310
the seeds in A. caven and A. aroma, and the results showed that these species have
physical dormancy imposed by an impermeable seed coat (Funes and Venier 2006).
Moreover, scarified seeds have proven to germinate equally in light and darkness at
all temperature regimes studied (Funes and Venier 2006). In a study of possible
nitrogen-fixing species that could be used for ecological rehabilitation of degraded
ecosystems in Chile, seeds of Argentinean populations of A. caven, A. aroma and
A. visco were assessed for survival after 6 years, plant growth and nutritive value.
A. caven populations presented >80% survival at the end of the 6 year of growth. In
contrast, A. visco and A. aroma showed survival rates <25% (Arredondo et al. 1998).
These three species failed to attain even 1 m in height after 6 years. About nutritive
values, the pods of A. aroma contain relatively high protein levels (10.4%).
Moreover, the leaves of A. visco and A. caven appear rich in protein with 32 and
18.5%, respectively (Arredondo et al. 1998). The results of these trials support that
new trees, shrubs (A. caven and A. visco in particular) and microorganisms can be
identified for artificial introduction to the “Espinal” region’s agroecosystems
(Arredondo et al. 1998).
The preliminary genetic results in P. affinis could indicate that, in the area with
higher agricultural intensification levels, remnant native forest fragments have a
high conservation value because of their high levels of genetic variability. However,
further sampling and analyses are required to better understand the observed patterns and to find the conservation threshold of the landscape that will allow preserving the genetic variability of the species in the area. Seedling production for active
restoration with this species appears as a possible task. In a germination study under
controlled conditions, 100% of germinated seeds were obtained in only 4 days with
a pre-germinative treatment of sulfuric acid 95% during 20 min (Castillo et al.
2015). Likewise, an experimental restoration with interesting results can be mentioned (Casermeiro et al. 2015). Sowing of pretreated seeds and planting of 80-cm
high seedlings were assayed in a grassland and in a secondary Prosopis sp. forest,
yielding a survival rate lower than 20% for the seeds at 3 months, but up to 68% for
the seedlings after 2 years.
For P. caldenia management and conservation, studies on genetic diversity,
breeding system and pollination distance should be expanded to the entire distribution range of the species, since the existing analyses are limited to restricted areas.
Hybrid swarms should be taken into account in areas of sympatry between P. caldenia and P. flexuosa. Although it has been achieved that the hybrid does not have
more vigour than its parentals (Velasco 2018), it will be necessary to deepen the
knowledge of these systems in order to be able to make decisions about the management and conservation of P. caldenia populations.
An interesting study of assisted regeneration was conducted in a degraded forest
of the species (Bistolfi 2016). Different treatments were compared in a field trial to
test the artificial recruitment of P. caldenia and P. flexuosa in weeded plots within a
productive ranch with livestock. Germinated seeds, 1-month-old seedlings and
1-year-old seedlings, were planted in early autumn and late spring. The first two
treatments resulted clearly inappropriate, since the seedlings died soon due to
drought stress or cattle trampling. The cattle was also a problem for the large
C. Pometti et al.
the seeds in A. caven and A. aroma, and the results showed that these species have
physical dormancy imposed by an impermeable seed coat (Funes and Venier 2006).
Moreover, scarified seeds have proven to germinate equally in light and darkness at
all temperature regimes studied (Funes and Venier 2006). In a study of possible
nitrogen-fixing species that could be used for ecological rehabilitation of degraded
ecosystems in Chile, seeds of Argentinean populations of A. caven, A. aroma and
A. visco were assessed for survival after 6 years, plant growth and nutritive value.
A. caven populations presented >80% survival at the end of the 6 year of growth. In
contrast, A. visco and A. aroma showed survival rates <25% (Arredondo et al. 1998).
These three species failed to attain even 1 m in height after 6 years. About nutritive
values, the pods of A. aroma contain relatively high protein levels (10.4%).
Moreover, the leaves of A. visco and A. caven appear rich in protein with 32 and
18.5%, respectively (Arredondo et al. 1998). The results of these trials support that
new trees, shrubs (A. caven and A. visco in particular) and microorganisms can be
identified for artificial introduction to the “Espinal” region’s agroecosystems
(Arredondo et al. 1998).
The preliminary genetic results in P. affinis could indicate that, in the area with
higher agricultural intensification levels, remnant native forest fragments have a
high conservation value because of their high levels of genetic variability. However,
further sampling and analyses are required to better understand the observed patterns and to find the conservation threshold of the landscape that will allow preserving the genetic variability of the species in the area. Seedling production for active
restoration with this species appears as a possible task. In a germination study under
controlled conditions, 100% of germinated seeds were obtained in only 4 days with
a pre-germinative treatment of sulfuric acid 95% during 20 min (Castillo et al.
2015). Likewise, an experimental restoration with interesting results can be mentioned (Casermeiro et al. 2015). Sowing of pretreated seeds and planting of 80-cm
high seedlings were assayed in a grassland and in a secondary Prosopis sp. forest,
yielding a survival rate lower than 20% for the seeds at 3 months, but up to 68% for
the seedlings after 2 years.
For P. caldenia management and conservation, studies on genetic diversity,
breeding system and pollination distance should be expanded to the entire distribution range of the species, since the existing analyses are limited to restricted areas.
Hybrid swarms should be taken into account in areas of sympatry between P. caldenia and P. flexuosa. Although it has been achieved that the hybrid does not have
more vigour than its parentals (Velasco 2018), it will be necessary to deepen the
knowledge of these systems in order to be able to make decisions about the management and conservation of P. caldenia populations.
An interesting study of assisted regeneration was conducted in a degraded forest
of the species (Bistolfi 2016). Different treatments were compared in a field trial to
test the artificial recruitment of P. caldenia and P. flexuosa in weeded plots within a
productive ranch with livestock. Germinated seeds, 1-month-old seedlings and
1-year-old seedlings, were planted in early autumn and late spring. The first two
treatments resulted clearly inappropriate, since the seedlings died soon due to
drought stress or cattle trampling. The cattle was also a problem for the large
C. Pometti et al.