The wood anatomy of Adesmia horrida Hook. & Arn. (Leguminosae, Papilionoideae) is described, usin... more The wood anatomy of Adesmia horrida Hook. & Arn. (Leguminosae, Papilionoideae) is described, using sam pies taken from both slopes of the Sierra de Uspallata in Mendoza, Argentina. Different rainfall values at the eastern and western slopes of the Sierra de Uspallata determine the type of porosity distribution: ringporous in dry environments and semi-ring-porous in more humid locations.
The wood anatomy is described for the Cupressaceae indigenous to southem South America: Austroced... more The wood anatomy is described for the Cupressaceae indigenous to southem South America: Austrocedrus chilensis, Pilgeroden- dron uviferum and Fitzroya cupressoides. The abundance and distributional pattern of axial parenchyma within each annual ring, height, and the presence or absence of nodules in the end walls of ray parenchyma are all useful anatomie al features for distinguishing between the three species. Physical characteristics such as odour and heartwood colour also can be used to separate these species. Axial parenchyma cell length and tracheid length show considerable interspecific variation. Tracheid lengths of Pilgerodendron, but not of Austrocedrus and Fitzroya, decrease with increasing latitude.
The anatomy and ultrastructure of subfossil wood of Fitzroya cup ressoides from the late Pleistoc... more The anatomy and ultrastructure of subfossil wood of Fitzroya cup ressoides from the late Pleistocene (>50,000 14C years before present) were compared with those of extant F. cupressoides trees from southern Chile, using light microscopy (polarized light and ftuorescence), scanning electron microscopy coupled with an energy dispersive X-ray spectroscopy system, and transmission electron microscopy. The ancient wood showed an unchanged gross wood structure, loss of cell wall birefringence, loss of lignin autoftuorescence, and a loss of the original microfibrillar pattern. The energy dispersive X-ray spectroscopy analysis indicated higher than normal contents of S, Cl, and Na in subfossil wood. Ultrastructural modifications in the cell wall of the subfossil wood could have important implications for further studies involving isotopic and wood anatomical measurements of ancient wood.
Weakening of the Summer Monsoon Over the Past 150 Years Shown by a Tree‐Ring Record From Shandong, Eastern China, and the Potential Role of North Atlantic Climate
Paleoceanography and paleoclimatology, Feb 23, 2023
Protein kinase C signals thromboxane induced increases in fibronectin synthesis and TGF.p bioacti... more Protein kinase C signals thromboxane induced increases in fibronectin synthesis and TGF.p bioactivity in mesangial cells. Previous studies have demonstrated that thromboxane (TX) stimulates matrix protein synthesis in mesangial cells (MC), and that this action is signalled by receptor mediated activation of protein kinase C (PKC). In the present study, we examined the hypothesis that activation of PKC by TX signals increases in transforming growth factor /3 (TGF-/3) bioactivity, which in turn induces enhanced matrix protein synthesis. In cultured rat MC, the TXAJ prostaglandin endoperoxide analogue U-46619, but not exogenous human platelet TGF-/31, activated PKC as reflected by enhanced in situ phosphorylation of MARCKS protein, an endogenous substrate of PKC. U-46619 and TGF-/31 stimulated fibronectin (Fn) synthesis in MC, as shown by [35S]methionine incorporation into immunoprecipitable Fn. Pan-specific rabbit anti-TGF-f3 antibody blocked the increases in Fn synthesis induced by exogenous TGF-/3 and those induced by U-46619 at 24 to 72 hours after addition. Anti-TGF-/3 antibody did not block the small increases in Fn synthesis observed six hours after addition of U-46619, suggesting that this acute response was not dependent on TGF-/3. Anti-TGF-13 antibody also failed to block activation of PKC by U-46619. U-46619 and 50 n of the PKC agonist phorbol dibutyrate (PDBu) significantly increased both the active fraction and total (latent plus active) TGF-/3 in MC culture media, as assayed with the mink lung epithelial cell bioassay system. PKC inhibition with bisindolylmaleimide GF 109203X (GFX) or down-regulation of PKC in MC by prior exposure to a high concentration (0.5 j.tM) of phorbol myristate acetate (PMA) blocked increases in TGF-/3 bioactivity induced by either U-46619 or PDBu. PKC down-regulation in MC also blocked increases in Fn synthesis induced by U-46619. By contrast, exogenous TGF-/3 stimulated Fn synthesis in both intact MC and in MC with down-regulated PKC. The findings indicate that activation of PKC by U-46619 signals an increase in TGF-j3 bioactivity, which in turn stimulates Fn synthesis in MC by processes not dependent on PKC. examined the possibility that TX activation of PKC is a signal to increase TGF-/3 bioactivity in MC, which in turn mediates the sustained increases in Fn synthesis observed in response to TX. Methods Rat MC culture
Dendroecology of Aspidosperma polyneuron Müll. Arg. (Apocynaceae) trees in two different geomorphological growth conditions in Atlantic forests, Paraná State, Brazil
Recent investigations indicate a warming of Atlantic Ocean surface waters since 1980, probably in... more Recent investigations indicate a warming of Atlantic Ocean surface waters since 1980, probably influenced by anthropic actions, inducing rainfall intensification mainly during the rainy season and slight reductions during the dry season in the Amazon. Under these climate changes, trees in upland forests (terra firme) could benefit from the intensification of the hydrological cycle and could also be affected by the reduction of precipitation during the dry season. Results of dendrochronological analyses, spatial correlations and structural equation models, showed that Scleronema micranthum (Ducke) Ducke (Malvaceae) trees exposed in fragmented areas and to edge effects in Central Amazonian terra firme forest were more sensitive to the increase in the Atlantic Ocean surface temperature and consequent northward displacement of the Intertropical Convergence Zone, mainly during the dry season. Therefore, we proved that in altered and potentially more stressful environments such as edges of fragmented forests, recent anthropogenic climatic changes are exerting pressure on tree growth dynamics, inducing alterations in their performance and, consequently, in essential processes related to ecosystem services.
Sex-related climate sensitivity of Araucaria araucana Patagonian forest-steppe ecotone
Forest Ecology and Management, Feb 1, 2016
Abstract Dioecious species offers the possibility to discern plant development in relation to sex... more Abstract Dioecious species offers the possibility to discern plant development in relation to sex. However, there is little information of the incidence of sex on tree-growth sensitivity to seasonal variations in climate. In this study we aim to examine the relationship between the climate and tree growth variability from Araucaria araucana inferred from independent male and female tree-ring chronologies derived from old growth forests growing on the xeric environments of NW Patagonia in Argentina. The analysis included 186 standing trees (93 males and 93 females) distributed in five forest stands. After applying a Generalized Linear Mixed Models (GLMMs), result suggests significant differences between tree-ring width related to both sex and climatic conditions. When considering the relationships between tree growth and climate, sensitivity of tree-ring variability to climate appeared to be sex-dependent. While male trees are more sensitive to land precipitation during part of the current growing period, female trees appears to be more sensitive to air surface temperature during the prior period of growth. At atmospheric circulation scales, male trees are more sensitive to the Southern Annular Mode index during the current period of growth. The reported differences in the sensitivity of the response to climate from both male and female trees can be attributed to different mechanisms in the use of the environmental resources. In relation to recent trends in climate experienced in northern Patagonia, these changes, if continued, may compromise the growth and reproductive fitness of the A. araucana forests.
Two millennial reconstructions of mean summer temperature departures from the eastern and western... more Two millennial reconstructions of mean summer temperature departures from the eastern and western slopes of the southern Andes (1120 and 3620 years, respectively) have been spectrally analyzed to determine the most significant modes of climate variations in southern South America during the last millennia. Blackman-Tukeyand Maximum Entropy spectral analyses of these reconstructions identify temperature oscillations with periods of 35.8,23.9,9.5,6.0-6.9,5.4-5.7,4.5-4.8, and 3.4-3.7 years. Because of the relatively flexible standardization used to derive the temperature reconstructions, a large part of the variance (related to the oscillations of summer temperature) is concentrated in short-term periods. A new set of eight long tree-ring chronologies from Fitzroya cupressoides (ranging from 1120 to 3620 years in length), has been used to develop a regional record of tree-ring variations during recent millennia in the southern Andes. A more conservative detrending than that used for developing the temperature reconstructions has been employed here to preserve the low frequency components in the tree-ring series. Maximum Entropy spectral analyses for different filter orders indicate prominent peaks at around 250,77,50,33,21,17,15, and 11 years. Some power is also seen at 4-7 years, probably associated with El Nino-Southern Oscillation events. The 11, 21 and 77-year terms may be related to long-term solar variations or long-term circulation of the Southern Oceans. Ocean-atmosphere model predictions suggest the possibility of using the South American tree-ring records to reconstruct past changes of the thermohaline circulation in the Atlantic Ocean.
Tree-ring-based hydroclimatic reconstruction for the northwest Argentine Patagonia since 1055 CE and its teleconnection to large-scale atmospheric circulation
Global and Planetary Change, Jul 1, 2021
Abstract State-of-the-art climate models project droughts of stronger intensity and longer persis... more Abstract State-of-the-art climate models project droughts of stronger intensity and longer persistence in many arid and semi-arid regions such as northern Patagonia, which constitutes a serious concern worldwide. Moisture availability has a significant influence on the dynamic, stability and function of terrestrial ecosystems. In this study, we used wood samples from 260 Austrocedrus chilensis trees growing in northwestern Patagonia to reconstruct the Standardized Precipitation Evapotranspiration Index (SPEI) for the last millennium (1055–2014). Our reconstruction explained 41.6% of the variance contained in the November–December SPEI at a 1-month scale for the period 1930–2013. The SPEI reconstruction has provided a long record of extreme pluvial (1060s, 1090s, 1200s, 1300s, 1360s, 1390s, 1400s, 1550s, 1580s, 1580s, 1630s, 1940s, 1960s, and 2000s) and drought events (1070s, 1150s, 1170s, 1180s, 1270s, 1310s, 1430s, 1450s, 1570s, 1600s, 1620s, and 1950s) for northwest Argentine Patagonia. Although the SPEI reconstruction indicates that the frequency of extreme events has increased since 1950, our record indicates that current levels have not exceeded those previously reached, particularly when compared to those recorded around the suggested periods for the Medieval Warm and towards the end of the Little Ice Age. The spatial and temporal relationships associated with the South Annular Mode and the Pacific Sea Surface Temperature variability as expressed by the Tripole Index indicated that the temporal variability observed in the SPEI reconstruction is modulated by hemispheric-scale atmospheric circulation dynamics. These climate forcings are likely responsible for the intensity and the rate of occurrence of extreme weather events in northwestern Patagonia. Furthermore, the SPEI reconstruction showed a spatial and temporal pattern similar to that observed in previous PDSI-based reconstructions. This study provides robust evidence of hydroclimatic variations for extratropical sectors of South America, improving our knowledge of the climate dynamics during the last millennium and allowing us to review the recently observed increase in wet and dry events in a long-term historical context.
Amazon forest fragmentation and edge effects temporarily favored understory and midstory tree growth
Trees-structure and Function, Jul 8, 2021
The current increase in deforestation rates of the Brazilian Amazon raises important questions ab... more The current increase in deforestation rates of the Brazilian Amazon raises important questions about the resilience of trees in distinct vertical profiles in the world’s largest tropical rainforest. Seeking to prove the existence of temporal differences in tree growth response after forest fragmentation and edge effects through a dendrochronological perspective, we revealed that Theobroma sylvestre Mart. (Malvaceae), a typically understory and midstory strata tree of the Amazon upland forest (terra firme), increased the basal area increment rates compared to the forest interior, mainly over the first 20 years after forest fragmentation and edge effects. This pattern could not be extrapolated to the entire vertical forest profile, considering previous dendrochronological evidences from trees located in the forest canopy that presented an opposite pattern, a negative increment rate after forest fragmentation and edge creation. These divergences suggest that trees under the canopy of Amazon terra firme forest can be more tolerant to environmental stress (i.e. more incidence of droughts) derived by microclimatic and structural changes in forest subjected to forest fragmentation and edge effects processes, however, future dendroclimatic studies may confirm these hypotheses. In this sense, we highlighted that the increase in basal area increment of trees in the understory and midstory exposed to edge effects may indicate an important component of above-ground biomass stock recovery after forest fragmentation. This fact should be considered in forest management and restoration practices, promoting a new perspective on forest resilience ability after forest fragmentation and its strong impact on plant productivity and capacities in long-term carbon storage.
Ecotones, as for example riparian zones, have long interested ecologists, due to their potential ... more Ecotones, as for example riparian zones, have long interested ecologists, due to their potential role in generating species biodiversity and evolutionary novelty, as well as their sensitivity to environmental changes. Along riparian areas, vegetation is recognized for its ecological importance in several ecosystemic processes. In the Central Monte Desert (central-west Argentina), Prosopis flexuosa grows in territories characterized by a permanent access to water reservoirs, e.g. along riverbanks, where the species forms the classic gallery forests. Despite the ecosystemic role of the different Prosopis species distributed in arid lands, thus far no analysis has been conducted regarding the relation between their radial growth and hydrological changes, namely streamflow variability, in riparian settings. To fill this gap of knowledge, we performed a dendrochronological analysis considering several riparian P. flexuosa trees differing in their spatial position in relation to the riverbank. Pointer years, correlation function, and regression analyses show differences in the dendrohydrological signal of the studied species, probably function of tree distance from the river. In this sense, radial growth of trees distributed near the riverbank is tightly coupled to spring-summer (September to March) streamflow variability, whereas for farthest trees the ring development is driven by a combination of winter and spring river discharge and late-summer precipitation amount. The presented results demonstrate the potentiality of P. flexuosa, and in a broader sense of the Prosopis genus, in dendrohydrological studies.
Removal of a non-climatically induced seven-year cycle from Nothofagus pumilio tree-ring width chronologies from Tierra del Fuego, Argentina for their use in climate reconstructions
Dendrochronologia, Oct 1, 2019
Abstract A pronounced seven-year cycle is one of the most prominent features of many Fuegian and ... more Abstract A pronounced seven-year cycle is one of the most prominent features of many Fuegian and southern Patagonian Nothofagus pumilio tree-ring width chronologies. However, the source of this variability is still unclear. Here we provide multiple lines of evidence that suggest this phenomenon comes from non-climatically induced ecological factors, most probably triggered by insect outbreaks. To test this hypothesis we removed the seven-year cycle, by means of Singular Spectrum Analysis, from a network of 44 tree-ring width chronologies, from the eastern Tierra del Fuego Island in Argentina. The chronologies that were filtered this way showed a stronger climatic response, and were more successfully modeled using the Vaganov-Shashkin-Lite (VS-Lite) process-based forward model of tree growth. We conclude that the removed periodicity does not have a climatic source. Additional evidence from direct observation of affected and non-affected trees during defoliation, due to Ormiscodes sp. outbreak in 2010, is provided. We also tested the hypothesis of probable masting effects on the growth of N. pumilio at a site with a 12-yr record of seed production, but this hypothesis was not confirmed. Taking into account the non-climatic nature of this signal, we explore the utility of corrected chronologies for reconstruction of climatic parameters in Tierra del Fuego, especially for summer temperature and frost day frequency. This study is the first systematic analysis of the pronounced high-frequency cyclicity in N. pumilio tree growth in southernmost South America.
The wood anatomy of Adesmia horrida Hook. & Arn. (Leguminosae, Papilionoideae) is described, usin... more The wood anatomy of Adesmia horrida Hook. & Arn. (Leguminosae, Papilionoideae) is described, using sam pies taken from both slopes of the Sierra de Uspallata in Mendoza, Argentina. Different rainfall values at the eastern and western slopes of the Sierra de Uspallata determine the type of porosity distribution: ringporous in dry environments and semi-ring-porous in more humid locations.
The wood anatomy is described for the Cupressaceae indigenous to southem South America: Austroced... more The wood anatomy is described for the Cupressaceae indigenous to southem South America: Austrocedrus chilensis, Pilgeroden- dron uviferum and Fitzroya cupressoides. The abundance and distributional pattern of axial parenchyma within each annual ring, height, and the presence or absence of nodules in the end walls of ray parenchyma are all useful anatomie al features for distinguishing between the three species. Physical characteristics such as odour and heartwood colour also can be used to separate these species. Axial parenchyma cell length and tracheid length show considerable interspecific variation. Tracheid lengths of Pilgerodendron, but not of Austrocedrus and Fitzroya, decrease with increasing latitude.
The anatomy and ultrastructure of subfossil wood of Fitzroya cup ressoides from the late Pleistoc... more The anatomy and ultrastructure of subfossil wood of Fitzroya cup ressoides from the late Pleistocene (>50,000 14C years before present) were compared with those of extant F. cupressoides trees from southern Chile, using light microscopy (polarized light and ftuorescence), scanning electron microscopy coupled with an energy dispersive X-ray spectroscopy system, and transmission electron microscopy. The ancient wood showed an unchanged gross wood structure, loss of cell wall birefringence, loss of lignin autoftuorescence, and a loss of the original microfibrillar pattern. The energy dispersive X-ray spectroscopy analysis indicated higher than normal contents of S, Cl, and Na in subfossil wood. Ultrastructural modifications in the cell wall of the subfossil wood could have important implications for further studies involving isotopic and wood anatomical measurements of ancient wood.
Weakening of the Summer Monsoon Over the Past 150 Years Shown by a Tree‐Ring Record From Shandong, Eastern China, and the Potential Role of North Atlantic Climate
Paleoceanography and paleoclimatology, Feb 23, 2023
Protein kinase C signals thromboxane induced increases in fibronectin synthesis and TGF.p bioacti... more Protein kinase C signals thromboxane induced increases in fibronectin synthesis and TGF.p bioactivity in mesangial cells. Previous studies have demonstrated that thromboxane (TX) stimulates matrix protein synthesis in mesangial cells (MC), and that this action is signalled by receptor mediated activation of protein kinase C (PKC). In the present study, we examined the hypothesis that activation of PKC by TX signals increases in transforming growth factor /3 (TGF-/3) bioactivity, which in turn induces enhanced matrix protein synthesis. In cultured rat MC, the TXAJ prostaglandin endoperoxide analogue U-46619, but not exogenous human platelet TGF-/31, activated PKC as reflected by enhanced in situ phosphorylation of MARCKS protein, an endogenous substrate of PKC. U-46619 and TGF-/31 stimulated fibronectin (Fn) synthesis in MC, as shown by [35S]methionine incorporation into immunoprecipitable Fn. Pan-specific rabbit anti-TGF-f3 antibody blocked the increases in Fn synthesis induced by exogenous TGF-/3 and those induced by U-46619 at 24 to 72 hours after addition. Anti-TGF-/3 antibody did not block the small increases in Fn synthesis observed six hours after addition of U-46619, suggesting that this acute response was not dependent on TGF-/3. Anti-TGF-13 antibody also failed to block activation of PKC by U-46619. U-46619 and 50 n of the PKC agonist phorbol dibutyrate (PDBu) significantly increased both the active fraction and total (latent plus active) TGF-/3 in MC culture media, as assayed with the mink lung epithelial cell bioassay system. PKC inhibition with bisindolylmaleimide GF 109203X (GFX) or down-regulation of PKC in MC by prior exposure to a high concentration (0.5 j.tM) of phorbol myristate acetate (PMA) blocked increases in TGF-/3 bioactivity induced by either U-46619 or PDBu. PKC down-regulation in MC also blocked increases in Fn synthesis induced by U-46619. By contrast, exogenous TGF-/3 stimulated Fn synthesis in both intact MC and in MC with down-regulated PKC. The findings indicate that activation of PKC by U-46619 signals an increase in TGF-j3 bioactivity, which in turn stimulates Fn synthesis in MC by processes not dependent on PKC. examined the possibility that TX activation of PKC is a signal to increase TGF-/3 bioactivity in MC, which in turn mediates the sustained increases in Fn synthesis observed in response to TX. Methods Rat MC culture
Dendroecology of Aspidosperma polyneuron Müll. Arg. (Apocynaceae) trees in two different geomorphological growth conditions in Atlantic forests, Paraná State, Brazil
Recent investigations indicate a warming of Atlantic Ocean surface waters since 1980, probably in... more Recent investigations indicate a warming of Atlantic Ocean surface waters since 1980, probably influenced by anthropic actions, inducing rainfall intensification mainly during the rainy season and slight reductions during the dry season in the Amazon. Under these climate changes, trees in upland forests (terra firme) could benefit from the intensification of the hydrological cycle and could also be affected by the reduction of precipitation during the dry season. Results of dendrochronological analyses, spatial correlations and structural equation models, showed that Scleronema micranthum (Ducke) Ducke (Malvaceae) trees exposed in fragmented areas and to edge effects in Central Amazonian terra firme forest were more sensitive to the increase in the Atlantic Ocean surface temperature and consequent northward displacement of the Intertropical Convergence Zone, mainly during the dry season. Therefore, we proved that in altered and potentially more stressful environments such as edges of fragmented forests, recent anthropogenic climatic changes are exerting pressure on tree growth dynamics, inducing alterations in their performance and, consequently, in essential processes related to ecosystem services.
Sex-related climate sensitivity of Araucaria araucana Patagonian forest-steppe ecotone
Forest Ecology and Management, Feb 1, 2016
Abstract Dioecious species offers the possibility to discern plant development in relation to sex... more Abstract Dioecious species offers the possibility to discern plant development in relation to sex. However, there is little information of the incidence of sex on tree-growth sensitivity to seasonal variations in climate. In this study we aim to examine the relationship between the climate and tree growth variability from Araucaria araucana inferred from independent male and female tree-ring chronologies derived from old growth forests growing on the xeric environments of NW Patagonia in Argentina. The analysis included 186 standing trees (93 males and 93 females) distributed in five forest stands. After applying a Generalized Linear Mixed Models (GLMMs), result suggests significant differences between tree-ring width related to both sex and climatic conditions. When considering the relationships between tree growth and climate, sensitivity of tree-ring variability to climate appeared to be sex-dependent. While male trees are more sensitive to land precipitation during part of the current growing period, female trees appears to be more sensitive to air surface temperature during the prior period of growth. At atmospheric circulation scales, male trees are more sensitive to the Southern Annular Mode index during the current period of growth. The reported differences in the sensitivity of the response to climate from both male and female trees can be attributed to different mechanisms in the use of the environmental resources. In relation to recent trends in climate experienced in northern Patagonia, these changes, if continued, may compromise the growth and reproductive fitness of the A. araucana forests.
Two millennial reconstructions of mean summer temperature departures from the eastern and western... more Two millennial reconstructions of mean summer temperature departures from the eastern and western slopes of the southern Andes (1120 and 3620 years, respectively) have been spectrally analyzed to determine the most significant modes of climate variations in southern South America during the last millennia. Blackman-Tukeyand Maximum Entropy spectral analyses of these reconstructions identify temperature oscillations with periods of 35.8,23.9,9.5,6.0-6.9,5.4-5.7,4.5-4.8, and 3.4-3.7 years. Because of the relatively flexible standardization used to derive the temperature reconstructions, a large part of the variance (related to the oscillations of summer temperature) is concentrated in short-term periods. A new set of eight long tree-ring chronologies from Fitzroya cupressoides (ranging from 1120 to 3620 years in length), has been used to develop a regional record of tree-ring variations during recent millennia in the southern Andes. A more conservative detrending than that used for developing the temperature reconstructions has been employed here to preserve the low frequency components in the tree-ring series. Maximum Entropy spectral analyses for different filter orders indicate prominent peaks at around 250,77,50,33,21,17,15, and 11 years. Some power is also seen at 4-7 years, probably associated with El Nino-Southern Oscillation events. The 11, 21 and 77-year terms may be related to long-term solar variations or long-term circulation of the Southern Oceans. Ocean-atmosphere model predictions suggest the possibility of using the South American tree-ring records to reconstruct past changes of the thermohaline circulation in the Atlantic Ocean.
Tree-ring-based hydroclimatic reconstruction for the northwest Argentine Patagonia since 1055 CE and its teleconnection to large-scale atmospheric circulation
Global and Planetary Change, Jul 1, 2021
Abstract State-of-the-art climate models project droughts of stronger intensity and longer persis... more Abstract State-of-the-art climate models project droughts of stronger intensity and longer persistence in many arid and semi-arid regions such as northern Patagonia, which constitutes a serious concern worldwide. Moisture availability has a significant influence on the dynamic, stability and function of terrestrial ecosystems. In this study, we used wood samples from 260 Austrocedrus chilensis trees growing in northwestern Patagonia to reconstruct the Standardized Precipitation Evapotranspiration Index (SPEI) for the last millennium (1055–2014). Our reconstruction explained 41.6% of the variance contained in the November–December SPEI at a 1-month scale for the period 1930–2013. The SPEI reconstruction has provided a long record of extreme pluvial (1060s, 1090s, 1200s, 1300s, 1360s, 1390s, 1400s, 1550s, 1580s, 1580s, 1630s, 1940s, 1960s, and 2000s) and drought events (1070s, 1150s, 1170s, 1180s, 1270s, 1310s, 1430s, 1450s, 1570s, 1600s, 1620s, and 1950s) for northwest Argentine Patagonia. Although the SPEI reconstruction indicates that the frequency of extreme events has increased since 1950, our record indicates that current levels have not exceeded those previously reached, particularly when compared to those recorded around the suggested periods for the Medieval Warm and towards the end of the Little Ice Age. The spatial and temporal relationships associated with the South Annular Mode and the Pacific Sea Surface Temperature variability as expressed by the Tripole Index indicated that the temporal variability observed in the SPEI reconstruction is modulated by hemispheric-scale atmospheric circulation dynamics. These climate forcings are likely responsible for the intensity and the rate of occurrence of extreme weather events in northwestern Patagonia. Furthermore, the SPEI reconstruction showed a spatial and temporal pattern similar to that observed in previous PDSI-based reconstructions. This study provides robust evidence of hydroclimatic variations for extratropical sectors of South America, improving our knowledge of the climate dynamics during the last millennium and allowing us to review the recently observed increase in wet and dry events in a long-term historical context.
Amazon forest fragmentation and edge effects temporarily favored understory and midstory tree growth
Trees-structure and Function, Jul 8, 2021
The current increase in deforestation rates of the Brazilian Amazon raises important questions ab... more The current increase in deforestation rates of the Brazilian Amazon raises important questions about the resilience of trees in distinct vertical profiles in the world’s largest tropical rainforest. Seeking to prove the existence of temporal differences in tree growth response after forest fragmentation and edge effects through a dendrochronological perspective, we revealed that Theobroma sylvestre Mart. (Malvaceae), a typically understory and midstory strata tree of the Amazon upland forest (terra firme), increased the basal area increment rates compared to the forest interior, mainly over the first 20 years after forest fragmentation and edge effects. This pattern could not be extrapolated to the entire vertical forest profile, considering previous dendrochronological evidences from trees located in the forest canopy that presented an opposite pattern, a negative increment rate after forest fragmentation and edge creation. These divergences suggest that trees under the canopy of Amazon terra firme forest can be more tolerant to environmental stress (i.e. more incidence of droughts) derived by microclimatic and structural changes in forest subjected to forest fragmentation and edge effects processes, however, future dendroclimatic studies may confirm these hypotheses. In this sense, we highlighted that the increase in basal area increment of trees in the understory and midstory exposed to edge effects may indicate an important component of above-ground biomass stock recovery after forest fragmentation. This fact should be considered in forest management and restoration practices, promoting a new perspective on forest resilience ability after forest fragmentation and its strong impact on plant productivity and capacities in long-term carbon storage.
Ecotones, as for example riparian zones, have long interested ecologists, due to their potential ... more Ecotones, as for example riparian zones, have long interested ecologists, due to their potential role in generating species biodiversity and evolutionary novelty, as well as their sensitivity to environmental changes. Along riparian areas, vegetation is recognized for its ecological importance in several ecosystemic processes. In the Central Monte Desert (central-west Argentina), Prosopis flexuosa grows in territories characterized by a permanent access to water reservoirs, e.g. along riverbanks, where the species forms the classic gallery forests. Despite the ecosystemic role of the different Prosopis species distributed in arid lands, thus far no analysis has been conducted regarding the relation between their radial growth and hydrological changes, namely streamflow variability, in riparian settings. To fill this gap of knowledge, we performed a dendrochronological analysis considering several riparian P. flexuosa trees differing in their spatial position in relation to the riverbank. Pointer years, correlation function, and regression analyses show differences in the dendrohydrological signal of the studied species, probably function of tree distance from the river. In this sense, radial growth of trees distributed near the riverbank is tightly coupled to spring-summer (September to March) streamflow variability, whereas for farthest trees the ring development is driven by a combination of winter and spring river discharge and late-summer precipitation amount. The presented results demonstrate the potentiality of P. flexuosa, and in a broader sense of the Prosopis genus, in dendrohydrological studies.
Removal of a non-climatically induced seven-year cycle from Nothofagus pumilio tree-ring width chronologies from Tierra del Fuego, Argentina for their use in climate reconstructions
Dendrochronologia, Oct 1, 2019
Abstract A pronounced seven-year cycle is one of the most prominent features of many Fuegian and ... more Abstract A pronounced seven-year cycle is one of the most prominent features of many Fuegian and southern Patagonian Nothofagus pumilio tree-ring width chronologies. However, the source of this variability is still unclear. Here we provide multiple lines of evidence that suggest this phenomenon comes from non-climatically induced ecological factors, most probably triggered by insect outbreaks. To test this hypothesis we removed the seven-year cycle, by means of Singular Spectrum Analysis, from a network of 44 tree-ring width chronologies, from the eastern Tierra del Fuego Island in Argentina. The chronologies that were filtered this way showed a stronger climatic response, and were more successfully modeled using the Vaganov-Shashkin-Lite (VS-Lite) process-based forward model of tree growth. We conclude that the removed periodicity does not have a climatic source. Additional evidence from direct observation of affected and non-affected trees during defoliation, due to Ormiscodes sp. outbreak in 2010, is provided. We also tested the hypothesis of probable masting effects on the growth of N. pumilio at a site with a 12-yr record of seed production, but this hypothesis was not confirmed. Taking into account the non-climatic nature of this signal, we explore the utility of corrected chronologies for reconstruction of climatic parameters in Tierra del Fuego, especially for summer temperature and frost day frequency. This study is the first systematic analysis of the pronounced high-frequency cyclicity in N. pumilio tree growth in southernmost South America.
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Papers by Fidel Roig