Context Better balancing agricultural production and biodiversity conservation is a central goal ... more Context Better balancing agricultural production and biodiversity conservation is a central goal for many landscapes. Yet, empirical work on how to best achieve such a balance has focused mainly on the local scale, thereby disregarding that landscape context might mediate biodiversity-agriculture trade-offs. Objectives Focusing on vertebrates in the Argentine Chaco, we evaluate how trade-offs between agriculture and biodiversity vary with landscape context, from landscapes where agricultural and natural areas are separated to landscapes where both are interspersed. Methods We modelled the distributions of 226 vertebrates and use the resulting maps to describe the species richness of ecosystem-service providing guilds. We calculated three agricultural intensity metrics, and evaluated how both species richness and agricultural intensity vary along a gradient of landscape configuration, while controlling for landscape composition. Results Species richness and agricultural yields both varied with landscape configuration. Biodiversity was highest in mixed landscapes where agricultural and natural area are interspersed, whereas agricultural yields showed a more heterogeneous response, with some yield metrics highest in mixed and others in separated landscapes. As a result, agriculture/biodiversity trade-offs depended strongly on landscape Electronic supplementary material The online version of this article (
QuestionWhat are the composition and spatial patterns of native woody plant communities in the so... more QuestionWhat are the composition and spatial patterns of native woody plant communities in the southern Great Chaco and Espinal?LocationCórdoba Province, central Argentina, an area of ca. 161,000 km2.MethodsWe collected 351 geo‐referenced relevés representative of the geographic, topographic and ecological variation of the Chaco and Espinal woody vegetation in central Argentina. The relevés were classified into vegetation types using the hierarchical ISOPAM method. Forest and shrubland types were described on the basis of diagnostic species occurrences and their distribution in relation to environmental factors. A map of the actual vegetation derived from remote‐sensed images (Landsat) and field data was used to describe the current distribution and abundance of the different vegetation types.ResultsThe classification of the 351 plots × 837 species matrix revealed two major clusters comprising seven woody vegetation types corresponding to Chaco lowland and mountain forests and shrub...
The Gran Chaco harbors high biodiversity, including many endemic species (3, 6, 7). This region i... more The Gran Chaco harbors high biodiversity, including many endemic species (3, 6, 7). This region is also a global deforestation hotspot (8) due to the recently accelerated expansion of cattle ranching and soybean cultivation there (9, 10). Given the agricultural potential of the region and the growing global demands for agricultural products, the pressure to convert additional natural ecosystems into agricultural land remains very high. Yet, only 9% of the Gran Chaco is currently protected (6). For these reasons, the Gran Chaco is one of the most threatened ecoregions worldwide. Various definitions of dry forests exist, but the Gran Chaco should not be neglected when raising awareness to the urgent conservation needs in the often forgotten neotropical dry forests.
Esta iniciativa esta orientada a proponer soluciones plausibles a dos problemas basicos que enfre... more Esta iniciativa esta orientada a proponer soluciones plausibles a dos problemas basicos que enfrenta la conservacion de la biodiversidad en la provincia de Cordoba: 1) establecer el grado de representacion del sistema existente de areas protegidas de la provincia de Cordoba; y 2) proponer nuevas areas que deberian protegerse para alcanzar un grado completo de representacion de la diversidad de Cordoba. Este nuevo sistema incluira tanto las areas estatales que puedan incorporarse, como propuestas de areas de conservacion privadas. A juzgar por estudios previos de los integrantes de la Red, la provincia de Cordoba no difiere de lo reportado para sistemas de areas protegidas de otros lugares del mundo, y se predice que el sistema actual no conserva adecuadamente la biodiversidad de la region, y que un sistema de areas protegidas privadas permitiria completar y complementar al sistema de reservas estatales existentes. Con el proposito de establecer la representatividad de la biodiversidad de la region por parte del sistema actual de areas protegidas, se procedera a realizar la cartografia de la vegetacion de toda la provincia, listados floristicos y descripciones de las comunidades vegetales de esas areas. A traves del empleo de indicadores de la biodiversidad (tipo de habitat y grupos taxonomicos particulares), se establecera el grado en que el sistema actual es representativo de la diversidad floristica de la provincia. Finalmente se estableceran vacios en el sistema de conservacion existente y se propondran nuevas areas para ser incorporadas al sistema provincial de areas protegidas. Ademas, el Proyecto proveera una base de datos floristico-corologica en la cual se incorporaran todas las especies y comunidades vegetales registradas en las areas protegidas del territorio provincial. Ademas de la cartografia, las listas de especies y comunidades, las bases de datos y la propuesta de un nuevo sistema de areas protegidas, el proyecto producira material grafico (2 libros) de alcance cientifico-tecnico y de divulgacion, respectivamente. A los efectos de la ejecucion del proyecto, se conformara una Red integrada por cientificos, docentes y tecnicos de las Universidades Nacionales de Cordoba y Rio Cuarto, de una Unidad Ejecutora del CONICET y de integrantes de una Organizacion No Gubernamental con alto impacto en localidades del interior provincial. Los miembros de la Red registran numerosos antecedentes en relacion a estudios floristicos, fitogeograficos y fitosociologicos del territorio de Cordoba, lo que confiere alta factibilidad a esta iniciativa.
Wildfires are a primary disturbance in the Sierras de Córdoba, Argentina, with approximately 2 15... more Wildfires are a primary disturbance in the Sierras de Córdoba, Argentina, with approximately 2 152 000 ha burned between 1993 and 2012. However, little is known about the spatial and temporal patterns of fires and their relationship with climate and vegetation in this area. Such information is of great value for fire risk assessment and the development of strategies for fire management. Our main objective was to analyze fire activity in four sierran ranges, assessing which weather and climate conditions were mostly related to fire activity, and which land cover types were mostly burned. We used a fire database of mid-high spatial resolution and a land cover map derived from Landsat imagery. Fire regimes were different among the different sierran ranges. The Sierras Chicas range was the most affected by fires, with the largest number of fire events, burned area, and fire frequency. Although large fires represented 3 % to 5 % of fire events, they accounted for 60 % to 86 % of total bu...
About 95% of the world's living species of vascular plants belong to families that are characteri... more About 95% of the world's living species of vascular plants belong to families that are characteristically mycorrhizal (Trappe 1977). The symbiotic root-fungus associations result from the coevolution between plants and fungi, which determined mycorrhizae to be the norm in terrestrial plant nutrition, not the exception (Trappe 1977, 1987, Brundrett and Cairney 2002). Among the seven types of mycorrhizae widely described (arbuscular, arbutoid, ectendo, ecto, ericoid, monotropoid, and orchidaceous), both arbuscular mycorrhizae (AM) and ectomycorrhizae (ECM) are the most abundant and widespread in forest communities (Allen et al. 2003; Smith and Read 2008). Forest communities cover approximately 33% of the world's land surface (Rumney 1968) being ECM the most frequent and widespread mycorrhizal type in forests and woodlands of cool temperate and boreal latitudes. Forests characterized by the dominance of ECM woody species would have extended both throughout the hemispheres and upwards in mountain areas at the expense of AM woodlands (Malloch et al. 1980). On the other hand, even though various tropical and subtropical trees throughout the world also form ECM (Moyersoen et al. 1998a, b,
In Argentina the Yungas forests are among the ecosystems most affected by human activity, with lo... more In Argentina the Yungas forests are among the ecosystems most affected by human activity, with loss of biodiversity. To assess the arbuscular mycorrhizal (AM) colonization and the arbuscular mycorrhizal fungi (AMF) spore numbers in these ecosystems, the roots of the most dominant native plants (one tree, Alnus acuminata; three herbaceous, Duchesnea indica, Oxalis conorrhiza, Trifolium aff. repens; and one shrub, Sambucus peruviana) were studied throughout the year from two sites of Yungas forests. Assessments of mycorrhizal colonization (percent root length, intraradical structures) were made by washing and staining the roots. Soil samples of each plant species were pooled and subsamples were obtained to determine AM spore numbers. The herbaceous species formed both Arum-and Paris-type morphologies, whereas the tree and the shrub species formed respectively single structural types of Arumand Paris-type. AM colonization, intraradical fungi structures and AMF spore numbers displayed variation in species, seasons and sites. D. indica showed the highest AM colonization, whereas the highest spore numbers was observed in the rhizosphere of A. acuminata. No correlation was observed between spore numbers and root length percentage colonized by AM fungi. Results of this study showed that Alnus acuminata is facultatively AM. The AM colonization, intraradical fungi structures and AMF spore numbers varied in species depending on phenological, climatic and edaphic conditions.
Synergistic combinations of climatic and land use changes have the potential to produce the most ... more Synergistic combinations of climatic and land use changes have the potential to produce the most dramatic impacts on land cover. Although this is widely accepted, empirical examples, particularly involving deforestation in Latin America, are still very few. The geographic extent and causes of deforestation in subtropical seasonally dry forests of the world have received very little attention. This is especially true for the Chaco forests in South America, which are being lost at an alarming rate, sometimes higher than those reported for tropical forests. On this basis, the aims of this study were to analyze the changes in land cover that have occurred during the last three decades of the 20th century in the Chaco forests of central Argentina, and to explain the factors that have driven those changes. Results show major land cover changes. Approximately 80% of the area that was originally undisturbed forest is now occupied by crops, pastures, and secondary scrub. The main proximate cause of deforestation has been agricultural expansion, soybean cultivation in particular. This appears as the result of the synergistic convergence of climatic, technological, and socioeconomic factors, supporting the hypothesis of a multiple-factor explanation for forest loss, while providing one of the very few existing analyses of changes in subtropical forests of the world. Keywords Agricultural expansion Á Climate change Á Deforestation Á Great Chaco Á Land use Á Proximate causes Á Underlying factors There is increasing recognition that land use change, through its impacts on land cover, is one of the global change drivers expected to have the largest impact on biodiversity by the end of the 21st century (Sala and others 2000; Foley and others 2005; Millennium Ecosystem Assessment 2005). Land use practices such as deforestation, grazing, and agriculture affect ecosystem structure and functioning and regional climate (Vitousek and others 1997; Baron and others 2000; Chapin and others 2000). There is also increasing acceptance that changes in land use and climate interact in complex ways, producing negative and positive feedbacks, so that their ecosystem consequences are not always easily predictable (McCarthy and others 2001; Peters and others 2004; Millennium Ecosystem Assessment 2005; Rudel and others 2005). For all these reasons, understanding land cover change and accounting for land use practices with greater geographic precision, especially in some understudied regions of the world, is highly desirable (Turner and Meyer 1994; Geist and Lambin 2002; Ramankutty and others 2002; Zak and others 2004). One of the primary causes of change in land cover is deforestation and agricultural expansion, but the factors (both proximate-human activities that directly affect the environment, so constituting proximate sources of change
Not all species are likely to be equally affected by habitat fragmentation; thus, we evaluated th... more Not all species are likely to be equally affected by habitat fragmentation; thus, we evaluated the effects of size of forest remnants on trophically linked communities of plants, leaf-mining insects, and their parasitoids. We explored the possibility of differential vulnerability to habitat area reduction in relation to species-specific and food-web traits by comparing species-area regression slopes. Moreover, we searched for a synergistic effect of these traits and of trophic level. We collected mined leaves and recorded plant, leaf miner, and parasitoid species interactions in five 100-m 2 transects in 19 Chaco Serrano woodland remnants in central Argentina. Species were classified into extreme categories according to body size, natural abundance, trophic breadth, and trophic level. Species-area slopes differed between groups with extreme values of natural abundance or trophic specialization. Nevertheless, synergistic effects of life-history and food-web traits were only found for trophic level and trophic breadth: area-related species loss was highest for specialist parasitoids. It has been suggested that species position within interaction webs could determine their vulnerability to extinction. Our results provide evidence that food-web parameters, such as trophic level and trophic breadth, affect species sensitivity to habitat fragmentation.
While much information is available about tropical and temperate ecosystems, there is a remarkabl... more While much information is available about tropical and temperate ecosystems, there is a remarkably little information as to land cover and land use changes in the subtropical biomes of the world. Here, we quantify changes in the spatial patterns of land cover types at the southern edge of the seasonally dry, subtropical Chaco forest of South America during the second half of the 20th century using a vegetation map printed in 1969 and a Landsat TM based digital map produced 30 years later. Results show a massive contraction of forest; ca. 1.2 million ha of original lowland and mountain subtropical dry forests and woodlands, 85% of the total, have been cleared in only 30 years. This loss of Chaco forests of 2.2% year À1 is consistent with or even exceeds, global trends. Forest vegetation now persists as fragments where there was formerly continuous cover. Most of undisturbed Chaco forest has now been converted to pasture or is undergoing secondary succession. Today, these new vegetation types, resulting mainly from agricultural expansion, have increased 10-fold in cover and now represent the commonest land cover types. The increased intensity of agricultural usage, possibly triggered by an increase in annual rainfall during the last decades, has been accompanied by changes in agricultural practices and a relative decline in the rural population.
Bidens pilosa L. is a summer annual that shows a particular phenological pattern in the Córdoba m... more Bidens pilosa L. is a summer annual that shows a particular phenological pattern in the Córdoba mountains, Argentina. Some individuals start flowering 1 month after germination (early type), but most of the population starts flowering 4 months after germination (normal type). The aims of this study were to (1) analyse whether differences in flowering phenology affect seed mass and seed production, and (2) assess whether possible differences in seed traits of the two parental phenological types would affect germinability, germination rate, seedling growth and flowering phenology of offspring under laboratory conditions. The study showed that the numbers of seeds per capitulum and per plant were greater in the normal type than in the early type plants. This can be related to plant height, since in the field, normal-type plants are larger than early type plants. However, early type plants produced heavier seeds than normal-type plants. Germination rate was faster in the early type seed...
Aims(1) to compare two series of precipitation data from different periods (1930–1950 and 1950–20... more Aims(1) to compare two series of precipitation data from different periods (1930–1950 and 1950–2000) in three sectors of the southern dry Chaco in the arid and semi‐arid sub‐regions; (2) construct maps showing the distribution of land‐cover units for 1979, 1999, 2004 and 2010 for the same three sectors; and (3) assess the changes in land‐cover units occurred between 1979 and 2010 in the three sectors.LocationSouthern extreme of the dry Chaco in NE and NW Córdoba Province, central Argentina.MethodsWe compared annual and growth period (November–March) precipitation among the three sectors and between two series of data corresponding to different periods (1930–1950 and 1950–2000) using repeated measures ANOVA, with the station as the subject variable, period as the within‐factor and sector as the between factor. Using three Landsat MSS (1979) and nine Landsat TM (1999, 2004 and 2010) images we mapped the distribution of eight land‐cover units for the whole study area. For each sector (...
We determined the drivers of fires in Semiarid Chaco mountains of Central Argentina. • We identif... more We determined the drivers of fires in Semiarid Chaco mountains of Central Argentina. • We identified the drivers' ranges at which fire activity was higher. • Climate was the most important driver, followed by human and biological predictors. • Fires were more frequent at intermediate levels of rainfall and productivity. • Fires were more frequent where temperature and productivity were more variable.
Context Better balancing agricultural production and biodiversity conservation is a central goal ... more Context Better balancing agricultural production and biodiversity conservation is a central goal for many landscapes. Yet, empirical work on how to best achieve such a balance has focused mainly on the local scale, thereby disregarding that landscape context might mediate biodiversity-agriculture trade-offs. Objectives Focusing on vertebrates in the Argentine Chaco, we evaluate how trade-offs between agriculture and biodiversity vary with landscape context, from landscapes where agricultural and natural areas are separated to landscapes where both are interspersed. Methods We modelled the distributions of 226 vertebrates and use the resulting maps to describe the species richness of ecosystem-service providing guilds. We calculated three agricultural intensity metrics, and evaluated how both species richness and agricultural intensity vary along a gradient of landscape configuration, while controlling for landscape composition. Results Species richness and agricultural yields both varied with landscape configuration. Biodiversity was highest in mixed landscapes where agricultural and natural area are interspersed, whereas agricultural yields showed a more heterogeneous response, with some yield metrics highest in mixed and others in separated landscapes. As a result, agriculture/biodiversity trade-offs depended strongly on landscape Electronic supplementary material The online version of this article (
QuestionWhat are the composition and spatial patterns of native woody plant communities in the so... more QuestionWhat are the composition and spatial patterns of native woody plant communities in the southern Great Chaco and Espinal?LocationCórdoba Province, central Argentina, an area of ca. 161,000 km2.MethodsWe collected 351 geo‐referenced relevés representative of the geographic, topographic and ecological variation of the Chaco and Espinal woody vegetation in central Argentina. The relevés were classified into vegetation types using the hierarchical ISOPAM method. Forest and shrubland types were described on the basis of diagnostic species occurrences and their distribution in relation to environmental factors. A map of the actual vegetation derived from remote‐sensed images (Landsat) and field data was used to describe the current distribution and abundance of the different vegetation types.ResultsThe classification of the 351 plots × 837 species matrix revealed two major clusters comprising seven woody vegetation types corresponding to Chaco lowland and mountain forests and shrub...
The Gran Chaco harbors high biodiversity, including many endemic species (3, 6, 7). This region i... more The Gran Chaco harbors high biodiversity, including many endemic species (3, 6, 7). This region is also a global deforestation hotspot (8) due to the recently accelerated expansion of cattle ranching and soybean cultivation there (9, 10). Given the agricultural potential of the region and the growing global demands for agricultural products, the pressure to convert additional natural ecosystems into agricultural land remains very high. Yet, only 9% of the Gran Chaco is currently protected (6). For these reasons, the Gran Chaco is one of the most threatened ecoregions worldwide. Various definitions of dry forests exist, but the Gran Chaco should not be neglected when raising awareness to the urgent conservation needs in the often forgotten neotropical dry forests.
Esta iniciativa esta orientada a proponer soluciones plausibles a dos problemas basicos que enfre... more Esta iniciativa esta orientada a proponer soluciones plausibles a dos problemas basicos que enfrenta la conservacion de la biodiversidad en la provincia de Cordoba: 1) establecer el grado de representacion del sistema existente de areas protegidas de la provincia de Cordoba; y 2) proponer nuevas areas que deberian protegerse para alcanzar un grado completo de representacion de la diversidad de Cordoba. Este nuevo sistema incluira tanto las areas estatales que puedan incorporarse, como propuestas de areas de conservacion privadas. A juzgar por estudios previos de los integrantes de la Red, la provincia de Cordoba no difiere de lo reportado para sistemas de areas protegidas de otros lugares del mundo, y se predice que el sistema actual no conserva adecuadamente la biodiversidad de la region, y que un sistema de areas protegidas privadas permitiria completar y complementar al sistema de reservas estatales existentes. Con el proposito de establecer la representatividad de la biodiversidad de la region por parte del sistema actual de areas protegidas, se procedera a realizar la cartografia de la vegetacion de toda la provincia, listados floristicos y descripciones de las comunidades vegetales de esas areas. A traves del empleo de indicadores de la biodiversidad (tipo de habitat y grupos taxonomicos particulares), se establecera el grado en que el sistema actual es representativo de la diversidad floristica de la provincia. Finalmente se estableceran vacios en el sistema de conservacion existente y se propondran nuevas areas para ser incorporadas al sistema provincial de areas protegidas. Ademas, el Proyecto proveera una base de datos floristico-corologica en la cual se incorporaran todas las especies y comunidades vegetales registradas en las areas protegidas del territorio provincial. Ademas de la cartografia, las listas de especies y comunidades, las bases de datos y la propuesta de un nuevo sistema de areas protegidas, el proyecto producira material grafico (2 libros) de alcance cientifico-tecnico y de divulgacion, respectivamente. A los efectos de la ejecucion del proyecto, se conformara una Red integrada por cientificos, docentes y tecnicos de las Universidades Nacionales de Cordoba y Rio Cuarto, de una Unidad Ejecutora del CONICET y de integrantes de una Organizacion No Gubernamental con alto impacto en localidades del interior provincial. Los miembros de la Red registran numerosos antecedentes en relacion a estudios floristicos, fitogeograficos y fitosociologicos del territorio de Cordoba, lo que confiere alta factibilidad a esta iniciativa.
Wildfires are a primary disturbance in the Sierras de Córdoba, Argentina, with approximately 2 15... more Wildfires are a primary disturbance in the Sierras de Córdoba, Argentina, with approximately 2 152 000 ha burned between 1993 and 2012. However, little is known about the spatial and temporal patterns of fires and their relationship with climate and vegetation in this area. Such information is of great value for fire risk assessment and the development of strategies for fire management. Our main objective was to analyze fire activity in four sierran ranges, assessing which weather and climate conditions were mostly related to fire activity, and which land cover types were mostly burned. We used a fire database of mid-high spatial resolution and a land cover map derived from Landsat imagery. Fire regimes were different among the different sierran ranges. The Sierras Chicas range was the most affected by fires, with the largest number of fire events, burned area, and fire frequency. Although large fires represented 3 % to 5 % of fire events, they accounted for 60 % to 86 % of total bu...
About 95% of the world's living species of vascular plants belong to families that are characteri... more About 95% of the world's living species of vascular plants belong to families that are characteristically mycorrhizal (Trappe 1977). The symbiotic root-fungus associations result from the coevolution between plants and fungi, which determined mycorrhizae to be the norm in terrestrial plant nutrition, not the exception (Trappe 1977, 1987, Brundrett and Cairney 2002). Among the seven types of mycorrhizae widely described (arbuscular, arbutoid, ectendo, ecto, ericoid, monotropoid, and orchidaceous), both arbuscular mycorrhizae (AM) and ectomycorrhizae (ECM) are the most abundant and widespread in forest communities (Allen et al. 2003; Smith and Read 2008). Forest communities cover approximately 33% of the world's land surface (Rumney 1968) being ECM the most frequent and widespread mycorrhizal type in forests and woodlands of cool temperate and boreal latitudes. Forests characterized by the dominance of ECM woody species would have extended both throughout the hemispheres and upwards in mountain areas at the expense of AM woodlands (Malloch et al. 1980). On the other hand, even though various tropical and subtropical trees throughout the world also form ECM (Moyersoen et al. 1998a, b,
In Argentina the Yungas forests are among the ecosystems most affected by human activity, with lo... more In Argentina the Yungas forests are among the ecosystems most affected by human activity, with loss of biodiversity. To assess the arbuscular mycorrhizal (AM) colonization and the arbuscular mycorrhizal fungi (AMF) spore numbers in these ecosystems, the roots of the most dominant native plants (one tree, Alnus acuminata; three herbaceous, Duchesnea indica, Oxalis conorrhiza, Trifolium aff. repens; and one shrub, Sambucus peruviana) were studied throughout the year from two sites of Yungas forests. Assessments of mycorrhizal colonization (percent root length, intraradical structures) were made by washing and staining the roots. Soil samples of each plant species were pooled and subsamples were obtained to determine AM spore numbers. The herbaceous species formed both Arum-and Paris-type morphologies, whereas the tree and the shrub species formed respectively single structural types of Arumand Paris-type. AM colonization, intraradical fungi structures and AMF spore numbers displayed variation in species, seasons and sites. D. indica showed the highest AM colonization, whereas the highest spore numbers was observed in the rhizosphere of A. acuminata. No correlation was observed between spore numbers and root length percentage colonized by AM fungi. Results of this study showed that Alnus acuminata is facultatively AM. The AM colonization, intraradical fungi structures and AMF spore numbers varied in species depending on phenological, climatic and edaphic conditions.
Synergistic combinations of climatic and land use changes have the potential to produce the most ... more Synergistic combinations of climatic and land use changes have the potential to produce the most dramatic impacts on land cover. Although this is widely accepted, empirical examples, particularly involving deforestation in Latin America, are still very few. The geographic extent and causes of deforestation in subtropical seasonally dry forests of the world have received very little attention. This is especially true for the Chaco forests in South America, which are being lost at an alarming rate, sometimes higher than those reported for tropical forests. On this basis, the aims of this study were to analyze the changes in land cover that have occurred during the last three decades of the 20th century in the Chaco forests of central Argentina, and to explain the factors that have driven those changes. Results show major land cover changes. Approximately 80% of the area that was originally undisturbed forest is now occupied by crops, pastures, and secondary scrub. The main proximate cause of deforestation has been agricultural expansion, soybean cultivation in particular. This appears as the result of the synergistic convergence of climatic, technological, and socioeconomic factors, supporting the hypothesis of a multiple-factor explanation for forest loss, while providing one of the very few existing analyses of changes in subtropical forests of the world. Keywords Agricultural expansion Á Climate change Á Deforestation Á Great Chaco Á Land use Á Proximate causes Á Underlying factors There is increasing recognition that land use change, through its impacts on land cover, is one of the global change drivers expected to have the largest impact on biodiversity by the end of the 21st century (Sala and others 2000; Foley and others 2005; Millennium Ecosystem Assessment 2005). Land use practices such as deforestation, grazing, and agriculture affect ecosystem structure and functioning and regional climate (Vitousek and others 1997; Baron and others 2000; Chapin and others 2000). There is also increasing acceptance that changes in land use and climate interact in complex ways, producing negative and positive feedbacks, so that their ecosystem consequences are not always easily predictable (McCarthy and others 2001; Peters and others 2004; Millennium Ecosystem Assessment 2005; Rudel and others 2005). For all these reasons, understanding land cover change and accounting for land use practices with greater geographic precision, especially in some understudied regions of the world, is highly desirable (Turner and Meyer 1994; Geist and Lambin 2002; Ramankutty and others 2002; Zak and others 2004). One of the primary causes of change in land cover is deforestation and agricultural expansion, but the factors (both proximate-human activities that directly affect the environment, so constituting proximate sources of change
Not all species are likely to be equally affected by habitat fragmentation; thus, we evaluated th... more Not all species are likely to be equally affected by habitat fragmentation; thus, we evaluated the effects of size of forest remnants on trophically linked communities of plants, leaf-mining insects, and their parasitoids. We explored the possibility of differential vulnerability to habitat area reduction in relation to species-specific and food-web traits by comparing species-area regression slopes. Moreover, we searched for a synergistic effect of these traits and of trophic level. We collected mined leaves and recorded plant, leaf miner, and parasitoid species interactions in five 100-m 2 transects in 19 Chaco Serrano woodland remnants in central Argentina. Species were classified into extreme categories according to body size, natural abundance, trophic breadth, and trophic level. Species-area slopes differed between groups with extreme values of natural abundance or trophic specialization. Nevertheless, synergistic effects of life-history and food-web traits were only found for trophic level and trophic breadth: area-related species loss was highest for specialist parasitoids. It has been suggested that species position within interaction webs could determine their vulnerability to extinction. Our results provide evidence that food-web parameters, such as trophic level and trophic breadth, affect species sensitivity to habitat fragmentation.
While much information is available about tropical and temperate ecosystems, there is a remarkabl... more While much information is available about tropical and temperate ecosystems, there is a remarkably little information as to land cover and land use changes in the subtropical biomes of the world. Here, we quantify changes in the spatial patterns of land cover types at the southern edge of the seasonally dry, subtropical Chaco forest of South America during the second half of the 20th century using a vegetation map printed in 1969 and a Landsat TM based digital map produced 30 years later. Results show a massive contraction of forest; ca. 1.2 million ha of original lowland and mountain subtropical dry forests and woodlands, 85% of the total, have been cleared in only 30 years. This loss of Chaco forests of 2.2% year À1 is consistent with or even exceeds, global trends. Forest vegetation now persists as fragments where there was formerly continuous cover. Most of undisturbed Chaco forest has now been converted to pasture or is undergoing secondary succession. Today, these new vegetation types, resulting mainly from agricultural expansion, have increased 10-fold in cover and now represent the commonest land cover types. The increased intensity of agricultural usage, possibly triggered by an increase in annual rainfall during the last decades, has been accompanied by changes in agricultural practices and a relative decline in the rural population.
Bidens pilosa L. is a summer annual that shows a particular phenological pattern in the Córdoba m... more Bidens pilosa L. is a summer annual that shows a particular phenological pattern in the Córdoba mountains, Argentina. Some individuals start flowering 1 month after germination (early type), but most of the population starts flowering 4 months after germination (normal type). The aims of this study were to (1) analyse whether differences in flowering phenology affect seed mass and seed production, and (2) assess whether possible differences in seed traits of the two parental phenological types would affect germinability, germination rate, seedling growth and flowering phenology of offspring under laboratory conditions. The study showed that the numbers of seeds per capitulum and per plant were greater in the normal type than in the early type plants. This can be related to plant height, since in the field, normal-type plants are larger than early type plants. However, early type plants produced heavier seeds than normal-type plants. Germination rate was faster in the early type seed...
Aims(1) to compare two series of precipitation data from different periods (1930–1950 and 1950–20... more Aims(1) to compare two series of precipitation data from different periods (1930–1950 and 1950–2000) in three sectors of the southern dry Chaco in the arid and semi‐arid sub‐regions; (2) construct maps showing the distribution of land‐cover units for 1979, 1999, 2004 and 2010 for the same three sectors; and (3) assess the changes in land‐cover units occurred between 1979 and 2010 in the three sectors.LocationSouthern extreme of the dry Chaco in NE and NW Córdoba Province, central Argentina.MethodsWe compared annual and growth period (November–March) precipitation among the three sectors and between two series of data corresponding to different periods (1930–1950 and 1950–2000) using repeated measures ANOVA, with the station as the subject variable, period as the within‐factor and sector as the between factor. Using three Landsat MSS (1979) and nine Landsat TM (1999, 2004 and 2010) images we mapped the distribution of eight land‐cover units for the whole study area. For each sector (...
We determined the drivers of fires in Semiarid Chaco mountains of Central Argentina. • We identif... more We determined the drivers of fires in Semiarid Chaco mountains of Central Argentina. • We identified the drivers' ranges at which fire activity was higher. • Climate was the most important driver, followed by human and biological predictors. • Fires were more frequent at intermediate levels of rainfall and productivity. • Fires were more frequent where temperature and productivity were more variable.
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