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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... 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.
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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... 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.
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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... 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.
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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... 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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Significant gaps remain in understanding the response of plant reproduction to environmental change. This is partly because measuring reproduction in long‐lived plants requires direct observation over many years and such datasets have... more
Significant gaps remain in understanding the response of plant reproduction to environmental change. This is partly because measuring reproduction in long‐lived plants requires direct observation over many years and such datasets have rarely been made publicly available. Here we introduce MASTREE+, a data set that collates reproductive time‐series data from across the globe and makes these data freely available to the community. MASTREE+ includes 73,828 georeferenced observations of annual reproduction (e.g. seed and fruit counts) in perennial plant populations worldwide. These observations consist of 5971 population‐level time‐series from 974 species in 66 countries. The mean and median time‐series length is 12.4 and 10 years respectively, and the data set includes 1122 series that extend over at least two decades (≥20 years of observations). For a subset of well‐studied species, MASTREE+ includes extensive replication of time‐series across geographical and climatic gradients. Here...
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Abstract Global Climate Models project that observed climate trends are likely to be preserved and the number of extreme events will be increasing during the rest of the 21st century, which may have a detrimental impact on forest... more
Abstract Global Climate Models project that observed climate trends are likely to be preserved and the number of extreme events will be increasing during the rest of the 21st century, which may have a detrimental impact on forest ecosystems. These impacts may include forest decline and widespread dieback of the most vulnerable biomes, such as the Mediterranean Forest of Central Chile (MFCC). Nothofagus macrocarpa and Austrocedrus chilensis are two canopy-dominant, endangered tree species in the mountains of MFCC. Here, we project tree growth of these species based on tree-ring width chronologies, a simplified version of a process-based model, and climate change projections. We used the tree ring information derived from ~400 trees from 12 sites distributed across MFCC in combination with the simplified version of process-based Vaganov-Shashkin tree-growth model (VS-Lite) to forecast changes in tree growth for the next four decades. Tree growth projections were made on the basis of monthly values of temperature and precipitation from the output of 35 climate models based on two ensembles of CO2 emission scenarios of the IPCC AR5 (RCP 8.5: higher-emission scenario, and RCP 2.6: lower-emission scenario). For the MFCC region these scenarios result in temperature rise ranging between 0.5 °C and 2.0 °C, and a precipitation decrease between 5% and 20% by the year 2065, as related to historical conditions. Our results showed that the VS-Lite model is capable of reproducing tree growth decline during the recent extreme dry period, i.e. 2010–2018, which supports its use for tree growth projections in the MFCC region. According to the modeling results, we find that tree growth in both N. macrocarpa and A. chilensis forests distributed in the MFCC region will be adversely affected by future climate changes, mainly starting from the year 2035, under both scenarios. Our work provides evidence of the degree of vulnerability of Mediterranean mountain forests in central Chile according to current climate change projections. The projected decline in tree growth indicates serious risks in the dynamics and survival of these forests relatively soon, so alerts are given about this situation which may require to counteract the deleterious effects of global change on vegetation in this region.
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The identification of the forest structure could give insights of the processes that determine certain aspects of the population dynamics over time. To address this concern in the Araucaria araucana forests of northwestern Patagonia in... more
The identification of the forest structure could give insights of the processes that determine certain aspects of the population dynamics over time. To address this concern in the Araucaria araucana forests of northwestern Patagonia in Argentina, 14 forest stands distributed along a strong precipitation gradient were analyzed. A suite of components of the forest structure were considered in order to determine (1) the relationship between climate and tree growth variability, (2) the age structure of each study site by defining age classes through the tree-ring analysis, (3) the relationship between tree age, tree height, and stem diameter, and (4) sex ratio. Xeric forests were affected significantly and negatively by the temperature of the current growing season, while mesic forests were more affected during winter months. Precipitation showed a positive effect on growth at the beginning of the growing season in all forests. Age distribution in the xeric and mesic environments showed a preponderance of trees between 51 and 300, and 51 and 250 years old, respectively. Broadly, male and female trees were more abundant in xeric and mesic forests, respectively. The tree age-diameter and tree height-diameter relationships were significantly positive in both mesic and xeric environments. Through these elements, some aspects of the A. araucana trees and forests in their natural distribution area were revealed, which consolidate a better understanding of the ecology and dynamics of these endemic forests and provide tools for designing proper conservation strategies.
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Abstract Sustainable forestry requires accurate ecological information such as species composition, growth rates and recruitment dynamics. Tree growth rates are usually obtained through long-term periodic re-measurements of individual... more
Abstract Sustainable forestry requires accurate ecological information such as species composition, growth rates and recruitment dynamics. Tree growth rates are usually obtained through long-term periodic re-measurements of individual trees or through the analysis of tree growth rings in stem cross sections. However, tree growth ring analysis was traditionally thought to be only possible in biomes with strong seasonality such as those found in high latitude temperate regions. A lack of data on the occurrence and characteristics of tree rings in tropical trees may be due to a lack of investigations. Here we characterise the growth rings of 183 tree species from seven forest types across an altitudinal gradient in northern and central Peru at macro- and microscopic levels. A correspondence analysis showed an association between phylogenetic relatedness and the level of distinctiveness in the growth rings. Deciduous species of seasonally dry tropical forests were associated with distinct growth rings and mainly delimited by marginal parenchyma, while indistinct growth rings were associated with evergreen trees from lowland Amazonian and pre-montane wet forests. Additionally, for the first time the presence of growth ring boundaries defined by marginal phloem is reported in two tropical tree species, Gallesia integrifolia (Spreng.) Harms and Vochysia mapirensis Rusby. This contribution represents the most exhaustive record to date of the occurrence and anatomy of growth rings in trees of the Peruvian tropics, which can be used to inform future dendrochronological studies.
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Fil: Arco Molina, Julieta Gabriela. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mendoza. Instituto Argentino de Nivologia, Glaciologia y Ciencias Ambientales. Provincia de Mendoza.... more
Fil: Arco Molina, Julieta Gabriela. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mendoza. Instituto Argentino de Nivologia, Glaciologia y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivologia, Glaciologia y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivologia, Glaciologia y Ciencias Ambientales; Argentina
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During the late 1950s and early 1960s, thermonuclear tests added considerable amounts of 14C to the atmosphere. Since that time the amount has declined, which is owed to the exchange and dispersal of 14C into the Earth's carbon... more
During the late 1950s and early 1960s, thermonuclear tests added considerable amounts of 14C to the atmosphere. Since that time the amount has declined, which is owed to the exchange and dispersal of 14C into the Earth's carbon reservoirs, creating an isotopic chronometer (the 14C bomb peak) to all living organisms. In this study, we make use of this alternative radiometric method to compare dendrochronological ages with the 14C signature of wood samples, as a way to independently confirm the annual nature of the growth rings of Araucaria araucana trees growing in a northern Patagonia (38°52′S, 70° 34′W) site, represented by a forest of old living specimens of ca. 900 years. High precision 14C-AMS of selected tree-rings from two trees confirms the annual frequency of the ring formation against an existing dataset of atmospheric 14C values in the SH Zone 1–2, validating these tree specimens for further use on improving the temporal resolution of the 14C age calibration curve for the Southern Hemisphere.