Dendroclimatology

To understand the effect of climate on tree-ring features, such as width or density, tree-ring data have to be calibrated against instrumental records. The high degree of multicollinearity among monthly time series of climate data violates the assumption of independent predictor variables in ordinary least squares regression. Bootstrapped confidence intervals of parameter estimates via regression against the principle components of the predictor variables are a possible solution to that problem. Package bootRes for R implements a flexible interface for bootstrapped response and correlation function analysis and tackles some shortcomings of currently available software. Given the increasing popularity of the free R software for statistical analysis, bootRes should facilitate both using R as a computational environment among tree-ring scientists and implementing new approaches to dendroclimatic calibration.

The causes for the decline and collapse of the Roman Empire have long preoccupied historians, but until very recently, few Roman historians have paid any attention to the role of the most devastating and definitive cause: adverse climate change.  Tacitus blamed corruption and moral decadence; Christian historians attributed the decline to the wrath of God; Edward Gibbon pointed to barbarian invasions and Christianity; and modern historians have identified over 200 possible causes.  More startlingly, historians rarely mention one of the most significant environmental disasters in human history: the climate catastrophe of 536 CE. This event—triggered by massive volcanic eruptions that filled the sky with ash and reduced solar energy around the world—caused the Dark Age Cold Period, crop failures, famine, and plague. This incident, more than any other, ended any chance the Roman Empire had to reconstitute itself after the barbarian invasions of the fourth and fifth centuries.
While decadence and invasion certainly played a part in Rome’s decline, solar cycles, violent volcanic activity, and cooler climate-loving bacteria also played significant roles. Because both ancient and many modern historians rarely knew and barely understood these silent killers, they continued to blame the usual suspects. Who could fault them?  Nearly five centuries after the dawn of the Age of Science, however, scholars have no excuse for not re-examining mounting evidence. It is time to consider the data that scientific studies produce about the role of climate change in history and to revise the narrative that many historians continue to ignore. 
Evidence derived from new scientific methods—unavailable to previous historians—now reveals that environmental issues played a significant role in the rise and decline of the Roman Empire in both the West and the East. Adverse climatic change in Europe, North Africa, and even Southwest and Central Asia contributed not only to Rome's inability to feed its population (and the Western army by 444 CE), but also to the westward migrations of the Huns, the Goths, other Germanic peoples, and later the Arabs.  Finally, bacteria-carrying fleas on vermin that thrived under ideal climate conditions set off a time bomb that wiped out as much as half of the Mediterranean’s estimated 75 million population in the early sixth century.
In an age of rapid climate change and states in collapse or decline because of it, it is more important than ever to understand the mechanisms of environmental catastrophe on human society and its ability to adapt to it.  Modern failed states like Syria, Afghanistan, and Yemen offer bitter lessons of what happens when states are unable to understand the relationship between human societies and their natural environments. The Roman Empire offers one of the best examples of how environmental catastrophe served as a catalyst for disease and how these two forces together were catalysts for a failing state.  To better comprehend the tragedy of the current situation, it is useful to start by reviewing what historians have said over the centuries about the causes of the decline of Rome and climate change.

Dendrochronological principles were performed for determining the age of trees of “Moena Amarilla” Nectandra 45eticulate (Ruiz & Pav.) Mez. The anatomical structure was described of 10 sample trees to analyze tree rings and evaluated their dendroclimatology and dendroecology potential that could support forest management and silviculture in rainforest. Each sample was extracted at 1,3m. The COFECHA program was used to synchronize the growth rings; as well as Arstan and RESPO software, to calibrate tree ring widths with the weather. The tree rings were defined by the concentration of fibers with thick walls and vessels groups of large diameter. The mean age was 102 years to the year 2011 (94-123 years), with a density of 0,52 to 0,68 g / cm3. Anatomically is highlighted: diffuse-porous; vessels distributed diagonally, never lonely, accompanied by radial multiples; tangential diameter of 140-200 microns; 6-17 vessels / mm2; Rating intravascular 9-14 microns; plates of simple drilling, scalariform and combined; septate fibers with simple punctuation, restricted to radial walls; paratracheal axial parenchyma; uniseriate and multiseriate, 2-3 cells wide; oil and / or mucilage present. Periodic annual increment (PAI) accumulated was 43,10 cm and Mean Annual Increment (MAI) accumulated was 32.10 cm; Also the master growth curve by identifying the potential to be applied to forest management forests. The Pearson correlation was low for growth and climate variables: 0,2490 directly temperature, and -0,0348, indirect precipitation, being anthropogenic factors, timber percent, type of soil use and hydrological factor that could have affected the results.

Tree rings from the Alpine area have been widely used to reconstruct variations in summer temperature. In contrast, estimates of changes in the hydrological cycle are rather scarce. In order to detect altitudinal and species-specific patterns of growth responses to anomalous dry and wet conditions, a large network of 53 tree-ring width site chronologies along the Rhone valley (Valais, Switzerland) covering the 1751-2005 period was compiled and analyzed. A total of 1,605 measurement series from four conifer species-pine, larch, spruce, fir-were detrended to allow inter-annual to multi-decadal scale variability to be preserved. Site chronologies were combined to four altitudinal (colline: \800 m asl, sub-montane: 800-1,000 m asl, montane: 1,000-1,450 m asl, sub-alpine:[1,450 m asl) and species-specific mean time-series. These records were compared with temperature, precipitation, and drought (scPDSI) data. Among the altitudinal records, the colline chronologies showed highest correlation with June precipitation and scPDSI (0.5 and 0.7). Altitudinal effects, via control on climatic conditions, were superimposed upon species-specific characteristics in affecting tree growth and response to moisture variations. In particular, species-specific differences affected the significance level of drought response, with decreasing drought sensitivity towards higher elevations. Growth conditions were found to be optimal at *1,300 m asl, with precipitation/drought limiting tree growth below and temperature above. Common years of extreme drought and low growth for the colline sites occurred in 1921, 1944, 1976, 1992, and 1998. Our results demonstrate the potential of lower elevation conifers for reconstructing long-term changes in Alpine hydro-climate.

Recent work has linked historical crises, both regional and local, with palaeoclimatic estimates of global and hemispheric climate change. Such studies tend to underemphasize the spatiotemporal and socioeconomical disparity of human suffering and adaptive capacity as well as the complexities of past climate change. We focus herein on the effects in Scotland of a severely cold climate episode in the 1690s, associated with major tropical volcanic events including a large unidentified tropical eruption in 1695. A tree-ring based summer temperature reconstruction from the northern Cairngorms region identifies the 1690s as the coldest decade in Scotland for the last 750 years. Archival sources meanwhile reveal the 1690s as likely the worst era of crop failure, food shortage, and mortality ever documented in Scottish history. The connection appears simple-volcanic cooling triggered famine-but the drivers towards famine are far more complex. Although the unusual coldness of the 1690s was near-hemispheric in scale, it had a differential impact across northwestern Europe. Within Scotland, both lowlands and highlands experienced dire conditions, but distinct factors exacerbated the suffering in each region. We integrate historical and palaeoclimatic records to explore the influence of the volcanic cold pulse of the 1690s and its consequences in Scotland. We find that while cooling temperatures characterized the regional to larger-scale climate, vulnerability and response potential were diverse and shaped by local circumstances. The Scottish crisis of the 1690s, in the context of the kingdom's failing economy, influenced investors from all parts of society, including the nobility and entire communities, to fund the ill-fated expedition to colonize Darien in modern-day Panama. The climate crisis and the colony's collapse hindered Scotland's already sluggish economy, motivating unification with England soon after.

Maize agriculture is dependent on two primary environmental factors, precipitation and temperature. Throughout the Eastern Mesa Verde region, fluctuations of these factors dramatically influenced demographic shifts, land use patterns, and social and religious transformations of farming populations during several key points in prehistory. While many studies have looked at the influence climate
played in the depopulation of the northern Southwest after A.D. 1000, the role that climate played in the late Basketmaker III through the Pueblo I period remains unclear. This article demonstrates how fluctuations in precipitation patterns interlaced with micro- and macro- regional temperature fluctuations may have pushed and pulled human settlement and subsistence patterns across the region. Specifically, we infer that preferences for certain types of farmlands dictated whether a community used alluvial fan verses dryland farming practices, with the variable success of each type determined by shifting climate patterns.
We further investigate how dramatic responses to environmental stress, such as migration and massacres, may be the result of inherited social structures of land tenure and leadership, and that such responses persist in the Eastern Mesa Verde area throughout the Pueblo I period.

The first dendrochronological network of European beech (Fagus sylvatica L.) from eastern limit of its distribution was established covering the species’ altitudinal range (210–1160 m a.s.l.) and three eco-regions. Statistical analysis revealed spatial trends among the 14 chronologies, with increasing tree-ring variability and synchronicity towards the east, particularly expressed by rBAR (mean interseries correlation). By means of HCA (Hierarchical Cluster Analysis) and PCA (Principal Component Analysis), the chronologies were divided into three main groups: a Mountain, Plateau and Eastern class. These correspond to the Alpine South, Continental and Pannonian bioclimatological zones. Dendroclimatological analysis revealed a general climate response pattern, with summer temperatures, April–May precipitation and April–June drought being the main limiting factors in the study area. The intensity of the correlations increases towards the eastern distribution limits and decreases towards the upper treeline of European beech. Similarly, the length of the climate-sensitive period changes, with the precipitation window increasing from April in the Mountains region to March–May in the East region and the scPDSI (self-calibrated Palmer drought severity index) window increasing from April–June in the Mountains to the previous July to the current September in the East. The western and uppermost site shows signs of being limited by low July temperatures. This chronology network represents a sensitive monitoring instrument to quantify the impact and adaptability of European beech to actual and future climatic change.

Studies associated with climate change and variability are of great importance at both the global and local scale in the global climate crisis. In this study, change-point detection and trend analysis were carried out on mean, maximum, minimum air temperatures and total precipitation based on monthly, seasonal and annual scale in Bartın province located in the western Black Sea Region of Turkey. For this aim, 4-different homogenei-ty tests (von Neumann test, Pettitt test, Buishand range test and standard normal homogeneity test) for change-point detection, Modified Mann-Kendall test and Şen's innovative trend test for trend analysis, and Sen's slope test for the magnitude estimation of trends were used. According to the test results, the summer temperatures in particular show increasing trends at the 0.001 significance level. Mean maximum temperature in August, mean minimum temperature in June and August, and mean temperature in July and August are in increasing trend at the 0.001 significance level. Over a 51 year period (1965-2015) in Bartın province, the highest rate of change per decade in air temperatures is in August (0.55°C for T max , 0.46°C for T min and 0.43°C for T mean) based on Sen's slope. However, the study showed that apart from October precipitation, there is no significant trend in monthly, seasonal and annual precipitation in Bartın. Increasing trends in mentioned climate variables are also visually very clear and strong in Şen's innovative trend method, and they comply with the statistical results. As a result, the study revealed some evidence that temperatures will increase in the future in Bartın and its environs.

We present here the first statistically calibrated and verified tree-ring reconstruction of climate from continental Southeast Asia. The reconstructed variable is March-May (MAM) Palmer Drought Severity Index (PDSI) based on ring widths from 22 trees (42 radial cores) of rare and long-lived conifer, Fokienia hodginsii (Po Mu as locally called) from northern Vietnam. This is the first published tree ring chronology from Vietnam as well as the first for this species. Spanning 535 years, this is the longest cross-dated tree-ring series yet produced from continental Southeast Asia. Response analysis revealed that the annual growth of Fokienia at this site was mostly governed by soil moisture in the pre-monsoon season. The reconstruction passed the calibration-verification tests commonly used in dendroclimatology, and revealed two prominent periods of drought in the mid-eighteenth and late-nineteenth centuries. The former lasted nearly 30 years and was concurrent with a similar drought over northwestern Thailand inferred from teak rings, suggesting a ''mega-drought'' extending across Indochina in the eighteenth century. Both of our reconstructed droughts are consistent with the periods of warm sea surface temperature (SST) anomalies in the tropical Pacific. Spatial correlation analyses with global SST indicated that ENSO-like anomalies might play a role in modulating droughts over the region, with El Niño (warm) phases resulting in reduced rainfall. However, significant correlation was also seen with SST over the Indian Ocean and the north Pacific, suggesting that ENSO is not the only factor affecting the climate of the area. Spectral analyses revealed significant peaks in the range of 53.9-78.8 years as well as in the ENSO-variability range of 2.0 to 3.2 years.

We present the European Russia Drought Atlas (ERDA) that covers the East European Plain to the Ural Mountains from 1400-2016 CE. Like the Old World Drought Atlas (OWDA) for the Euro-Mediterranean region, the ERDA is a one-half degree gridded reconstruction of summer Palmer Drought Severity Indices estimated from a network of annual tree-ring chronologies. Ensemble point-by-point regression is used to generate the ERDA with the identical protocols used for developing the OWDA. Split calibration/validation tests of the ERDA indicate that it has significant skill over most of its domain and is much more skillful than the OWDA where they overlap in the western part of ERDA domain. Comparisons to historical droughts over European Russia additionally support the ERDA's overall validity. The ERDA has been spatially smoothed and infilled using a local regression method to yield a spatially complete drought atlas back to 1400 CE. EOF analysis indicates that there are three principal modes of hydroclimatic variability in the ERDA. After Varimax rotation, these modes correlate significantly with independent climate data sets extending back to the late nineteenth century in a physically interpretable way and relate to atmospheric circulation dynamics of droughts and heatwaves over European Russia based on more recent instrumental data.

The dating process needs a set of historical, archaeological and mathematical postulations. The accepted error must be adapted to the aim : the way the dates will be used by other specialists, a date being either an accessory in a large speech or an essential node in a demonstration. The error effect is different in a local analyse, i.e. about a building, and in a research concerning thousands of wood pieces of a large area, which in it is necessary to know better the nature of the error. In the aim to rebuild the climate of the last millenary from trees of Northern France and low lands near the frontiers (ESCARSEL program), we are proposing a way to sort dendrochronological results coming from archaeology and history respecting the way they were build.

Ongoing climate change strongly affects high-elevation environments in the European Alps, influencing the cryosphere and the biosphere and causing widespread retreat of glaciers and changes in biomes. Nevertheless, high-elevation areas often lack long meteorological series, and global datasets cannot represent local variations well. Thus, proxy data, such as tree rings, provide information on past climatic variations from these remote sites. Although maximum latewood density (MXD) chronologies provide better temperature information than those based on tree-ring width (TRW), MXD series from the European Alps are lacking. To derive high-quality temperature information for the Rhaetian Alps, Pinus cembra L. trees sampled at approximately 2000 m a.s.l. were used to build one MXD chronology spanning from 1647 to 2015. The MXD data were significantly and highly correlated with seasonal May-September mean temperatures. The MXD chronology showed a generally positive trend since the middle of the 19th century, interrupted by short phases of climatic deterioration in the beginning of the 20th century and in the 1970s, conforming with the temperature trends. Our results underline the potential for using Pinus cembra L. MXD to reconstruct mean temperature variations, especially during the onset and latter part of the growing season, providing additional information on parts of the growing season not inferred from TRW. Future studies on MXD for this species will increase the availability of temporal and spatial data, allowing detailed climate reconstructions.

This study presents an annually resolved dendrochronological reconstruction of hydrological impacts on the Roman and early-medieval landscape in the Low Countries of northwestern Europe. Around 600 hydrologically sensitive ring-width patterns, mostly oak (Quercus robur/petraea) as well as some ash (Fraxinus excelsior) and elm (Ulmus sp.), were selected from an initial dataset of >5000 and compiled into two chronologies that span the first millennium AD. Their content and (dis)similarities to established tree-ring chronologies from this and surrounding regions were used to assess their provenance, which in both cases is in the area where the majority of the wood was recovered. Instances of high groundwater levels and/or inundation were catalogued by identifying multi-year intervals of strongly reduced annual growth that occurred simultaneously throughout the research area. The resulting record contains 164 events dated between AD 1 and 1000, of which 21 have a recurrence frequency ≥50 years. One-third of the ≥50-yr events date between AD 185 and 282, making this the most flood-intense interval of the first millennium. The severest reconstructed impact of the first millennium dates to AD 602. A comparison to historically documented river floods/sea breaches and drought/heat spells shows that the predominant cause of the inferred impacts in the research area was river overflow. Synchronous inundation responses of oaks preserved in former bogs in Lower Saxony (NW Germany) indicate that half of the reconstructed events occurred on a supra-regional level, pointing to regional precipitation as a main forcing. River floods documented in written sources do not seem to have affected tree growth in Lower Saxony in a significant manner, indicating that the majority of documented floods most likely were caused by hydrological circumstances upstream of the catchments of the Rhine and/or Meuse. Reconstructed flood impacts during the Early Middle Ages coincide remarkably well with construction and repair of Rhine revetments at the early-medieval site of Leiderdorp-Plantage in the western Netherlands.

A substantial amount of macro-botanical remains has been recorded at Tel Megiddo since the initiation of the renewed excavations in 1992. We constructed a database with 1,162 identified samples and analysed them diachronically. This dataset enables us to trace environmental trends and human impact on the vegetation in the vicinity of the site during the Bronze and Iron Ages (~3,500-500 BCE). The earlier periods in the studied sequence are characterised by a higher availability of common natural arboreal elements (oak, conifers and terebinth) and the later periods by a dramatically reduced presence of these elements, with a much stronger occurrence of anthropogenically dependent species (olive), foreign species (cedar of Lebanon, sycamore fig), and less prevalent forest/maquis elements. Our investigation also provides some context for the appearance of both horticultural and rare/special species in the assemblage (almond, walnut, myrtle, laurel, sage). The appearance of prestigious species such as the imported cedar in one sector of the site (Area H) provides botanical support to other finds which rendered this area an elite neighbourhood.

About 100 wood samples (oak tree) taken in several old buildings of the city Autun (Burgundy, France), the most part of them coming from the Saint-Nazaire sector (Terreaux Place), were dated from the middle age and modern periods. Dating being accepted, the wood is studied here from dendro-climatological (meteorological) and dendro-provenance (trade interpretations) point-of-views. Specific formal methods are experimented in this paper.

Three hundred and seventy-seven tree-ring width site chronologies including all eight principal forest tree species within Central Europe (51 to 151E; 431 to 531N) are expressed as Cropper-values and mapped using a Geographical Information System (here after referred to as GIS). Spatial classification of positive and negative growth anomalies and their occurrence within altitudinal zones, results in nine differing subgroups of pointer years. In total, 39 years between 1901 and 1971AD are subdivided into these groups. The other 32 years show only growth anomalies in less than 40% of the research area, and therefore were excluded from further investigations. Climatological interpretation of the growth patterns of the nine groups documents mutual temperature and precipitation forcings. Extreme positive pointer years represent optimal growth conditions, i.e., moderate cool and wet conditions during the growing season. For the other years we summarize (i) warm and wet (warm and dry) springs result in positive (negative) anomalies in the Central European lowlands and (ii) warm (cold) summers result in positive (negative) anomalies in the Central European highlands. In some years, however, similar climatological conditions yield to divergent growth response patterns.

Precipitation around Cyprus, a relatively small island, is generally consistent in year-to-year variation in all dimensions except amplitude, with the higher elevations in the west generally receiving more precipitation. An annual record of precipitation was found in tree-rings of the predominant pine species, Pinus brutia Ten., which grows from the lower foothills up to 1400 m in altitude across the island. Tree-ring chronologies from four sites in west-central Cyprus are used here to reconstruct the annual September to August precipitation and a drought record for AD 1830-2006, with the drought reconstruction extending back to 1756. A minimum of 40% of the variance in annual precipitation and drought occurrence is explained by the variance in the tree-ring widths in all cases. Our drought assessment indicates that, on average, annual droughts occur once every 5 years and sustained droughts, 2-6 years in length, have occurred in small clusters of time, from 1806-1824, 1915-1934 and 1986-2000, when the winter North Atlantic Oscillation was in a predominantly positive phase. These results suggest that a sustained drought period has a mean return time probability of one in 70-100 years. This study provides the first long-term annual precipitation reconstruction and drought assessment at low to mid-elevations for Cyprus and will aid in future plans for drought mitigation.

The North American Dendroecological Field week (NADEF) is an intensive dendrochronology workshop, funded in part by the National Science Foundation. The 2019 Introductory Group at NADEF developed two precisely dated tree-ring width chronologies for Pinus contorta (lodgepole pine) and Pinus flexilis (limber pine) at the Wolf Knob site ca. 5 km west of Beartooth Lake, WY, within the bounds of the Shoshone National Forest (SNF), in the Greater Yellowstone Ecosystem (GYE). Wolf Knob is a semi-arid, S- to SW-facing, mid- to high-elevation site, making it an ideal location to examine the climate sensitivity of annual tree-ring width increments. Here, we show that two co-located Pinus species exhibit differing climate–growth relationships, with P. contorta exhibiting relatively weak correlations with precipitation (r = 0.37; p < 0.01) and temperature (r = –0.23; p < 0.05) during the late summer, and
P. flexilis exhibiting stronger overall correlations with both cool-season (r = 0.48; p < 0.01) and warm season precipitation (r = 0.51; p < 0.01) as well as with snowpack records (r = 0.45; p < 0.05). Our results suggest these two Pinus species may face disparate threats in the face of regional climate change, with P. flexilis being particularly vulnerable to drought conditions and declining snowpacks in the GYE.
The differing seasonal climate sensitivities of the two species is likely caused by microsite conditions (e.g. soil moisture capacity, incoming solar radiation) and distinct species-climate responses, underscoring the importance of not only site selection, but also microsite and individual selection in dendroclimatological sampling. Finally, this work contributes to identifying Snow Water Equivalent (SWE)-sensitive tree-ring proxies in the GYE, critical for understanding ongoing warming-induced snowpack declines across western North America, particularly given the projections of a largely snow-free (April 1) GYE by 2075.

Abstract
Under the background of climate change, precipitation and temperature variability have occurred widely
and frequently in Morocco in recent years. However, relatively few studies investigated this phenomenon.
Using tree rings to study climate variability has some advantages such as accurate dating, strong continuity
and high resolution. In this study, 80 tree cores from 40 trees of Cedrus atlantica M. were collected from two
forest sites Ain Khahla (Site I) and Bikrit (Site II) located in the Middle Atlas region of Morocco. Analysis of
increment cores showed that trees in both forest stands were between 85-349 years and between 268-644
years old in Site I and Site II, respectively. Mean tree ring width was greater (1.570 mm/year) in the first
site than in the second one (0.730 mm/year). Series intercorrelation was 0.268 for Ain Khahla and 0.355
for Bikrit. Values of Expressed Population Signals (EPS) obtained were higher than 0.940 in both sites. The
high mean sensitivity obtained, superior to 0.2, indicates a high inter-annual variability in ring widths and
that chronology was sensitive to yearly environmental change. A positive precipitation effect was found in
March for site I. High autumn and spring temperatures in both the previous and current year generally had a
negative impact on tree-ring width during the growing season only in Ain Khahla. It is suggested that these
chronologies have a high potential for future dendroclimatic studies. However, there is a need for larger
sample sizes and further extension of these chronologies into the past.
Keywords: Cedrus atlantica, Climate, Growth, Morocco, Tree ring, Width, Chronology
Resumo
Sob o cenário das alterações climáticas, tem ocorrido uma variabilidade da precipitação e da temperature
ampla e freqüente no Marrocos, nos últimos anos. No entanto, relativamente poucos estudos investigaram
esse fenômeno. O uso dos anéis de crescimento de árvores para estudar a variabilidade climática apresenta
vantagens como a datação precisa, forte continuidade e alta resolução. Neste estudo, 80 amostras do lenho
de 40 árvores de Cedrus atlantica M. foram coletadas em dois sítios das florestas de Ain Khahla (Sítio I) e
Bikrit (Sítio II) localizados na região do Médio Atlas, Marrocos. A análise das amostras do lenho das árvores
mostrou que as árvores dos dois povoamentos florestais tinham de 85-349 anos e 268-644 anos de idade
nos Sítios I e II, respectivamente. A média da largura dos anéis de crescimento foi maior (1.570 mm/ano),
no primeiro Sítio em relaçao ao segundo (0.730 mm/ano). O valor da intercorrelação das séries foi de 0,268
para Ain Khahla e de 0.355 para Bikrit. Os valores obtidos dos Sinais Expressivos da População (EPS) foram
superiores a 0.940 nos dois sítios. A alta sensibilidade média obtida superior a 0.2 indica uma alta variabilidade
inter-anual da largura dos anéis de crescimento e a cronologia foi sensível à mudança ambiental anual.
O efeito positivo da precipitação foi encontrado em março para o Sítio I. As altas temperaturas de outono
e de primavera no ano anterior e atual tiveram, geralmente, um impacto negativo na largura dos anéis de
crescimento durante a estação de crescimento apenas em Ain Khahla. Sugere-se que estas cronologias de
anéis de crescimento têm um elevado potencial para futuros estudos dendroclimáticos. No entanto, há necessidade
de aumentr o número de amostras e a extensão das cronologias em relação ao passado.
Palavras-chave: Cedrus atlântica, Clima, Crescimento, Marrocos, Anéis de crescimento, Largura, Cronologia

Hypothesized large-scale climatic extremes require verification from distantregions in order toconfirm the magnitude and timing of such events. Three of the most massivehypothesized volcanic events of the past two millennia, occurring in or aboutAD 536, 934 and1258, had profound climatic and demographic repercussions over much of Europe,the MiddleEast, and other areas, according to historical accounts recently described inStothers (1998, 1999,2000) as well as other research. Here we report on frost ring and otherdendrochronologicalevidence derived from a 1738-year tree-ring chronology from Mongolia andmillennial-scaletree-ring data from northern Siberia which demonstrate that these three eventsmay have alsoimpacted conditions in these distant regions.

Dendroclimatology in the Eastern Mediterranean (EM) region has made important contributions to the understanding of climate variability on timescales of decades to centuries. These contributions, beginning in the mid-20th century, have value for resource management, archaeology, and climatology. A gradually expanding tree-ring network developed by the first author over the past 15 years has been the framework for some of the most important recent advances in EM dendroclimatology. The network, now consisting of 79 sites, has been widely applied in large-scale climatic reconstruction and in helping to identify drivers of climatic variation on regional to global spatial scales. This article reviews EM dendroclimatology and highlights contributions on the national and international scale.

This paper presents updated tree-ring width (TRW) and maximum density (MXD) from Torneträsk in northern Sweden, now covering the period AD 500-2004. By including data from relatively young trees for the most recent period, a previously noted decline in recent MXD is eliminated. Non-climatological growth trends in the data are removed using Regional Curve Standardization (RCS), thus producing TRW and MXD chronologies with preserved lowfrequency variability. The chronologies are calibrated using local and regional instrumental climate records. A bootstrapped response function analysis using regional climate data shows that tree growth is forced by April-August temperatures and that the regression weights for MXD are much stronger than for TRW. The robustness of the reconstruction equation is verified by independent temperature data and shows that 63-64% of the instrumental inter-annual variation is captured by the tree-ring data. This is a significant improvement compared to previously published reconstructions based on tree-ring data from Torneträsk. A divergence phenomenon around AD 1800, expressed as an increase in TRW that is not paralleled by temperature and MXD, is most likely an effect of major changes in the density of the pine population at this northern tree-line site. The bias introduced by this TRW phenomenon is assessed by producing a summer temperature reconstruction based on MXD exclusively. The new data show generally higher temperature estimates than previous reconstructions based on Torneträsk tree-ring data. The late-twentieth century, however, is not exceptionally warm in the new record: On decadal-to-centennial timescales, periods around AD 750, 1000, 1400, and 1750 were equally warm, or warmer. The 200-year long warm period centered on AD 1000 was significantly warmer than the late-twentieth century (p \ 0.05) and is supported by other local and regional paleoclimate data. The new tree-ring evidence from Torneträsk suggests that this ''Medieval Warm Period'' in northern Fennoscandia was much warmer than previously recognized.

Giant sequoias (Sequoiadendron giganteum [Lindl.] J. Buchholz) preserve a detailed history of fire within their annual rings. We developed a 3000 year chronology of fire events in one of the largest extant groves of ancient giant sequoias, the Giant Forest, by sampling and tree-ring dating fire scars and other fire-related indicators from 52 trees distributed over an area of about 350 ha. When all fire events were included in composite chronologies, the mean fire intervals (years between fires of any size) declined as a function of increasing spatial extent from tree, to group, to multiple groups, to grove scales: 15.5 yr (0.1 ha), 7.4 yr (1 ha.), 3.0 yr (70 ha), and 2.2 yr (350 ha), respectively. We interpreted widespread fires (i.e., fire events recorded on ≥2 trees, or ≥25 % of all trees recording fires within composites) to have occurred in areas of 70 ha to 350 ha at mean intervals ranging from about 6 yr to 35 yr. We compared the annual, multi-decadal and centennial variations in Giant Forest fire frequency with those documented in tree-ring and charcoal-based fire chronologies from four other giant sequoia groves in the Sierra Nevada, and with independent tree-ring-based reconstructions of summer drought and temperatures. The other giant sequoia fire histories (tree rings and charcoal-based) were significantly (P < 0.001) correlated with the Giant Forest fire frequency record and independent climate reconstructions, and confirm a maximum fire frequency during the warm and drought-prone period from 800 C.E. to 1300 C.E. (Common Era). This was the driest period of the past two millennia, and it may serve as an analog for warming and drying effects of anthropogenic

Recent tree-ring studies in Mongolia provide evidence of unusual warm ing that is in agreement with large-scale reconstructed and recorded temperatures for the Northern Hemisphere and the Arctic . The Mongo lian proxy record for temperature extends back over 450 years and is an important addition to the global tree-ring database. Precipitation recon structions based on tree rings reflect recent increases but show that the increases are within the long-term range of variations. There is evi dence for quasi-solar periodicity in long-term reconstructed precipita tion variation, also shown by previous studies . Mongolia has excellent sampling resources for future studies .

We developed ring-width chronologies of Cedrus deodara [(Roxb.) G. Don] and Pinus gerardiana (Wall. Ex. Lamb) from a homogeneous moisture stressed area in Kinnaur, Himachal Pradesh. Running correlation using a 50-year window with overlap of 25 years showed strong correlations between these species chronologies during the entire common period (AD 1310. Response function analysis indicated that except for January-February, precipitation has a direct relationship with growth of these species. We therefore combined both the species chronologies to develop a statistically calibrated reconstruction of March-July precipitation that spans from AD 1310-2004, and explains 46% of the variance contained in the instrumental data from the calibration period 1951-1994. In the past 694 years of the reconstruction, the wettest period was in the twentieth century and the driest in the eighteenth century (1773-1802). The relationships observed between reconstructed precipitation and Indian summer monsoon on interdecadal scale, SOI, PDO and NAO indicate the potential utility of such longterm reconstructions in understanding the large-scale climate variability. Multi-taper method (MTM) spectral analysis indicated significant (p \ 0.05) spectral peaks at 2-4, 6, 8, 10, 30, 33, 37 and 40-42 years in the reconstructed precipitation data.

Autor: Bach. Mariana León (UNALM)
Asesor: Dr. Jose Luis Marcelo Peña (UNJ)

El cambio climático del último siglo está asociado estrechamente al avance industrial, que aumentó las concentraciones de carbono y ha repercutido en el aumento de la temperatura. Estas consecuencias generan cambios en la dinámica de la vegetación de los bosques. Actualmente los bosques estacionalmente secos (BES) de la región tropical poseen sólo el 10% de la cobertura de su distribución original, y solo en el norte del Perú se encuentra uno de los BES más importante de la región neotropical. Sin embargo, no se conoce con exactitud la respuesta de los árboles de estos bosques a las variaciones del clima y mayor oferta de CO2.
En la presente investigación se aplicó el análisis dendrocronológico para obtener información registrada en el leño dentro de los últimos 70 años, y evaluar la influencia de los factores climáticos como la precipitación y temperatura en el crecimiento y anatomía de los árboles de Juglans neotropica (nogal) y Cedrela kuelapensis (cedro). Estas especies son representantes de los BES del Marañon, siendo ésta última, especie endémica y amenazada por la región. Para tal fin se tomaron 20 muestras de madera mediante el método “no destructivo” que consiste en obtener tarugos de 5 mm de diámetro del árbol a la altura del pecho (DAP) (Krottenthaler et al.2015; Marcelo-Peña 2017). De cada árbol fueron extraídos dos o tres radios con la ayuda del barreno de Pressler como sugiere Rosero (2009). También fueron extraídas muestras de leño de 25 mm de diámetro utilizando una sonda metálica con tres dientes de corte acoplada a una perforadora Stihl BT45 (Krottenthaler et al.2015; Marcelo- Peña 2017).
Estas muestras fueron recogidas de la localidad de Colcamar, provincia de Luya, departamento de Chachapoyas. Por medio de los anillos de crecimiento analizados mediante los programas FMT y COFECHA, se determinaron series cronológicas de 61 años, desde 1958 al 2018 y 122 años, desde 1897 al 2018; para Juglans neotropica y Cedrela kuelapensis, respectivamente. En la caracterización y análisis de los anillos de
crecimiento de las especies mencionadas, se demostró que C. kuelapensis presenta una mayor sensibilidad frente a las condiciones ambientales, debido a que expresa una alta variabilidad de longitudes de anillos de crecimiento. Las tasas de crecimiento diamétrico anual promedio fueron de 4.16 mm/año y 2.29 mm/año, para Juglans neotropica y Cedrela kuelapensis, respectivamente. Además se demostró que los años más secos influyen seriamente a la estructura anatómica macroscópica y microscópica de las especies en estudio.

Palabras clave: Anillos de crecimiento, BES, cambio climático, dendrocronología, COFECHA, estructura anatómica del leño.