196
humid environment (Luis Hansen, pers. comm.). It is used as fuel and for construction and manufacture of barrels, hoops, poles, drawers, joinery, tool handles, packaging, furniture and openings. Thin and flexible branches were and are still used to
make wicker baskets and furniture. The bark contains salicin, phenols and oxalates
that have febrifuge, analgesic, sedative, tonic, astringent and antispasmodic properties for medicinal and veterinary use. It is also a honey plant and an ornamental tree
used in gardens, urban green spaces and roads (Larroulet et al. 2011; Rosso and
Scarpa 2019).
7.2.2 The Main Threats to Its Conservation
Although Salix humboldtiana has a continental distribution and in Argentina crosses
various ecosystems, in the marginal populations of the Patagonian steppe, its conservation acquires a high value. In this sense, it is perhaps among the most threatened
tree species in Patagonia. A great loss of its genetic diversity in its southernmost
range can be presumed to have occurred in the last 250 years. The extinction of several populations has been confirmed when compared to historical registers (Falkner
1774; Moreno 1876; Entraigas 1960), and in several river shores, just very few isolated individuals constitute the entire current presence of the species. In turn, in most
of the rivers of Argentina, the natural distribution of S. humboldtiana is highly fragmented. One of the main causes of the critical situation of this species in its southern
range is the massive use of its wood during the European colonization of the Negro
River valley, close to the northern border of Patagonia. There are mentions of thousands of trees cut down per week (Entraigas 1960; Gómez Otero and Bellelli 2006)
to build the first villages (houses, fortifications, churches, fences and even boats).
Remains of willow beams can still be seen in very old houses of Carmen de Patagones,
built at the end of the eighteenth and the beginning of the nineteenth centuries.
More recently, the introduction of highly vigorous and invasive exotic Salix
clones has affected the remaining natural stands of S. humboldtiana. The higher
vegetative propagation capacity of these clones (Thomas et al. 2012; Lewerentz
et al. 2019) contributed to the reduction of the native willow’s habitat. Additionally,
interspecific hybridization occurs and has been reported in systems dominated by
the exotic willows. The low clonal capacity of S. humboldtiana compared with
Eurasian willows and poplars made this species vulnerable to competitive exclusion
(Thomas et al. 2012; Thomas and Leyer 2014). Already Hauman et al. (1947)
reported the scarcity of S. humboldtiana along the Patagonian river banks in the
mid-twentieth century. Alluvial floodplains, low-lying surfaces composed of fluvial
deposits adjacent to river channels (Balian and Naiman 2005), are typical Salix
humboldtiana habitats in most of the rivers of Argentina. However, nowadays they
are covered mainly by exotic species.
In Limay River (a main affluent of the Negro River), for example, the synchronized colonization of Populus nigra cv. italica and Salix fragilis f. fragilis after
floods higher than 1290 m
3
/s installed a new emerging interspecific competition
scenario with the native willow in the channels, strips and island plains. This
P. Marchelli et al.
humid environment (Luis Hansen, pers. comm.). It is used as fuel and for construction and manufacture of barrels, hoops, poles, drawers, joinery, tool handles, packaging, furniture and openings. Thin and flexible branches were and are still used to
make wicker baskets and furniture. The bark contains salicin, phenols and oxalates
that have febrifuge, analgesic, sedative, tonic, astringent and antispasmodic properties for medicinal and veterinary use. It is also a honey plant and an ornamental tree
used in gardens, urban green spaces and roads (Larroulet et al. 2011; Rosso and
Scarpa 2019).
7.2.2 The Main Threats to Its Conservation
Although Salix humboldtiana has a continental distribution and in Argentina crosses
various ecosystems, in the marginal populations of the Patagonian steppe, its conservation acquires a high value. In this sense, it is perhaps among the most threatened
tree species in Patagonia. A great loss of its genetic diversity in its southernmost
range can be presumed to have occurred in the last 250 years. The extinction of several populations has been confirmed when compared to historical registers (Falkner
1774; Moreno 1876; Entraigas 1960), and in several river shores, just very few isolated individuals constitute the entire current presence of the species. In turn, in most
of the rivers of Argentina, the natural distribution of S. humboldtiana is highly fragmented. One of the main causes of the critical situation of this species in its southern
range is the massive use of its wood during the European colonization of the Negro
River valley, close to the northern border of Patagonia. There are mentions of thousands of trees cut down per week (Entraigas 1960; Gómez Otero and Bellelli 2006)
to build the first villages (houses, fortifications, churches, fences and even boats).
Remains of willow beams can still be seen in very old houses of Carmen de Patagones,
built at the end of the eighteenth and the beginning of the nineteenth centuries.
More recently, the introduction of highly vigorous and invasive exotic Salix
clones has affected the remaining natural stands of S. humboldtiana. The higher
vegetative propagation capacity of these clones (Thomas et al. 2012; Lewerentz
et al. 2019) contributed to the reduction of the native willow’s habitat. Additionally,
interspecific hybridization occurs and has been reported in systems dominated by
the exotic willows. The low clonal capacity of S. humboldtiana compared with
Eurasian willows and poplars made this species vulnerable to competitive exclusion
(Thomas et al. 2012; Thomas and Leyer 2014). Already Hauman et al. (1947)
reported the scarcity of S. humboldtiana along the Patagonian river banks in the
mid-twentieth century. Alluvial floodplains, low-lying surfaces composed of fluvial
deposits adjacent to river channels (Balian and Naiman 2005), are typical Salix
humboldtiana habitats in most of the rivers of Argentina. However, nowadays they
are covered mainly by exotic species.
In Limay River (a main affluent of the Negro River), for example, the synchronized colonization of Populus nigra cv. italica and Salix fragilis f. fragilis after
floods higher than 1290 m
3
/s installed a new emerging interspecific competition
scenario with the native willow in the channels, strips and island plains. This
P. Marchelli et al.