81
markers), together with characterization of micro-environmental conditions. At
stand scale, the influence of site condition, altitude and post-harvest stand structure
on regeneration composition and establishment was studied in two sites located
along Lácar watershed, where mean annual precipitation level has a drastic variation.
Globally, these studies indicated that canopy cover after intervention is a key
factor modelling regeneration dynamics in mixed forest, but other factors such as
site and forest structure are also relevant and should be taken into consideration
(Sola et al. 2020a). The pioneer and widely distributed species N. dombeyi has been
favoured in all managed areas, while N. obliqua was associated to low altitude and
open microsites (reduced basal area of mature trees and low competition of
understory species) and N. alpina was restricted to shady conditions with low water
stress and high altitude (Sola et al. 2020a). In this way, N. alpina resulted
underrepresented within the total regeneration. A similar trend of species
composition change has been reported after the implementation of the group
selection cutting silvicultural system (Dezzotti et al. 2003). Weinberger and Ramirez
(1999) showed that in sites with low precipitation levels, juvenile stages of N. alpina
became established only in shady conditions (with cover >40%). Thus, reproductive
strategies do not depend only on light but on the interaction with other environmental
factors, such as temperature and water economy.
The modification of relative abundance of species in the post-harvest population
that followed the implemented management was found altering the global genetic
diversity of the mixed forest; however, no impact was detected at species level (Sola
et al. 2016). The use of species-specific markers also allowed to determine that the
level of introgressive hybridization between N. alpina and N. obliqua was not
changed by management (Sola et al. 2016). Therefore, the potential negative genetic
impact of increasing interindividual distances resulting from harvesting could be
counterbalanced by high gene flow, suggesting that evolutionary processes were
maintained at pre-harvest levels or that derived changes had compensatory effects
on genetic diversity at species level (Fageria and Rajora 2013). Accordingly, the
comparison of historical (indirect) and contemporary (direct) gene dispersal
estimates (see before in this Chapter) revealed that the recent history (20 years ago)
of logging activities within the study area has not significantly affected the patterns
of gene dispersal distance (Sola et al. 2020b). The residual tree density maintaining
species composition and the homogeneous spatial distribution of trees (followed by
the applied silvicultural system) possibly allowed the maintenance of gene dispersal.
Concluding, these studies provide important information to plan management,
conservation and restoration of Nothofagus mixed forests based on improved
knowledge of the regeneration dynamics and the dispersal pattern. Sola et al.
(2020a) proposed a set of recommendations depending on the site conditions that
contributes in a practical way to the sustainable use of this forest and can be summarized as: (i) in sites with stressful conditions, a first harvest of low intensity could
be applied (residual canopy cover greater than 60%), to facilitate seedling establishment; (ii) in mixed stands of the three species, a larger proportion of N. dombeyi
individuals could be harvested, favouring higher seed availability of the other species, in order to maintain the original composition in the new generation; (iii) in
3 Raulí (Nothofagus alpina = N. nervosa): The Best Quality Hardwood in Patagonia
markers), together with characterization of micro-environmental conditions. At
stand scale, the influence of site condition, altitude and post-harvest stand structure
on regeneration composition and establishment was studied in two sites located
along Lácar watershed, where mean annual precipitation level has a drastic variation.
Globally, these studies indicated that canopy cover after intervention is a key
factor modelling regeneration dynamics in mixed forest, but other factors such as
site and forest structure are also relevant and should be taken into consideration
(Sola et al. 2020a). The pioneer and widely distributed species N. dombeyi has been
favoured in all managed areas, while N. obliqua was associated to low altitude and
open microsites (reduced basal area of mature trees and low competition of
understory species) and N. alpina was restricted to shady conditions with low water
stress and high altitude (Sola et al. 2020a). In this way, N. alpina resulted
underrepresented within the total regeneration. A similar trend of species
composition change has been reported after the implementation of the group
selection cutting silvicultural system (Dezzotti et al. 2003). Weinberger and Ramirez
(1999) showed that in sites with low precipitation levels, juvenile stages of N. alpina
became established only in shady conditions (with cover >40%). Thus, reproductive
strategies do not depend only on light but on the interaction with other environmental
factors, such as temperature and water economy.
The modification of relative abundance of species in the post-harvest population
that followed the implemented management was found altering the global genetic
diversity of the mixed forest; however, no impact was detected at species level (Sola
et al. 2016). The use of species-specific markers also allowed to determine that the
level of introgressive hybridization between N. alpina and N. obliqua was not
changed by management (Sola et al. 2016). Therefore, the potential negative genetic
impact of increasing interindividual distances resulting from harvesting could be
counterbalanced by high gene flow, suggesting that evolutionary processes were
maintained at pre-harvest levels or that derived changes had compensatory effects
on genetic diversity at species level (Fageria and Rajora 2013). Accordingly, the
comparison of historical (indirect) and contemporary (direct) gene dispersal
estimates (see before in this Chapter) revealed that the recent history (20 years ago)
of logging activities within the study area has not significantly affected the patterns
of gene dispersal distance (Sola et al. 2020b). The residual tree density maintaining
species composition and the homogeneous spatial distribution of trees (followed by
the applied silvicultural system) possibly allowed the maintenance of gene dispersal.
Concluding, these studies provide important information to plan management,
conservation and restoration of Nothofagus mixed forests based on improved
knowledge of the regeneration dynamics and the dispersal pattern. Sola et al.
(2020a) proposed a set of recommendations depending on the site conditions that
contributes in a practical way to the sustainable use of this forest and can be summarized as: (i) in sites with stressful conditions, a first harvest of low intensity could
be applied (residual canopy cover greater than 60%), to facilitate seedling establishment; (ii) in mixed stands of the three species, a larger proportion of N. dombeyi
individuals could be harvested, favouring higher seed availability of the other species, in order to maintain the original composition in the new generation; (iii) in
3 Raulí (Nothofagus alpina = N. nervosa): The Best Quality Hardwood in Patagonia