Tree-ring Series Research Articles

A WIGGLE-MATCHED 297-YR TREE-RING OXYGEN ISOTOPE RECORD FROM THAILAND: INVESTIGATING THE 14C OFFSET INDUCED BY AIR MASS TRANSPORT FROM THE INDIAN OCEAN

ABSTRACTRegional offsets from Northern Hemisphere radiocarbon (14C) calibration curves are widely recognized for monsoon Asia and often hinder accurate 14C dating. In this paper, we explore the possible linkage between summer monsoon intensity and 14C offsets using tree-ring δ18O and 14C data from Thailand. We developed a 297-yr floating tree-ring δ18O chronology comprising seven teak log-coffin samples from the Ban Rai rock shelter site, northwestern Thailand. The outermost ring of our chronology was estimated to date from 358–383 CE, within a 95.4% (2σ) probability range, based on a total of 10 14C measurements that were wiggle-matched against a mixed calibration curve evenly weighted from the IntCal20 and SHCal20 curves. Backward trajectory analysis showed that an intensified (weakened) summer monsoon detected in a modern tree-ring δ18O chronology was most likely to be induced by increased (decreased) air mass transport from the tropical Indian Ocean, which is an area of intense upwelling where the 14C concentration is lower than the atmospheric 14C level. However, partly because of the limited sample size and dating uncertainty, the direct linkage between the tree-ring δ18O series and 14C records obtained from our teak log-coffin samples could not be statistically verified.

Re-assessment of tree-ring radiocarbon age series for the “Millennium Eruption” of Changbaishan / Paektu volcano in relation to the precise date of 946 CE

Volcanic eruptions that are not historically attested are often dated by “wiggle matching” sequential radiocarbon measurements of the rings of trees killed by the eruption against a calibration curve. Although evidence for contamination by exposure to 14C-free geogenic carbon is well documented, it is generally assumed that the radiocarbon ages are unbiased by such “old” carbon. The ‘Millennium Eruption’ of Changbaishan / Paektu volcano (China/DPR Korea) provides an opportunity to test this assumption, since several age estimates were made before the acceptance of a precise eruption year of 946 CE. Accordingly, we develop a methodology that enables testing of assumptions and evaluation of discrepancies between reported wiggle match series. We then use it to correct for contamination levels of up to 4.5% old carbon to eight wiggle match date series for the Millennium Eruption. Without the need to discard ring ages, we find agreement indices as high as, or higher than, those for the published dates. Five of the eight series yielded high-agreement-index eruption dates closer to 946 CE than the published dates. None of the five yielded a best result without recognising some degree of contamination. Differences between the eruption dates reveal a weak association with the direction of the sampled tree from the caldera, but no relationship with distance. Our results suggest that old carbon contamination can lead to over-estimation of eruption ages by years, decades, or more. In addition, our results show that anomalously younger ages can also be a problem in radiocarbon series and these cannot be easily overcome at present by this methodology.

Tree rings as an ecological indicator of the reaction of Swiss stone pine (Pinus cembra L.) to climate change and disturbance regime in the extreme environment of cliff forests

Tree rings are an ecological indicator, useful for studying the adaptation of trees in a changing environment, especially in the unique habitat of high-elevation cliff forests. The main aim of this study was to characterize tree-ring changes in Stone pine (Pinus cembra L.) growing in the extreme conditions of cliff forests of the Western Carpathians (at elevation 1300–1600 m a.s.l.), in order to reconstruct the growth release pattern and to better understand the influence of climate. The study was based on 104 tree ring series covering a 449-year-long chronology (1561–2009). In the last century, mean annual temperature has increased by +2.0 °C and precipitation has decreased slightly in the Tatras. The growth of stone pine was strongly related to summer temperature of June and July. In the last decades, the negative influence of summer precipitation on tree growth has abated; this may be related to warmer summers and decreasing precipitation. Temperature of the previous autumn, winter, and early spring, which had a significant influence on stone pine growth in the past, is not an important factor now. In the extreme environment of mountain cliffs, the influence of temperature and precipitation on tree growth is not stable over time under changing climate. The current changes in climate seem to promote stone pine and its potential upward elevational shift. The numerous past disturbance events have affected a limited number of trees, suggesting that single individuals have been randomly eliminated from the cliff stands during the last three centuries. Our results highlight the complex pattern of the reaction of stone pine on cliffs to changes in the environment. Swiss stone pine, a long-lived tree species, shows high adaptability for colonization of mountain cliffs and is an excellent object for studying the response of plants to changing climate. Understanding the effect of interactions between climate, disturbances, and the radial growth of trees in extreme environments of cliff forests on different temporal scales (monthly, seasonal, yearly) should increase our knowledge of such ecologically valuable areas.

Combined tree-ring width and wood anatomy chronologies provide insights into the radial growth and hydraulic strategies in response to an extreme drought in plantation-grown Mongolian pine trees

Mongolian pine (Pinus sylvestris var. Mongolica) is among the most commonly used coniferous afforestation tree species for building shelter forests in vast areas of northern China, yet it is at a high risk of mortality in the context of increased frequency of extreme drought events associated with anticipative climate change. Understanding the long-term ecophysiological response to climate extremes is of great relevance for taking appropriate practices for the sustainability-oriented management of Mongolian pine plantations in drought-prone environments. Here, the hydraulic strategy behind the response of the radial growth of Mongolian pine trees planted in a water-limited area of northern China to the extreme drought event from 2001 to 2004 was retrospectively investigated by combining standard dendrochronological methods and quantitative wood anatomy. We found that water-related climatic variables acted as the main factors regulating the radial growth and xylem tracheid size of the Mongolian pine trees at the study site, and the extreme drought significantly reduced xylem theoretical hydraulic conductivity and almost stagnated the trunk radial increment. Immediately after this climatic extreme, the stem growth sharply increased to a level substantially higher than that preceding the extreme drought, which was probably attributable to the reduction of inter-tree competitions for resources due to the mortality of a large number of trees caused by the extreme drought event. Around the extreme drought event, tree ring width was significantly proportional to the number of earlywood tracheid cell layers but was uncorrelated with tracheid size metrics, alongside a clear hydraulic safety-efficiency trade-off among the stem xylem traits obtained from tree ring series. This study stresses the role that xylem hydraulics play in modulating the radial growth of plantation-grown Mongolian pine trees during extreme droughts by adjusting xylem structural characteristics and hence hydraulic transport functions.

Quantitative relative humidity reconstruction combining tree-ring with ice core oxygen isotope records

As one of the driest regions in the Asia, the ecological conditions in Northwest China are very fragile. Although relative humidity (RH) plays a vital role in the environment, the lack of long-term RH records hinders the development of reliable scenarios for future extreme environmental conditions in this region. We developed a new method for quantitative regional RH reconstruction; in this method, the signals of precipitation oxygen isotope ratios (δ18O) and temperature in the tree-ring δ18O series are removed to extract the RH signal from the tree-ring δ18O records to the greatest extent. We then combined published millennium tree-ring δ18O, ice core δ18O, and paleo-temperature data to reconstruct a new millennium-long RH record around Delingha, Qinghai, China, on the edge of the northeastern Tibetan Plateau (TP). The reconstructed RH was closely related to both temperature and rainfall, and revealed cycles of approximately 35, 85, 130–160 and 200 years, which are associated with solar insolation variations, Pacific decadal oscillation, and the Atlantic multidecadal variability. With continuous global warming, RH may decrease as the contribution of the temperature increase becomes larger than that of the precipitation over the northeastern TP. This study provides a basis for a new method of RH reconstruction based on different paleoclimate archives.

Life histories of Abies alba and Picea abies growing in old-growth forests driven by natural gap-phase dynamics

We analyzed growth trajectories recorded in the tree-ring series of Norway spruce Picea abies (L.) H. Karst. and silver fir Abies alba Mill. co-occuring with European beech Fagus sylvatica L. in old-growth forests driven by natural stand dynamics. The study sites were localized in five old-growth stands in the Western Carpathians (Central Europe). We characterized the life histories of 218 individual trees by using 25 metrics which refer to the age of the trees, number of release events, reaction to releases, radial increment and basal area increment. We found a large variation in the dbh-age relationship. The life histories of most trees included two or three (in single cases up to seven) release events. We did not find tree age as an important factor in determining post-release growth response. The maximal basal area increment was frequently registered at the terminal stage of tree life. The life histories of spruces and firs did not significantly differ. We concluded that in natural forests driven by gap-phase dynamics, the history of release events is the primary driver of tree growth and that tree age plays a secondary role. After reaching the overstory, trees can continue growing without significant symptoms of aging until extrinsic forces cause their death. Our results indicate that in the studied ecosystem the persistence of less shade-tolerant spruce is not attributable to the niche differentiation and site partitioning mechanism. An alternative hypothesis based on shifts in stand densities, species composition and climatic factors is more probable.

High resolution radiocarbon spike confirms tree ring dating with low sample depth

Radiocarbon (14C) has been used to date carbon-rich objects in Earth science, archeology, and history since the 1940s. New methods, using spikes in 14C caused by solar proton events, can be used to annually date wood when crossdating is not possible, such as when sample size is low, samples are floating in time, or external disturbances lead to insecure dates. Here, we use a spike in radiocarbon during a solar energetic particle (SEP) event in 774/775 CE to confirm crossdating of a poorly-replicated King Billy pine (Athrotaxis selaginoides) chronology. Low sample depth between 1498 and 1523 CE (two trees) prevented confident dating of the early period of the chronology. Three core samples with strong correlation with the master chronology that likely included the 774/775 CE Miyake SEP event were identified for radiocarbon isotope analysis. We sectioned segments centered on the estimated 774/775 CE date and then isolated the holocellulose in each sample. Samples were sent to an accelerator mass spectrometry (AMS) for radiocarbon measurements. The AMS data confirmed the crossdating accuracy of the tree ring series and reinforces the applicability of this technique to anchor poorly dated tree ring series in time. In addition, we found sample processing with a microtome proved superior for holocellulose extractions and yielded more accurate 14C measurements. We recommend sampling with a microtome, processing at least three samples per year, and including sample masses greater than 100 ug C to confirm dating using radiocarbon spikes.

TREE RINGS AS ARCHIVES OF ATMOSPHERIC POLLUTION BY FOSSIL CARBON DIOXIDE IN BRATISLAVA

ABSTRACTResults of radiocarbon (14C) analysis of a tree-ring series from Bratislava, Slovakia, covering the period from 1970 to 2004 are presented. For a part of this time period, monthly 14C measurements of atmospheric carbon dioxide from Bratislava sampling station are compared with the tree-ring results. The effects of fossil CO2 emissions on 14C levels in the environment are emphasized by comparison with atmospheric clean air reference values (Schauinsland, Germany). The presented results from Bratislava are also set against the previously measured tree-ring series from Low Tatras mountain region in Slovakia, representing regional clean air radiocarbon levels in the biosphere. The observed 14C levels of Bratislava tree rings and atmospheric CO2 in 1970s and 1980s are significantly lower than clean air data, indicating severe fossil CO2 pollution in Bratislava during this time period.

Moisture, Not Temperature, in the Pre-Monsoon Influences Pinus wallichiana Growth along the Altitudinal and Aspect Gradients in the Lower Himalayas of Central Nepal

Changing climate can strongly affect tree growth and forest productivity. The dendrochronological approach to assessing the impact of climate change on tree growth is possible through climate–growth correlation analysis. This study uses an individual tree-based approach to model Pinus wallichiana (P. wallichiana) radial growth response to climate across the physiographic gradients in the lower distributional range of Nepal. This study sampled six sites across the Makwanpur district of central Nepal that varied in elevation and aspect, obtaining 180 tree-ring series. Climate data series were obtained from Climate Research Unit (CRU 4.0). The pair correlation approach was used to assess P. wallichiana growth response to climate and site-level physiographic variables such as site-level environmental stress. The study also determined long-term growth trends across the elevation and aspect gradients. Trees at sites with higher elevation and northeast aspect (NEA) were more responsive to winter and spring precipitation, whereas trees with lower elevation and northwest aspect (NWA) were more responsive to winter and spring precipitation. Basal area increment (BAI) analysis showed the variation of growth at site-level environmental stress, suggesting that the sensitivity of forest ecosystems to changing climate will vary across the lower growth limit of P. wallichiana due to differences in local physiographic conditions.

On the significance of long-term trends in tree-ring N isotopes – The interplay of soil conditions and regional NOx emissions

As anthropogenic nitrogen (N) emissions have been rising for decades, it is critical to develop natural archives that help understand how natural processes were modified in the past. Tree-ring δ15N values may represent such an indicator but its validity as faithful record of N cycling changes is still debated. Here we produce long-tree-ring δ15N series for five white spruce stands from two boreal regions submitted to moderate industrial N inputs. The obtained δ15N series show sharp differences among stands, even from the same region, despite the fact that they show similar increases in intrinsic water use efficiency (iWUE), a proxy for foliar strategies derived from δ13C values. The statistical modeling of these series and the basal area increment (BAI) of the trees allow to suggest that the mechanisms controlling the isotopic fractionation of N assimilated by tree rings are decoupled from the foliar strategies under the anthropogenic N emissions. The iWUE trends mainly reflect rise of pCO2 and changes in air quality. The long-term δ15N trends echo different biogeochemical processes responding to N deposition due to distinct original soil pH at the various sites. We contend that tree-ring δ15N series can record changes in the forest N cycle, but their rigorous interpretation requires laborious work, particularly an understanding of the biogeochemistry in the soil immediately around the investigated trees.“Seek simplicity and distrust it”, Alfred North Whitehead.

Coupled Hydro-Climatic Signals in the Radial Growth of Oaks Benefitting from Groundwater Availability

Lowland forests benefiting from groundwater availability are important ecosystems in Central Europe, both from ecological and economic perspectives. Besides a great reduction in their extent in the historical times and further shifts in the land use and water management regimes intensified during the industrial era, continuing changes in the groundwater and overall hydro-climatic conditions can pose significant challenges to them. Although tree-ring analyses serve as widely used tools to assess the climatic impact on tree growth and vitality, few studies have attempted to investigate the effects of subsurface hydrology on interannual fluctuations in xylem production. In this study, we compared the tree-ring width series of pedunculate oak (Quercus robur L.) from a forested area in southwestern Hungary with the time series of monthly groundwater depth and climatic variables over the period of 1920–2017 with a specific focus on 1961–2017. The radial growth of the studied trees showed the strongest relationship with late winter and early spring groundwater and drought conditions preceding the growing season, differing from the commonly reported climatic signals marked by early summer meteorological conditions of the vegetation season. The results suggest that the groundwater recharge during the dormant period preceding the vegetation season and the groundwater levels in early spring were among the key limiting factors on tree growth in the study area. In the growing years starting with a sufficiently high groundwater table, even scarce summer precipitation did not seem to limit radial growth drastically. However, unfavorable shifts in climatic conditions during the past few decades and the associated uncertainties in the future groundwater regime imply that additional active measures aimed at maintaining and restoring groundwater conditions may well be highly beneficial for sustaining groundwater-dependent forest ecosystems and their productivity.

Linking wood density records of common beech (Fagus sylvatica L.) with temperature and precipitation variability from a temperate lowland site.

European lowland beech stands are under pressure by current climate change and increased drought spells. Climate sensitivity of trees is most commonly studied by examining tree-ring width records and wood density-based time series, yet the potential of the latter is underexplored for hardwoods and beech (Fagus sylvatica L.) in particular. Here, we investigate how variability in radial growth, Maximum Latewood Density (MXD) and intra-annual wood density records in lowland beech are related to monthly and daily temperature (T) and precipitation (P) records, as well as the Standardized Precipitation Evapotranspiration Index (SPEI), during the past 50 years. 45 increment cores were collected from healthy (co-) dominant beech trees in Flanders (northern Belgium). We used X-ray micro-Computed Tomography (XµCT) to obtain wood density and tree-ring width series. By dividing every tree-ring into 4 sectors of equal radial width, we also assessed climatic forcings on intra-annual wood density variability (meanQi, i = 1:4). Water availability (SPEI) is the most important factor limiting radial growth, whereas MXD is correlated with summer temperature (period May-July, r = 0.334). Scanning resolution (110, 60, 20 µm) proves to be an important parameter when interpreting MXD values. We found that to quantify climate signals at the end of the growing season, density values should be representative for a relatively large part of the latewood. Our results also suggest that a sector approach is useful by showing climatic influences during the entire growing season. Wood density at the beginning of the growing season is mainly influenced by water availability (meanQ1∼SPEI, r = 0.416), whereas towards the end of the growing season only significant correlations with temperature were observed (meanQ4∼T, r = 0.347). We recommend to further explore MXD values for hardwood trees in lowland Europe.

A 230-Year Summer Precipitation Variations Recorded by Tree-Ring δ18O in Heng Mountains, North China

To explore the history of the changes in monsoon precipitation and their driving mechanisms in the context of global warming, climatology studies using tree-ring stable oxygen isotopes (δ18O) were carried out in Shanxi Province, China. Based on a tree-ring δ18O series from Pinus tabulaeformis Carr. on Heng Mountain, a 230-year June–July precipitation sequence from 1784 to 2013 AD was reconstructed that explained 45% of the total variance (44% after adjusting the degrees of freedom). The reconstructed sequence captured the characteristics of the variations in precipitation. Periods of drought occurred mainly in 1820–1840 AD, 1855–1865 AD, 1895–1910 AD, 1925–1930 AD, and 1970–1995 AD, and wet periods occurred mainly in 1880–1895 AD, 1910–1925 AD, and 1935–1960 AD. The dry and wet years in the precipitation reconstruction corresponded well to the years in which disaster events were documented in historical records. A spatial correlation analysis with Climatic Research Unit (CRU)-gridded precipitation data indicated that the reconstructed precipitation provided good regional representation and reflected large-scale June–July precipitation changes in northern China. In addition, the reconstructed precipitation sequence was also significantly correlated with the dry and wet index (DWI) and other tree-ring dry/wet reconstructions from the surrounding areas. The correlation between the reconstructed precipitation and the Asian monsoon index showed that the precipitation can indicate the intensity of the Asian summer monsoon. Moreover, a significant negative correlation was found between the El Niño–Southern Oscillation (ENSO) and the reconstructed precipitation. At the decadal scale, the negative phase of the Pacific Decadal Oscillation (PDO) and the positive phase of the Atlantic Multidecadal Oscillation (AMO) may co-promote summer precipitation in the study area.

Process representation of conifer tree-ring growth is improved by incorporation of climate memory effects

Process modeling of tree growth responses to climate can improve our understanding of the functioning of tree growth under climate change, but these models do not consider so-called memory effects. Further, memory effects are unstudied in temperate forests of China, which is showing high vulnerability to climate warming. Here, we integrate a process-based Vaganov–Shashkin–Lite (VS-Lite) model of tree ring formation with the stochastic antecedent modeling (SAM) approach, to quantify the current and antecedent climatic drivers of the tree-ring width chronologies of 109 conifers in temperate China. Based on climate-response patterns, tree-ring width series were clustered into “warm-dry,” “cold-dry,” and “cold-wet.” The VS-Lite results indicated growth in the “warm-dry” and “cold-dry” sites were primarily constrained by current soil moisture, while growth in the “cold-wet” sites was mainly constrained by cotemporaneous temperature. Compared to VS-Lite alone, we found significant improvements in model fit for the SAM framework in all forest types. Notably, antecedent drivers explained 14%, 11%, and 21% of the growth variations in “warm-dry,” “cold-dry,” and “cold-wet” sites, respectively, challenging the assertion that long memory is only important in dry forests. Commonality analysis revealed that growth in “cold-dry” and “cold-wet” sites was determined by antecedent climate while growth in the “cold-dry” and “warm-dry” clusters were determined by the endogenous (autoregressive) memory. In “warm-dry” and “cold-wet” sites, growth was significantly affected by antecedent temperature in opposite directions, whereas in the “cold-dry” sites it was affected by antecedent soil moisture conditions and soil moisture-temperature interactions. Our combined process-empirical model demonstrates that memory is prevalent across temperate forests in China and also improves representation of tree growth in diverse forests under novel climate conditions of the future.

Peculiarities of tree-ring series in larch affected by the ground fire of 1908

Peculiarities of tree-ring series in larch affected by the ground fire of 1908

Climate-growth relationships of Daniellia oliveri (Rolfe) Hutch. & Dalziel in the Sudanian zone of Mali, West Africa

Tree rings depend on seasonal variation in radial tree growth. Where they can be identified, their interannual variation may reflect climate variability. Compared to its use in temperate and boreal regions, tree-ring analysis has been less applied in tropical Africa, with weaker seasonality. Daniellia oliveri often forms the tallest trees in agroforestry parklands of the Sudanian savanna zone of Mali but its growth response to climate (rainfall, temperature) variability has not been documented. We analyzed six stem disks of D. oliveri and used standard dendrochronological methods to process the samples. Contrary to earlier literature likely based on more humid parts of the species distribution range, D. oliveri formed distinct growth ring boundaries in our study area. The mean annual radial growth was 2.73 ± 0.56 mm. All measured tree-ring series were successfully cross-dated with a GLK (Gleichläufigkeit) value of 76.3 ± 5.6. The final tree-ring chronology covers the period 1909-2021. After removing age-related growth trends, the tree-ring width index showed a significant relationship with records of annual rainfall (r2 = 0.46, n = 100 years, p < 0.001). The relationship between wet-season (June to September) precipitation and the residual chronology was slightly higher (r2 = 0.50, n = 100 years, p < 0.001). However, no significant correlation was found for temperature. These results imply that D. oliveri can be successfully used for dendrochronological studies with relevance for the management and restoration of the ecosystems in the Sudanian zone of West Africa, where long-term rainfall records are scarce.

Usporedna analiza utjecaja klimatskih čimbenika na radijalni rast autohtonih vrsta borova (Pinus spp.) u središnjoj Bosni i Hercegovini

In central Bosnia and Herzegovina, in the Zavidovići-Teslić area, the study of the radial growth of Austrian and Scots pine (autochthonous pine species) trees was conducted using the dendrochronological method in order to identify the differences between the species in terms of the influence of climatic variables on the tree ring formation. Trees were sampled in five experimental areas or five sites. The first site had a Scots pine stand, while the second had an Austrian pine stand, and the other three sites had mixed stands of Scots and Austrian pine. Cross-dating was conducted using visual on-screen techniques of CDendro software and statistical methods using Cofecha software. The tree ring series were standardized using the Arstan program and cubic smoothing spline. It produced Scots pine regional chronology, 145 years long (1870-2014), and Austrian pine regional chronology, 180 years long (1835-2014). Correlation analysis of the relationship between the index of tree-ring width and precipitation and temperature in the characteristic periods of the year showed a negative effect of temperature (except in winter months) and a positive effect of precipitation on the tree ring formation. The statistically significant dependence of the tree-ring width index on the SPEI indices indicates a significant impact of moisture deficiency on the tree ring formation in the period from June to August (r = 0.33 in June, r = 0.45 in July and r = 0.47 in August) for Scots pine and in the period from June to September (r = 0.36 in June, r = 0.43 in July, r = 0.47 in August and r = 0.30 in September) for Austrian pine. The analysis of the relationship between climatic parameters and the chronologies of Scots and Austrian pine shows similar relationships between radial growth and climate but the influence of climate is somewhat more pronounced in Austrian pine. In the study area, the radial growth of both tree species is significantly determined by climate conditions. In other words, the chronology of these species has a good climatic signal, especially the drought signal in the summer months.

Specifics of slope movements on slopes with contrasting structural conditions: Evidence from tree-ring records

The geological structure of a slope is one of the key factors that drives the development of landslide types. Various landslide types, although occurring in the same locality, can result in different spatio-temporal dynamics of their movements. Moreover, the presence of shallow creep movements on such slopes can modify the effect of slide movements and possibly cause the false impression of landslide activity. The nonstandard combination of detailed tree-ring-based (dendrogeomorphic) approaches involving the careful assessment of growth disturbance properties (the duration, intensity, mutual ratio of different disturbances), the statistical testing of the spatial pattern of disturbed trees, the analysis of possible extreme precipitation triggers, and geophysical sounding was used in this study in an attempt to distinguish creep and slide movements and assess the general slope movement activity on slopes with contrasting geological structures. Data from 1032 tree-ring series of 516 disturbed individuals of common spruce (Picea abies (L.) Karst.) enabled the reconstruction of 13 slope movements on all three studied sites (3, 7, and 3) for the last approximately 70 years. Although some indices correspond with the general assumption of a specific landslide type to the structure of induced growth disturbances (e.g., an increased ratio of reaction wood on rotational landslides), the advanced dendrogeomorphic approach used suggests that not all dated events are of slide origin and that creep movements significantly modify the effect of original slide movement on tree growth. Some dated events are probably the result of only creep movements themselves. Thus, the present study critically assesses results of the dendrogeomorphic dating of various landslides, presents contrasting behavior of slope movements on slopes with contrasting geological structures, and recommends the use of more advanced tree-ring-based approaches for more effective dendrogeomorphic research of landslides.

Diversification of landslide areas as a means for reducing noise in dendrogeomorphic dating

The result of tree-ring-based reconstruction of past landslide events is often the development of a single total chronology. This approach can be very effective for small homogeneous landslides. However, compiling chronological data from heterogeneous (often independent) zones of large complex landslide areas into one chronology can induce over- or underestimation of some events, resulting in lowered reliability of the reconstruction. The solution for elimination of this effect can lie in the diversification of complex landslide areas into homogeneous zones with separate analyses. The aim of this study was to quantify the effect of this separation on detected slope movement events and to define parameters whose investigation could distinguish events (sliding) from noise (creeping). For this purpose, 412 tree-ring series from 206 disturbed common spruce ( Picea abies (L.) Karst.) occupying complex landslide areas were dendrogeomorphically analysed. The landslide area was divided into five homogeneous zones using geomorphic mapping, LiDAR-based DEM and geophysical sounding (ERT). Five events (verified in individual zones) were detected in the total chronology. Two extra events in the total chronology (28.6%) were considered noise. Moreover, two zonal events were detected but not recorded in the total chronology. This indicates that the noise in the total chronology of the complex landslide area could reach more than a quarter of dated events. Next, true slide events and noise (caused by creep) were differentiated in the structure of growth disturbances (reaction wood vs. abrupt growth suppression) and their proportion in event reconstruction, spatial patterns of trees containing slope movement signals, and the character of triggers. Thus, for better filtering of noise from signals in tree-ring-based chronologies of landslides, not only observations of dendrogeomorphic index values but also the morphology of landslides and characteristics of dated processes must be considered.

Influence of Local Climate and ENSO on the Growth of Cedrela odorata L. in Suriname

In this study, we used retrospective dendroclimatological analyses to explore whether El Niño Southern Oscillation (ENSO) and local precipitation patterns have an influence on tree growth in Suriname, a country located on the Guiana Shield, as annual precipitation patterns on the Guiana Shield are related to ENSO. Discs were taken from 20 trees of Cedrela odorata, whose stem forms very distinct annual growth rings, for tree ring analyses. The trees grew in unmanaged tropical wet forests of Suriname. The tree-ring series of individual trees started between 1836 and 1931 and extended over a period of 84–180 years. The 20 dated series were utilized for constructing a tree-ring chronology. Unlike many other studies that used local anomalies such as flood pulse, precipitation, and drought events to describe the influence of El Niño on tree growth, we used monthly precipitation and ENSO indices as predictors of tree growth to calculate response and correlation functions. The study observed that tree ring growth of Cedrela odorata is influenced by precipitation in August and June of the current year and in August of the previous year, as well as by the ENSO indices SSTA, TSA, TNA, and NAO. Systematic increases in the strength of the El Niño southern oscillation (ENSO) teleconnection due to climate change could affect the growth of trees on the Guiana Shield.