on reducing sensitivity should consider connectivity and genetic flux (Moritz et al.
2008), preservation of microhabitat quality (Marini et al. 2011) and control of
grazing (Nagy and Grabherr 2009). Similarly, reductions in the risk of disturbance
may favour the preservation of habitats and small populations against the adverse
effects of climate change (Millar et al. 2007). In fact, the management of sensitivity
often comes to focus on population-level processes involving the enhancement of
genetic variability (Maudet et al. 2002) and population size, as well as the control of
antagonists (predators, pathogens, pests, parasites) (McKinney et al. 2009).
Nevertheless, some of these actions may in themselves involve trade-offs: for
instance, disturbance often contributes to species co-existence, giving rise to a
complex picture that we shall discuss below.
Forest die-off clearly illustrates the difficulties in managing ecosystems, even
locally, when the major threats are global. Forest die-off accompanied by tree
mortality is increasingly being reported in many biomes across the world, including
mountain areas of North and South America and Europe (Suarez et al. 2004; Bigler
et al. 2006; van Mantgem et al. 2009; Allen et al. 2010; Smith et al. 2015) (see also
Camarero 2017a). Many factors, such as the capacity of soils to store water,
antagonistic biotic interactions and stand structure can significantly contribute to
this phenomenon (Raffa et al. 2008; Galiano et al. 2010; Bell et al. 2014). In many
cases climate, and more particularly drought and heat episodes, is closely associated
with this decline (Suarez et al. 2004; Bigler et al. 2006; Allen et al. 2010, 2015;
Anderegg et al. 2013; Williams et al. 2012; Smith et al. 2015). Importantly, the
trend towards warming is increasingly accompanied by climatic variability, which
results in pulses of extreme weather. This feature reveals a major component of the
new abiotic environment of the next future (Easterling et al. 2000). Reducing
exposure to this global threat is thus far beyond the scope of local managers.
However, they probably can reduce forest’s vulnerability to drought by acting on
drivers that amplify tree mortality. In such forests, the vulnerability could be
decreased by controlling antagonists (Sturrock et al. 2011) or by managing forest
composition and structure (Grant et al. 2013). However, these practices, although
common in forests managed for commercial purposes, could clash with the criteria
for intervention in preserved areas. This conflict is particularly acute when adaptive
management, which involves learning from experimental settings, is proposed as a
rational alternative for improving the future health of forests (Millar et al. 2007).
This controversy can only be solved by a straightforward definition and prioritisation of conservation goals by social agents. The transcendental values of forests as
sanctuaries or social icons can support the effort to identify these goals and formulate specific local decisions. In any case, even in today’s humid mountains in
temperate regions, managers will probably have to come to terms with the management of water availability in the near future (Grant et al. 2013).
These reinforcing co-drivers may interact with climate and with each other in
complex ways involving feedbacks (either positive or negative) and trade-offs
(McDowell et al. 2011; Jactel et al. 2012). For instance, Scots pine is experiencing
high mortality rates in some mountain areas in the Pyrenees due to a combination
of increasing drought, poorly developed soils and mistletoe infestation
2 Trade-offs in High Mountain Conservation
47
2008), preservation of microhabitat quality (Marini et al. 2011) and control of
grazing (Nagy and Grabherr 2009). Similarly, reductions in the risk of disturbance
may favour the preservation of habitats and small populations against the adverse
effects of climate change (Millar et al. 2007). In fact, the management of sensitivity
often comes to focus on population-level processes involving the enhancement of
genetic variability (Maudet et al. 2002) and population size, as well as the control of
antagonists (predators, pathogens, pests, parasites) (McKinney et al. 2009).
Nevertheless, some of these actions may in themselves involve trade-offs: for
instance, disturbance often contributes to species co-existence, giving rise to a
complex picture that we shall discuss below.
Forest die-off clearly illustrates the difficulties in managing ecosystems, even
locally, when the major threats are global. Forest die-off accompanied by tree
mortality is increasingly being reported in many biomes across the world, including
mountain areas of North and South America and Europe (Suarez et al. 2004; Bigler
et al. 2006; van Mantgem et al. 2009; Allen et al. 2010; Smith et al. 2015) (see also
Camarero 2017a). Many factors, such as the capacity of soils to store water,
antagonistic biotic interactions and stand structure can significantly contribute to
this phenomenon (Raffa et al. 2008; Galiano et al. 2010; Bell et al. 2014). In many
cases climate, and more particularly drought and heat episodes, is closely associated
with this decline (Suarez et al. 2004; Bigler et al. 2006; Allen et al. 2010, 2015;
Anderegg et al. 2013; Williams et al. 2012; Smith et al. 2015). Importantly, the
trend towards warming is increasingly accompanied by climatic variability, which
results in pulses of extreme weather. This feature reveals a major component of the
new abiotic environment of the next future (Easterling et al. 2000). Reducing
exposure to this global threat is thus far beyond the scope of local managers.
However, they probably can reduce forest’s vulnerability to drought by acting on
drivers that amplify tree mortality. In such forests, the vulnerability could be
decreased by controlling antagonists (Sturrock et al. 2011) or by managing forest
composition and structure (Grant et al. 2013). However, these practices, although
common in forests managed for commercial purposes, could clash with the criteria
for intervention in preserved areas. This conflict is particularly acute when adaptive
management, which involves learning from experimental settings, is proposed as a
rational alternative for improving the future health of forests (Millar et al. 2007).
This controversy can only be solved by a straightforward definition and prioritisation of conservation goals by social agents. The transcendental values of forests as
sanctuaries or social icons can support the effort to identify these goals and formulate specific local decisions. In any case, even in today’s humid mountains in
temperate regions, managers will probably have to come to terms with the management of water availability in the near future (Grant et al. 2013).
These reinforcing co-drivers may interact with climate and with each other in
complex ways involving feedbacks (either positive or negative) and trade-offs
(McDowell et al. 2011; Jactel et al. 2012). For instance, Scots pine is experiencing
high mortality rates in some mountain areas in the Pyrenees due to a combination
of increasing drought, poorly developed soils and mistletoe infestation
2 Trade-offs in High Mountain Conservation
47