400
The apogee reached by the cultivation of A. angustifolia started to decline in the
1960s for several reasons. The main was related to the promotion of the “yellow
pines” native to the south of USA: Pinus elliottii var. elliottii and Pinus taeda, which
became the raw material for the pulp industry. These fast-growing species quickly
replaced A. angustifolia not only for chemical transformation but also for sawn
timber due to their lower prices, even in the large size pieces now achieved by
means of multilaminated beams. The decorative value of the A. angustifolia lumber
never got a reflection in its price. From a silvicultural point of view, some shortcomings should be mention, like its lower growth rate and its good-quality site requirements, the difficulty in obtaining seeds, and their recalcitrant character (they cannot
be stocked for a long period).
The mentioned decline becomes evident through the evolution of the area covered by plantations of A. angustifolia, which went from 25,000 ha in 1975 (Cozzo
1975) to 20,000 ha in 1997 (SAGYP 1997), 18,000 ha in 2000 (Min. Ecol. 2001),
and 16,000 ha in 2010 (SIFIP 2010) and has probably dropped even more nowadays. These data are not only evidence of the decline of the cultivation of the species
but also reflect the fact that it is the most cultivated native species in Argentina.
In the 1970s, INTA initiated a series of investigations toward optimizing the
cultivation of A. angustifolia. The first trials of geographical variation were installed
(Fahler and Di Lucca 1980), and trials of planting density and thinning were also
established (Crechi et al. 2001, 2009); studies on the determination of defective
cylinder were performed (Fassi et al. 1993), and seed production was monitored as
well (Fassola et al. 1999).
15.4 Reproductive Biology of Araucaria angustifolia
So far, natural trees of A. angustifolia are restricted to small forest fragments or to
isolated individuals because of indiscriminate logging during the last century and
the agricultural expansion (Luna and Fontana 2017). The drastic decline of its distribution area has reduced the connectivity between the population remnants (Pinazo
et al. 2016) leading to a limited pollination and to a decrease in the genetic diversity.
Consequently, the natural regeneration is scarce: seedlings are hardly found in the
native forests, although the species is not strictly heliophilous and would be able to
be established in the understory (Duarte et al. 2002). Reforestation, as an active
restoration measure, could partially mitigate this critical situation, but this kind of
practice has been severely restricted by the progressive decrease in the volume of
seeds produced during the last years in Argentina (Fassola et al. 1999).
Thus, the fall in seed production may be due to the reproductive isolation after
habitat fragmentation. A direct relationship between pollen and seed production
often occurs in woody plants (Cour and van Campo 1980), then the smaller number
of seeds detected could be attributed to a diminished pollination. According to
Allison (1990), a deficient pollination negatively affects both fertilization of the
ovules and seed production. Indeed, studies of controlled pollination carried out by
M. E. Gauchat et al.
The apogee reached by the cultivation of A. angustifolia started to decline in the
1960s for several reasons. The main was related to the promotion of the “yellow
pines” native to the south of USA: Pinus elliottii var. elliottii and Pinus taeda, which
became the raw material for the pulp industry. These fast-growing species quickly
replaced A. angustifolia not only for chemical transformation but also for sawn
timber due to their lower prices, even in the large size pieces now achieved by
means of multilaminated beams. The decorative value of the A. angustifolia lumber
never got a reflection in its price. From a silvicultural point of view, some shortcomings should be mention, like its lower growth rate and its good-quality site requirements, the difficulty in obtaining seeds, and their recalcitrant character (they cannot
be stocked for a long period).
The mentioned decline becomes evident through the evolution of the area covered by plantations of A. angustifolia, which went from 25,000 ha in 1975 (Cozzo
1975) to 20,000 ha in 1997 (SAGYP 1997), 18,000 ha in 2000 (Min. Ecol. 2001),
and 16,000 ha in 2010 (SIFIP 2010) and has probably dropped even more nowadays. These data are not only evidence of the decline of the cultivation of the species
but also reflect the fact that it is the most cultivated native species in Argentina.
In the 1970s, INTA initiated a series of investigations toward optimizing the
cultivation of A. angustifolia. The first trials of geographical variation were installed
(Fahler and Di Lucca 1980), and trials of planting density and thinning were also
established (Crechi et al. 2001, 2009); studies on the determination of defective
cylinder were performed (Fassi et al. 1993), and seed production was monitored as
well (Fassola et al. 1999).
15.4 Reproductive Biology of Araucaria angustifolia
So far, natural trees of A. angustifolia are restricted to small forest fragments or to
isolated individuals because of indiscriminate logging during the last century and
the agricultural expansion (Luna and Fontana 2017). The drastic decline of its distribution area has reduced the connectivity between the population remnants (Pinazo
et al. 2016) leading to a limited pollination and to a decrease in the genetic diversity.
Consequently, the natural regeneration is scarce: seedlings are hardly found in the
native forests, although the species is not strictly heliophilous and would be able to
be established in the understory (Duarte et al. 2002). Reforestation, as an active
restoration measure, could partially mitigate this critical situation, but this kind of
practice has been severely restricted by the progressive decrease in the volume of
seeds produced during the last years in Argentina (Fassola et al. 1999).
Thus, the fall in seed production may be due to the reproductive isolation after
habitat fragmentation. A direct relationship between pollen and seed production
often occurs in woody plants (Cour and van Campo 1980), then the smaller number
of seeds detected could be attributed to a diminished pollination. According to
Allison (1990), a deficient pollination negatively affects both fertilization of the
ovules and seed production. Indeed, studies of controlled pollination carried out by
M. E. Gauchat et al.