapt to new conditions and if humans can preserve alpine plants and prevent
extinctions. We have seen above that the small-scale heterogeneity of the alpine
landscape may provide habitat for alpine plants in a changing climate (Scherrer and
Körner 2011). Adaptation of alpine plants through gene flow may also provide
mechanisms to withstand changing environmental conditions (Cortes et al. 2014).
Nevertheless, upward migration of trees and plants from lower elevation will
reduce the area with high-alpine habitat, and, in mountain ranges with human land use,
measures for conservation and restoration need to be considered. On the one hand,
moderate grazing can prevent or slow down tall competitive plants from outcompeting
small alpine plants. On the other hand, if grazing pressure increases because alpine
habitat decreases, erosion in steep areas might be the consequence. Also, pressures
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strikingly lower losses of high-alpine species (Randin et al. 2009). Thus, in alpine
terrain with its high microsite diversity, coexistence between new colonisers and
persisting high-alpine species may be possible if they do not show any niche
overlap nor occupy the same microsites.
Even if species occupy the same microsite, they do not automatically out-compete
each other. Neighbour facilitation, whereby plant individuals benefit from the presence of their interspecific neighbours, is a widespread phenomenon, especially under
harsh environmental conditions (Brooker et al. 2008; Callaway et al. 2002; Choler
et al. 2001; Wipf et al. 2006). Positive neighbour interactions can affect alpine plant
diversity as much as climate (Cavieres et al. 2014). Neighbours can, e.g. ameliorate
the microclimatic, environmental, and soil conditions while competing for the same
resources at the same time (space, light, nutrients). If this facilitative force outbalances
the competition, then facilitation fosters the coexistence of plant species on a small
spatial scale (Kikvidze et al. 2001; Rixen and Mulder 2009) and could also play a
major role in the colonisation of new sites through species from lower altitudes. There
is even evidence that positive species interactions can extend species distributions into
otherwise unfavourable habitats (le Roux et al. 2012). Hence, it is conceivable that
facilitative neighbour interactions enable the coexistence of high-alpine species and
new colonisers on mountain summits, which could counterbalance projected
extinctions. Nevertheless, shifts in net interactions with environmental severity may
differ among indicators of severity, growth forms and scales (Dullinger et al. 2007).
Ongoing and future research will need to target at understanding if upward migration
of plant species will lead to a loss of high-alpine specialists, or if the mosaic of
microhabitats within one elevation range will provide enough buffer to prevent species loss, or if facilitation between neighbours enables the coexistence in the same
microhabitat.
12.7 From Knowledge to Action? Towards Conservation
of High Mountain Flora
Facing ongoing climate and vegetation change, the question remains if plants can
adapt to new conditions and if humans can preserve alpine plants and prevent
extinctions. We have seen above that the small-scale heterogeneity of the alpine
landscape may provide habitat for alpine plants in a changing climate (Scherrer and
Körner 2011). Adaptation of alpine plants through gene flow may also provide
mechanisms to withstand changing environmental conditions (Cortes et al. 2014).
Nevertheless, upward migration of trees and plants from lower elevation will
reduce the area with high-alpine habitat, and, in mountain ranges with human land use,
measures for conservation and restoration need to be considered. On the one hand,
moderate grazing can prevent or slow down tall competitive plants from outcompeting
small alpine plants. On the other hand, if grazing pressure increases because alpine
habitat decreases, erosion in steep areas might be the consequence. Also, pressures
296
C. Rixen and S. Wipf