4
2. Paraná pine forests, which occupy areas above 600 m asl, with a colder climate
than the previous district, where the main species of the dominant stratum is
Araucaria angustifolia, accompanied by Podocarpus lambertii, Drimys brasiliensis, and several species of the families Myrtaceae and Lauraceae. Between
both districts, there is a large ecotone where the emblematic “yerba mate” (Ilex
paraguariensis) can be found, i.e., a small tree whose leaves are daily consumed
as a particular infusion throughout Argentina, Uruguay, Paraguay, and southern
Brazil and Chile.
1.2.2 Yungas Rainforest
Called in Argentina “Selva Tucumano-Oranense,” it extends along the eastern
slopes of the Andes, forming a narrow strip from Venezuela to the northwest of
Argentina. Its climate is cooler than that of adjoining forest formations and has a
high humidity, caused not only by the abundant orographic precipitations originated
on the humidity brought by the winds coming from the Atlantic Ocean but also by
the permanent fogs that characterize this cloud jungle. In Argentina, the average
rainfall in this formation is from 1000 to 3000 mm per year and is concentrated in
summer, between the months of December and March. Its altitudinal range goes
from 400 m to 3000 m asl and is accompanied by the aforementioned gradient of
precipitation and also by a gradient of average annual temperatures ranging from
26 °C at the base to 14 °C in the higher parts, with the presence of frost in all its
extension and occasional snowfall in the heights. Some genera and even species are
repeated in the Alto Paraná Rainforest revealing possible vicariance processes.
The altitudinal gradient thus defines three floristic districts:
1. Piedmont Rainforest (“Selva Pedemontana”), up to 500 m asl; it marks the transition with the Humid Chaco, with which it shares some elements. It contains
species of high timber value, among which Cedrela balansae, Amburana cearensis, Anadenanthera colubrina var. cebil, Handroanthus impetiginosus, and
Cordia trichotoma stand out.
2. Montane Rainforest (“Selva Montana”), between 500 and 1800 m asl; it is a
cloud forest, dense, humid, and shady, with vines and epiphytes. Three strata
characterize this rainforest, the highest formed by emerging trees over 30 m
height, such as Cedrela angustifolia, Juglans nigra, and Phoebe porphyria; the
one of the middle composed of medium-sized trees and finally the lowest stratum made of bushes and a layer of herbs and mosses.
3. Temperate Montane Forest (“Bosque Montano”), occupying the slopes from
1500 to 2500 m asl, it is composed of conifers and deciduous species and has a
much lower biodiversity. There, pure stands of Podocarpus parlatorei can be
found and, at the highest sites, pure stands of Alnus acuminata, finally appearing
the small tree Polylepis australis, which is the woody species that reaches the
transition with the meadows of the alpine tundra.
M. J. Pastorino
2. Paraná pine forests, which occupy areas above 600 m asl, with a colder climate
than the previous district, where the main species of the dominant stratum is
Araucaria angustifolia, accompanied by Podocarpus lambertii, Drimys brasiliensis, and several species of the families Myrtaceae and Lauraceae. Between
both districts, there is a large ecotone where the emblematic “yerba mate” (Ilex
paraguariensis) can be found, i.e., a small tree whose leaves are daily consumed
as a particular infusion throughout Argentina, Uruguay, Paraguay, and southern
Brazil and Chile.
1.2.2 Yungas Rainforest
Called in Argentina “Selva Tucumano-Oranense,” it extends along the eastern
slopes of the Andes, forming a narrow strip from Venezuela to the northwest of
Argentina. Its climate is cooler than that of adjoining forest formations and has a
high humidity, caused not only by the abundant orographic precipitations originated
on the humidity brought by the winds coming from the Atlantic Ocean but also by
the permanent fogs that characterize this cloud jungle. In Argentina, the average
rainfall in this formation is from 1000 to 3000 mm per year and is concentrated in
summer, between the months of December and March. Its altitudinal range goes
from 400 m to 3000 m asl and is accompanied by the aforementioned gradient of
precipitation and also by a gradient of average annual temperatures ranging from
26 °C at the base to 14 °C in the higher parts, with the presence of frost in all its
extension and occasional snowfall in the heights. Some genera and even species are
repeated in the Alto Paraná Rainforest revealing possible vicariance processes.
The altitudinal gradient thus defines three floristic districts:
1. Piedmont Rainforest (“Selva Pedemontana”), up to 500 m asl; it marks the transition with the Humid Chaco, with which it shares some elements. It contains
species of high timber value, among which Cedrela balansae, Amburana cearensis, Anadenanthera colubrina var. cebil, Handroanthus impetiginosus, and
Cordia trichotoma stand out.
2. Montane Rainforest (“Selva Montana”), between 500 and 1800 m asl; it is a
cloud forest, dense, humid, and shady, with vines and epiphytes. Three strata
characterize this rainforest, the highest formed by emerging trees over 30 m
height, such as Cedrela angustifolia, Juglans nigra, and Phoebe porphyria; the
one of the middle composed of medium-sized trees and finally the lowest stratum made of bushes and a layer of herbs and mosses.
3. Temperate Montane Forest (“Bosque Montano”), occupying the slopes from
1500 to 2500 m asl, it is composed of conifers and deciduous species and has a
much lower biodiversity. There, pure stands of Podocarpus parlatorei can be
found and, at the highest sites, pure stands of Alnus acuminata, finally appearing
the small tree Polylepis australis, which is the woody species that reaches the
transition with the meadows of the alpine tundra.
M. J. Pastorino