A review of the structure and dynamics of araucaria mixed forests in southern Brazil and northern Argentina

Abstract

The Araucaria Mixed Forests (AMF) are subtropical conifer-hardwood mixed forests that are part of the Atlantic forest floristic dominion in Brazil and Argentina. The AMF is dominated by the conifer Araucaria angustifolia (hereafter araucaria), accompanied by a diversity of angiosperms. Its distribution largely corresponds to the 13°C isotherm and is associated with overall lower temperature, frost-prone, and wetter climates than neighboring vegetation types. Palynological research and bioclimatic modelling have yielded somewhat conflicting results but suggest intense forest-grassland dynamics, with grasslands possibly dominating the landscape during the drier and colder last glacial maximum. Araucaria is a cultural keystone species whose distribution has been greatly fostered by Amerindian activity in the last few millennia. Angiosperms form a lower layer beneath araucaria canopies, and they seem to be geographically structured into a wetter and colder eastern and a drier and hotter western portion. Araucaria attain large sizes and high longevity but is unable to regenerate under the shade cast by angiosperm canopies and need large-scale disturbances for successfully complete their life-cycles. This cycle has been synthesised in the non-equilibrium Lozenge model of forest dynamics. Regeneration opportunities arise from the frequent multiple treefall gaps produced by the tornado and windstormprone climate of subtropical South America and by the grazing-, fire-, and nurse-plant successional dynamics of the forest-grassland mosaic. Dispersal is mediated by a complex web of interactions with birds and mammals. A review of the dynamics of southern Oceanic Temperate Forests indicates that the dynamics of the AMF fits a prevailing pattern in these forests that corresponds to the Lozenge model. Deforestation and degradation by logging and cattle grazing have impacted most of the AMF original range. Similarly to what happened to Agathis australis in New Zealand, the establishment of commercial plantations still need incentives and research to thrive and produce large-scale environmental benefits.

The influence of fire and cattle grazing on Araucaria population structure in forest-grasslands mosaics

“…In areas with fire and grazing, both canopy openness and araucaria densities were greater, with more seedlings and adults. A closed canopy can hamper araucaria plants of growing into later stages while fire and grazing can affect araucaria population structure by killing young and juvenile plants (Souza, 2020). Our results corroborate this idea because araucaria seedlings were unable to reach later ontogenetic stages in grasslands and shrublands where fire and grazing are promoted.…”

“…The understanding of mechanisms by how the resulting mosaics are kept or what drives their dynamics is either limited or recent (Blanco et al, 2014;Sühs et al, 2020). Grasslands and forests have normally sharp boundaries, but shrublands tend to occur in between these two habitats and the extent of shrublands grows quickly as fire and grazing are prevented (Blanco et al, 2014;Sühs et al, 2020), and together with windstorms and tornadoes, disturbances have been suggested as key in shaping Araucaria forests, grasslands and associated habitats (Souza, 2020). Across such landscapes, the distribution and density of araucaria stages differed between forest and the other two habitats, with forests showing the highest overall araucaria densities.…”

The influence of fire and cattle grazing on Araucaria population structure in forest-grasslands mosaics

“…In areas with fire and grazing, both canopy openness and araucaria densities were greater, with more seedlings and adults. A closed canopy can hamper araucaria plants of growing into later stages while fire and grazing can affect araucaria population structure by killing young and juvenile plants (Souza, 2020). Our results corroborate this idea because araucaria seedlings were unable to reach later ontogenetic stages in grasslands and shrublands where fire and grazing are promoted.…”

“…The understanding of mechanisms by how the resulting mosaics are kept or what drives their dynamics is either limited or recent (Blanco et al, 2014;Sühs et al, 2020). Grasslands and forests have normally sharp boundaries, but shrublands tend to occur in between these two habitats and the extent of shrublands grows quickly as fire and grazing are prevented (Blanco et al, 2014;Sühs et al, 2020), and together with windstorms and tornadoes, disturbances have been suggested as key in shaping Araucaria forests, grasslands and associated habitats (Souza, 2020). Across such landscapes, the distribution and density of araucaria stages differed between forest and the other two habitats, with forests showing the highest overall araucaria densities.…”

Historical and current environmental selection on functional traits of trees in the Atlantic Forest biodiversity hotspot

“…Conservative leaves also characterize mixed conifer–hardwood forests in southern Brazil and northern Argentina, where cold stress become an important effect along with shading (Souza, 2020). Under cold stress, leaves can suffer dehydration, low enzymatic activity, damage to the membrane or even necrosis, which are avoided by investing in C‐rich physical structures that increase durability (Yadav, 2010).…”

“…Under cold stress, leaves can suffer dehydration, low enzymatic activity, damage to the membrane or even necrosis, which are avoided by investing in C‐rich physical structures that increase durability (Yadav, 2010). It has been suggested that mixed conifer–hardwood forests have the most distinct phylogenetic composition in the Atlantic Forest due to the presence of the conifer Araucaria angustifolia as well as sets of species of Austral‐Antarctic origin (Rezende et al, 2020; Souza, 2020). Myrtaceae, Melastomataceae and Lauraceae are abundant families in this region as well (Duarte et al, 2014).…”

Landscape management among the Guarani of the Atlantic Forest of Misiones, Argentina: the case of the Syagrus romanzoffiana (Cham.) Glassman (Arecaceae) palm tree

“…Such changes in population ecological behavior at different successional stages after disturbances were proposed for the Paraná pine, Araucaria angustifolia (Bertol.) Kuntze (Araucariaceae) in several studies carried out in the Atlantic Forest region (Bortoncello 2008;Paludo et al 2009;Souza 2020). In general, to determine the impact of the use of the resource in the short term, it is necessary to carry out periodic measurements and determine the dynamics of the populations in each settlement incorporating other factors that may affect distribution patterns (palm grove size, socio-economic characteristics, other productive activities, and access to other resources as welfare programs of government agencies, and NGOs).…”

The influence of fire and cattle grazing on Araucaria population structure in forest-grasslands mosaics

“…In areas with fire and grazing, both canopy openness and araucaria densities were greater, with more seedlings and adults. A closed canopy can hamper araucaria plants of growing into later stages while fire and grazing can affect araucaria population structure by killing young and juvenile plants (Souza, 2020). Our results corroborate this idea because araucaria seedlings were unable to reach later ontogenetic stages in grasslands and shrublands where fire and grazing are promoted.…”

“…The understanding of mechanisms by how the resulting mosaics are kept or what drives their dynamics is either limited or recent (Blanco et al, 2014;Sühs et al, 2020). Grasslands and forests have normally sharp boundaries, but shrublands tend to occur in between these two habitats and the extent of shrublands grows quickly as fire and grazing are prevented (Blanco et al, 2014;Sühs et al, 2020), and together with windstorms and tornadoes, disturbances have been suggested as key in shaping Araucaria forests, grasslands and associated habitats (Souza, 2020). Across such landscapes, the distribution and density of araucaria stages differed between forest and the other two habitats, with forests showing the highest overall araucaria densities.…”

Historical and current environmental selection on functional traits of trees in the Atlantic Forest biodiversity hotspot

“…Conservative leaves also characterize mixed conifer–hardwood forests in southern Brazil and northern Argentina, where cold stress become an important effect along with shading (Souza, 2020). Under cold stress, leaves can suffer dehydration, low enzymatic activity, damage to the membrane or even necrosis, which are avoided by investing in C‐rich physical structures that increase durability (Yadav, 2010).…”

“…Under cold stress, leaves can suffer dehydration, low enzymatic activity, damage to the membrane or even necrosis, which are avoided by investing in C‐rich physical structures that increase durability (Yadav, 2010). It has been suggested that mixed conifer–hardwood forests have the most distinct phylogenetic composition in the Atlantic Forest due to the presence of the conifer Araucaria angustifolia as well as sets of species of Austral‐Antarctic origin (Rezende et al, 2020; Souza, 2020). Myrtaceae, Melastomataceae and Lauraceae are abundant families in this region as well (Duarte et al, 2014).…”

Landscape management among the Guarani of the Atlantic Forest of Misiones, Argentina: the case of the Syagrus romanzoffiana (Cham.) Glassman (Arecaceae) palm tree

“…Such changes in population ecological behavior at different successional stages after disturbances were proposed for the Paraná pine, Araucaria angustifolia (Bertol.) Kuntze (Araucariaceae) in several studies carried out in the Atlantic Forest region (Bortoncello 2008;Paludo et al 2009;Souza 2020). In general, to determine the impact of the use of the resource in the short term, it is necessary to carry out periodic measurements and determine the dynamics of the populations in each settlement incorporating other factors that may affect distribution patterns (palm grove size, socio-economic characteristics, other productive activities, and access to other resources as welfare programs of government agencies, and NGOs).…”

The influence of fire and cattle grazing on Araucaria population structure in forest-grasslands mosaics

“…In areas with fire and grazing, both canopy openness and araucaria densities were greater, with more seedlings and adults. A closed canopy can hamper araucaria plants of growing into later stages while fire and grazing can affect araucaria population structure by killing young and juvenile plants (Souza, 2020). Our results corroborate this idea because araucaria seedlings were unable to reach later ontogenetic stages in grasslands and shrublands where fire and grazing are promoted.…”

“…The understanding of mechanisms by how the resulting mosaics are kept or what drives their dynamics is either limited or recent (Blanco et al, 2014;Sühs et al, 2020). Grasslands and forests have normally sharp boundaries, but shrublands tend to occur in between these two habitats and the extent of shrublands grows quickly as fire and grazing are prevented (Blanco et al, 2014;Sühs et al, 2020), and together with windstorms and tornadoes, disturbances have been suggested as key in shaping Araucaria forests, grasslands and associated habitats (Souza, 2020). Across such landscapes, the distribution and density of araucaria stages differed between forest and the other two habitats, with forests showing the highest overall araucaria densities.…”

Historical and current environmental selection on functional traits of trees in the Atlantic Forest biodiversity hotspot

“…Conservative leaves also characterize mixed conifer–hardwood forests in southern Brazil and northern Argentina, where cold stress become an important effect along with shading (Souza, 2020). Under cold stress, leaves can suffer dehydration, low enzymatic activity, damage to the membrane or even necrosis, which are avoided by investing in C‐rich physical structures that increase durability (Yadav, 2010).…”

“…Under cold stress, leaves can suffer dehydration, low enzymatic activity, damage to the membrane or even necrosis, which are avoided by investing in C‐rich physical structures that increase durability (Yadav, 2010). It has been suggested that mixed conifer–hardwood forests have the most distinct phylogenetic composition in the Atlantic Forest due to the presence of the conifer Araucaria angustifolia as well as sets of species of Austral‐Antarctic origin (Rezende et al, 2020; Souza, 2020). Myrtaceae, Melastomataceae and Lauraceae are abundant families in this region as well (Duarte et al, 2014).…”

Landscape management among the Guarani of the Atlantic Forest of Misiones, Argentina: the case of the Syagrus romanzoffiana (Cham.) Glassman (Arecaceae) palm tree

“…Such changes in population ecological behavior at different successional stages after disturbances were proposed for the Paraná pine, Araucaria angustifolia (Bertol.) Kuntze (Araucariaceae) in several studies carried out in the Atlantic Forest region (Bortoncello 2008;Paludo et al 2009;Souza 2020). In general, to determine the impact of the use of the resource in the short term, it is necessary to carry out periodic measurements and determine the dynamics of the populations in each settlement incorporating other factors that may affect distribution patterns (palm grove size, socio-economic characteristics, other productive activities, and access to other resources as welfare programs of government agencies, and NGOs).…”