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A Macrozone is a socioecological region with shared geographic and demographic characteristics. Within the Chilean Austral Macrozone (43° to 56° SL), the native temperate forests serve as a crucial resource, offering multiple ecosystem services to local communities. These forests significantly support animal husbandry practices involving cattle, horses and sheep. However, introducing these exotic species affects natural regeneration and compromises their long-term sustainability. This study proposes a new classification of the temperate forests in the Chilean Austral Macrozone based on structure parameters and determine their relationships with animal husbandry and natural regeneration. Data were obtained from Chile's National Forest Inventory (NFI) (2001–2010), including 195 inventory plots (500 m2) with 21 tree species. We redefined the forest categories described in NFI according to the proportional basal area of each tree species at each plot. We used two levels of analysis: forest composition (Level 1), which includes general categories such as mono-specific (dominated by a single tree species), bi-specific (dominated by two tree species), and multi-specific forests (dominated by multiple tree species), and forest type (Level 2), which includes specific species (e.g., Nothofagus pumilio) or species groups (e.g., N. pumilio - N. dombeyi) with economic relevance. We evaluated the data using univariate and multivariate analyses. We found 18 forest types in the Austral Macrozone, in contrast to the three traditionally recognized forest types used in the NFI (e.g., lenga, evergreen, coihue de Magallanes). Livestock was observed in all forest types, where Nothofagus forests showed that regeneration in N. antarctica and N. pumilio were higher with livestock than without livestock breeding (Hedges' g > 0.51). The natural regeneration of the studied forests was influenced by animal husbandry, environmental variables (bioclimatic and topographic factors), and forest structure. Our data suggested the importance of using more forest types than the three classics to generate tools or recommendations that are more focused on the particularities of each one. The classification must be based on forest parameters obtained during NFI. The proposed forest type classification reflects the complexity and richness of the forests in a better way, which could improve forest management and the development of public policies related to climate change and sustainability. Finally, although livestock pressure was observed in all forest types, the impact over some areas (e.g., N. antarctica) needs special attention in the forest management and conservation planning for the Chilean Austral Macrozone.

Proxy climate records, such as those derived from tree rings, are necessary to extend relatively short instrumental meteorological observations into the past. Tierra del Fuego is the most austral territory with forests in the world, situated close to the Antarctic Peninsula, which makes this region especially interesting for paleoclimatic research. However, high-quality, high-resolution summer temperature reconstruction are lacking in the region. In this study we used 63 tree-ring width chronologies of Nothofagus pumilio and Nothofagus betuloides and partial least squares regression (PLSR) to produce annually resolved December-to-February temperature reconstruction. The resulting reconstruction extends back to AD 1765 and explains 37–50% of instrumental temperature variability. We found that observed summer temperature variability in Tierra del Fuego is primarily driven by the fluctuations of atmospheric pressure systems both in the South Atlantic and South Pacific, while it is insignificantly correlated to major hemispheric modes: El Niño–Southern Oscillation and Southern Annular Mode. This fact makes our reconstruction important for climate modelling experiments, as it represents specific regional variability. Our reconstruction can be used for direct comparison with model outputs to better understand model limitations or to tune a model. The reconstruction can contribute to larger scale reconstructions based on paleoclimatic data assimilation. Moreover, we showed that PLSR has improved performance over principal component regression (PCR) in the case of multiple tree-ring predictors. According to these results, PLSR may be a preferable method over PCR for the use in automated tree-ring based reconstruction approaches, akin widely used point-by-point regression. [ABSTRACT FROM AUTHOR]

Tree mortality is a key process in forest dynamics. Despite decades of effort to understand this process, many uncertainties remain. South American broadleaf species are particularly under-represented in global studies on mortality and forest dynamics. We sampled monospecific broadleaf Nothofagus pumilio forests in northern Patagonia to predict tree mortality based on stem growth. Live or dead conditions in N. pumilio trees can be predicted with high accuracy using growth rate as an explanatory variable in logistic models. In Paso Córdova (CO), Argentina, where the models were calibrated, the probability of death was a strong negative function of radial growth, particularly during the six years prior to death. In addition, negative growth trends during 30 to 45 years prior to death increased the accuracy of the models. The CO site was affected by an extreme drought during the summer 1978–1979, triggering negative trends in radial growth of many trees. Individuals showing below-average and persistent negative trends in radial growth are more likely to die than those showing high growth rates and positive growth trends in recent decades, indicating the key role of droughts in inducing mortality. The models calibrated at the CO site showed high verification skill by accurately predicting tree mortality at two independent sites 76 and 141 km away. Models based on relative growth rates showed the highest and most balanced accuracy for both live and dead individuals. Thus, the death of individuals across different N. pumilio sites was largely determined by the growth rate relative to the total size of the individuals. Our findings highlight episodic severe drought as a triggering mechanism for growth decline and eventual death for N. pumilio, similar to results found previously for several other species around the globe. In the coming decades, many forests globally will be exposed to more frequent and/or severe episodes of reduced warm-season soil moisture. Tree-ring studies such as this one can aid prediction of future changes in forest productivity, mortality, and composition.

Lenga (Nothofagus pumilio) is a tree of primary importance that is native to Patagonia. Its cyclical production of seeds and the lack of protocols that would conserve them for several years creates a bottleneck for the regular production of seedlings. However, this species has the capacity to form natural seedling banks, where seedlings under a closed canopy tolerate long periods of suppression practically without growing. This suggests that a similar effect could be achieved in the nursery, thus allowing plants (rather than seeds) to be artificially stored. In this study, we analyze the feasibility of a management system with deferred pricking out and growing as an alternative for the production of lenga seedlings. The system consisted of germinating the seeds the same year they were collected and maintaining the seedlings for three years at a very low growth rate, forming a dense "seedling bank", by controlling nutrients and limiting space. Then, the seedlings were pricked out and grown under standard production conditions for two years. The quality of 560 seedlings grown with this system was compared with that of plants grown intensively in forestry seedling trays and with reference values, using two-sample and one-sample t-tests, respectively. The seedlings with deferred growth reached similar slenderness and stem/root ratio to the plants grown intensively, and were also similar in terms of reference values for other analyzed size variables (collar diameter and stem height). Although preliminary, the results suggest the feasibility of this technological proposal and justify further improvement. [ABSTRACT FROM AUTHOR]

It is widely accepted that global warming is affecting forests near the tree line by increasing tree growth in these cold‐limited environments. However, since about 1970, a reduction in tree growth near the tree line has been observed in response to warming and increased drought stress. This reduction in tree growth has been mainly reported in forests of the northern hemisphere but less studied in southern forests. In this study, we investigated tree populations of Nothofagus pumilio located near the arboreal altitudinal limit in the central Patagonian Andes (45–47° S, Aysén region, Chile). In this region, warming has been accompanied by increased drought conditions since the 2000s. We explored whether this climatic variability has promoted or reduced tree growth at the regional scale in tree lines of these broadleaved temperate forests of central Patagonia. We constructed tree‐ring chronologies and determined common growth patterns and trends, and then analyzed the influence of recent climate. We detected a significant change in the slope of regional growth trends between the periods 1955–1985 and 1985–2015. We found that positive growth trends in the period 1955–1985 were associated with warmer and drier springs. However, after 1985, we found a stabilization in N. pumilio growth associated with a steady increase in temperature in autumn. Our results support the idea that more frequent warm autumns, with very thin or no snow cover, have stabilized tree growth due to water deficit at the end of the growing season of N. pumilio. The predicted climate change scenario of increasing temperatures and drought in central Patagonia may increase competition among trees for water, particularly at the end of the growing season. Consequently, we could expect a decreasing forest growth trend in central Patagonia, potentially impacting forest dynamics of these southern forests. [ABSTRACT FROM AUTHOR]

Rising temperature has been associated with increased occurrence of herbivorous insect outbreaks, explained by several direct and indirect mechanisms. Whereas natural enemies are known key drivers of forest‐defoliating insect cycles, indirect effects of temperature on insect's ability to defend against pathogens and parasitoids (e.g., immunocompetence), as well as the interaction with other mechanisms (e.g., diet), remain less explored. The aim of this study is to evaluate the effect of temperature and diet on the performance and immune response of the model lepidopteran system Ormiscodes amphimone (Saturniidae) and its host plants Nothofagus spp. (Nothofagaceae).Larvae of O. amphimone were reared under two temperature conditions (ambient 18:6°C and warmed, 21:6°C; light: dark, 14:10 h) and on leaves of two of their preferred Nothofagus host plants, which vary in quality (lower N. antarctica–higher N. pumilio). We measured developmental time, female pupal weight as a proxy of fitness, relative growth rate, nutritional indices and melanisation of a monofilament as a proxy of immune response.Results showed that an average rise of 2°C favours larval immunocompetence, potentially decreasing mortality exerted by parasitoids. Moreover, depending on diet, an increase in temperature can either maintain (on more nutritious N. pumilio leaves) or enhance (on less nutritious N. antarctica leaves) larval nutritional efficiency, performance and female pupal weight.Hence, an increase in temperature could enhance O. amphimone population growth, through attenuating differences caused by diet and enhancing immunocompetence, favouring outbreak frequency, severity and area. [ABSTRACT FROM AUTHOR]

Abstract It is widely accepted that global warming is affecting forests near the tree line by increasing tree growth in these cold‐limited environments. However, since about 1970, a reduction in tree growth near the tree line has been observed in response to warming and increased drought stress. This reduction in tree growth has been mainly reported in forests of the northern hemisphere but less studied in southern forests. In this study, we investigated tree populations of Nothofagus pumilio located near the arboreal altitudinal limit in the central Patagonian Andes (45–47° S, Aysén region, Chile). In this region, warming has been accompanied by increased drought conditions since the 2000s. We explored whether this climatic variability has promoted or reduced tree growth at the regional scale in tree lines of these broadleaved temperate forests of central Patagonia. We constructed tree‐ring chronologies and determined common growth patterns and trends, and then analyzed the influence of recent climate. We detected a significant change in the slope of regional growth trends between the periods 1955–1985 and 1985–2015. We found that positive growth trends in the period 1955–1985 were associated with warmer and drier springs. However, after 1985, we found a stabilization in N. pumilio growth associated with a steady increase in temperature in autumn. Our results support the idea that more frequent warm autumns, with very thin or no snow cover, have stabilized tree growth due to water deficit at the end of the growing season of N. pumilio. The predicted climate change scenario of increasing temperatures and drought in central Patagonia may increase competition among trees for water, particularly at the end of the growing season. Consequently, we could expect a decreasing forest growth trend in central Patagonia, potentially impacting forest dynamics of these southern forests.

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Recent climatic trends, such as warming temperatures, decrease in rainfall, and extreme weather events (e.g., heatwaves), are negatively affecting the performance of forests. In northern Patagonia, such conditions have caused tree growth reduction, crown dieback, and massive die-back events. However, studies looking at these consequences in the southernmost temperate forest (Nothofagus betuloides and Nothofagus pumilio) are much scarcer, especially in southernmost South America (SSA). These forests are also under the influence of the positive phase of Antarctic Oscillation (AAO, also known as Southern Annular Mode, SAM) that has been associated with increasing trends in temperature, drought, and extreme events in the last decades. This study evaluated the growth patterns and the climatic response of eight new tree-ring chronologies from Nothofagus species located at the upper treeline along different environmental gradients in three study areas: Punta Arenas, Yendegaia National Park, and Navarino Island in SSA. The main modes of the ring-width index (RWI) variation were studied using principal component analysis (PCA). We found that PC1 has the higher loadings for sites with precipitation values over 600 mm/yr, PC2 with N. betuloides sites, and PC3 with higher loadings for sites with precipitation values below 600 mm/yr. Our best growth-climate relationships are between N. betuloides and AAO and the most northeastern site of N. pumilio with relative humidity (which coincides with heatwaves and extreme drought). The climatic signals imprinted in the southernmost forests are sensitive to climatic variability, the climate forcing AAO, and the effects of climate change in the last decades. [ABSTRACT FROM AUTHOR]

In many tree species, trunk forking plays a major role in crown construction, and stands out as an indicator of the architectural transition between juvenile and adult trees. We aimed to evaluate the effects of trunk forking on height and diameter growth of Nothofagus pumilio trees in an even-aged monospecific stand in northern Patagonia, Argentina. We used cataphyll scars and ringwidth measurements to compared yearly increments in mean trunk length and diameter of trees with forked and unforked trunks. After approximately 50 years of growth, trees with a forked trunk had reached larger radial growth than unforked trees, but there was no difference in height between the two groups. The larger trunk volume of forked trees suggests that they may have a competitive advantage over unforked trees; trunk forking could therefore, influence dominance/suppression relationships. Our results suggest that morphogenetic processes associated with trunk forking influence the establishment of size hierarchies in dense stands of Nothofagus pumilio. [ABSTRACT FROM AUTHOR]

The resistance of different genotypes to abiotic stress may be due to genetic effects and/or to phenotypic plasticity allowing them to acclimate to variable conditions. The contribution of one or the other mechanism determines different strategies with implications for the species conservation and adaptive management. In this study, the ecophysiological response to drought of Nothofagus pumilio provenance sites (humid, mesic and xeric) from contrasting precipitation regimes was evaluated in a common garden trial. Seedlings were submitted to progressive drought by withdrawing irrigation (control vs water deficit). Assuming a genetic base determined by selection pressures, populations from more xeric sites are expected to show higher resistance to drought, e. g., higher resistance to xylem cavitation and safety margin, stronger stomatal control and osmotic adjustment. Vulnerability to cavitation curves were performed, and the percentage loss of conductivity (P12, P50, P88 and slope) was obtained. The water potential at turgor loss point (TLP) and the osmotic potential at full turgor (π100) were calculated from pressure–volume curves. The humid site showed a significantly higher P50 value than the mesic and the xeric sites. Pre-dawn water potential differed between the provenances from xeric and mesic conditions under severe water deficit. Natural selection was inferred from the comparison of differentiation at neutral markers and phenotypic traits (FST vs. PST), with signals of adaptive variation (PST > FST) for stomatal density, specific leaf area, TLP, π100 and stomatal conductance. Results suggest a differential adaptive capacity to drought of N. pumilio provenance sites that could be evidencing local adaptation to their home environment. [ABSTRACT FROM AUTHOR]

Recent climatic trends, such as warming temperatures, decrease in rainfall, and extreme weather events (e.g., heatwaves), are negatively affecting the performance of forests. In northern Patagonia, such conditions have caused tree growth reduction, crown dieback, and massive die-back events. However, studies looking at these consequences in the southernmost temperate forest (Nothofagus betuloides and Nothofagus pumilio) are much scarcer, especially in southernmost South America (SSA). These forests are also under the influence of the positive phase of Antarctic Oscillation (AAO, also known as Southern Annular Mode, SAM) that has been associated with increasing trends in temperature, drought, and extreme events in the last decades. This study evaluated the growth patterns and the climatic response of eight new tree-ring chronologies from Nothofagus species located at the upper treeline along different environmental gradients in three study areas: Punta Arenas, Yendegaia National Park, and Navarino Island in SSA. The main modes of the ring-width index (RWI) variation were studied using principal component analysis (PCA). We found that PC1 has the higher loadings for sites with precipitation values over 600 mm/yr, PC2 with N. betuloides sites, and PC3 with higher loadings for sites with precipitation values below 600 mm/yr. Our best growth-climate relationships are between N. betuloides and AAO and the most northeastern site of N. pumilio with relative humidity (which coincides with heatwaves and extreme drought). The climatic signals imprinted in the southernmost forests are sensitive to climatic variability, the climate forcing AAO, and the effects of climate change in the last decades.

Los Andes patagónicos tienen como vegetación característica los bosques de Nothofagus, que se extienden desde los 37° a los 55° S. En particular, N. pumilio (lenga) es la especie más ampliamente distribuida tanto en la Argentina como en Chile, y por ser decidua representa un notable pulso estacional de materia orgánica a los arroyos de cabecera. Estos arroyos tienen su origen en las alturas de las montañas y drenan las laderas hacia aguas bajas. Hace más de una década que se realizan estudios en la cuenca del Challhuaco, ubicada en la zona norte y en el extremo este de los Andes patagónicos. Los estudios abarcaron tanto aspectos estructurales como funcionales de la ecología de arroyos e incluyen el análisis de nutrientes y materia orgánica a lo largo de la cuenca, y relaciones alimentarias entre los diferentes componentes de sus tramas tróficas, desde productores primarios, descomponedores de detrito vegetal e invertebrados bentónicos hasta consumidores superiores como la trucha arcoíris. El objetivo de esta revisión fue integrar los resultados obtenidos sobre el funcionamiento de los sistemas fluviales de cabecera andino-patagónicos y su respuesta a factores de cambio espaciales (a lo largo de una cuenca) y temporales (entre estaciones). Finalmente, se destacan los conflictos y las amenazas más importantes que enfrentan estos sistemas (modificaciones en la cobertura vegetal, introducción de ganado, cambio climático) para señalar los aspectos que se deberían incorporar a las políticas de conservación, incluyendo un manejo sustentable de las actividades forestales y la cría de ganado.

Patagonian Andes has Nothofagus forests as characteristic vegetation, which extends from 37° to 55° S. In particular, N. pumilio (lenga) is the most widely distributed species, both in Argentina and Chile, and as it is a deciduous species, it represents an important organic matter input to headwater streams. These streams are originated in high altitude mountains and drain the forest downstream. We have been studying the ecology of Challhuaco catchment, in the Northeast of Patagonian Andes, for more than a decade. These studies encompassed both structural and functional aspects of stream ecology, including nutrient and organic matter analysis along the catchment, and feeding relationship between the different components of food webs, from primary producers, leaf litter decomposers and benthic macroinvertebrates to top consumers, as the rainbow trout. In this review we aimed to gather and relate results of a catchment that may be used as a model to extrapolate to other Andean Patagonian catchments. Finally, we indicated some conflicts and threats to which these systems are exposed, to point out the aspects that should be incorporated into conservation policies including a more sustainable management of forestry and cattle raising. [ABSTRACT FROM AUTHOR]

Aim: To assess the relative roles of long‐term (millennial‐scale) climatic change, fire and volcanic disturbance on the dynamics of Araucaria–Nothofagus forests of south‐central Chile. Through this analysis, we provide insight into how these iconic ecosystems may respond to future ash‐fall events under anticipated changes to climate and burning regimes. Location: Lago Cilantro is a small lake located in south‐central Chile (38°51′36.72 S, 71°17′14.52 W, 1,400 m asl), proximal to several active volcanos within the Southern Volcanic Zone of the Andes Mountain range. Taxon: Araucaria araucana (Araucariaceae); Nothofagus spp. (Nothofagaceae). Methods: We developed a continuous 8,700‐year long pollen and charcoal record from Lago Cilantro. We compared these results with proxies of regional climatic change and used a combination of principal component analysis and superposed epoch analysis to test the relationship between tephra deposition and pollen composition. Results: We detect a shift in dominance from Araucaria araucana to Nothofagus species between ~8.7 and ~5.5 ka (ka = 1,000 years before present‐1950 CE), in concert with increasing regional precipitation and decreasing local‐scale fire activity. A reversal in this trend occurred after ~4 ka, contemporaneous with a reduction in regional precipitation. Centennial‐scale increases in Araucaria araucana from ~0.2 to 0.9 ka, ~5.2 to 4.2 ka and ~8.6 to 7 ka are associated with reductions in fire return intervals. We found 24 tephra layers in this record; tephra >2 cm thickness are associated with short‐term (<100 year) compositional shifts in the pollen spectra, while a single large (255 cm) tephra at ~3 ka is associated with a substantial reduction in Nothofagus and no change in Araucaria. Main Conclusions: Climate change drove millennial‐scale shifts in Araucaria–Nothofagus forests and fire regimes near Lago Cilantro. A shortening of the fire return interval is associated with an increase in the importance of Araucaria, supporting the notion that recurrent fires are required to allow this tree species to compete with Nothofagus. Tephra deposition triggered short‐term compositional responses in this system that appears to be overwhelmed by climate and fire at longer time‐scales. Araucaria araucana can survive and potentially outcompete Nothofagus following the deposition of very thick tephra, thanks to its thick bark and tall canopy (>15 m). [ABSTRACT FROM AUTHOR]

Background and Aims Plants have the potential to adjust the configuration of their hydraulic system to maintain its function across spatial and temporal gradients. Species with wide environmental niches provide an ideal framework to assess intraspecific xylem adjustments to contrasting climates. We aimed to assess how xylem structure in the widespread species Nothofagus pumilio varies across combined gradients of temperature and moisture, and to what extent within-individual variation contributes to population responses across environmental gradients. Methods We characterized xylem configuration in branches of N. pumilio trees at five sites across an 18° latitudinal gradient in the Chilean Andes, sampling at four elevations per site. We measured vessel area, vessel density and the degree of vessel grouping. We also obtained vessel diameter distributions and estimated the xylem-specific hydraulic conductivity. Xylem traits were studied in the last five growth rings to account for within-individual variation. Key Results Xylem traits responded to changes in temperature and moisture, but also to their combination. Reductions in vessel diameter and increases in vessel density suggested increased safety levels with lower temperatures at higher elevation. Vessel grouping also increased under cold and dry conditions, but changes in vessel diameter distributions across the elevational gradient were site-specific. Interestingly, the estimated xylem-specific hydraulic conductivity remained constant across elevation and latitude, and an overwhelming proportion of the variance of xylem traits was due to within-individual responses to year-to-year climatic fluctuations, rather than to site conditions. Conclusions Despite conspicuous adjustments, xylem traits were coordinated to maintain a constant hydraulic function under a wide range of conditions. This, combined with the within-individual capacity for responding to year-to-year climatic variations, may have the potential to increase forest resilience against future environmental changes. [ABSTRACT FROM AUTHOR]

Questions: Fire is a key factor influencing Araucaria araucana forests, but the impact of fire severity on the understorey vegetation is not well understood. In this study we seek to answer the following questions: (a) how do initial plant diversity, composition and spatial distribution of the understorey vegetation change in response to different levels of fire severity; and (b) does the abundance of dominant tree species exhibit different patterns across a fire severity gradient shortly after fire? Location: Old‐growth Araucaria araucana–Nothofagus pumilio forests in the Andes of south‐central Chile (38° S, 71° W) burned in 2015. Methods: We evaluated the post‐fire plant regeneration across a fire severity gradient ranging from unburned forests to areas of high fire severity. One year after fire (in February 2016), we measured woody and herbaceous species richness, abundance, height, origin (native vs exotic species), life forms and the spatial pattern of plant recovery. Results: Plant species richness and abundance were significantly higher within the unburned forest and low fire severity areas one year after fire, compared to areas of high and moderate fire severity. Overall, nearly 50% of the species present in the unburned forest were not found in areas of high severity, including the tree Nothofagus pumilio. Rapid vegetative resprouting of pioneer species such as Chusquea culeou resulted in an aggregated spatial distribution of plants after fire. Conclusions: Plant diversity and the abundance of Araucaria araucana and Nothofagus pumilio were reduced in areas of high fire severity one year after fire. Exotic species were more abundant within areas of low severity, being likely mediated by cattle browsing. Our research makes clear the potential changes in forest composition and structure if dominant tree species are not capable of recovering after fire. We recommend the exclusion of cattle within fire‐affected areas and planting Nothofagus pumilio in areas of high fire severity. [ABSTRACT FROM AUTHOR]

The lenga forests (Nothofagus pumilio) are the main native forest resource of the Andean Patagonian region. The aim of this research is to inform the species of oribatid mites, and new records, associated to the decomposition process of the lenga wood. Samples of soil and decayed wood were taken under a test of the decomposition process. Twenty-one genera and 26 species of oribatid mites were registered; two of them are new records for Chubut province. [ABSTRACT FROM AUTHOR]

Premise: Fire scars on trees are created by excessive heat from a fire that kills the vascular cambium. Although, fires are one of the most important forest disturbances in Patagonia, the effects of fire on tree physiology and wood anatomy are still unknown. In this study, we hypothesized that abnormal functioning of the cambium after a fire will induce anatomical changes in the wood. We also assumed that these anatomical changes would affect xylem safety transport. Methods: We quantified wood anatomical traits in Nothofagus pumilio, the dominant subalpine tree species of Patagonia, using two approaches: time and distance. In the first, anatomical changes in tree rings were compared before, during, and after fire occurrence. In the second, the spatial extent of these changes was evaluated with respect to the wound by measuring anatomical traits in sampling bands in two directions (0° and 45°) with respect to the onset of healing. Results: Reductions in lumen diameter and vessel number were the most conspicuous changes associated with fire damage and observed in the fire ring and subsequent post‐fire rings. In addition, the fire ring had more rays than in control rings. In terms of distance, anatomical changes were only restricted to short distances from the wound. Conclusions: Post‐fire changes in wood anatomical traits were confined close to the wound margins. These changes might be associated with a defense strategy related to the compartmentalization of the wound and safety of water transport. [ABSTRACT FROM AUTHOR]

• Understory species presence and response depend on the analysed landscape scale. • Forest understory assemblages varies at within a single forest type in a region. • Sharing species among different ecosystem types reduces local extinction hazards. • Particular and complementary strategies should be implemented for conservation. Understory vegetation is essential to forest functioning, integrity and provision of ecosystem services, but forest management often overlook understory conservation. As species distribution depends on many drivers, and diversity indicators varied with scales, it is difficult to define appropriate strategies for conservation, even in a single forest type. Moreover, many understory plant species occurred at both forests and non-forest ecosystems, and the assemblage could vary at sub-regional scales. Then, forest specialist species may not be similarly threatened in different ecosystem types or sub-regions. Therefore, we wonder if the variation of the understory plant assemblage of a single forest type at a sub-regional scale occurs in different forest types; how do vary the understory species assemblages compared to non-forest ecosystems at each sub-region; and how do vary the management effects on different forest types in a local scale within different sub-regions. For this, we studied understory vegetation richness and cover in three Nothofagus forest types and three non-forest ecosystems across four sub-regions of Tierra del Fuego, Argentina. We evaluated correlations, nestedness, relational patterns (by Non-metrical multidimensional scaling-NMS and Multi-response permutational procedure-MRPP) and Indicator Species Analysis-ISA, for 229 vascular plants distributed in 554 plots. Regarding local scale, we asssesed two main productive managements: timber harvesting in N. pumilio and livestock use in N. antarctica forests. Understory assemblages varied within each single forest type among different sub-regions (p < 0.033 for all MRPP), and different indicator plant species occurred at different geographic zones for two forest types (e.g., Adenocaulon chilen sis in SE for N. pumilio forests, and Cotula scariosa in NW for N. antarctica forests), but not in forests with a nested understory distribution pattern (N. betuloides). Ecosystem types shared a high quantity of species (>40 %), except in SE zone. However, all ecosystem types significantly differed in every zone (p < 0.025), except grasslands and shrublands in NW (p = 0.165). Grasslands stand out as the species richest ecosystem in NW, SW and SE zones (between 62 and 123 spp.), highlighting their importance for conservation. Landscape heterogeneity emerged as an important mechanisms enriching species richness from neighbouring habitats, while in managed stands, resource availability seemed the main driver. Regarding the local scale, higher impacted by harvested condition in N. pumilio forests showed differences with less impacted conditions despite the zone, with some common indicator species (e.g., Taraxacum officinale). However, differences between aggregate retention and primary forests depends on the locality. Concerning N. antarctica forests, livestock homogeneizes the assemblages between zones, although indicator species remains different across zones, with dominance of exotics introduced for forage in NE (e.g., Poa pratensis). The presence of the same species in forests and non-forest ecosystems reduce the local extinction hazards in Tierra del Fuego. However, conservation strategies should be implemented at every sub-region. New natural reserves could be an alternative for conservation in zones without natural reserves, but complemented with land-sharing in managed forests. The consideration of potential differences among geographic zones could bring a more clear alternative to improve conservation at sub-regional scales where the same forest type cover large regions. [ABSTRACT FROM AUTHOR]

The effects and consequences of global warming on the productivity of the Patagonian forest are still unknown. The use of Unmanned Aerial Vehicles (UAV) promotes new knowledge of the most pristine and unknown sub-antarctic forests located in Chilean Patagonia. This work presents an initial approach to spatialize biochemicals over the Patagonian forests using ultra-high spatial resolution imagery acquired from UAVs equipped with a multispectral (visible, near-infrared, and thermal) sensor. The images were obtained in multiple flights over the Cerro Castillo National Park (Aysén Region, Chile), and several Vegetation Indices (VIs) were estimated. Leaves of Nothofagus pumilio (Poepp. et Endl.) Krasser (Nothofagaceae) individuals were extracted after the flights and were then used to determine the biochemicals traits of chlorophylls (Chl-a and Chl-b) and carotenoids pigments, as well as the total phenolic content (TPC), total flavonoids content (TFC), and the DPPH radical scavenging assay. Their relationships with multiple VIs was analyzed in order to assess the spatiality of the biochemicals traits in the forest during it most productive phenological stage. Results showed high correlations for the biochemical traits pigments (R2 > 0.75) with the indices DVI, MCARI, and MSAVI1 as the best performing indices, while further spectral availability is needed for significant correlations with biochemicals traits related to the antioxidant capacity. Spatialization of the biochemical traits within UAV imagery was also performed evaluating their representation in the forest. This work allowed us to identify the different spectral behavior of the N. pumilio species, its relation to biochemical traits, and their spatialization, thus presenting the first step to developing a monitoring protocol for the evaluation of the Patagonian forests under the current global warming scenarios in the region.

El fuego tiene impactos importantes en la estructura y funcionamiento de ecosistemas naturales. En marzo de 2015 un incendio de gran magnitud afectó bosques de alto valor ecológico de Araucaria araucana-Nothofagus pumilio (araucaria-lenga) en la Reserva Nacional China Muerta (Chile, 38° S), donde las adaptaciones al fuego son poco frecuentes en la flora nativa. El objetivo del presente trabajo fue evaluar los cambios en la composición florística del bosque en un gradiente de severidad de fuego (i.e., alta, media y baja severidad) un año después del disturbio. Se hipotetiza que las zonas más afectadas por el fuego presentarán una composición de especies distinta a la de zonas menos afectadas, con una menor riqueza y abundancia de especies nativas, y que las especies exóticas se verán favorecidas por el fuego poco severo. Se establecieron 20 parcelas de 100 m2 cada una en todo el gradiente de severidad de fuego, incluyendo un bosque adyacente no quemado que sirvió como referencia. En cada parcela se registró la riqueza y abundancia de toda la flora vascular (nativas y exóticas). Se analizó y comparó la riqueza y abundancia de especies, la composición y similitud florística entre los distintos niveles de severidad. Se encontró que la riqueza y abundancia de especies son significativamente más bajas en áreas de alta y media severidad de fuego. La riqueza y abundancia de especies exóticas fue mayor en áreas de baja severidad de fuego, las cuales estuvieron sujetas a pastoreo después del fuego. Existe un rápido cambio composicional de la comunidad de plantas en el bosque de Araucaria-Nothofagus un año después del incendio, sugiriendo un potencial cambio en la estructura del bosque si las especies arbóreas dominantes no se recuperan después del fuego.

Aims: Rising temperature and declining summer precipitation due to the 1970s‐climate shift in southern South America have reduced forest productivity at dry sites. Here, we worked with the most widespread Southern Hemisphere tree line species, Nothofagus pumilio, across contrasting climatic conditions and determined whether rising atmospheric CO2 concentrations as well as warmer and drier climatic conditions provoked by the 70s‐climatic shift have been causing systematic changes in tree line growth rates and intrinsic water‐use efficiency (iWUE). Location: 36–54°S, southern Andes. Time period: 1950–2010. Major taxa studied: Nothofagus pumilio. Methods: We worked at five disparate climatic tree line locations, spanning 18 degrees of latitude; at each location, we sampled trees at four different elevations, including tree line elevation. We quantified the variation in annual tree‐ring width (TRW) as a function of climate, elevation, tree age, size, annual CO2 concentrations and location, using linear mixed‐effects models and interpreted TRW trends in relation to iWUE and isotope (δ13C and δ18O) signalling. Results: Across locations, the patterns of tree line growth occurring in the 1980–2010 period exhibited a clear and significant negative trend, in contrast to the previous 1950–1980 period. We found an increase in iWUE and δ18O across time and locations. Given that an increase in δ18O indicates a decrease in stomatal conductance, we assert that drought‐induced stomatal closure appears to be causing the reduction in growth. Main conclusions: We show unequivocal evidence that warmer and drier summer conditions translated into a decrease in growth rates along the elevational tree line of the southern Andes, reverting previous growth improvements linked to climate warming. An improvement in iWUE at all locations is most likely explained by decreased stomatal conductance given the rising δ18O signal. An iWUE–growth decoupling may act as an ecological strategy to respond to drought. [ABSTRACT FROM AUTHOR]

Wood is one of the main reservoirs of carbon (C) and nutrients in Nothofagus pumilio (Poepp. & Endl.) Krasser forests; hence, its decomposition is essential for C and nutrient cycling. Chemical traits are one of the factors affecting wood decomposition, but there is little information describing these chemical characteristics. Our objective was to analyze the chemical traits of N. pumilio fine woody material (FWM) and their relationships with decomposition. We determined the contents of nitrogen (N), phosphorus (P), C, hemicellulose, cellulose, lignin, and extractives in two diameter categories (branches and twigs) and in two decay classes (DC1, sound wood; DC2, intermediate stage of decomposition). We also determined the decomposition rate constant (k) of each type of material. Contents of P, extractives, C, and hemicellulose in DC1 and C, cellulose, and lignin in DC2 showed differences between diameters. In twigs, all chemical traits showed differences between DCs, but in branches, only N and C showed differences. Mean k was similar between diameters and was greater in DC2 than in DC1. Hemicellulose and P showed positive relations with increasing decomposition, whereas cellulose showed a negative one. Our results support the use of classical DCs. We hypothesize that the presence (or absence) and proportional amount of bark partially explain the differences found between DCs and between diameters. [ABSTRACT FROM AUTHOR]

Forest harvesting is one of the main economic practices in South Patagonia. The impacts produced by forest harvesting have been studied by numerous investigations. And it is known that forest harvesting affects the decomposition of soil organic matter. However, there is no data about how the harvesting by variable-retentions affect this decomposition. Our objective was to determine how impact variable-retention upon decomposition and nutrient release in Nothofagus pumilio forest soils. We hypothesized that variable-retention accelerate decomposition and nutrient release. We compared primary and harvested forests with two types of retentions (aggregated and dispersed) and two times [1 and 5 years after harvesting (YAH)]. To measure litter decomposition, we used bag technique for to determine organic matter loss. We determined carbon; nitrogen; calcium; potassium; magnesium and lignin concentrations in decomposing material. We analysed the data using linear mixed models ANOVA. Decomposition rates were estimated as derivate of the linear mixed model for the logarithm of the remaining leaf litter weight. We found that dispersed retentions treatment had the highest decomposition rates. Primary forest and aggregated retentions had the smaller slopes of the decomposition model. Dispersed and aggregated retention 5 YAH retained more nitrogen compared to primary forest. Dispersed retention 5 YAH had the lowest C/N ratio. Primary forest had higher Lignin/N ratio at 540 incubation days. Dispersed retention 5 YAH released more phosphorus compared to primary forest. Dispersed and aggregated retention 1 YAH had higher C/P ratio. Dispersed retention 5 YAH presented the most mineralization of potassium in the initial time of decomposition. We conclude that the harvesting by variable-retentions had an immediate negative effect on litter decomposition and the nutrients dynamics. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present a first assessment of the use of woody vegetation resources for combustion by hunter-gatherer societies in eastern areas of Tierra del Fuego. For this purpose, carbonized wood fragments from the archeological context of the Heshkaia 35 site (Moat Bay, Tierra del Fuego, Argentina) were analyzed. Results show a local use of woody material from diverse plant species (Nothofagus pumilio, Nothofagus sp., Drymis winteri, and Maytenus magellanica). A comparison of these results with the data available from other archeological sites of the southern coast of Tierra del Fuego offers a comparative perspective on the management of these resources within the region. [ABSTRACT FROM AUTHOR]

The genus Nothofagus is considered as one of the most interesting plant genera, not only for the living species but also due to the fossil evidence distributed throughout the Southern Hemisphere. Early publications postulated a close relationship between fossil and living species of Nothofagus. However, the intrageneric phylogenetic relationships are not yet fully explored. This work assesses the placement of fossil representatives of genus Nothofagus, using different search strategies (Equal Weight and Implied Weight), and it analyses relationships with the extant species from South America (Argentina and Chile). The relationships of fossil taxa with the monophyletic subgenera Brassospora, Fuscospora, Lophozonia, and Nothofagus and the monophyly of the clades corresponding to the four subgenera are tested. A timecalibrated tree is generated in an approach aiming at estimating the divergence times of all the major lineages. The results support the inclusion of most fossil taxa from South America into the subgenera of Nothofagus. The strict consensus tree shows the following species as closely related: Nothofagus elongata + N. alpina; N. variabilis + N. pumilio; N. suberruginea + N. alessandri; N. serrulata + N. dombeyi, and N. crenulata + N. betuloides. The species N. simplicidens shares a common ancestor with N. pumilio, N. crenulata, and N. betuloides. This contribution is one of the first attempts to integrate fossil and extant Nothofagus species from South America into a phylogenetic analysis and an approach for a time-calibrated tree. [ABSTRACT FROM AUTHOR]

The identification of disturbance events using disturbance chronologies has become a valuable tool in reconstructing disturbance history in temperate forests worldwide; yet detailed reconstructions of disturbance history and their effect on the structure and dynamics of the old-growth Nothofagus forests in the southern Patagonia are scarce. We reconstructed forest dynamics and disturbance history of an old-growth N. pumilio forest in the Toro River Valley, Santa Cruz, Argentina using dendroecological techniques. Since a variation in the disturbance regimes was expected with changing elevation, we sampled at different elevations. We found distinct differences in forest structure, dynamics, and disturbance history with changes in the elevation. The disturbance chronologies provided robust evidence that forests in the study area have been subjected to multiple disturbance events over the last 200 years. Yet, recognizing the agent of disturbance could be difficult in these montane forests and further studies are required. Moreover, disturbances might have varied from frequent, moderate- to high-severity events to less frequent and more severe events. This study represents the first of its kind for the temperate forests of Patagonia.

A 204 year-long record of δ18O in tree-ring cellulose of southern beech (Nothofagus pumilio) from a site near Perito Moreno Glacier (50°S) in Southern Patagonia was established to assess its potential for a climate reconstruction. The annually resolved oxygen isotope chronology is built out of seven individual tree-ring δ18O series with a significant mean inter-series correlation (r = 0.61) and is the first of its kind located in Southern America south of 50°S. Over a common period from 1960 to 2013 of available stationary and high-resolution gridded CRU TS v. 4.01 data, the δ18O chronology exhibits a strong sensitivity toward hydroclimatic as well as temperature parameters as revealed by correlation analyses. Among these, positive correlations with maximum temperature in the first part of the summer season (CRU rONDJ = 0.51, p < 0.01) and negative correlations with precipitation in the latter half of the vegetation period (CRU rONDJ = −0.54, p < 0.01) show the highest sensitivities. A strong supra-regional influence of the Southern Annular Mode (SAM) is clearly recorded in this chronology as indicated by significant positive correlations during the vegetation period (rONDJ = 0.62, p < 0.01). This indicates that the presented δ18O-chronology shows great promise to reconstruct the influence and variability of the SAM within the last two centuries in southern South America. The modulation of positive and negative anomalies within this series can be interlinked to changes in moisture source origin as revealed by backward trajectory modeling. Additionally, these anomalies can be directly associated to positive or negative phases of the Antarctic Oscillation Index (AAOI) and therefore the strength of the Westerlies. Aligned by the analysis on the influence of different main weather types on the δ18O chronology it is shown that such time-series hold the potential to additionally capture their respective influence and change during the last centuries.

Highlights • Severe fires are increasingly affecting forest ecosystems worldwide. • Soil microorganisms and nutrients were measured one-year after fire in A. araucana forests. • A positive response of microorganisms and FDA activity were found after fire. • Soil nutrients (N, P and K) were significantly higher in burned areas. • Vegetation recovery in burned areas exhibited reduced species richness and diversity. Abstract Soil contains a wide variety of microorganisms that are responsible for fundamental ecological processes. However, increased frequency and severity of fires reduce microbial diversity and alter soil nutrient availability, affecting vegetation recovery. By using a large-scale wildfire that burned endangered Araucaria araucana forests in south-central Chile (38°S), we assessed the short-term post-fire response of microorganisms, soil nutrients, and plant recovery. One year after fire, we sampled soils from burned and unburned areas, and measured the number of bacterial and fungal colony forming units, and the microbiological activity of the soil. We also measured soil nutrients (N, P, and K), organic matter content and species richness, abundance and plant diversity after fire. We found a significant increase in microbiological activity in burned soils (BS) compared to unburned soils (UBS), with bacteria and fungi being four and seven times greater in BS than in UBS, respectively. Concentrations of N, P and K were also greater in BS than in UBS. Plant species richness was two times higher in unburned than in burned areas, with a drastic reduction of the dominant tree species Araucaria araucana and Nothofagus pumilio after fire. The changes in soil properties after fire may be related to organic matter mineralization, the contribution of nutrients from ashes, or due to post-fire conditions (e.g., increased soil temperature after canopy removal by fire). Overall, our study shows a positive, short-term response in soil microorganisms abundance and nutrient content, but a rapid initial reduction of plant diversity of the main dominant tree species in these forest ecosystems after a severe fire. Further research is necessary as vegetation results are only preliminary and they can vary in the short-to-medium term. Our study provides insightful clues to delve into more applied research aimed at the post-fire restoration of the endemic, long-lived Araucaria araucana forests. [ABSTRACT FROM AUTHOR]

Nothofagus pumilio forests in the Southern Patagonia region of Chile are highly degraded because of clearing for human settlements, extensive livestock grazing, and more recently, the impact of coal mining operations. Most of these legacy areas have remained as extensive meadows of non-native grasses and legumes with limited Nothofagus pumilio forest recovery due to dry soil moisture conditions and exposure to high wind and solar radiation. Therefore, active reforestation is needed to reclaim Nothofagus pumilio forests from abandoned grassland or disturbances caused by surface mine operation. In this study, a surface coal mine operation and an abandoned meadow established in the 1950 s needed to be restored back to N. pumilio forest on Riesco Island, in Southern Chilean Patagonia. We compared the establishment success of Nothofagus pumilio seedlings on replicated blocks under two conditions (experimental treatments): (i) four blocks of meadow previously disturbed by livestock grazing, (MS), and (ii) four blocks where a deep layer of the soil profile was removed, mixed, and then replaced simulating recommendations used for reclaiming surface coal mines (RS). To improve Nothofagus pumilio establishment and protection at each block under both soil conditions, seedlings were planted both unprotected and protected from wind and solar radiation using four different types of shelters: shade cloth, irregular log piles, white polypropylene shelters, and woody branches. Soil physical and chemical properties, seedling survival and growth, leaf water potential, and stomatal conductance were measured. Results at the end of the first and fourth growing seasons showed better conditions for seedling growth in the RS treatment. Mean survival rates began to be different following the second growing season with values of 84.7 ± 2.9% in RS and 60.2 ± 3.2% survival in MS treatments, respectively. At the end of the study, the difference between the treatments was even geater with values of 75.4 ± 5.5% and 32.2 ± 7.1%. Soil removal and replacement significantly changed soil physical properties, but values were still adequate for vegetation development. The use of shelters significantly influenced four-year survival rates of seedlings planted on the disturbed MS treatment with 60 ± 8.2% survival in plastic shelters and less than 25.5 ± 6.5% for all other shelters. The effects of the shelters were less clear in the RS treatment. Our study showed that Nothofagus pumilio restoration on abandoned grassland and reclaimed mine sites in Patagonia is a feasible option when soil conditions and planting techniques improve soil water availability, and when seedling are protected against excessive solar radiation and wind. [ABSTRACT FROM AUTHOR]

Abstract: Terrestrial inputs of dissolved organic matter (DOM) make a significant contribution to the carbon pool of headwaters and the reactivity of this pool depends on its source and diagenetic state, being influenced by photochemical and biological processes. The main goal of this study was to characterise the composition and reactivity of soil and leaf litter DOM from a native forest of Nothofagus pumilio (Nothofagaceae), and from natural stream water, evaluating the effect of degradation processes. Photo‐ and biodegradation laboratory experiments were conducted using DOM leached from soil and leaf litter, while the impact of photodegradation alone was also analysed through laboratory assays using stream water. The effects of photo‐ and biodegradation were evaluated through changes in the concentration of dissolved organic and inorganic carbon (DOC and DIC, respectively) and optical DOM proxies (absorbance and fluorescence). In the initial characterisation, DOM from soil and water leachates showed naturally high humification, aromaticity and lignin content compared with the DOM of leaf litter leachate rich in non‐humic compounds. Photo‐ and biodegradation increased humification of the DOM. DOM from leaf litter leachate was more bioavailable than DOM from soil leachate, as reflected by the higher growth of bacteria, DOC consumption and DIC production. In general, biodegradation increased DOM molecular weight, aromaticity and lignin content. Changes in fluorescent DOM (FDOM) showed a trend characterised by the loss of labile protein‐like compounds and an increase in refractory humic‐like components. Long‐rod shaped bacteria were more abundant in leaf litter leachate, suggesting their preference for labile DOM, whereas cocci dominated in the humic and more biorecalcitrant DOM from soil leachate. This study showed a continuum of DOM humification, with decreasing DOM reactivity from leaf litter leachate towards soil leachate and stream water. Soil leachate DOM was probably the main source of stream water DOM, as reflected by their similar signatures and close positioning in the reactivity continuum, although carbon mineralisation was much lower in soil leachate than stream water. [ABSTRACT FROM AUTHOR]

Chilean temperate rainforests have unique climatic, edaphic and biotic conditions, constituting pre-industrial blueprint ecosystems. Mycorrhizal associations play a central role in the biogeochemical processes of these ecosystems' functioning. Baseline forest ecology studies are necessary in order to better understand diversity patterns, specifically regarding mycorrhizal symbiosis. Therefore, here we describe the vegetation characteristics and the mycorrhizal relationships of vascular plants in a Nothofagus pumilio forest. We also describe, via morphological methods, the ectomycorrhizal diversity present in this forest. Additionally, we determined whether ectomycorrhizal inoculation confers positive growth effects on N. pumilio seedlings. We found that from 46 vascular plant species identified in this study, 42 (91%) were mycorrhizal and of these 33 (72%) were associated with arbuscular mycorrhizae (AM), two (the dominant trees N. pumilio and N. dombeyi) were forming ectomycorrhizae (EM), five were associated with ericoid mycorrhizae, two with orchid mycorrhizae, and four were nonmycorrhizal. Additionally, 26 EM species were detected of which 15 belong to Cortinarius. Finally, there were clear differences in the growth of N. pumilio seedlings inoculated with the ectomycorrhizal fungus Laccaria laccata compared to noninoculated plants. We suggest that mycorrhizal fungi play a key role in seedling colonization of harsh environments such as the Andean treeline. [ABSTRACT FROM AUTHOR]

Variable retention mitigates harmful effects of traditional practices on biodiversity of forest ecosystems, preserving habitats for species affiliated with closed forests and providing habitats for early-seral species. In Nothofagus pumilio forests variable retention effects on several taxa have been actively monitored in short- and medium-terms. However, these have rarely been investigated further than six years since harvesting, seldom considering multiple taxonomic groups in the same research. Furthermore, there is a lack of information about responses along the regional gradient of a forest natural distribution. We evaluated the effect of variable retention on plant and beetle assemblages, seven to eleven years after harvesting, in three locations along a regional gradient of the natural distribution of N. pumilio forest in Tierra del Fuego, Argentina. We surveyed three silvicultural treatments (aggregated retention-AR, dispersed retention-DR, old growth forests-OGF) at three localities, where we characterized understory vascular plant and beetle communities during mid-summer by species richness, abundance, Shannon-Wiener diversity and Pielou evenness indices, as well as community structure. We found 58 plants and 45 species of beetles. Assemblages of old growth forests showed differences among the three locations along the studied regional gradient, with only 25% of plants and one beetle shared among them. Plant distribution may be driven by microclimatic and geographical conditions, while availability of food resources or habitat structural complexity could influence beetles. Likewise, variable retention modified original assemblages with greater effects in DR than in AR. However, this trend was not uniform for each taxa or locality, and seems to be related to the composition of original assemblages and the influx of species from surrounding environments. The specialist vs. generalist quantities in the original assemblage could influence the resistance/resilience of the community, since old growth assemblages with a greater proportion of generalist and/or non-sensitive species could maintain more similarity between aggregates and old growth forest. The influx of species (mainly generalists or exploiters) occurred mainly in DR, generating higher dissimilarities between DR and OGF. The correlation between taxa was not so clear for all locations; therefore, retention effects cannot be generalized among taxa and localities. Finally, the utility of potential bioindicators in the whole region could differ for a particular locality, and vice versa. Particularities in the biotic assemblages of different taxa in a regional gradient are important for management and conservation planning, and support variable retention as a useful strategy to combine conservation and production objectives in a managed landscape. [ABSTRACT FROM AUTHOR]

The extent to which a vertical trunk is differentiated from its branches is a key trait for the architecture of trees and may affect interspecific relationships., In this study, we analysed the effect of soil water availability on biomass partitioning for Nothofagus pumilio by means of a nursery experiment. Juvenile trees were subject to three irrigation conditions: no irrigation, intermediate irrigation and high irrigation. Irrigation conditions emulated the mean precipitation of the most representative environments inhabited by N. pumilio., Changes in soil water availability modified the biomass partitioning patterns of trees. In comparison to the other two conditions, high irrigation caused: (i) a higher ratio of biomass partitioning to stems than roots; (ii) more trunk growth in relation to its branches; and (iii) more photosynthetic organs relative to the aboveground biomass. Trunk size relative to that of its most recent branches was not increased by water availability., Water availability may play a significant role in the capacity of N. pumilio for space occupation due to the effects on axis differentiation. [ABSTRACT FROM AUTHOR]

In recent decades, southernmost South America (50–56° S) has experienced marked climate change (regional warming, decreased precipitation, reduced snow cover, and increased frequency of heat waves) related to variations in atmospheric circulation over varied timescales. In this paper, we develop oxygen isotopes from tree-ring cellulose (δ18O TRC) as a proxy for climate and atmospheric circulation in order to extend the regional meteorological record to deeper time intervals. Our work focuses on Nothofagus forests in two areas: (i) deciduous N. pumilio forest in the steppe transition zone near Punta Arenas and (ii) humid evergreen N. betuloides forest in the Navarino Island region. To investigate the potential for reconstructing palaeoclimate, δ18O TRC variations were correlated with local climate parameters as well as regional (Amundsen Sea Low, ASL) and hemispheric (Antarctic Oscillation, AAO) atmospheric circulation modes for the last 60 years. N. betuloides δ18O TRC variations show an overall positive trend, indicating isotopic enrichment over the study period, whereas no trend is recorded for the N. pumilio record. The strongest relationships with climate, together with the widest spatial representativeness, occur in the N. betuloides chronology during the growing season (spring to austral summer) and extend spatially from mid to high latitudes. In contrast, the sensitivity of the records is limited to summer months, and spatial correlations are much more limited. In addition, the N. betuloides record shows greater potential for reconstructing local climate features such as soil water (r = − 0.76), wind speed (r = 0.69), and precipitation (r = − 0.66), as well as regional (ASL, r = − 0.80) and hemispheric (AAO, r = 0.77) patterns of extratropical atmospheric circulation. Overall, we conclude that the N. betuloides record represents the most valuable tree-ring climate proxy for southernmost South America over past centuries. • Two annual oxygen isotope (δ18O) records from Nothofagus tree rings in southern South America are established. • Strong climatic signals in δ18O from Nothofagus betuloides and N. pumilio are related to local and regional climatic variations. • Differences in climatic sensitivity among δ18O records are related to species-specific responses and site specificities. • δ18O TRC record of N. betuloides from Navarino Island shows strong relationships with soil water content (r = − 0.76) with regional (ASL, r = − 0.80) and hemispheric (AAO, r = 0.77) extratropical atmospheric circulation. • δ18O TRC records from N. betuloides forests show high potential to reconstruct climate variations during the last 400–500 years. [ABSTRACT FROM AUTHOR]

Tree mortality is a key process in forest dynamics. Despite decades of effort to understand this process, many uncertainties remain. South American broadleaf species are particularly under-represented in global studies on mortality and forest dynamics. We sampled monospecific broadleaf Nothofagus pumilio forests in northern Patagonia to predict tree mortality based on stem growth. Live or dead conditions in N. pumilio trees can be predicted with high accuracy using growth rate as an explanatory variable in logistic models. In Paso Córdova (CO), Argentina, where the models were calibrated, the probability of death was a strong negative function of radial growth, particularly during the six years prior to death. In addition, negative growth trends during 30 to 45 years prior to death increased the accuracy of the models. The CO site was affected by an extreme drought during the summer 1978−1979, triggering negative trends in radial growth of many trees. Individuals showing below-average and persistent negative trends in radial growth are more likely to die than those showing high growth rates and positive growth trends in recent decades, indicating the key role of droughts in inducing mortality. The models calibrated at the CO site showed high verification skill by accurately predicting tree mortality at two independent sites 76 and 141 km away. Models based on relative growth rates showed the highest and most balanced accuracy for both live and dead individuals. Thus, the death of individuals across different N. pumilio sites was largely determined by the growth rate relative to the total size of the individuals. Our findings highlight episodic severe drought as a triggering mechanism for growth decline and eventual death for N. pumilio, similar to results found previously for several other species around the globe. In the coming decades, many forests globally will be exposed to more frequent and/or severe episodes of reduced warm-season soil moisture. Tree-ring studies such as this one can aid prediction of future changes in forest productivity, mortality, and composition.