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region of Monte, with rainfall less than 300 mm. On the other hand, the semi-arid
Chaco and the humid Chaco border the Espinal region to the south, which is a transition area with the Pampas region (Cabrera 1976; Naumann 2006).
From a physiognomic point of view, the Chaco region is characterized by the
presence of an open semi-deciduous xerophytic forest, with dominance of “quebrachos” (Schinopsis spp. and Aspidosperma quebracho-blanco), interspersed with
large bushy areas caused by fire, clearing, and subsequent abandonment (where
species of the Acacia genus dominate), and “low” zones (i.e., old river beds, microrelief) with more closed forests dominated by “algarrobos” (Prosopis spp.) or
Enterolobium contortisiliquum (mainly to the north). In floodable areas Prosopis
ruscifolia dominates, and on the humid Chaco palm groves can be found, with
grasslands and algarrobos as secondary woody species (Cabrera 1976; Brown and
Pacheco 2006; Oyarzabal et al. 2018). On the other hand, the Chaco is a region
deeply modified by human activity, mainly by selective logging, overgrazing, fire,
and deforestation.
The Chaco soils are, in general, heavy and with hydromorphism problems to the
east, while the central strip, between the isohyets of 700 and 800 mm, presents
developed soils, some with good agricultural quality (locally known as the “agricultural dome” or “Chaco dome”). To the west, in the semi-arid and arid Chaco, soils
are less developed, in some areas with excessive drainage or salinity problems, typical of arid and semi-arid regions (Giménez and Moglia 2003a, b; Panigatti 2010).
The forests of the Chaco are currently in a state of great vulnerability to climate
change. Considering a moderate scenario, such as A2 according to the report of the
Intergovernmental Panel on Climate Change (IPCC 2014), a warming is projected
for the entire region with respect to the period 1960–2010 that ranges from 0 to 1 °C
in the near future (year 2050) and up to 2.5–3.5 °C in the distant future (year 2100)
in the north of the region. Regarding rainfall, no major changes in the average
annual precipitation are foreseeing. However, the greatest climatic risk would come
from the variability of rainfall magnified by the change in land use and the high
probability of extreme drought events (MAyDS 2015).
The four Chaco subregions are characterized by the dominance of some of the
quebracho forest species, emblematic both from a floristic and a cultural point of
view. The humid Chaco is characterized by the presence of Schinopsis balansae, the
semi-arid Chaco by Schinopsis lorentzii and the Chaco serrano by Schinopsis
haenkeana. In the arid Chaco, these three species of red quebracho disappear and
only the white quebracho Aspidosperma quebracho-blanco becomes dominant,
whose distribution covers the entire Chaco region (Morello and Adámoli 1974;
Cabrera 1976). In the strip that separates the humid from the semi-arid Chaco
(700–800 mm of average annual precipitation, agricultural quality soils), a particular forest develops, known as “of the three quebrachos” (S. balansae, S. lorentzii,
and A. quebracho-blanco). Also in this strip grows Schinopsis heterophylla, a putative hybrid between S. balansae and S. lorentzii (Muñoz 2000).
Along with quebrachos, algarrobos (Prosopis spp.) complete the most emblematic native forest species in the region. According to the traditional taxonomy of the
genus, both the humid and semi-arid Chaco are characterized by Prosopis alba and
8 Subtropical Dry Forests: The Main Forest Ecoregion of Argentina
region of Monte, with rainfall less than 300 mm. On the other hand, the semi-arid
Chaco and the humid Chaco border the Espinal region to the south, which is a transition area with the Pampas region (Cabrera 1976; Naumann 2006).
From a physiognomic point of view, the Chaco region is characterized by the
presence of an open semi-deciduous xerophytic forest, with dominance of “quebrachos” (Schinopsis spp. and Aspidosperma quebracho-blanco), interspersed with
large bushy areas caused by fire, clearing, and subsequent abandonment (where
species of the Acacia genus dominate), and “low” zones (i.e., old river beds, microrelief) with more closed forests dominated by “algarrobos” (Prosopis spp.) or
Enterolobium contortisiliquum (mainly to the north). In floodable areas Prosopis
ruscifolia dominates, and on the humid Chaco palm groves can be found, with
grasslands and algarrobos as secondary woody species (Cabrera 1976; Brown and
Pacheco 2006; Oyarzabal et al. 2018). On the other hand, the Chaco is a region
deeply modified by human activity, mainly by selective logging, overgrazing, fire,
and deforestation.
The Chaco soils are, in general, heavy and with hydromorphism problems to the
east, while the central strip, between the isohyets of 700 and 800 mm, presents
developed soils, some with good agricultural quality (locally known as the “agricultural dome” or “Chaco dome”). To the west, in the semi-arid and arid Chaco, soils
are less developed, in some areas with excessive drainage or salinity problems, typical of arid and semi-arid regions (Giménez and Moglia 2003a, b; Panigatti 2010).
The forests of the Chaco are currently in a state of great vulnerability to climate
change. Considering a moderate scenario, such as A2 according to the report of the
Intergovernmental Panel on Climate Change (IPCC 2014), a warming is projected
for the entire region with respect to the period 1960–2010 that ranges from 0 to 1 °C
in the near future (year 2050) and up to 2.5–3.5 °C in the distant future (year 2100)
in the north of the region. Regarding rainfall, no major changes in the average
annual precipitation are foreseeing. However, the greatest climatic risk would come
from the variability of rainfall magnified by the change in land use and the high
probability of extreme drought events (MAyDS 2015).
The four Chaco subregions are characterized by the dominance of some of the
quebracho forest species, emblematic both from a floristic and a cultural point of
view. The humid Chaco is characterized by the presence of Schinopsis balansae, the
semi-arid Chaco by Schinopsis lorentzii and the Chaco serrano by Schinopsis
haenkeana. In the arid Chaco, these three species of red quebracho disappear and
only the white quebracho Aspidosperma quebracho-blanco becomes dominant,
whose distribution covers the entire Chaco region (Morello and Adámoli 1974;
Cabrera 1976). In the strip that separates the humid from the semi-arid Chaco
(700–800 mm of average annual precipitation, agricultural quality soils), a particular forest develops, known as “of the three quebrachos” (S. balansae, S. lorentzii,
and A. quebracho-blanco). Also in this strip grows Schinopsis heterophylla, a putative hybrid between S. balansae and S. lorentzii (Muñoz 2000).
Along with quebrachos, algarrobos (Prosopis spp.) complete the most emblematic native forest species in the region. According to the traditional taxonomy of the
genus, both the humid and semi-arid Chaco are characterized by Prosopis alba and
8 Subtropical Dry Forests: The Main Forest Ecoregion of Argentina