Tree-ring Signals Research Articles

Drivers of intra-seasonal δ13 C signal in tree-rings of Pinussylvestris as indicated by compound-specific and laser ablation isotope analysis.

Carbon isotope composition of tree-ring (δ13 CRing ) is a commonly used proxy for environmental change and ecophysiology. δ13 CRing reconstructions are based on a solid knowledge of isotope fractionations during formation of primary photosynthates (δ13 CP ), such as sucrose. However, δ13 CRing is not merely a record of δ13 CP . Isotope fractionation processes, which are not yet fully understood, modify δ13 CP during sucrose transport. We traced, how the environmental intra-seasonal δ13 CP signal changes from leaves to phloem, tree-ring and roots, for 7year old Pinus sylvestris, using δ13 C analysis of individual carbohydrates, δ13 CRing laser ablation, leaf gas exchange and enzyme activity measurements. The intra-seasonal δ13 CP dynamics was clearly reflected by δ13 CRing , suggesting negligible impact of reserve use on δ13 CRing . However, δ13 CP became increasingly 13 C-enriched during down-stem transport, probably due to post-photosynthetic fractionations such as sink organ catabolism. In contrast, δ13 C of water-soluble carbohydrates, analysed for the same extracts, did not reflect the same isotope dynamics and fractionations as δ13 CP , but recorded intra-seasonal δ13 CP variability. The impact of environmental signals on δ13 CRing , and the 0.5and 1.7‰ depletion in photosynthates compared ring organic matter and tree-ring cellulose, respectively, are useful pieces of information for studies exploiting δ13 CRing .

Snowpack Dynamics Influence Tree Growth and Signals in Tree Rings of Tianshan Mountain, Central Asia

Snow is an important source of freshwater in the Tianshan Mountains of Central Asia. This study established 18 tree ring width chronologies and compound chronologies and analyzed the effects of snow depth, measured both by remote sensing and at meteorological stations, on the radial growth of spruce trees. The results showed that the established standard chronology of tree ring width is suitable for the analysis of tree ring climatology. The correlation coefficient of the ring width index (RWI) and the remote sensing snow depth was greater than that of the meteorological station snow depth. For the remote sensing snow depth, the correlation coefficients were greater in the winter and spring months compare to other periods, while the correlation coefficients of the meteorological stations were greater only in the winter. The nonlinear method (BRNN) showed good fitting in the reconstruction of the historical snow depth. The reconstructed snow depth exhibited a decreasing trend in the Bharakonu Mountains (BM), Narathi Mountains (NM), and Halke mountains (KM) sub-regions in the overall reconstructed period; however, the trends were inconsistent in both the historical and the observed periods, indicating the importance of reconstructing snow depth in the Tianshan Mountains.

The climatic signal in tree rings of the common oak (<i>Quercus robur</i> L.) on the south-eastern border of its range in the Ural River basin, Russia

Aim. The objective of this study was to identify and analyze the climatic signal contained in the tree-rings of common oak on the southeastern border of its range in Russia (Ural River basin).Material and Methods. The materials for the study were tree-rings in samples of common oak wood from three sites in the southern part of the Dziau-tyube ridge. Measurements of ring-width were performed on the MBS binocular microscope and on the Lintab measuring complex with the TSAP-WinTM software package. The construction of tree-ring chronologies was carried out in the ARSTAN program. Dendroclimatic analysis was carried out in the R package treeclim.Results. The limiting climatic factors for the radial growth of the common oak on the southeastern border of its range are precipitation during the winter-spring season and the initial period of vegetation and to the greatest extent with the precipitation in March-May. It was shown that the strength of this climatic signal in oak tree rings was not constant over time. The dynamics of this signal are characterized by the presence of local periods of decline, the beginning of which is timed to the years of mass gypsy moth outbreaks.Conclusions. Since the beginning of the 1980s, there has been a significant decrease in the relationship of radial growth with the amount of precipitation for March-May. The reason for this change, in our opinion, could be a strong change in the condition of trees and stands caused by the consistent impact of strong oak defoliation caused by Gypsy moths and late spring frosts.

Impact of disturbance signatures on tree-ring width and blue intensity chronology structure and climatic signals in Carpathian Norway spruce

Tree radial growth is influenced by climatic and various non-climatic factors, which can complicate the extraction of climate signals from tree rings. We investigated the influence of disturbance on tree-ring width (RW) and latewood blue intensity (BI) chronologies of Norway spruce from the Carpathian Mountains to explore the extent to which disturbance can affect temperature signals in tree rings. Overall, ∼15000 high-elevation Norway spruce tree cores from 34 sites grouped into four regions (Slovakia, Ukraine, North and South Romania) were analyzed. The curve intervention detection (CID) method was applied to detect and correct identified disturbance trends. RW chronology structural comparisons were performed among disturbance-affected and disturbance-corrected chronologies for various spatial (regional / site) scales and sampling subsets. Structural comparisons were also performed for RW and BI chronologies developed from separate groups of series (i.e., disturbed, and undisturbed) for five sites exhibiting clear disturbance trends. Temperature sensitivity was assessed for all chronology variants of both parameters. We found that disturbance trends only affected RW chronologies at the site/subset scale with relatively small series replication and were not detected at the regional scale. Unlike RW, BI chronologies were generally unaffected by disturbance. BI data also contained much stronger growing season temperature signals, which appeared to be both spatially and temporally more coherent. Whereas highly replicated and spatially extensive datasets can help minimize or eliminate disturbance trends in RW chronologies, this potential influence should be considered when interpreting climatic signals in tree rings and reconstructing historical climate in weakly replicated periods. On the other hand, BI is a promising alternative tree ring parameter with stronger and more stable growing season temperature signals, whose seemingly disturbance-free chronology structure does not appear to suffer from this ecological bias, and therefore represents a more suitable parameter for dendroclimatological research.

Chemical Signals in Tree Rings from Northern Patagonia as Indicators of Calbuco Volcano Eruptions since the 16th Century

The Calbuco volcano ranks third in the specific risk classification of volcanoes in Chile and has a detailed eruption record since 1853. During 2015, Calbuco had a sub-Plinian eruption with negative impacts in Chile and Argentina, highlighting the need to determine the long-term history of its activity at a high-resolution time scale to obtain a better understanding of its eruptive frequency. We developed a continuous eruptive record of Calbuco for the 1514–2016 period by dendrochemical analysis of Fitzroya cupressoides tree rings at a biennium resolution using inductively coupled plasma–mass spectrometry. After comparing the chemical record of 20 elements contained in tree rings with historical eruptions, one group exhibited positive anomalies during (Pb/Sn) and immediately after (Mo/P/Zn/Cu) eruptions, with a Volcanic Explosivity Index (VEI) ≥ 3, and so were classified as chemical tracers of past eruptions (TPE). The tree-ring width chronology also exhibited significant decreases in tree growth associated with eruptions of VEI ≥ 3. According to these records, we identified 11 new eruptive events of Calbuco, extending its eruptive chronology back to the 16th century and determining a mean eruptive frequency of ~23 years. Our results show the potential to use dendrochemical analysis to infer past volcanic eruptions in Northern Patagonia. This information provides a long-term perspective for assessing eruptive history in Northern Patagonia, with implications for territorial planning.

Tree-ring reconstruction of March-June precipitation from the Atlas cedar forest of Mount Takoucht, Béjaïa (northern Algeria)

Aim of study: A March-June precipitation has been reconstructed for the period 1830-2015 using Atlas cedar (Cedrus atlantica Manetti) tree-ring records. Area of study: Atlas cedar forest of Mount Takoucht (Béjaïa, northern Algeria). Material and methods: Seasonal correlations were computed in order to identify the best period of the year for the climate reconstruction. The temporal stability of the tree-ring signal for precipitation was checked using the split-sample calibration-verification procedure. The reconstruction was performed using the transfer function method. Main results: The reconstructed data revealed high interannual to decadal variation in late winter to early summer precipitation. Wet conditions dominated during the 1830s and 1840s and were followed by sustained dry conditions during the mid-19th century, which registered two of the most severe droughts (1858 and 1869) over the period of reconstruction. Relatively moderate climate conditions marked the late 19th and early 20th centuries. A gradual return towards drier conditions was observed from the 1920s and reached high frequencies of drought around mid-20th century. After an exceptional prolonged wet period of 24 years (1966-1989), the reconstruction registered its highest frequency in extreme dry/wet events: the decade 1993-2002 recorded the highest drought frequency of the reconstruction, with the third most severe dry event (1999), while the last years were marked by a clear shift toward wet conditions. Research highlights: These findings provide relevant records on past climate variability in one of the rainiest areas in Algeria and constitute valuable knowledge for specific drought and wet periods monitoring in the region. Keywords: Dendrochronology; climate reconstruction; Cedrus atlantica; Algeria.

Intraseasonal Climatic Signal in Tree Rings of Conifers in the Permafrost Zone of Siberia

Intraseasonal Climatic Signal in Tree Rings of Conifers in the Permafrost Zone of Siberia

Diverging growth performance of co-occurring trees (Picea abies) and shrubs (Pinus mugo) at the treeline ecotone of Central European mountain ranges

Although there are ample data on growth trends and climate growth relationships of trees from the leading edge of their distribution at treeline, information from the neighbouring trailing edge of the vegetation belt dominated by alpine shrubs is missing. We expected trees at their upper limit to exhibit unambiguous temperature limitation with a clearly positive growth response to recent warming. On the other hand, shrubs at the lower limits of their distribution and because of their low-stature are assumed to be less constrained by temperature, with ambiguous growth trends as compared to trees. We collected tree-ring series from sites with co-occurring Norway spruce (Picea abies) and Mountain pine (Pinus mugo) in four mountain ranges of Central Europe (the High Tatras, the Hrubý Jeseník Mts, the Krkonoše Mts and the Bavarian Alps), assembled a suite of tree-ring chronologies containing either long-term trends or high-frequency variability, and compared climate-growth relationships and growth trends between spruce and pine. Our results show that in all areas under study, growth patterns of spruce statistically differ from those of pine. The growth of spruce is characterized by a tight relationship with June–July temperatures, maximum correlations ranging between 0.5 and 0.6. The climatic signal in tree-rings of pine is also characterized by a significant influence of summer temperature, albeit weaker than that observed in spruce (mostly between 0.3 and 0.4). All sites exhibited increasing growth trends for spruce since the 1980s; trend slopes for pine were either less positive (Hrubý Jeseník and Krkonoše Mts) or negative (High Tatras). To conclude, the growth of spruce at its leading edge clearly resembled temperature-limited growth with corresponding recent growth acceleration, while the response of low-stature mountain pine to warming was weaker because of its tight coupling with microsite conditions and the location at the trailing edge of its distribution.

Testing the performance of dendroclimatic process-based models at global scale with the PAGES2k tree-ring width database

Tree-rings are one of the most commonly used proxies for reconstructing past climates at annual resolution. The climate information is generally deduced from tree-rings using statistical relationships, but the assumed linearity and stationarity may be inadequate. Process-based models allow for non-stationarity and non-linearity; however, many challenges are associated with their application for global scale reconstructions. In this study, we aim to test the feasibility of using the mechanistic model MAIDEN at the global scale for paleoclimate reconstructions based on data assimilation by applying it to the PAGES2k tree-ring width database. We also compare its performance with the simpler model VS-Lite, often used in global applications. Both models are skillful in terms of calibration and verification correlations for a similar number of sites (63 and 64 for VS-Lite and MAIDEN, respectively). VS-Lite tends to perform better for sites where the climate signal in tree-rings is strong and clear. By contrast, MAIDEN’s performance is likely mostly limited by the lack of data (for example, daily Gross Primary Production data or phenological timings) needed to accurately calibrate the model. However, when the calibration is robust, both models reproduce well the observed link between climate and tree-growth. In general, VS-Lite tends to overestimate the climate signal in tree-rings compared to MAIDEN, which better reproduces the magnitude of the climate signal on average. Our results show that both models are complementary and can be applied at the global scale to reconstruct past climates using an adequate protocol designed to exploit existing tree-ring data.

The role of extreme rain events in driving tree growth across a continental‐scale climatic range in Australia

Rainfall regimes in many parts of the world have become increasingly dominated by fewer, but more extreme, rainfall events. Understanding how tree growth responds to changes in the frequency and intensity of rain events is critical to predicting how climate change will impact on forests and woodlands in the future. In this study, we used five tree‐ring records of the native Australian conifer Callitris columellaris that span a large (> 20°) latitudinal and climatic gradient from the mesic (tropical) north to the xeric (semi‐arid) south of Australia to investigate how inter‐annual and spatial variation in the delivery of rainfall (the intensity and frequency of rain events) influences tree growth. In semi‐arid biomes (~300–400 mm rainfall annually), tree growth is most strongly related to the amount of rainfall from heavy (> 75th percentile) rain days or the number of extreme (> 90th percentile) rain days, regardless of differences in the seasonal distribution and average intensity of rainfall among sites. Our findings also indicate that there is likely a minimum threshold amount of daily rainfall (~5 mm) that is required to stimulate tree growth in the semi‐arid zone. In contrast, in the tropics (> 800 mm annual rainfall), inter‐annual variation in growth is best explained by total growing season rainfall or the number of rain days > ~5 mm (~50th percentile of rain days) rather than extreme rainfall. Our findings indicate that not all rain events are important for driving tree growth, which has important implications for interpreting climatic signals in tree rings. Our findings also indicate that projected increases in the intensity of extreme rain events are likely to have contrasting impacts on tree growth across biomes, with greater and positive impacts on growth in semi‐arid biomes and potentially negative impacts on growth in tropical biomes of Australia.

Radiocarbon bomb-peak signal in tree-rings from the tropical Andes register low latitude atmospheric dynamics in the Southern Hemisphere

South American tropical climate is strongly related to the tropical low-pressure belt associated with the South American monsoon system. Despite its central societal role as a modulating agent of rainfall in tropical South America, its long-term dynamical variability is still poorly understood. Here we combine a new (and world's highest) tree-ring 14C record from the Altiplano plateau in the central Andes with other 14C records from the Southern Hemisphere during the second half of the 20th century in order to elucidate the latitudinal gradients associated with the dissemination of the bomb 14C signal. Our tree-ring 14C record faithfully captured the bomb signal of the 1960's with an excellent match to atmospheric 14C measured in New Zealand but with significant differences with a recent record from Southeast Brazil located at almost equal latitude. These results imply that the spreading of the bomb signal throughout the Southern Hemisphere was a complex process that depended on atmospheric dynamics and surface topography generating reversals on the expected north-south gradient in certain years. We applied air-parcel modeling based on climate data to disentangle their different geographical provenances and their preformed (reservoir affected) radiocarbon content. We found that air parcel trajectories arriving at the Altiplano during the bomb period were sourced i) from the boundary layer in contact with the Pacific Ocean (41%), ii) from the upper troposphere (air above the boundary layer, with no contact with oceanic or continental carbon reservoirs) (38%) and iii) from the Amazon basin (21%). Based on these results we estimated the ∆14C endmember values for the different carbon reservoirs affecting our record which suggest that the Amazon basin biospheric 14C isoflux could have been reversed from negative to positive as early as the beginning of the 1970's. This would imply a much faster carbon turnover rate in the Amazon than previously modelled.

不同去趋势方法对树轮气候信号识别的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 不同去趋势方法对树轮气候信号识别的影响 DOI: 10.5846/stxb202004170920 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划（2017YFD060040301）；河北省教育厅青年拔尖人才项目（BJ2020025）；国家自然科学基金（41601045）；河北农业大学引进人才项目（YJ201918） Influences of different detrending methods on identifying the climate signals from tree-ring analysis Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:树木生长受到气候因子、随年龄增长的内在生长趋势、环境干扰和其他扰动信号的影响。目前存在不同的去趋势方法对树木年轮进行去趋势以识别树木生长中的气候信号。以往的研究多基于单个方法识别树轮气候信号，而不同去趋势方法识别的树轮气候信号可能会有一定的差别。为了对比不同去趋势方法对树轮气候信号识别的影响，我们基于国际年轮数据库网站获取中国西部地区68个点的树轮宽度数据，采用最常用的"signal-free"方法（SsfCrn）、线性和负指数函数法（std）、67%样条函数法（spline）、firedman方法、以及基于经验模式分解去趋势方法（EEMD）5种去趋势方法分别建立树轮年表，并对比分析同一地点的不同年表对气候响应的异同。结果表明：不同去趋势方法得到的年表对温度、降水以及相对湿度等气候因素的响应具有明显差异。其中，SsfCrn去趋势方法建立的年表对温度（月平均温、月最低温、月平均最低温）响应中相关最高的样点在所有样点中占比最高；EEMD去趋势方法建立的年表对降水量、相对湿度和月最高温响应中相关最高的样点在所有样点中占比最高；firedman去趋势方法建立的年表对月平均最高温响应中相关最高的样点在所有样点中占比最高。研究结果表明SsfCrn，EEMD和firedman方法在识别树轮气候信号方法具有一定的优势。在不同研究区域中，不同去趋势方法建立的年表对不同气候条件响应有差异，因此选择不同的去趋势方法识别树木生长趋势，分析哪种方法可以更好的反应气候变化对树木生长的影响显得尤为重要。 Abstract:Tree radial growth is influenced by climate factors such as temperature, precipitation and relative humidity, its intrinsic growth trend (increments of age), environmental disturbances, and unexplained variability of other signals. Tree ring chronologies were obtained using detrending method to remove the intrinsic growth trend of trees to retain climate signals in tree rings. Currently, there are many detrending methods which can be used to develop tree ring chronologies. Climate signals from tree rings were mainly identified using one detrending method in most previous studies, however, the identified climate signals can be different from the changes in detrending methods. To compare influences of different detrending methods on identifying the climate signals from tree ring analysis, we obtained the width data of the tree ring of 68 sites in the western region of China from the international tree ring database. The commonly used "signal-free" method (shorted as SsfCrn), linear and negative exponential function method (shorted as std), 67% spline function method (shorted as Spline), firedman method, and ensemble empirical mode decomposition-based (shorted as EEMD) detrending method were used to establish tree ring chronology, respectively. The similarities and differences of how tree growth responses to climate with different tree ring chronologies were compared. The results showed that there were significant differences in how trees responded to climate factors such as temperature, precipitation and relative humidity, based on the tree ring chronology obtained by different detrending methods. The chronology had higher correlation with temperature (monthly average temperature, monthly lowest temperature, and monthly average lowest temperature) when using SsfCrn detrending method than other detrending methods in most sites of the study region. The chronology had higher correlation with precipitation, relative humidity, and monthly maximum temperature when using EEMD-based detrending method than other detrending methods in most sites of the study region. The chronology had higher correlation with average monthly maximum temperature when using firedman detrending method than other detrending methods in most sites of the study region. Our results suggested that the chronologies developed with SsfCrn, EEMD and firedman methods are more suitable to detect growth-climate relationship than other methods. Tree ring chronologies obtained with different detrending methods responded differently to the same climatic factors and the same tree ring chronology had different responses to different climatic conditions in different research areas. Therefore, choosing proper detrending methods to identify tree growth trends is particularly important to detect the influences of climate changes on tree growth. 参考文献 相似文献 引证文献

DfoliatR: An R package for detection and analysis of insect defoliation signals in tree rings

We present a new R package to provide dendroecologists with tools to infer, quantify, analyze, and visualize growth suppression events in tree rings. dfoliatR is based on the OUTBREAK program and builds on existing resources in the R computing environment and the well-used dplR package. It is designed to aid research in the ecology of insect defoliation events and to reconstruct defoliator outbreak chronologies, but can be applied to other studies where host–non-host comparisons are useful. dfoliatR performs an indexing procedure to remove climatic signals in the host-tree series that are represented in the non-host chronology, or other annually-resolved climate series. It then infers defoliation events in individual trees based on user-specified thresholds. Site-level analyses identify outbreak events that synchronously affect user-defined numbers or proportions of involved host trees. Functions are provided for summary statistics and graphics of tree- and site-level series. We evaluated dfoliatR against OUTBREAK, using eight datasets including 222 host-trees, and found that dfoliatR improves on OUTBREAK with greater user control, identification of defoliation events, computing capacity, and both the statistical summary and graphical outputs. We provide two example data sets and script to enable users to gain familiarity with the package and its capabilities. The source code is available in the Comprehensive R Archive Network (CRAN) and on GitHub.

Dendrochronological study of painted chests from the collection of the Gorenjska Museum in Kranj

Painted chests are an important part of museum collections of folk art in the Alpine region. At the Gorenjska Museum in Kranj, we examined over 30 chests mostly made of Norway spruce (Picea abies) and selected 18 of them for dendrochronological analysis. We took high resolution images of the radial boards of the constructional parts of the chests for tree-ring analyses. We constructed tree-ring chronologies for each of the 18 chests. Nine of them were dendrochronologically dated (eight spruce chests and one silver fir) with the end dates ranging from 1742 to 1882. The study of the chest made of silver fir (Abies alba) is presented in detail. Half of the chests could not be dated, mainly due to the low number of tree-rings or large variability of tree-ring signal of spruce in Slovenia and consequently lack of adequate reference chronologies. The results show that dendrochronology can be used to determine age and obtain information about chests that cannot be obtained from other sources.

Impact of high flows of an Arctic river on ring widths of floodplain trees

The tree-ring signal for flooding along the Ob River, a large Arctic River in western Siberia, is investigated using a combination of floodplain tree-ring sites from riparian and non-riparian settings. A conceptual model is presented contrasting tree-growth responses of riparian and non-riparian trees to unusually severe flooding. A set of five riparian ( Salix and Populus) tree-ring chronologies is developed and used in combination with existing floodplain non-riparian Larix and Pinus chronologies in a binary classification tree (CT) model to classify high-flood years, defined as a Salekhard water-level gage reading in the seasonal window from May 1 to August 31 of above 470 cm for 82 or more consecutive days. Correlation and regression identifies a nonlinear relationship of riparian ring widths to discharge and flooding: higher annual discharge generally leads to higher growth, but the relationship reverses in extreme-flood years. Micrographs highlight the suppression of width and occasional distortion of cell anatomy in selected trees. CT modeling guided by cross-validation yields a CT model with a primary split on the riparian ring width and secondary split on the non-riparian ring width. The model successfully identifies four of the eight most severe high-flow years, 1934–2014. The model further identifies two years (1885 and 1914) before the start of the gaged record in 1934 as high-flow years. No appreciable difference is found in frequency of high-flow years before and after 1956, when the first major reservoirs began filling upstream of the Lower Ob. The CT modeling approach is proposed as a novel approach to dealing with nonlinearity in reconstructing flood history of Arctic rivers from tree rings.

Volcanic activity signals in tree-rings at the treeline of the Popocatépetl, Mexico

The Popocatépetl volcano resumed its eruptive activity in 1994 and is still active. The largest eruption recorded during this new stage of activity occurred in December 2000. We traced the volcanic activity signal in tree-rings from Pinus hartwegii trees located in the north slope of the volcano, located at ∼3 km from the volcanic cone. Annually resolved tree-ring widths, elemental and stable δ13C and δ18O isotope composition were measured during the period 1989–2014 to study the effects of the volcanic activity on trees. Our results indicate a high increase in the concentration of metal elements (Co, Cr, Cu, Fe, Li, Mo, Ni, Pb, Rb, Sr, Ti, Zn) in tree rings following the major 2000 volcanic eruption, compared to the pre-eruption period from 1989 to 1993. Other chemical elements such as Al, K and S peaked 2 years later, in the 2003 tree ring, that matched with the formation of a very narrow ring that year. This sharp reduction of growth was probably driven by a combination of harsh climatic conditions (drought) with the lagged negative effects of the 2000 eruption. Carbon isotope discrimination (Δ13C) and δ18O increased from 1995 to 2006, suggesting reduced stomatal conductance, photosynthetic activity and water use efficiency due to the large dust veil covering the study zone. The variation of relevant elements (Ca, Mn) showing significant correlations with tree growth, Δ13C and δ18O can be attributed to the selective availability of elements following the soil acidification caused by the volcanic activity. Our findings suggest that the recent activity of the Popocatépetl might have increased tree vulnerability, as reflected in the sharp reduction of growth following the drought recorded 2 years after the large eruption of December 2000. Our results warn about the cumulative negative effects of volcanic activity and harsh climatic conditions on tree growth and functioning.

Climate signals in tree rings of Paubrasilia echinata (Leguminosae-Caesalpinioidea) from the Atlantic Forest of Brazil

Tree-ring chronologies were built for wild and cultivated Paubrasilia echinata, a presently endangered species. Significantly P. echinata showed measurably different growth patterns related to the environment where wild and cultivated trees have grown. Paubrasilia echinata once grew so abundantly along the tropical coast of South America that the names given to the tree by early Europeans colonists—Bresil, Brasil, Brazil—became synonymous with an entire geography. Today, despite restoration and protection efforts, the species remains under threat of extinction throughout Brazil’s Atlantic Forest. Considering the past overexploitation and ongoing climate changes, the future of P. echinata significantly depends upon human understanding of the species’ growth dynamics and growth-climate relations. Therefore, this work aims to: (1) demonstrate the feasibility of calendar dating P. echinata tree rings; (2) build chronologies by analyzing its growth rings; and (3) establish with detail the specific influence of climate on annual radial xylem production. Differences in vessel and axial parenchyma frequency, local distended rays and marginal parenchyma were the wood anatomical markers used to distinguish boundaries between adjacent rings so that dendrochronological methods could be applied. For climate-growth responses, we developed tree-ring width chronologies from wild and cultivated trees. Results revealed that seasonal rainfall is the most important factor influencing P. echinata growth. More specifically, positive correlation was observed between the tree-ring chronology of wild trees and precipitation during the rainy months of the growing season, while the tree-ring chronology of cultivated trees correlated negatively with precipitation in months before the growth period. Wild trees showed increment growth rates lower than planted trees. Rainfall’s observed effect on P. echinata is, of course, not surprising. However, our results contribute a detailed quantitative record of that effect, which expands the body of ecological knowledge regarding P. echinata necessary for ongoing conservation efforts under current and future human-caused climate change.

Linking drought legacy effects across scales: From leaves to tree rings to ecosystems.

Severe drought can cause lagged effects on tree physiology that negatively impact forest functioning for years. These "drought legacy effects" have been widely documented in tree-ring records and could have important implications for our understanding of broader scale forest carbon cycling. However, legacy effects in tree-ring increments may be decoupled from ecosystem fluxes due to (a) postdrought alterations in carbon allocation patterns; (b) temporal asynchrony between radial growth and carbon uptake; and (c) dendrochronological sampling biases. In order to link legacy effects from tree rings to whole forests, we leveraged a rich dataset from a Midwestern US forest that was severely impacted by a drought in 2012. At this site, we compiled tree-ring records, leaf-level gas exchange, eddy flux measurements, dendrometer band data, and satellite remote sensing estimates of greenness and leaf area before, during, and after the 2012 drought. After accounting for the relative abundance of tree species in the stand, we estimate that legacy effects led to ~10% reductions in tree-ring width increments in the year following the severe drought. Despite this stand-scale reduction in radial growth, we found that leaf-level photosynthesis, gross primary productivity (GPP), and vegetation greenness were not suppressed in the year following the 2012 drought. Neither temporal asynchrony between radial growth and carbon uptake nor sampling biases could explain our observations of legacy effects in tree rings but not in GPP. Instead, elevated leaf-level photosynthesis co-occurred with reduced leaf area in early 2013, indicating that resources may have been allocated away from radial growth in conjunction with postdrought upregulation of photosynthesis and repair of canopy damage. Collectively, our results indicate that tree-ring legacy effects were not observed in other canopy processes, and that postdrought canopy allocation could be an important mechanism that decouples tree-ring signals from GPP.

Assessment of the recurrence intervals of rockfall through dendrogeomorphology and counting scar approach: A comparative study in a mixed forest stand from the Vercors massif (French Alps)

As direct observations of rockfalls are rare and difficult to obtain over long timescales, stem injuries and their dating with dendrogeomorphic techniques have been applied frequently in the past to reconstruct process activity. However, the analysis of tree-ring samples requires considerable temporal efforts, which can be detrimental in applied research and expert opinions. To compensate for this shortcoming, several studies have lately explored the potential of the counting of visible scars as an alternative method to dendrogeomorphology as it requires much less time and human efforts to reconstruct spatial patterns of rockfall activity. Yet, to date, both approaches have not been compared at the same site. In this paper, based on the extensive analysis of 278 conifer and broadleaved trees (from which 1097 tree-ring cores were extracted) from a mixed forest plot of the Vercors Massif (French Alps), we demonstrate that both methods provide similar spatial patterns of rockfall activity with a strong increase of recurrence intervals down the talus slope and a clear lateral zonation of activity. Despite this apparent convergence between both approaches, our study also evidences that rockfall frequencies strongly differ with tree species and diameter: the visual inspection of conifer stems and the analysis of tree-ring signals in large-diameter broadleaved trees typically lead to an overestimation of recurrence intervals. Based on these findings, we recommend giving priority to the scar-counting approach on small diameter (<15 cm) broadleaved stems and to restrict tree-ring analysis to old conifers that are more susceptible – through the identification of tangential rows of traumatic resin ducts – to provide reliable estimations of long recurrence intervals (as generally observed in the lower portions of the slope). These guidelines should help to improve the reliability of recurrence interval maps of rockfall process activity in forests further, but also to improve cost-benefit ratios of future studies.

From xylogenesis to tree rings: wood traits to investigate tree response to environmental changes

ABSTRACTIt is noteworthy that the largest part of global vegetation biomass depends on a thin layer of cells: the vascular cambium. Understanding the wood formation processes and relationships with environmental factors is a crucial and timely research question requiring interdisciplinary efforts, also to upscale the information gained and to evaluate implications for tree growth and forest productivity.We provide an overview of wood formation processes up to tree-ring development, bearing in mind that the combined action of intrinsic factors and environmental drivers determines the anatomical traits of a tree ring formed at a specific time and position within the tree’s architecture. After briefly reviewing intrinsic factors, we focus attention on environmental drivers highlighting how a correct interpretation of environmental signals in tree rings must be grounded in a deep knowledge of xylogenesis and consequent wood anatomical traits. We provide guidelines on novel methods and approaches recently developed to study xylem formation. We refer to existing literature on established techniques for retrospective analyses in tree-ring series of anatomical and isotopic traits, to assess long-term ecophysiological responses to environmental variations, also giving advice on possible bias because of interand within-tree variability.Finally, we highlight that, once the temporal axis of intra-annual tree-ring variability of xylem traits is established by xylogenesis analysis, a multidisciplinary approach linking classical dendro-ecology, wood functional traits (dendro-anatomy) and eco-physiology (here focusing on dendro-isotopes) allows a better interpretation of past environmental events hidden in tree rings, and more reliable forecasts of wood growth in response to climate change.