500
Facilitating natural population spread would be its preferred option to try to save the
threatened species. Position 3 represents an intermediate alternative that may range
broadly between positions 1 and 2, stating that AM is necessary to preserve biodiversity despite recognized risks. Those risks can and must be minimized through
careful restrictions on actions, planning, monitoring, and adaptive management.
These constraints will require scientific knowledge and a board of experts to conduct the AM process. Obviously, this will come at a significant cost and could therefore only be implemented for a few species of highest concern.
As a complementary and even alternative strategy to AM, to increase connectivity between threatened ecosystems and threat-free sites has been proposed (Lawler
and Olden 2011; Thomas et al. 2014). Greater connectivity would be achieved
through the elimination or at least the permeation of artificial barriers that impede
the free movement of species, ultimately achieving an effect similar to that of AM.
Although AM is a strategy that focuses on species, it can also be thought in an
intraspecific dimension (Fady et al. 2015). It has been called within-species assisted
migration (Richardson et al. 2009) or assisted gene flow (Aitken and Whitlock
2013). Thus, the provenance to be planted could be chosen in reference to the environmental conditions of the future, in such a way as to deliberately use an exotic
provenance, that is, different from the local one, considering that the local one is on
the way to extinction. In this sense, the method would require making an analogy
between the predicted future environment and a current environment for which the
adaptation of the genetic pool (provenance) to be used has been proven.
Foresters have utilized exotic provenances since at least the nineteenth century in
Europe for productive purposes, and maladaptation experiences are abundant (e.g.,
Johnson et al. 2004; Timbal et al. 2005). Therefore, it is now well recognized that
assisted gene flow is risky both for the target species themselves and for the ecosystems they will compose (Fady et al. 2015). However, it could be a reasonable solution when local genetic pools are not able to adapt to the ongoing changes and show
undoubted signs of decline, such as adult tree mortality above an acceptable threshold and severe drop or lack of natural regeneration, even failing assisted regeneration with local resources. In this case, assisted gene flow would be a sort of genetic
rescue through the hybridization of local and exotic genetic pools. Outbreeding
depression could still be a result, and ecological risks cannot be discarded either
(Fady et al. 2015). In this sense, the guidance of Operational Genetic Management
Units, such as Seed Zones, Genetic Zones, or Provenance Regions, could help to
minimize the genetic risks inherent in the use of exotic germplasm.
Although assisted gene flow is the strategy implemented, since adaptation to a
predicted but unknown environment is the key issue, two main considerations must
guide the election of the propagation material: (i) the genetic pool to be used must
be highly variable so as to give the chance for the future generations to count with
different alternatives to adapt, and (ii) phenotypic plasticity of the genetic material
must be particularly valorized, since it will be key for the current generation to survive and produce offspring. Phenotypic plasticity of fundamental adaptive traits
should perhaps be the most relevant selection criterion in a low intensity breeding
program ruled by the pressure of climate change.
M. J. Pastorino et al.
Facilitating natural population spread would be its preferred option to try to save the
threatened species. Position 3 represents an intermediate alternative that may range
broadly between positions 1 and 2, stating that AM is necessary to preserve biodiversity despite recognized risks. Those risks can and must be minimized through
careful restrictions on actions, planning, monitoring, and adaptive management.
These constraints will require scientific knowledge and a board of experts to conduct the AM process. Obviously, this will come at a significant cost and could therefore only be implemented for a few species of highest concern.
As a complementary and even alternative strategy to AM, to increase connectivity between threatened ecosystems and threat-free sites has been proposed (Lawler
and Olden 2011; Thomas et al. 2014). Greater connectivity would be achieved
through the elimination or at least the permeation of artificial barriers that impede
the free movement of species, ultimately achieving an effect similar to that of AM.
Although AM is a strategy that focuses on species, it can also be thought in an
intraspecific dimension (Fady et al. 2015). It has been called within-species assisted
migration (Richardson et al. 2009) or assisted gene flow (Aitken and Whitlock
2013). Thus, the provenance to be planted could be chosen in reference to the environmental conditions of the future, in such a way as to deliberately use an exotic
provenance, that is, different from the local one, considering that the local one is on
the way to extinction. In this sense, the method would require making an analogy
between the predicted future environment and a current environment for which the
adaptation of the genetic pool (provenance) to be used has been proven.
Foresters have utilized exotic provenances since at least the nineteenth century in
Europe for productive purposes, and maladaptation experiences are abundant (e.g.,
Johnson et al. 2004; Timbal et al. 2005). Therefore, it is now well recognized that
assisted gene flow is risky both for the target species themselves and for the ecosystems they will compose (Fady et al. 2015). However, it could be a reasonable solution when local genetic pools are not able to adapt to the ongoing changes and show
undoubted signs of decline, such as adult tree mortality above an acceptable threshold and severe drop or lack of natural regeneration, even failing assisted regeneration with local resources. In this case, assisted gene flow would be a sort of genetic
rescue through the hybridization of local and exotic genetic pools. Outbreeding
depression could still be a result, and ecological risks cannot be discarded either
(Fady et al. 2015). In this sense, the guidance of Operational Genetic Management
Units, such as Seed Zones, Genetic Zones, or Provenance Regions, could help to
minimize the genetic risks inherent in the use of exotic germplasm.
Although assisted gene flow is the strategy implemented, since adaptation to a
predicted but unknown environment is the key issue, two main considerations must
guide the election of the propagation material: (i) the genetic pool to be used must
be highly variable so as to give the chance for the future generations to count with
different alternatives to adapt, and (ii) phenotypic plasticity of the genetic material
must be particularly valorized, since it will be key for the current generation to survive and produce offspring. Phenotypic plasticity of fundamental adaptive traits
should perhaps be the most relevant selection criterion in a low intensity breeding
program ruled by the pressure of climate change.
M. J. Pastorino et al.