485
However, in some cases forests could have been affected to the point of local
extinction, thus forcing foresters to use exotic seed sources to carry out the restoration. Even without going to that extreme, the degradation is often so strong that only
few trees remain from the original forest, which makes it inadvisable to obtain seeds
from these remnants. Using seeds exclusively from those few trees would cause a
significant reduction in the genetic diversity of the future afforestation due to genetic
drift, with a resulting reduction in their adaptability. In addition, inbreeding could
be also a consequence, leading to the appearance of deleterious phenotypes (Carr
and Dudash 2003).
Genetic drift is the aleatory variation of allelic and genotypic frequencies in the
population from one generation to the next, which occurs by random crossing
between parents. This common phenomenon in any sexually reproducing population has drastic consequences for small ones, such as the population composed of
the few remaining trees in a strongly degraded forest. It is highly probable that some
(at random) low frequent alleles are not represented in the next generation simply
because the few parents that carry them randomly fail to leave offspring. The consequence is the irreversible loss of those allelic variants in the population. Low
frequent alleles commonly have low relevance for the adaptation to the current conditions, but might be quite important for the adaptation to the future environment. If
the seedlings used in the plantation come exclusively from the seeds of a population
composed by few trees, this drift effect would occur in the plantation itself.
Inbreeding refers to self-pollination and to crossbreeding between related individuals and often leads to depressed phenotypes due to the expression of recessive
alleles. In this case, this process would occur in the plantation, because selfing is
accentuated due to the low availability of pollinators, and also in the next generations of the established forest, because a large portion of the planted seedlings
would have a close kinship.
All these risks must be considered in a forestation program with native species,
to weigh the probability of occurrence of any of these undesirable effects based on
the particular conditions of each case, thus assisting decision-making (Frankham
et al. 2011; Byrne et al. 2011).
18.2 Should We Think About Productivity or
the Preservation of Genetic Identity?
In a program of active restoration of degraded ecosystems, two basic objectives can
be identified from a genetic point of view: that of “authenticity” and that of “functionality” (Clewell 2000; Falk et al. 2001). Authenticity refers to replicating the
original genetic pool and involves ethical principles. Although this cannot be fully
achieved, the degree of authenticity can be measured, and therefore a certain goal
can be arbitrarily set.
18 Questions, Perspectives and Final Considerations of Planting Native Species…
However, in some cases forests could have been affected to the point of local
extinction, thus forcing foresters to use exotic seed sources to carry out the restoration. Even without going to that extreme, the degradation is often so strong that only
few trees remain from the original forest, which makes it inadvisable to obtain seeds
from these remnants. Using seeds exclusively from those few trees would cause a
significant reduction in the genetic diversity of the future afforestation due to genetic
drift, with a resulting reduction in their adaptability. In addition, inbreeding could
be also a consequence, leading to the appearance of deleterious phenotypes (Carr
and Dudash 2003).
Genetic drift is the aleatory variation of allelic and genotypic frequencies in the
population from one generation to the next, which occurs by random crossing
between parents. This common phenomenon in any sexually reproducing population has drastic consequences for small ones, such as the population composed of
the few remaining trees in a strongly degraded forest. It is highly probable that some
(at random) low frequent alleles are not represented in the next generation simply
because the few parents that carry them randomly fail to leave offspring. The consequence is the irreversible loss of those allelic variants in the population. Low
frequent alleles commonly have low relevance for the adaptation to the current conditions, but might be quite important for the adaptation to the future environment. If
the seedlings used in the plantation come exclusively from the seeds of a population
composed by few trees, this drift effect would occur in the plantation itself.
Inbreeding refers to self-pollination and to crossbreeding between related individuals and often leads to depressed phenotypes due to the expression of recessive
alleles. In this case, this process would occur in the plantation, because selfing is
accentuated due to the low availability of pollinators, and also in the next generations of the established forest, because a large portion of the planted seedlings
would have a close kinship.
All these risks must be considered in a forestation program with native species,
to weigh the probability of occurrence of any of these undesirable effects based on
the particular conditions of each case, thus assisting decision-making (Frankham
et al. 2011; Byrne et al. 2011).
18.2 Should We Think About Productivity or
the Preservation of Genetic Identity?
In a program of active restoration of degraded ecosystems, two basic objectives can
be identified from a genetic point of view: that of “authenticity” and that of “functionality” (Clewell 2000; Falk et al. 2001). Authenticity refers to replicating the
original genetic pool and involves ethical principles. Although this cannot be fully
achieved, the degree of authenticity can be measured, and therefore a certain goal
can be arbitrarily set.
18 Questions, Perspectives and Final Considerations of Planting Native Species…