• Energy Research

Tree-ring chronologies are widely used to reconstruct high-to low-frequency variations in growing season temperatures over centuries to millennia. The relevance of these timeseries in large-scale climate reconstructions is often determined by the strength of their correlation against instrumental temperature data. However, this single criterion ignores several important quantitative and qualitative characteristics of tree-ring chronologies. Those characteristics are (i) data homogeneity, (ii) sample replication, (iii) growth coherence, (iv) chronology development, and (v) climate signal including the correlation with instrumental data. Based on these 5 characteristics, a reconstruction-scoring scheme is proposed and applied to 39 published, millennial-length temperature reconstructions from Asia, Europe, North America, and the Southern Hemisphere. Results reveal no reconstruction scores highest in every category and each has their own strengths and weaknesses. Reconstructions that perform better overall include N-Scan and Finland from Europe, E-Canada from North America, Yamal and Dzhelo from Asia. Reconstructions performing less well include W-Himalaya and Karakorum from Asia, Tatra and S-Finland from Europe, and Great Basin from North America. By providing a comprehensive set of criteria to evaluate tree-ring chronologies we hope to improve the development of large-scale temperature reconstructions spanning the past millennium. All reconstructions and their corresponding scores are provided at www.blogs.uni-mainz.de/fb09climatology.

Abstract Predicted warmer temperatures and more frequent extreme climatic events in the southern Andes will affect the dynamics of the Patagonian forests. These environmental changes may differentially alter the probability of Nothofagus pumilio establishment across its altitudinal range of distribution. We monitored fruit rain, seedling emergence and survival at the lower and upper elevation boundaries of N. pumilio forests in Santa Cruz (49° 22'S − 72º 56' W), Argentina. From 2012 to 2018, recruitment and mortality were evaluated biannually in the field. Seedling establishment was tested in relation to drought, based on the SPEI (Standardized Precipitation Evapotranspiration Index), and changes in elevation. Fruit rain was consistently higher at low elevation and the abundance of fruits was not affected by drought intensity. Seedling emergence was ~ 11 to 19 times larger at the upper forest boundary, in particular during years characterized by warm-dry climatic conditions in spring-early summer. In contrast, seedling abundance was ~ 3 times larger at low elevations during relatively cold-wet growing seasons. Over the period 2012 to 2018, dominated by dry-warm spring and summers, survival probability curves for seedlings and juvenile trees were higher at upper than lower elevations. Our results show contrasting effects of climate on tree establishment at the elevation limits, with positive and negative drought effects at high and low elevations, respectively. Predicted increase of extreme drought events during the XXI century could be detrimental for N. pumilio establishment at dry, low-elevation forests.

AbstractTree ring δ18O chronologies from two native species (Fitzroya cupressoides and Nothofagus pumilio) in northern Patagonia were developed to assess their potential for paleoclimate reconstructions. The five annually resolved cellulose δ18O chronologies (two for F. cupressoides and three for N. pumilio) are located on the Andes along the steep west‐to‐east precipitation gradient. Over the common 60 years long interval, the five site‐δ18Ocell chronologies exhibit a strong common signal as indicated by the significant mean intercorrelation (r = 0.61, p < 0.05) and the high percentage (65%) of total variance explained by the first empirical orthogonal function. Although correlation analyses reveal that the two mean species‐δ18Ocell chronologies are mainly modulated by December–May temperature, the N. pumilio chronology shows a greater sensitivity to record temperature variations (r = 0.57, p < 0.05). The δ18Ocell of N. pumilio contains a regional temperature signal representative of a large area in southern South America under the influence of the Southern Annular Mode. This study indicates that δ18Ocell in N. pumilio is a promising proxy to reconstruct past variations in temperature in South America south of 38°S.

Context: Tropical forest ecosystems play a critical role in the functioning of the Earth; thus, a better understanding of the influences of climate on tree growth is needed to estimate changes in forest productivity and consequently in carbon sink variations at regional and global scales.Aims: In the context of global environmental changes, our study aimed at using the growth rings of A. tomentosum Mart. to establish the relationships between radial growth and climatic variations.Methods: The anatomical characterization of the wood elements facilitated the precise annual band delimitation and the rejection of samples with false rings and growth anomalies. A tree-ring chronology was developed using traditional dendrochronological methods and the relationships with climate determined using correlation functions.Results: The chronology is based on 20 individuals and covers the period 1843–2015. Tree-ring statistics indicate an important common signal in growth variations between trees (R-bar = 0.31, EPS = 0.90). Interannual variations in A. tomentosum Mart. are directly related to total annual precipitation (r = 0.76) and inversely to mean annual temperature (r = − 0.44). These relationships are similar to those documented for other commercial species (Centrolobium microchaete, Schinopsis brasiliensis) from tropical dry forests in South America, suggesting a consistent climatic influence on tree growth at a regional scale.Conclusion: The strong dependence of tree growth on climate variability is a major concern, as climate change scenarios for tropical dry forests in South America predict an increase in the frequency and intensity of droughts, which in turn would reduce the A. tomentosum Mart. growth during the twenty-first century

Abstract. Despite the great number and variety of glaciers in southern South America, in situ glacier mass balance records are extremely scarce and glacier–climate relationships are still poorly understood in this region. Here we use the longest (> 35 years) and most complete in situ mass balance record, available for glaciar Echaurren Norte in the Andes at ~34° S, to develop a minimal glacier surface mass balance model that relies on nearby monthly precipitation and air temperature data as forcing. This basic model is able to explain 78 % of the variance in the annual glacier mass balance record over the 1978–2013 calibration period. An attribution assessment indicates that precipitation variability constitutes the most important forcing modulating annual glacier mass balances at this site. A regionally-averaged series of mean annual streamflow records from both sides of the Andes is then used to estimate, through simple linear regression, this glacier's annual mass balance variations since 1909. The reconstruction model captures 68 % of the observed glacier mass balance variability and shows three periods of sustained positive mass balances embedded in an overall negative trend totaling almost −42 m w.eq. over the past 105 years. The three periods of sustained positive mass balances (centered in the 1920s–1930s, in the 1980s and in the first decade of the 21st century) coincide with several documented glacier advances in this region. Similar trends observed in other shorter glacier mass balance series suggest the glaciar Echaurren Norte reconstruction is representative of larger-scale conditions and could be useful for more detailed glaciological, hydrological and climatological assessments in this portion of the Andes.

Les événements climatiques extrêmes, tels que les gelées tardives au printemps pendant le rinçage des feuilles, ont des impacts considérables sur la croissance radiale des feuillus tempérés. Bien que toutes les espèces de feuillus soient potentiellement vulnérables, les dommages dépendent des particularités du climat local, de l'espèce et de sa phénologie. L'impact des gelées de fin de printemps a été largement étudié dans l'hémisphère Nord, mais l'incidence potentielle dans les espèces d'arbres de l'hémisphère Sud est encore mal connue. Ici, nous reconstruisons l'occurrence du gel printanier dans 30 peuplements de l'arbre à feuilles caduques Nothofagus pumilio dans son aire de répartition septentrionale dans les Andes patagoniennes. Nous avons identifié des réductions de la largeur des cernes des arbres au niveau du peuplement non associées à des épisodes de sécheresse régionaux ou locaux, correspondant à des températures printanières minimales inhabituelles pendant le dépliage des feuilles. Plusieurs gelées printanières ont été identifiées le long de la distribution septentrionale de N. pumilio, étant plus fréquentes dans les forêts argentines plus continentales. Le gel printanier en 1980 avait la plus grande étendue spatiale. Les gelées printanières de 1980 et 1992 ont également provoqué des dommages dans les vergers régionaux. Les dommages causés par le gel printanier ont été associés à (i) une période de températures anormalement chaudes au début du dépliage des feuilles, suivie (ii) de températures glaciales. Cette étude nous aide à mieux comprendre les contraintes climatiques qui pourraient déterminer la croissance et la dynamique futures des forêts de feuillus andines et l'utilisation potentielle des cernes d'arbres comme archives des événements extrêmes des gelées printanières dans le nord de la Patagonie. Los eventos climáticos extremos, como las heladas tardías en primavera durante el lavado de hojas, tienen un impacto considerable en el crecimiento radial de los árboles de hoja ancha templados. Aunque todas las especies de hoja ancha son potencialmente vulnerables, el daño depende de las particularidades del clima local, la especie y su fenología. El impacto de las heladas de finales de la primavera ha sido ampliamente investigado en el hemisferio norte, pero la incidencia potencial en las especies de árboles del hemisferio sur aún es poco conocida. Aquí, reconstruimos la ocurrencia de heladas primaverales en 30 rodales del árbol caducifolio Nothofagus pumilio en su rango de distribución norte en los Andes patagónicos. Identificamos reducciones del ancho de los anillos de los árboles a nivel del rodal no asociadas con eventos de sequía regionales o locales, que coinciden con temperaturas mínimas inusuales de primavera durante el despliegue de las hojas. Se identificaron varias heladas primaverales a lo largo de la distribución norte de N. pumilio, siendo más frecuentes en los bosques argentinos más continentales. Las heladas de primavera en 1980 tuvieron la mayor extensión espacial. Las heladas de primavera de 1980 y 1992 también provocaron daños en los huertos regionales. El daño por heladas primaverales se asoció con (i) un período de temperaturas inusualmente cálidas al comienzo del despliegue de la hoja, seguido de (ii) temperaturas de congelación. Este estudio ayuda a ampliar nuestra comprensión de las limitaciones climáticas que podrían determinar el crecimiento futuro y la dinámica de los bosques caducifolios andinos y el uso potencial de los anillos de árboles como archivos de eventos extremos de heladas primaverales en el norte de la Patagonia. Extreme climatic events, such as late frosts in spring during leaf flush, have considerable impacts on the radial growth of temperate broadleaf trees. Albeit, all broadleaved species are potentially vulnerable, damage depends on the particularities of the local climate, the species, and its phenology. The impact of late spring frosts has been widely investigated in the Northern Hemisphere, but the potential incidence in Southern Hemisphere tree species is still poorly known. Here, we reconstruct spring frost occurrence at 30 stands of the deciduous tree Nothofagus pumilio in its northern range of distribution in the Patagonian Andes. We identified tree ring-width reductions at stand level not associated with regional or local drought events, matching unusual minimum spring temperatures during leaf unfolding. Several spring frosts were identified along the northern distribution of N. pumilio, being more frequent in the more continental Argentinean forests. Spring frost in 1980 had the largest spatial extent. The spring frosts in 1980 and 1992 also induced damages in regional orchards. Spring frost damage was associated with (i) a period of unusually warm temperatures at the beginning of leaf unfolding, followed by (ii) freezing temperatures. This study helps expand our understanding of the climatic constraints that could determine the future growth and dynamics of Andean deciduous forests and the potential use of tree-rings as archives of extreme events of spring frosts in northern Patagonia. الأحداث المناخية المتطرفة، مثل الصقيع المتأخر في الربيع أثناء تدفق الأوراق، لها تأثيرات كبيرة على النمو الشعاعي لأشجار الأوراق العريضة المعتدلة. على الرغم من أن جميع الأنواع ذات الأوراق العريضة معرضة للخطر، إلا أن الضرر يعتمد على خصائص المناخ المحلي والأنواع والظواهر الخاصة بها. تم التحقيق على نطاق واسع في تأثير الصقيع في أواخر الربيع في نصف الكرة الشمالي، ولكن لا يزال الحدوث المحتمل في أنواع الأشجار في نصف الكرة الجنوبي غير معروف بشكل كافٍ. هنا، نعيد بناء حدوث الصقيع الربيعي في 30 منصة للشجرة المتساقطة Nothofagus pumilio في نطاق توزيعها الشمالي في جبال الأنديز الباتاغونية. حددنا انخفاضات في عرض حلقة الشجرة على مستوى الحامل لا ترتبط بأحداث الجفاف الإقليمية أو المحلية، مما يطابق الحد الأدنى غير العادي من درجات حرارة الربيع أثناء كشف الأوراق. تم تحديد العديد من الصقيع الربيعي على طول التوزيع الشمالي لـ N. pumilio، كونها أكثر تكرارًا في الغابات الأرجنتينية القارية. كان للصقيع الربيعي في عام 1980 أكبر امتداد مكاني. كما تسبب الصقيع الربيعي في عامي 1980 و 1992 في أضرار في البساتين الإقليمية. ارتبط تلف الصقيع الربيعي بـ (1) فترة من درجات الحرارة الدافئة بشكل غير عادي في بداية ظهور الأوراق، تليها (2) درجات الحرارة المتجمدة. تساعد هذه الدراسة على توسيع فهمنا للقيود المناخية التي يمكن أن تحدد النمو والديناميكيات المستقبلية لغابات الأنديز المتساقطة والاستخدام المحتمل لحلقات الأشجار كأرشيف للأحداث المتطرفة لصقيع الربيع في شمال باتاغونيا.