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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]

Given the steady decline in the genetic health of tree species populations as adaptation is being outpaced by the speed of human-induced climate change, forest management measures are urgently required. In this context, human translocation of pre-adapted genotypes from source populations whose current climatic conditions are closer to those that recipient populations will experience in the future, the so-called Assisted Gene Flow (AGF), has the potential to reduce the risk of maladaptation and to make more resilient communities. Here, we introduce a metric we call the Mean Offset Ratio (MOR), which is a population pre-adaption measurement useful for AGF as it aims to increase adaptive genetic variation and decrease the risk in maladaptation of recipient populations. We applied MOR to the iconic South American conifer Araucaria araucana and found that populations having the highest risk of maladaptation in the southern Andean piedmonts could benefit from the introduction of genotypes coming from the northern higher elevation Andean populations, which are at the lowest risk of maladaptation. For one metapopulation (Coastal), no translocation possibilities were observed, both as donor and recipient populations. Despite some limitations, we assert that MOR is a useful tool for AGF purposes and could be applied to other tree species. This is the first study to use a genomic approach to inform adaptive forest management actions such as AGF in a long-lived and endangered South American conifer in the face of ongoing climate change. • We proposed a genome offset-based metric (Mean Offset Ratio, MOR) to search for pre-adapted populations to future environmental conditions (RCP 4.5, year 2070) to support assisted gene flow (AGF) in trees, and then we applied it to Araucaria araucana. • Results suggest that AGF is partially possible to implement for Andes Mountain range metapopulation. Maps of pre-adapted populations and AGF-based translocations are presented. • For Coastal metapopulation, AGF would not be possible to implement due to the lack of both donor and recipient populations. • Spatial and climate complexity of local adaptation and evolutionary responses to environmental changes could be better understood and modeled harnessing landscape genomic tools. However, field trials to validate these predictions are needed. [ABSTRACT FROM AUTHOR]

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]

Abstract: It has been predicted that subalpine forests will be negatively affected by global warming; however, direct responses to experimental warming have been scarcely examined in these systems. In this study we evaluated the effects of higher temperatures with and without water addition on the survival and growth of recently emerged (small) and large seedlings of the widely distributed species Nothofagus pumilio in subalpine forests of the southern Chilean Andes. We also examined the variations in seedling traits related to carbon balance in order to infer the causal mechanisms of survival and growth responses. Treatments of open top chambers (OTCs) were combined with watering in two locations with differing climates: Antillanca (40°S, humid) and Cerro Castillo (46°S, drier). OTCs increased mean and maximum air temperatures by 0.6°C and 2–3°C, respectively, and decreased soil humidity by 56% in Antillanca and 30% in Cerro Castillo, fulfilling methodological expectations and climate model predictions. After two complete growing seasons, the survival, relative growth rate (RGR), biomass, and a suite of seedling traits were measured and analyzed using mixed-effects models. Warming and warming in combination with watering significantly increased large seedling survival in Cerro Castillo. In Antillanca, warmer conditions increased the height, biomass, and leaf area of small seedlings, and the RGR of large seedlings. In this location, warming also caused lower leaf carbon isotopic composition in both age classes and higher specific leaf area in small seedlings, suggesting whole-plant carbon gain improvements; warming did not produce any drought effects. Our results indicate that warming produces positive effects on the seedling establishment of N. pumilio in the southern Andes, highlighting the importance of site-specific effects in response to climate change in widespread species. Site-specific effects can most likely explain the discrepancies between the results of this study and the predictions outlined by previous studies for these forests. [Copyright &y& Elsevier]

• We predict climate change-related genetic offset for Araucaria araucana. • According genomic-environmental association of 18,988 unlinked SNPs, 896 were detected as putatively adaptive. • Temperature annual range as most important selective force driving adaptive divergence. • Piedmonts in Southern Andes Mountain range were identified as areas of higher genetic offset. Understanding adaptive genetic variation is key for predicting the evolutionary response of species and populations to climate change, decisively influencing management and conservation decisions. Landscape genomics provides a framework to disentangle the effects of local adaptation from those of geographic distance and demographic history, through genomic analysis and the modeling of genotype-environment relationships. This approach can inform how evolutionary forces shape the neutral and adaptive genetic structure, helping to identify those populations subject to a greater risk of maladaptation due to anthropogenic climate change, i.e., the "genetic offset". Using restriction-site associated DNA sequencing (RAD-Seq) and more than 49,000 single nucleotide polymorphisms screened from 12 locations of Araucaria araucana in Chile, we assessed the genetic structure and predicted the genetic offset of this emblematic tree species under two future climate scenarios. Using generalized dissimilarity modeling (GDM) we found that the temperature annual range was the most important variable shaping the observed patterns of adaptive divergence. Our results show that populations living in the piedmont of the southern Andes Mountain range are at the greatest risk of maladaptation, while populations living in the high elevation zones in the Andes Mountain range are at the lowest risk. This study constitutes an important tool for forestry management and conservation of A. araucana forests. [ABSTRACT FROM AUTHOR]

We developed multiple a priori hypotheses to link the observed spatial patterns with colonisation processes in the high alpine cushion plant, Azorella madreporica. We conducted this study in the Molina River basin (33°20′ S, 70°16′ W, 3600 m a.s.l.), in the Andes of central Chile, approximately 50 km east of Santiago. We mapped and measured size (as a surrogate for age) of individual cushions in two populations and used a standard spatial analytical tool (semivariograms) to test our alternative a priori hypotheses related to colonisation mode of the cushion species. In both populations, the size distribution of A. madreporica reflected a negative exponential or inverse-J pattern, typical of uneven-aged populations, where most of the cushions belonged to relatively smaller size classes, in effect, a regular success in the establishment of seedlings, where all size classes of cushions were represented in the population. The results were site-specific, where best-fit semivariograms for spatial cushion's size distribution suggested a gradual colonisation in one population and an episodic colonisation in the other population. Microsite distribution proved to be homogeneous at both sites. Thus, the study of the spatial explicit size-age population distribution of an alpine species provides valuable information about the frequency, magnitude and site variation of the reproductive pulses in these harsh environments. [ABSTRACT FROM AUTHOR]

Aim The general model for Nothofagus regeneration dynamics states that the species of this genus tend to occur in frequent, coarse-scale disturbance sites and/or in harsh conditions. The aim of this study is to test this regeneration model in deciduous mediterranean Nothofagus glauca forests at the northern limit of range of this genus, which include some of the most diverse but least well understood forests in the region. The study also aimed to advance general understanding of the ecological role of N. glauca in these forests, and its response to disturbance, by examining the composition, structure and regeneration patterns of N. glauca forests in the mediterranean zone following three different disturbance histories: mature, post-logging, and post-landslide second growth. Location The study was conducted at the southern limit of the mediterranean climatic zone, in the foothills of the Andes (36°35′ S, 71°28′ W) in south-central Chile, near the south limit of range of N. glauca. Study sites were located at a range of altitudes between 660 and 850 m a.s.l. Methods Two fully mapped 0.12–0.14-ha plots were located at each of three sites in order to sample age, composition, structure, canopy density and spatial patterns of the stands. The spatial description of sites was estimated with point-pattern analysis using Ripley's L-function (univariate and bivariate versions). Shannon's index was used to account for stand structural diversity by height class. Leaf area index (LAI) and canopy density were assessed with fisheye digital photos. Results Nothofagus glauca was the dominant canopy tree species at all sites. In the mature site there was abundant regeneration of N. glauca saplings, leading to a complex open canopy and an all-aged structure with a total basal area (BA) of 21–33 m2 ha−1 (including all tree species), despite the presence of shade-tolerant tree species and the bamboo Chusquea cumingii. The canopy was complex (Shannon's index up to 1.7), but was relatively open (16%). There was no evidence of a shift in regeneration from shade-intolerant Nothofagus species towards more shade-tolerant species. In the post-logging secondary growth stand an evenly aged structure prevailed, with patchy, more open canopies (15–21%, total BA = 9–38 m2 ha−1), but with a less diverse canopy structure. The last site, located in the debris fan of a landslide, presented the lowest LAI and highest canopy opening (23–30%) where the site occupancy is not yet complete (total BA = 14–23 m2 ha−1). At the harshest sites, saplings had a positive spatial association with adult trees, which suggests facilitation from adult trees to saplings. Main conclusions Our study supports the general model for Nothofagus regeneration dynamics, except that N. glauca does not attain sufficient canopy density to require disturbance for regeneration, even in the best sites. Nothofagus glauca can be both a pioneer in harsh site conditions, as well as a gap strategist in mature forests. In these generally harsh sites, the most species, the densest canopies and the most diverse structures occur in the oldest forests. Low canopy density allowed for diverse understorey species at all sites. [ABSTRACT FROM AUTHOR]