33
the generation of gaps that facilitate the regeneration dynamics (Rebertus and
Veblen 1993).
Fire is another disturbance affecting these forests and the most important since
European colonization (Veblen and Lorenz 1988). After human settlement, most
fires are of anthropic origin, although natural fires due to lightning bolts also occur,
particularly in the north. Some species have clear traits that indicate adaptations to
fire, for example, the thick bark of Araucaria araucana and Fitzroya cupressoides,
or the resprouting ability of Nothofagus antarctica, N. obliqua, and N. alpina (Burns
1993). Fires in Patagonia showed a strong climatic influence at an annual scale.
Years of extreme fire occurrence are associated with dry winter-springs of La Niña
events and with warm summers after El Niño events (Veblen et al. 1999). The
greater propensity of shrublands to burn together with an increase in anthropogenic
ignitions accelerates the replacement of forests by shrublands (Mermoz et al. 2005).
Certainly, the disturbances that affected the region on a broad scale were the
climate changes during the Neogene (ca. 23–2.6 My BP). Like in all regions of the
planet, climatic conditions in Patagonia were highly variable during the Cenozoic
(that includes the Neogene and the Quaternary), particularly since the Miocene,
with the occurrence of multiple cold-warm climatic cycles (Rabassa 2008).
Continental and alpine-type glaciations are very well represented in Patagonia and
Tierra del Fuego, with the occurrence of glaciations already at the end of the
Miocene (ca. 5–6 My; Rabassa 2008). The Great Patagonian Glaciation was dated
about 1 My before present (Singer et al. 2004) being the glaciation with the maximum expansion of ice in extra-Andean Patagonia (Flint and Fidalgo 1969; Rabassa
et al. 2005). The Last Glacial Maximum (LGM) occurred about 18,000–20,000 years
ago (Porter 1981), when the ice covered the Patagonian Region beyond the mountain ranges and toward the plains (Rabassa and Clapperton 1990; Glasser et al.
2008). However, pollen diagrams suggested that floristic elements of modern
Patagonian forests were present during the LGM in low abundance and in a discontinuous pattern along both slopes of the Andes (e.g., Heusser et al. 1999; Henríquez
et al. 2017; Moreno et al. 2019) indicating that forest species persisted at multiple
micro-climatically favorable refugia (Markgraf et al. 1995). Some of these refugia
become the center of expansion of the biota after the ice retreated (e.g., Pastorino
and Gallo 2002; Marchelli and Gallo 2006; Azpilicueta et al. 2009; Marchelli et al.
2010; Mathiasen and Premoli 2010; Premoli et al. 2010). These complex scenario
left an imprint in the vegetation patterns and, particularly, in the genetic structure of
populations within species (see details for each species in the different chapters of
this section of the book).
2.2 Social Aspects
Patagonia is one of the main tourist regions from Argentina, highly appreciated both
within the country and abroad. Its main feature relies on the exotic and wild natural
landscapes, relatively little affected by humans. With a population density of only
2 Temperate Subantarctic Forests: A Huge Natural Laboratory
the generation of gaps that facilitate the regeneration dynamics (Rebertus and
Veblen 1993).
Fire is another disturbance affecting these forests and the most important since
European colonization (Veblen and Lorenz 1988). After human settlement, most
fires are of anthropic origin, although natural fires due to lightning bolts also occur,
particularly in the north. Some species have clear traits that indicate adaptations to
fire, for example, the thick bark of Araucaria araucana and Fitzroya cupressoides,
or the resprouting ability of Nothofagus antarctica, N. obliqua, and N. alpina (Burns
1993). Fires in Patagonia showed a strong climatic influence at an annual scale.
Years of extreme fire occurrence are associated with dry winter-springs of La Niña
events and with warm summers after El Niño events (Veblen et al. 1999). The
greater propensity of shrublands to burn together with an increase in anthropogenic
ignitions accelerates the replacement of forests by shrublands (Mermoz et al. 2005).
Certainly, the disturbances that affected the region on a broad scale were the
climate changes during the Neogene (ca. 23–2.6 My BP). Like in all regions of the
planet, climatic conditions in Patagonia were highly variable during the Cenozoic
(that includes the Neogene and the Quaternary), particularly since the Miocene,
with the occurrence of multiple cold-warm climatic cycles (Rabassa 2008).
Continental and alpine-type glaciations are very well represented in Patagonia and
Tierra del Fuego, with the occurrence of glaciations already at the end of the
Miocene (ca. 5–6 My; Rabassa 2008). The Great Patagonian Glaciation was dated
about 1 My before present (Singer et al. 2004) being the glaciation with the maximum expansion of ice in extra-Andean Patagonia (Flint and Fidalgo 1969; Rabassa
et al. 2005). The Last Glacial Maximum (LGM) occurred about 18,000–20,000 years
ago (Porter 1981), when the ice covered the Patagonian Region beyond the mountain ranges and toward the plains (Rabassa and Clapperton 1990; Glasser et al.
2008). However, pollen diagrams suggested that floristic elements of modern
Patagonian forests were present during the LGM in low abundance and in a discontinuous pattern along both slopes of the Andes (e.g., Heusser et al. 1999; Henríquez
et al. 2017; Moreno et al. 2019) indicating that forest species persisted at multiple
micro-climatically favorable refugia (Markgraf et al. 1995). Some of these refugia
become the center of expansion of the biota after the ice retreated (e.g., Pastorino
and Gallo 2002; Marchelli and Gallo 2006; Azpilicueta et al. 2009; Marchelli et al.
2010; Mathiasen and Premoli 2010; Premoli et al. 2010). These complex scenario
left an imprint in the vegetation patterns and, particularly, in the genetic structure of
populations within species (see details for each species in the different chapters of
this section of the book).
2.2 Social Aspects
Patagonia is one of the main tourist regions from Argentina, highly appreciated both
within the country and abroad. Its main feature relies on the exotic and wild natural
landscapes, relatively little affected by humans. With a population density of only
2 Temperate Subantarctic Forests: A Huge Natural Laboratory