127
secondary contact zones that are therefore established constitute genetic reservoirs
relevant for their conservation and might enrich sources of material in ex situ breeding programs (Petit et al. 2003; Grivet et al. 2008).
The identification of a contact zone where the northern lineages mixed with the
southern lineages was inferred for N. pumilio and N. antarctica (Soliani et al. 2015).
These results are in agreement with previously reported evidence of contact zones
for Patagonian taxa, e.g., in fishes (Zemlak et al. 2008), forest trees (Pastorino et al.
2009), and herbs (Cosacov et al. 2010; Sérsic et al. 2011). The high allelic richness,
low level of inbreeding, and a lack of evidence of genetic bottlenecks in populations
around the contact zone add support to the meeting of colonization routes from
northern and southern refugia (Soliani et al. 2015). In addition, the contact zone
might be the result of immigrants from local or nearby refugia that remained in
unglaciated areas at central latitudes. The described patterns of genetic variation
were taken into consideration for the definition of preliminary operational genetic
management units of N. pumilio and N. antarctica in Argentina (see next section).
The identification of at least one population with high level of genetic diversity
within each unit could be considered as base material for future breeding programs.
5.3.2 Impact of Selective Logging on Patterns of Genetic
Diversity: A Case Study in Nothofagus pumilio
Logging is one of the human activities that has impacted on the natural evolution of
the forest, by altering the genetic diversity and structure of main species like trees
(Rajendra et al. 2014). In particular, the removing of trees and the impoverishment
of a forest could lead to within-population changes in genetic variation and diversity, which is the key to adaptation (El-Kassaby et al. 2003; Finkeldey and Ziehe
2004). Signs of impact could be a decrease in allelic richness or modifications in
heterozygote proportions, a reduction in allele frequencies, or loss of variants
between the adult cohort and its regeneration (Cornuet and Liukart 1996; Rajora
et al. 2000). Then, erosive forces (i.e., genetic drift, selection) might affect the remnant population. Logging could also affect the spatial genetic structure, i.e., the
amount and distribution of genetic variation between and within local populations
and individuals of a species, with consequences in regeneration recruitment.
In Patagonian natural forests, selective extraction in a high grading management
system was implemented over many decades (Bava and Rechene 2004; Bava et al.
2006; González et al. 2006). The removal of best-featured individual trees (stem
straightness and best sanitary conditions) was the most frequent technique employed,
which may be expected to induce changes in allelic richness or modifications in the
spatial distribution of alleles. Because of its excellent wood properties (high quality,
long-time durability; González et al. 2006), N. pumilio has historically been one of
the most exploited native species in Patagonia, threatening its populations.
5 Nothofagus pumilio and N. antarctica: The Most Widely Distributed…
secondary contact zones that are therefore established constitute genetic reservoirs
relevant for their conservation and might enrich sources of material in ex situ breeding programs (Petit et al. 2003; Grivet et al. 2008).
The identification of a contact zone where the northern lineages mixed with the
southern lineages was inferred for N. pumilio and N. antarctica (Soliani et al. 2015).
These results are in agreement with previously reported evidence of contact zones
for Patagonian taxa, e.g., in fishes (Zemlak et al. 2008), forest trees (Pastorino et al.
2009), and herbs (Cosacov et al. 2010; Sérsic et al. 2011). The high allelic richness,
low level of inbreeding, and a lack of evidence of genetic bottlenecks in populations
around the contact zone add support to the meeting of colonization routes from
northern and southern refugia (Soliani et al. 2015). In addition, the contact zone
might be the result of immigrants from local or nearby refugia that remained in
unglaciated areas at central latitudes. The described patterns of genetic variation
were taken into consideration for the definition of preliminary operational genetic
management units of N. pumilio and N. antarctica in Argentina (see next section).
The identification of at least one population with high level of genetic diversity
within each unit could be considered as base material for future breeding programs.
5.3.2 Impact of Selective Logging on Patterns of Genetic
Diversity: A Case Study in Nothofagus pumilio
Logging is one of the human activities that has impacted on the natural evolution of
the forest, by altering the genetic diversity and structure of main species like trees
(Rajendra et al. 2014). In particular, the removing of trees and the impoverishment
of a forest could lead to within-population changes in genetic variation and diversity, which is the key to adaptation (El-Kassaby et al. 2003; Finkeldey and Ziehe
2004). Signs of impact could be a decrease in allelic richness or modifications in
heterozygote proportions, a reduction in allele frequencies, or loss of variants
between the adult cohort and its regeneration (Cornuet and Liukart 1996; Rajora
et al. 2000). Then, erosive forces (i.e., genetic drift, selection) might affect the remnant population. Logging could also affect the spatial genetic structure, i.e., the
amount and distribution of genetic variation between and within local populations
and individuals of a species, with consequences in regeneration recruitment.
In Patagonian natural forests, selective extraction in a high grading management
system was implemented over many decades (Bava and Rechene 2004; Bava et al.
2006; González et al. 2006). The removal of best-featured individual trees (stem
straightness and best sanitary conditions) was the most frequent technique employed,
which may be expected to induce changes in allelic richness or modifications in the
spatial distribution of alleles. Because of its excellent wood properties (high quality,
long-time durability; González et al. 2006), N. pumilio has historically been one of
the most exploited native species in Patagonia, threatening its populations.
5 Nothofagus pumilio and N. antarctica: The Most Widely Distributed…