benefit from greater protection from pathogens, pests and widespread disturbances
than populations in well-connected areas. However, this isolation is not sufficient to
protect them from global processes such as climate change and pollution, as these
are transmitted through the atmosphere. Significantly, high mountains are usually
situated in sparsely populated areas, due to their low accessibility, in contrast with
lowlands and coastal areas, where the most human population is concentrated, all
over the world. The human-driven impact on high mountain areas is, therefore,
lower in comparison with these densely populated regions. Nevertheless, historically human presence has played an important role in configuring mountain
ecosystems. For instance, in the Alps and Pyrenees, human activity has been regularly recorded since Neolithic times (Tinner et al. 2005; Gassiot Ballbè et al.
2017), and it has profoundly modified the landscape over the last centuries
(Colombaroli et al. 2010; Pèlachs et al. 2017). Isolation and low population density
also provide high mountains with emotional and aesthetic values that are often
idealised. These habitats commonly play host to sanctuaries, or an entire mountain
system can be seen as a sanctuary in itself. This perception coincides with the
concept of preservation and may contribute to the conservation of natural systems.
Interestingly, low accessibility may imply fewer resources for conservation. On the
other hand, these remote areas may experience looser control by centres of decision
over the conservation practices carried out there.
Second, high mountain habitats provide harsh living conditions. The altitudinal
gradient implies a decrease in temperature and a prolonged duration of snow cover,
which combine to shorten the periods of growth. Moreover, strong winds, low
water availability at high altitudes and the scanty soil development associated with
steep slopes and erosion result, overall, in a pronounced abiotic stress. In consequence, vegetation cover is reduced, leading to mutually reinforcing feedback (for
instance, between vegetation cover, water retention and soil erosion). Also, high
altitude favours the passage of pollutants from the troposphere to the ground
(Camarero 2017b) and a loss of atmospheric protection against ionising radiation.
Therefore, only relatively few species are able to persist in these extreme conditions. These species typically present low growth rates and life cycles adapted to the
short duration of favourable conditions (Laiolo and Obeso 2017). The environmental conditions specific to high mountains, along with their geographic isolation,
have forged an adaptive landscape that has shaped the characteristic functional and
compositional traits of its biota. Another consequence is a noticeable fragility in
these ecosystems, as the resident species are often pushed to their limits of ecophysiological tolerance. Nevertheless, selective pressure may have favoured
adaption to these environments. Simultaneously, species tolerant of a broad range
of conditions are often found here, far from the competition withstood by other
species. Also, importantly, low growth rates and short periods of growth limit
population recovery after disturbances or harsh environmental conditions, thus
reducing resilience.
Another characteristic of high mountain ecosystems is that they tend to exhibit
steep environmental gradients over relatively short distances. These gradients are
largely determined by topography and aspect, which determine the radiation
2 Trade-offs in High Mountain Conservation
39
than populations in well-connected areas. However, this isolation is not sufficient to
protect them from global processes such as climate change and pollution, as these
are transmitted through the atmosphere. Significantly, high mountains are usually
situated in sparsely populated areas, due to their low accessibility, in contrast with
lowlands and coastal areas, where the most human population is concentrated, all
over the world. The human-driven impact on high mountain areas is, therefore,
lower in comparison with these densely populated regions. Nevertheless, historically human presence has played an important role in configuring mountain
ecosystems. For instance, in the Alps and Pyrenees, human activity has been regularly recorded since Neolithic times (Tinner et al. 2005; Gassiot Ballbè et al.
2017), and it has profoundly modified the landscape over the last centuries
(Colombaroli et al. 2010; Pèlachs et al. 2017). Isolation and low population density
also provide high mountains with emotional and aesthetic values that are often
idealised. These habitats commonly play host to sanctuaries, or an entire mountain
system can be seen as a sanctuary in itself. This perception coincides with the
concept of preservation and may contribute to the conservation of natural systems.
Interestingly, low accessibility may imply fewer resources for conservation. On the
other hand, these remote areas may experience looser control by centres of decision
over the conservation practices carried out there.
Second, high mountain habitats provide harsh living conditions. The altitudinal
gradient implies a decrease in temperature and a prolonged duration of snow cover,
which combine to shorten the periods of growth. Moreover, strong winds, low
water availability at high altitudes and the scanty soil development associated with
steep slopes and erosion result, overall, in a pronounced abiotic stress. In consequence, vegetation cover is reduced, leading to mutually reinforcing feedback (for
instance, between vegetation cover, water retention and soil erosion). Also, high
altitude favours the passage of pollutants from the troposphere to the ground
(Camarero 2017b) and a loss of atmospheric protection against ionising radiation.
Therefore, only relatively few species are able to persist in these extreme conditions. These species typically present low growth rates and life cycles adapted to the
short duration of favourable conditions (Laiolo and Obeso 2017). The environmental conditions specific to high mountains, along with their geographic isolation,
have forged an adaptive landscape that has shaped the characteristic functional and
compositional traits of its biota. Another consequence is a noticeable fragility in
these ecosystems, as the resident species are often pushed to their limits of ecophysiological tolerance. Nevertheless, selective pressure may have favoured
adaption to these environments. Simultaneously, species tolerant of a broad range
of conditions are often found here, far from the competition withstood by other
species. Also, importantly, low growth rates and short periods of growth limit
population recovery after disturbances or harsh environmental conditions, thus
reducing resilience.
Another characteristic of high mountain ecosystems is that they tend to exhibit
steep environmental gradients over relatively short distances. These gradients are
largely determined by topography and aspect, which determine the radiation
2 Trade-offs in High Mountain Conservation
39