Local Chronologies Research Articles

Dendrochronology and extreme climate signals recorded in seven Icelandic shrubs: A multi-species approach in the sub-Arctic

Iceland, located in the climatologically sensitive subarctic zone, is one of the key areas for studying climate change and the current Arctic warming. Poor and rich heathland covers approximately 30% of Iceland, with heath vegetation being the area’s most important vegetation type. Prostrate and erect dwarf shrub and shrub species are the primary sources of dendrochronological information on the changes and characteristics of Iceland’s climate. Here, we investigate the dendrochronological potential of seven common Icelandic heathland species (Dryas octopetala, Calluna vulgaris, Salix arctica, Salix herbacea, Empetrum nigrum, Juniperus communis nana, and Betula nana) and explore the impact of climate conditions on their growth, particularly with regard to extreme meteorological events. We conducted comparative analyses among species and observed their climatic responses in a climatically, morphologically, and geologically homogeneous setting in north-eastern Iceland. After sampling, measurements, and cross-dating, we constructed local chronologies for the seven species. Of approximately 200 samples, only 113 were included in the final shrub chronologies. All chronologies covered at least 50 years, with few of them exceeding 100 years. Dendroclimatological analysis indicated that above-average temperatures in June and summer positively influence the growth of D. octopetala (June–September), J. communis (July–August), B. nana (July–August), C. vulgaris (June–August), and S. arctica (August–September). The opposite is observed for S. herbacea and E. nigrum. Climate–growth correlations indicate that the growth of these species is negatively correlated with temperature and positively correlated with winter and summer precipitation. Furthermore, among the long-lived woody species growing in Iceland, seven common species were used to assess the impact of extreme meteorological conditions on their growth. The most pronounced extreme year in the wood anatomy of Icelandic shrubs was 1979, depicted as very narrow or missing rings and as the blue ring in J. communis.

Dendrochronological Analysis of One-Seeded and Intermediate Hawthorn Response to Climate in Poland

Although the hawthorn is not a forest-forming species, and it has no high economic significance, it is a very valuable component of forests, mid-field woodlots or roadside avenues. The literature, however, lacks information on the growth rate, growth phases, or growth–climate–habitat relationship for trees of this genus. This work aimed to establish the rate of growth of Craraegus monogyna and C. xmedia Bechst growing in various parts of Poland, in various habitats; analyze the growth–climate relationship; and distinguish dendrochronological regions for these species. Samples were taken using a Pressler borer from nine populations growing in different parts of Poland, from a total of 192 trees (359 samples). The tree-ring width was measured down to 0.01 mm. The average tree-ring width in the studied hawthorn populations ranged from 1.42 to 3.25 mm/year. Using well-established cross-dating methods, nine local chronologies were compiled with tree ages between 45 and 72 years. Dendroclimatic analyses (pointer year analysis, correlation and response function analysis) were performed for a 33-year period from 1988 to 2020, for which all local chronologies displayed EPS > 0.85. The tree-ring width in the hawthorn populations depended mostly on temperature and rainfall through the May–August period. High rainfall and the lack of heat waves through these months cause an increase in cambial activity and the formation of wide tree rings. Conversely, rainfall shortages through this period, in conjunction with high air temperatures, caused growth depressions. Cluster analysis enabled the identification of two dendrochronological regions among the hawthorn in Poland: a western and eastern region, and a single site (CI), whose separation was most likely caused by contrasting habitat and genetic conditions. The obtained results highlight the need for further study of these species in Poland and other countries.

Dendrochronology and dendroclimatology of yew in Poland

This study concerns dendrochronology and dendroclimatology of yew growing in Poland. The yew (Taxus baccata L.), a long-lived, slow-growing tree, is regarded as a species threatened with extinction. The eastern boundary of its range transects Poland. The analyses were performed on 34 yew populations which are protected as parts of nature reserves, as nature monuments, or which are planned to be protected. Samples were collected using Pressler borer from a total of 774 trees yielding 1307 profiles. Classical dating techniques (including cross-dating method) were subsequently used to reconstruct 34 local chronologies. Average tree-ring width was 0.84 mm and ranged from 0.27 to 1.47 mm. For most stands, the age of the yew trees is overestimated. The studied populations most frequently are 100–200 years old, and the oldest yew trees in Poland are growing in the KS population (age estimated at 500–600 years). Average tree-ring width was found to be strongly dependent on the chronology length/tree age. The 674 pointer years calculated for the local chronologies served as a basis for determining pointer years for the entire study area. Negative years include: 1862, 1865, 1917, 1927, 1940, 1947, 1956, 1963, 1969, 1976, 1979, 1993, 1996, and 2003. Positive years are: 1884, 1914, 1916, 1965, 1977, 1988, 1997, and 2007. Analysis of weather conditions in those years demonstrated a strong relationship between tree-ring width and air temperature in winter, pre-spring, and early spring. Higher-than-average temperatures during those seasons correlate positively with yew tree-ring width. Response function analysis performed for local and regional chronologies point to a dominant role of air temperature in December of the year preceding growth and in January, February, and March of the current year (linear relationships). June precipitation is an additional factor affecting tree-ring width in some areas of northern and northwestern Poland: the higher the precipitation, the wider the tree-rings. The results obtained, particularly those concerning growth-climate relationships and dendroclimatic regionalisation, can be used in the on-going programme of yew restitution in Poland.

Inscrevendo a história do Novo Mundo na história universal: Cronologias coloniais e conhecimento astral na América Hispânica do final do século XVII

Abstract In this article, we study historical and astronomical works published between 1680 and 1690 by Diego Andrés Rocha, oidor of the Royal Audience of Lima, and the Creole intellectual Carlos de Sigüenza y Góngora, viceregal cosmographer of New Spain. We contend that for these Spanish American colonial authors, history writing and the knowledge of celestial phenomena were inextricably linked within a shared epistemic framework. Astronomy and astrology provided them with a foundation for reasoning, judging the weight of disparate evidence, and establishing the legitimacy of competing claims related to the chronology of the New World, especially regarding theories about the ancient origins of the Indians. We show how the mobilization of astral knowledge in the establishment of local chronologies offered an answer to politically charged questions about the place of the Americas in the universal history of empire and Christian redemption, as well as the authors’ own place in their respective colonial societies.

Climate signal strength in tree-ring width of spruce growing in the Solovetsky Islands (Russia)

In this study we used 14 spruce tree-ring width local chronologies from sites that are located in different landscape conditions. The climatic response function for the entire period (116 years) shows that all local chronologies without exception have a positive relationship with June temperature (from 0.196 to 0.408) despite quite different local environmental conditions. This finding allowed us to combine all tree-ring width local chronologies into a composite spruce chronology covering the period of 1676–2016 CE with EPS exceeding the 0.85 threshold. The composite chronology was scaled against June air temperatures (CRU TS 4.01) in order to reconstruct it. Monthly air temperature records from the Arkhangelsk weather station were used as an additional source to validate tree-ring based June temperature reconstruction. It is quite remarkable that our reconstruction matches the Archangelsk records not only in the 20th-early 21st centuries but also in the 19th century, confirming the reliability of the reconstruction over more than two centuries. We also used daily records from the nearest Kem’-Port station to identify a more precise target-window. Current research shows that the spruce response to daily temperature is not limited by June, but also extends up to almost half of July. The warmest reconstructed year occurred in 1856 as confirmed by the data published in the local chronicle. The cooling recorded in the historical evidences (describing extremely severe ice conditions in the Arctic seas during the Great Northern Expedition (1733–1743)) was not corroborated by our reconstruction. In the study, we discuss the reasons of the discrepancies found between Solovki June temperature reconstructions and other data such as different seasonality of the compared records, real local climate warming in Solovki, the applied standardization technique, and low of chronologies’ replication. The most reliable part of the reconstruction part lasting from the early 19th to the early 21st centuries is also discussed in terms of its properties like wavelength analyses, and the assessment of influence of volcanic eruptions.

Dendroclimatic analysis and cartographic modeling of the climatic response of Fagus sylvatica during growth in a sector of the central Cantabrian Mountains

The wide distribution of the common beech (Fagus sylvatica) in Europe reveals its great adaptation to diverse conditions of temperature and humidity. This interesting aspect explains the context of the main objective of this work: to carry out a dendroclimatic analysis of the species Fagus sylvatica in the Polaciones valley (Cantabria), an area of transition with environmental conditions from a characteristic Atlantic type to more Mediterranean, at the southern limit of its growth. The methodology developed is based on the analysis of 25 local chronologies of growth rings sampled at different altitudes along the valley, generating a reference chronology for the study area. Subsequently, the patterns of growth and response to climatic variations are estimated through the response and correlation function, and the most significant monthly variables in the annual growth of the species are obtained. Finally, these are introduced into a Geographic Information System (GIS) where they are cartographically modeled in the altitudinal gradient through multivariate analysis, taking into account the different geographic and topographic variables that influence the zonal variability of the species response. The results of the analyses and cartographic models show which variables are most determinant in the annual growth of the species and the distribution of its climatic response according to the variables considered.

Discovering the Unknown History of the Utilization of Pinus heldreichii in Wooden Structures by Means of Dendroarchaeology: A Case Study from Metsovo (Northern Greece)

(1) Background: Pinus heldreichii is a long-living tree subalpine species commonly used for climate reconstruction. Nevertheless, its potential for dendroarchaeology and dating of historical timber remains unknown. In Metsovo and in the surrounding area of Pindus National Park (Northern Greece) it is commonly used for the construction of buildings and wooden objects and artifacts. (2) Methods: We examined timber found in historical buildings within the study area and we tried to date it using local reference chronologies of Bosnian and Black pines. (3) Results: Bosnian pine chronologies can be used to date timber from historical buildings, while they can also be used as reference chronologies against Black pines, giving very high cross-dating values. Therefore, and since the macroscopic identification of the two species’ timber is impossible, the analysis of wood anatomy is necessary to distinguish the two species in the case of historical wood. (4) Conclusions: The current paper presents the first application of dendroarchaeology for Bosnian pine and highlights the potential of the species in studying cultural heritage and the human past.

Differences in Growth–Climate Relationships among Scots Pines Growing on Various Dune Generations on the Southern Baltic Coast

This study focuses on analyzing the growth rate and growth–climate relationship in Scots pine (Pinus sylvestris L.) growing on coastal dunes of different ages on the Southern Baltic coast. Podzols have developed on these dunes. Depending on dune age, however, podzols are characterized by a different degree of development and richness, which represents the main factor differentiating the studied habitats: the oldest brown dunes (BD), younger yellow dunes (YD), and the youngest white dunes (WD). Samples were taken from 68 trees using Pressler borers. Using classic cross-dating methods, local chronologies were compiled that served as the basis for further analyses. Basic analyses of soil properties were also performed. Trees growing on brown dunes display the widest tree-rings and the highest rate of cumulative radial growth. Both rates are the lowest for trees growing on white dunes (WD). The dominant meteorological factor shaping tree-ring widths is late winter/early spring air temperature (February/March). However, in poorer habitats with inferior soil air–water conditions, rainfall sums and rainfall distribution through the year become progressively more significant factors. On white dunes (WD), the strongest growth–climate correlations are obtained for summer precipitation. These results identify habitat richness as the main factor shaping growth dynamics in Scots pines growing on dunes. Due to the protective function of the studied tree stands (coast protection), and in light of the rising sea levels and increasing storm intensities, further studies are required, aiming at understanding all interrelationships occurring in these valuable ecosystems.

Degree of connectivity in reconstructed precipitation dynamics and extremes for semiarid regions across South Siberia

Tree rings from forest-steppes of temperate continental Asia are useful proxies for the moisture regime reconstructions, encompassing environmental variations such as warming climate, changing frequency and intensity of droughts. Heterogeneity of precipitation leaves open the question of the probability of spatially large-scale droughts in this macro-region. Theoretically, such events could be driven by global tele-connections and/or common astronomic cycles. We have attempted the precipitation reconstructions of two distant (~1000 km) intermountain valleys in South Siberia, based on the tree ring width of Pinus sylvestris L. To enhance the quality of the precipitation reconstruction models, networks of existing tree-ring data were expanded and daily precision of instrumental precipitation series was implemented for calibration. Within-region (150–200 km) common signal between local chronologies r = 0.37–0.90 (p < 0.05) allowed obtaining regional ones, registering precipitation up to annual temporal scale. High correlations of both regional chronologies with annual precipitation were found for period from previous July 22 to current July 21 (r = 0.71–0.72). These precipitation series were further reconstructed. Reconstruction models explaining 50–52% of variation were developed for the years 1753–2015 and 1798–2015. Although both valleys do not record many concurrent extreme precipitation events, some common and opposite extremes have been revealed. For both regions, an 11-year and 26–29-year cycles were commonly observed. These were probably associated with the solar activity and Pacific Decadal Oscillation (PDO). However, phase shifts of these cycles were recorded between the regions and with PDO. Stronger impact of oceanic air masses was observed in the eastern one of the two considered territories. Whereas higher significance of frequencies associated with astronomic cycles (solar and lunar-nodal) was found in the western one. Data availabilityTemperature and precipitation series of climatic stations were obtained from the website of All-Russia Research Institute of Hydrometeorological Information, World Data Centre (RIHMI-WDC, http://meteo.ru/data). Other climatic time series and solar activity series were obtained from the website of The Royal Netherlands Meteorological Institute (KNMI) Climate Explorer (https://climexp.knmi.nl). Used in the study tree-ring width measurements will be submitted to the International Tree-Ring Data Bank (ITRDB; https://www.ncei.noaa.gov/products/paleoclimatology/tree-ring) upon publication of the manuscript and with reference to it.

Climate Response in Tree-Rings of Sawara Cypress [Chamaecyparis pisifera (Siebold &amp; Zucc.) Endl.] in Poland

Sawara cypress [Chamaecyparis pisifera (Siebold &amp; Zucc.) Endl.] is originally from Japan. It was introduced to Europe in the latter half of the 19th century (in England and Holland in 1861, and in Poland in 1864). The aim of this study was to examine the influence of climatic conditions on tree-ring width among Sawara cypress populations growing in Poland. Additionally, other indicators determining the growth-climate relationship for the studied tree species were investigated such as false rings, missing rings, or frost rings. Five stands of Sawara cypress from northwestern and central Poland were selected for study. Samples were taken from 97 trees, using Pressler borers at breast-height. Tree-ring widths were measured down to 0.01 mm. Climatic data came from weather stations located the nearest to the study plots. Tree-ring width in the studied populations of Sawara cypress varies (from 1.94 to 4.47 mm). The oldest Sawara cypresses grow in Glinna Arboretum and are nearly 130 years old. The youngest ones grow in Rogów Arboretum (67 years old) and Wirty Arboretum (58 years old). Ten regional pointer years, including six negative and four positive ones, were determined for local chronologies. Negative pointer years were associated with the occurrence of cold winters and water shortages in summer. Positive pointer years are mostly periods with a warm winter season, early and warm spring, and with high precipitation totals during summer months. Correlation and response function analysis corroborates the results yielded by pointer year analysis. False rings carry an additional information on pluvial conditions in the summer period, and frost rings are an aid in dating dendrochronological series and indicate the occurrence of both very cold winters and persistent ground frost occurrences in the spring period. In comparison to native conifers, the Sawara cypress can be regarded as a fast-growing species. The knowledge of acclimatization, growth rate, and growth-climate relationship may be useful, especially in the time of a rapidly changing climate, increasing human impact, and highly intensified invasion of insect and fungal species attacking native forest-forming taxa.

Medieval oak chronology from Klaipėda, Lithuania

Klaipėda is a town in western Lithuania on the Baltic Sea coast. Oak timber was actively used to construct buildings in this town until the 17th century. Archaeological investigations began in Klaipėda’s old town in 1979, but it has not been possible to use oak timbers for dating due to the lack of regional chronologies. The goal of this study was to fill this gap by developing a well-replicated oak chronology from timber collected in Klaipėda between 1979 and 1987. The resulting oak chronology from Klaipėda spans 306 years from 1247 to 1552 and includes 62 oak timber cross-sections. The study suggests that the timber was felled in the same local woodland, and that tree-ring widths series from Klaipėda are temperature-sensitive. The negative pointer years mostly coincide with negative anomalies of reconstructed April‒September temperature from elsewhere in Europe. The constructed chronology was compared with local chronologies (Vilquro, Smarhoń, Gdańsk) and with oak chronologies made from imported oak timber of southeast Baltic origin (Baltic 1–3, Dutch). We assessed whether it is possible to determine the origins of the Baltic 1, Baltic 3 and Dutch oak chronologies compiled from imported timber. Based on available chronologies, it could be hypothesised that Baltic 1 and Dutch chronologies are originated from western Lithuania and Baltic 3 from eastern Lithuania.

Droughts in the area of Poland in recent centuries in the light of multi-proxy data

Abstract. The history of drought occurrence in Poland in the last millennium is poorly known. To improve this knowledge we have conducted a comprehensive analysis using both proxy data (documentary and dendrochronological) and instrumental measurements of precipitation. The paper presents the main features of droughts in Poland in recent centuries, including their frequency of occurrence, coverage, duration, and intensity. The reconstructions of droughts based on all the mentioned sources of data covered the period 996–2015. Examples of megadroughts were also chosen using documentary evidence, and some of them were described. Various documentary sources have been used to identify droughts in the area of Poland in the period 1451–1800 and to estimate their intensity, spatial coverage, and duration. Twenty-two local chronologies of trees (pine, oak, and fir) from Poland were taken into account for detecting negative pointer years (exceptionally narrow rings). The delimitation of droughts based on instrumental data (eight long-term precipitation series) was conducted using two independent approaches (Standard Precipitation Index, SPI, calculated for 1-, 3-, and 24-month timescales, and a new method proposed by authors). For delimitation of droughts (dry months), the criteria used were those proposed by McKee et al. (1993) and modified for the climate conditions of Poland by Łabędzki (2007). More than 100 droughts were found in documentary sources in the period 1451–1800, including 17 megadroughts. A greater than average number of droughts were observed in the second halves of the 17th century and the 18th century in particular. Dendrochronological data confirmed this general tendency in the mentioned period. Analysis of SPI (including its lowest values, i.e. droughts) showed that the long-term frequency of droughts in Poland has been stable in the last two or three centuries. Extreme and severe droughts were most frequent in the coastal part of Poland and in Silesia. Most droughts had a duration of 2 months (about 60 %–70 %) or 3–4 months (10 %–20 %). Frequencies of droughts with a duration of 5-or-more months were lower than 10 %. The frequency of droughts of all categories in Poland in the instrumental period 1722–2015 was greatest in winter, while in the documentary evidence (1451–1800) droughts in this season are rarely mentioned. The occurrence of negative pointer years (a good proxy for droughts) was compared with droughts delimited based on documentary and instrumental data. A good correspondence was found between the timing of occurrence of droughts identified using all three kinds of data (sources).

ELM Dendrochronology

Elm is generally considered to be unsuitable for dendrochronology, usually having too few rings, or having abrupt growth-rate changes that do not result from the external weather conditions. Samples rarely match each other in the same structure. A further difficulty is that even where it is known that the sequence is complete (the bark is still present), it is often not possible to distinguish sapwood rings by their appearance, even under a microscope. This is a significant problem as elm has been an important structural component of many British vernacular buildings over many centuries, but whereas dendrochronological dating of oak has transformed our understanding of thousands of buildings, by 2015 only four instances of dating elm had been made, two of those involving a single timber. When elm has been encountered, it has generally been dismissed from further dendrochronological study as a result of these known issues, but no systematic study has been undertaken to see whether these prejudices are justified. In order to get some evidence-based information about how elm might behave dendrochronologically, Historic England initiated a study: Developing the dendrochronology of elm in historic buildings, Project 7350, funded through its Heritage Protection Commissions. This resulted in over 70 buildings being looked at, with several being sampled, and the results are discussed here. At some sites an elm site master sequence could be derived, but potential matches with local oak chronologies were generally not strong enough to be considered dated. In one instance good matches with local oak sites were found, but subsequent radiocarbon analysis found these matches to be erroneous. At another site, five trees gave an 89-year ring sequence, but no acceptable matches were found with oak chronologies. Radiocarbon dating and oxygen isotope dating both gave the same dating results at this site, however, showing that these two methods appear to give the best hope of dating elm in the future.

Spatial variation of pine tree-ring growth in the Solovetsky Islands

The paper presents the results of an analysis of the spatial variability of pine tree-ring growth in the Solovetsky Islands. As a result of the field work, tree-ring network containing 14 dendrochronological pine sites in various habitats were developed. For each site, a local tree-ring width pine chronology (from 472 to 271 years) is obtained, representing pine growth features in different habitat conditions. A comparison between chronologies revealed synchronious growth of pine in various habitats in the late 17th, in the first half of the 18th and the beginning of the 19th centuries. The use of cluster analysis allowed to identify several groups of chronologies with similar characteristics. So, trees growing on swamps, on a sandy substrate and in a green-moss pine forest or in a mixed forest are allocated in separate clusters. This clustering is also confirmed by the results of a dendroclimatic analysis of local chronologies. It turned out that the increase in the pine’s growth in the mixed forest and in the green-moss pine forest depends on the July air temperature variation. Inside this group, samples from pine forests have a common feature – a positive relationship of growth with the precipitation of September. The only site located on the sands showed a different climatic signal than the other chronologies, namely, the dependence on the temperature of August.

Análisis dendroclimático y modelización cartográfica de la respuesta climática de Fagus sylvatica en su crecimiento, en un sector de la montaña cantábrica central

La amplia distribución del haya común (Fagus sylvatica) en Europa revela su gran adaptación a diversas condiciones de temperatura y humedad. Este interesante aspecto permite explicar el contexto del objetivo principal del presente trabajo: realizar un análisis dendroclimático de la especie Fagus sylvatica en el valle de Polaciones (Cantabria), un área de transición entre un ambiente característico de tipo atlántico hacia las condiciones de otro más mediterráneo, en el límite meridional de su crecimiento. La metodología desarrollada parte del análisis de 25 cronologías locales de anillos de crecimiento muestreadas en diversas altitudes a lo largo del valle, generando a su vez, una cronología de referencia para el área de estudio. Posteriormente, se estiman los patrones de crecimiento y de respuesta a las variaciones climáticas a través de la función respuesta y de correlación y, se obtienen las variables mensuales más significativas en el crecimiento anual de la especie. Finalmente, estas se introducen en un Sistema de Información Geográfica (SIG) donde se modelizan cartográficamente en el gradiente altitudinal mediante análisis multivariante, teniendo en cuenta las diversas variables geográficas y topográficas que inciden en la variabilidad zonal de respuesta de la especie. Los resultados de los análisis y modelos cartográficos muestran que variables son más determinantes en el crecimiento anual de la especie y la distribución de la respuesta climática de ésta en función de las variables consideradas.

노거수 수령 추정을 위한 지역별 연륜연대기 구축 및 활용

노거수 수령 추정을 위한 지역별 연륜연대기 구축 및 활용

Dating of violins – The interpretation of dendrochronological reports

Abstract We dendrochronologically analyzed the bellies of 10 violins differing in age, origin, number and width of tree rings, state of preservation as well as fabrication. All the bellies were made of Norway spruce (Picea abies). The dating of each violin was given as a calendar year (end date), as is usual in dendrochronological reports. We demonstrate how to interpret such reports in terms of age, origin, producer and authenticity of the instrument. Six violins were made by a known violin maker in Slovenia, who provided reliable information on the source of wood as well as on details on the wood processing. The dendrochronologically determined end dates varied from 1988 to 2005 and hence deviated by 5–22 years from the documented date of tree felling in 2010 and by 10–27 years from the years of the instrument fabrication (2014–2015). This explains why the end year (i.e., the dating of a violin) should always be considered as terminus post quem. The violins had relatively few tree rings (51–72) but it was possible to date them with local tree-ring chronologies, showing that adequate reference chronologies are essential for successful dating. An end date of 1929 was determined for violin of unknown provenance (violin 7). This date was repeatedly confirmed by numerous local chronologies and by various tree-ring sequences of instruments. The most significant statistical parameters of dating, obtained with German local chronologies and instruments, supported the opinion of experts that this instrument was probably made in a German workshop. Another violin (violin 14), privately owned in Slovenia, was dated with very high statistical values using several chronologies from the wider region of the Bohemian Forest. Its possible origin and end date 1893 confirmed the opinion of organologists that the instrument may have been made by a German workshop in the 19th century, thus proving the label “Joseph Guarnerius fecit Cremonae anno 1721” being false. Violin 15, from a private owner in Paris, dated 1748 with chronologies from the northern Alps, is in agreement with the opinion of experts that it may have been made in Paris around 1750, while the label “STRADEVARIUS [sic] Filius Cremona” proved to be a fake. Violin 13, of unknown age and origin, remained undated, although the treble side of the belly contained a very high number of tree rings (193), which usually increases the likelihood for dendrochronological dating. Its undatability is ascribed to possible measuring errors due to extremely narrow rings and a dark opaque varnish. Even the application of various equipment and methods (lenses, stereo microscope, high-quality digital image analysis) did not help to exactly identify the tree rings. This case demonstrates one of the limitations of dendrochronology.

Spatial reconstruction of Scottish summer temperatures from tree rings

ABSTRACTA detailed understanding of past temporal patterns and spatial expression of temperature variations is important to place recent anthropogenic climate change into a longer term context. In order to fill the current gap in our understanding of northwest European temperature variability, point‐by‐point principal component regression was used to reconstruct a spatial field of 0.5° temperature grids across Scotland. A sequence of reconstructions utilizing several combinations of detrending and disturbance correction procedures, and a selection of tree‐ring parameters [including ring width (RW), maximum latewood density (MXD) and blue intensity (BI)] was used in an evaluation of reconstruction skill. The high resolution of the reconstructed field serves also as a diagnostic tool to spatially assess the temperature reconstruction potential of local chronologies. Best reconstruction results, reaching calibration r2 = 65.8% and verification r2 = 63.7% in central Scotland over the 1901–1976 period, were achieved using disturbance‐corrected and signal‐free detrended RW chronologies merged with BI data after low‐pass (high‐pass) filtering the RW (BI) chronologies. Calibration and verification r2 &gt; 50% was attained for central, north and east Scotland, &gt;40% in west and northwest, and &gt;30% in southern Scotland with verification of nearly all grids showing some reconstruction skill. However, the full calibration potential of reconstructions outside central Scotland was reduced either due to residual disturbance trends undetected by the disturbance correction procedure or due to other climatic or non‐climatic factors which may have adversely affected the strength of the climate signal.

Influence of climatic factors on tree growth in riparian forests in the humid and dry savannas of the Volta basin, Ghana

The paper demonstrates the prospects and applications of dendrochronology for understanding climate change effects on riparian forests in the savanna landscape. Riparian trees in savannas have a potential for dendro-climatic studies, but have been neglected hitherto. We examined ring-width series of Afzelia africana (evergreen) and Anogeissus leiocarpus (deciduous) to study the influence of climatic factors on the growth of riparian trees in the humid (HS) and dry (DS) savanna zones of the Volta basin in Ghana. A total of 31 stem discs belonging to A. africana and A. leiocarpus were selected from HS and DS to establish species-specific local chronologies of tree growth. Each individual of A. africana and A. leiocarpus from the two savanna sites showed distinct growth rings. Cross-dating of individual tree-ring patterns was successful using standard dendrochronological techniques. The mean annual growth rates of A. africana in the HS (1.38 ± 0.09) and DS (1.34 ± 0.08) were not statistically different. Furthermore, mean annual growth rate of A. leiocarpus in the DS (3.75 ± 0.27) was higher than in the HS (2.83 ± 0.16) suggesting that species in drier environment can have higher growth rates when sufficient soil moisture is available. The growth rates of both species at the same sites were different, which might indicate different water use strategies. High correlations of individual tree-ring series of A. africana and A. leiocarpus trees at HS and DS suggest a strong climatic forcing controlled by the seasonal movement of the inter-tropical convergence zone. The annual growth of A. africana and A. leiocarpus at both the HS and DS was significantly correlated with local temperature and precipitation. The negative correlations of the growth of the two tree species to global sea surface temperatures were however, indications that the growth of riparian forests can be impacted during El Nino-Southern Oscillation years. The result of our study shows that riparian trees in the humid and dry savanna zones of West Africa can be successfully used for dendrochronological studies.

Growth-climate relationships at yew and wild service trees on the eastern edge of their range in Europe

Aim of study: The aim of the study was the construction of regional chronologies for South-Western Poland for yew (Taxus baccata L.) and wild service tree (Sorbus torminalis L.), two of the rarest native tree species on the edge of their range in Europe. The relationships growth-climate and incremental dynamics at both these species were investigated as well.Area of study: The eastern borders of the ranges of yew and wild service trees run across Poland. The majority of the yew occurrence sites are situated in South Poland, within the area of uplands and mountains, whereas the wild service tree grows in the western part of the country. The study plots (5 for yew trees, 4 for wild service trees) were located in nature reserves in SW Poland.Material and Methods: The research materials were cores from 200 trees (115 yew trees and 85 wild service trees). The annual growth widths were measured, then, local chronologies were constructed using classic methods of dating. Regional chronologies were based on yew trees with the Student’test t &gt; 6.0, and wild service trees with t &gt; 5.9. The chronologies were subjected to the indexation and used for dendroclimatological analyses: pointer years, correlation and response function.Main results: The yew chronology, spanning 219 years (1790-2008), was established on the basis of 51 samples, the average width of annual growths amounted to 0.61 mm. The wild service tree chronology, representing the period 1841-2013 (173 years), was produced from 37 samples, the average width of annual growth amounted to 0.60 mm (from 0.27 up to 0.58 mm). Dendroclimatological analyses of the yew indicated thermal conditions of the winter months and beginning of spring (straight correlations) as the predominating factor affecting the annual growth widths. Summer drought was an additional factor limiting growth. For the wild service trees cool and humid summer months in the growing season favour the formation of wide growths.Research highlights: On account of strong dispersion and limited small populations of these two tree species, there are few dendrochronological studies available. Therefore, every piece of information on the ecology of the yew and wild service tree allows us to broaden our knowledge of these rare species enriching the biodiversity of the native tree flora.Keywords: tree-ring width; Taxus baccata L.; Sorbus torminalis L.; dendroclimatology; Poland.