Tree-Ring Research: Recent submissions
Now showing items 21-40 of 727
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A Machine Learning Approach To Analyzing The Relationship Between Temperatures And Multi-Proxy Tree-Ring RecordsMachine learning (ML) is a widely unexplored field in dendroclimatology, but it is a powerful tool that might improve the accuracy of climate reconstructions. In this paper, different ML algorithms are compared to climate reconstruction from tree-ring proxies. The algorithms considered are multiple linear regression (MLR), artificial neural networks (ANN), model trees (MT), bagging of model trees (BMT), and random forests of regression trees (RF). April-May mean temperature at a Quercus robur stand in Slovenia is predicted with mean vessel area (MVA, correlation coefficient with April-May mean temperature, r = 0.70, p < 0.001) and earlywood width (EW, r = -0.28, p < 0.05). Similarly, June-August mean temperature is predicted with stable carbon isotope (delta C-13, r = 0.72, p < 0.001), stable oxygen (delta O-18, r = isotope 0.32, p < 0.05) and tree-ring width (TRW, r = 0.11, p > 0.05 (ns)) chronologies. The predictive performance of ML algorithms was estimated by 3-fold cross-validation repeated 100 times. In both spring and summer temperature models, BMT performed best respectively in 62% and 52% of the 100 repetitions. The second-best method was ANN. Although BMT gave the best validation results, the differences in the models' performances were minor. We therefore recommend always comparing different ML regression techniques and selecting the optimal one for applications in dendroclimatology.
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Climatic Drivers Of Ponderosa Pine Growth In Central IdahoDespite the widespread use of ponderosa pine as an important hydroclimate proxy, we actually understand very little about its climate response in the Northern Rockies. Here, we analyze two new ponderosa pine chronologies to investigate how climate influences annual growth. Despite differences in precipitation amount and timing and large elevation differences (1820 m versus 1060 m), ring width at both sites was strongly driven by water availability. The mid-elevation, water-limited site responded well to previous fall precipitation whereas the wetter, high-elevation site responded to growing season precipitation and temperature. When precipitation and temperature were simultaneously accounted for using the standardized precipitation evapotranspiration index, ring-width response between sites converged and appeared nearly identical. Water stress drove the timing of ponderosa pine growth by a combination of factors such as strong water dependence, and determinate growth physiology, as indicated by lag-1 autocorrelation. When analyzing response to single-month climate variables, precipitation from growing-season months dominates. When we examined seasonal variables, climate fromthe previous year became more important. Temporal fidelity of the climatic response at both sites maintained significance across the historical record, although the relationship weakened at the low-elevation site. The collection of new tree-ring data sets such as these for central Idaho improves our understanding of ponderosa pine growth response to climate.
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Dendroecological Approach To Assessing Carbon Accumulation Dynamics In Two Pinus Species From Northern MexicoGlobal climate change will alter forests by shifting species ranges, which has implications for their ecological functions. Annual tree-ring widths andwood density are useful proxies for carbon cycle studies across a range of species. Here, using a dendroecological approach we sought to understand the carbon accumulation rates of two representative pine species growing on contrasting wet (P. arizonica) and dry (P. cembroides) sites and reveal how such species cope with climate variability. Although the rate of carbon gain was not significantly different across sites, we found that variations in carbon accumulation responded differently to specific hydroclimate drivers, site conditions, or to functional features of each species, which are still to be explored. Overall, annual carbon accumulation (C) was less sensitive to climate variability than ring width and wood density. Annual C was more sensitive to rainfall in the cold season (P. arizonica) and to the start of spring (both species). Our species-specific approach provided a suitable basis for modeling projections in the long-term carbon balance in these forests. Using species-specific tree-ring data has the potential to yield better estimations given that tree rings reflect fine spatial and temporal resolution, thereby reducing the uncertainty in forest carbon budgets.
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Sensitivity Of Three Dominant Tree Species From The Upper Boundary Of Their Forest Type To Climate Change At Changbai Mountain, Northeastern ChinaWe quantified the growth dynamics and climatic responses of three tree species that have dominated Changbai Mountain: Korean pine (Pinus koraiensis), Yeddo spruce (Picea jezoensis), and Erman's birch (Betula ermanii). Standardization curves and moving correlations were used to assess growth rate trends and analyze changes in growth-climate relationships of trees at their upper forest boundaries and individual species elevation limits, respectively. Contrasting growth patterns were observed between trees at each upper forest boundary and species-specific upper elevation limits. Korean pines and Yeddo spruces grew faster at their upper forest boundaries than at their individual species limits. A higher growth rate of Erman's birches at their forest upper boundary only occurred before 1960. Relative to the strong effect of temperature on tree growth at individual upper elevation limits, the stable effect of precipitation and changing effect of temperature on tree growth were observed at the upper forest boundaries. Temperature increases have had a significantly negative effect on Korean pine and Erman's birch since 1980, whereas temperature increases were associated with Yeddo spruce growth. This study elucidated the differential growth patterns and temporal changes in climate-growth relationships of these species between their upper forest boundaries and elevation limits.
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Climatic Signal In Earlywood And Latewood In Conifer Forests In The Monarch Butterfly Biosphere Reserve, MexicoEarlywood (EW) and latewood (LW) chronologies can be used to analyze seasonal climatic variation. We constructed and analyzed total ring (RW), EW, and LW ring growth in Abies religiosa and Pinus pseudostrobus trees from the Monarch Butterfly Biosphere Reserve and evaluated their climatic signal (monthly precipitation and mean average, minimum and maximum temperatures) in the growth of tree rings by correlation and response function analyses. Precipitation during October and December of the previous year and during January, February, April, and May of the year of growth had a positive influence in the growth of both P. pseudostrobus and A. religiosa. Mean maximum temperatures had a negative effect on tree growth in both species. Additionally, growth of A. religiosa was more sensitive to variations of mean, minimum, and maximum temperatures in comparison with P. pseudostrobus, and monthly mean minimum temperature was positively correlated with EW and LW series in A. religiosa. We conclude that EW and LW growth of A. religiosa and P. pseudostrobus might be reduced by lower precipitation during the winter-spring season. Consequently, in the eventuality of warmer and drier climate during the latter season as projected by climate change scenarios, growth rates of A. religiosa could become severely affected, negatively impacting the overwintering habitat of the monarch butterfly (Danaus plexippus L.).
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How Do Droughts And Wildfires Alter Seasonal Radial Growth In Mediterranean Aleppo Pine Forests?Climate models project increasing temperatures, evapotranspiration, and droughts for the Mediterranean Basin, which will trigger more frequent and dangerous fire events. Here, we evaluate the combined effects of drought and wildfire on seasonal tree growth on Aleppo pine stands at the intra-and inter-annual level. Indexed earlywood width (EWI), latewood width (LWI), and latewood proportion (LWPI) series were obtained from unburned and burned stands located at four sites along a precipitation gradient in southeastern Spain. The combined effect of drought in 1994 and 1995 and wildfire in August 1994, negatively impacted seasonal growth in the short term (1994-1999 period) at the site with higher water availability. At the driest site, however, no significant effects were found. We found fewer negative pointer years at the wettest burned stand than at the wettest unburned stand during the post-fire 1994-2012 period, and the opposite pattern was found at the driest site, i.e. more negative pointer years at the driest burned stand than at the driest unburned stand. This result indicates that the drier sites were more sensitive to cumulative impact of drought and wildfire disturbances in the long term, whereas the wetter sites were more sensitive in the short term. Our results demonstrate the seasonal growth plasticity of Aleppo pine to combined disturbances depends on site water availability. This study will help forest managers to implement climate change strategies, such as prescribed fires (controlled low-medium severity fires) to prevent wildfire hazards more efficiently in Aleppo pine stands with high water availability.
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The First Dendrochronological Dating Of Timber From Tajikistan - Potential For Developing A Millennial Tree-Ring RecordWe are reporting the first dendrochronological dating of timber from Tajikistan. Thirty samples were collected from two old buildings from a village located in the western Pamir-Alay; eight cores were taken from temple. Most of the construction wood was juniper species. The object chronologies cross-dated well with the previously published chronology based on living juniper trees from western PamirAlay. The results of dating revealed that investigated structures are composed of wood coming from several periods. The oldest pieces of wood dated back to the 11th and 12th Centuries. Most timber samples come from the turn of the 17th and 18th Centuries, which were probably the period of intense development of the Artuch village. Besides dating of the wood samples from these historic structures, our investigation provides the opportunity to extend the currently existing regional tree-ring chronology for future climate reconstruction of the Pamir-Alay and High Asia. Dated sequences were assembled into a 1012-year chronology spanning the period 945-2014 C.E. and strengthened the replication of its earliest part (with critical 0.85 EPS value since the beginning of the 13th Century).
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Ensemble Empirical Mode Decomposition As An Alternative For Tree-Ring Chronology DevelopmentSince its establishment, tree-ring analysis has benefitted several scientific fields. Because of its many advantages, dendrochronology is a first choice to reconstruct past environmental variability. Two major concerns about the current tree-ring reconstruction paradigm are the subjective choices of detrending functions and the lack of fidelity to data of chronology generation methods. It is difficult to recover the original tree-ring data once they have been detrended and standardized. In this study, ensemble empirical mode decomposition (EEMD) is introduced as an objective high-fidelity stand-alone approach for developing tree-ring chronologies. Basic concepts of EEMD, recommended steps in developing chronologies, and available public domain programs are discussed. To demonstrate the potentials of EEMD for chronology development, two examples are provided, one for climate and the other for streamflow reconstructions. In both examples, EEMD chronologies show higher correlations with the instrumental data and have more power in their spectra than the ones developed based on the current tree-ring reconstruction approach. General usage concerns and cautions are also addressed.
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Tree-Ring Research Of Mexican Beech (Fagus Grandifolia Subsp Mexicana) A Relict Tree Endemic To Eastern MexicoMexican beech (Fagus grandifolia subsp. mexicana) has been classified as an endangered species because of its restricted distribution. The current distribution of Mexican beech, which is considered a Miocene relict, is limited to Tropical Montane Cloud Forests (TMCF) in the mountains of the Sierra Madre Oriental in eastern Mexico. We used dendroclimatic techniques to evaluate the effects of climate variability on the growth of Mexican beech within three forest fragments. The independent chronologies developed for the three sites were 152-178 years long. Cross-sections helped to assess the quality of the crossdating and detect false rings. Over the last 180 years, Mexican beech trees have lower mean radial growth than rates exhibited by other Fagus species. Mexican beech growth appears to be influenced by growing-season temperatures, especially mean maximum temperature. The response appears to be positive at the beginning of the growing season but becomes negative later. These results suggest that the persistence of Fagus-dominated forests in Mexico is dependent on local-scale climatic conditions of the TMCF. Mexican beech forests are associated with micro-climatic conditions that will control the fate of these forests in the face of on-going climate change.
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Climate Signal In Cork-Ring Chronologies: Case Studies In Southwestern Portugal And Northwestern AlgeriaIn temperate regions, the analysis of climate signals encoded in the wood rings allows assessing tree sensitivity to climate and its potential effects on growth and yield. In Mediterranean regions, the cork oak (Quercus suber L.) has received limited attention for dendrochronological studies because tree rings are faint and cork rings with a clear annual banding have been rather neglected. We analyzed the climatic signal of cork-ring chronologies for AD 1996-2010 from distinct regions in western Algeria [a mountain oak forest called Hafir-Zarieffet] and in southern Portugal [a peneplain wood-pasture called Benavente]. The goal was to evaluate the strength and consistency of climate signal and to assess cork growth sensitivity to climate variables (precipitation and temperature). Our results suggest that cork growth encodes a climatic signal. Trends of cork growth, via correlation analysis, including climate variables (on a monthly and seasonal basis) and Lang's index (on an annual basis) were successfully assessed. Drought-driven cork growth reduction is a threshold function of a P-T ratio, and with expected increase in the drought occurrence under changing climate, cork growth is likely to be similarly affected in both regions.
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Dendrochronological Reconstruction Of Environmental History Of Fagus Grandifolia Subsp Mexicana In MexicoGrowth-ring analysis is a valuable source of information for reconstructing environmental history. In this study, ring-width series of a sample of Fagus grandifolia subsp. mexicana were used to identify the main events that have affected populations of this species. Core samples were extracted in three representative beech forests in Mexico. These are forests where F. grandifolia subsp. mexicana dominates the canopy. A total of 3355 years of growth rings were measured and three ring-width chronologies were generated. Average annual ring widths were similar between the three sites and ranged from 0.98 to 1.08 mm. A pattern of multiple suppressions and releases was observed, mainly associated with local events, but with a slight climatic influence. Correlations between the ring-width index and climate variables were not statistically significant, with the exception of a seasonal January-June precipitation pattern (1982-2001). There has not been a large-scale disturbance of natural or human origin in the beech forests of the state of Hidalgo in the past 150 years, except in El Gosco, where anthropogenic disturbances have increased in the past decade.
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Growth-Ring Boundary Anatomy And Dendrochronological Potential In A Moist Tropical Forest In Northeastern BangladeshWe present the microscopic analysis of growth-ring boundary anatomy of 27 tree species from a moist tropical forest in Bangladesh and evaluate their dendrochronological potential. We observed high inter-species variability in the anatomical features that define growth-ring boundaries. Marginal parenchyma, fibre zones, and thick-walled latewood fibres were identified as the dominant anatomical features delineating growth-ring boundaries. The evaluation of growth-ring boundary distinctness in thin-sections and scanned images revealed that 25 out of 27 studied species (93%) showed distinct to fairly distinct growth-ring boundaries. Cluster analysis of wood anatomical features was used to select an additional 5 species for further investigation. Ring-width series of these species crossdated well within the same tree. Between trees crossdating was also successful in all 5 species. The Gleichlaufigkeit (GLK; i.e. the proportion of agreement/disagreement of inter-annual growth tendencies among the trees) varied among species between 0.55 and 0.71. A strong synchronization of tree-ring series between trees suggests that growth rings are annual and influenced by common environmental factors. The derived tree-ring series, estimated tree ages, and growth trajectories underline the high potential of our study area for answering a variety of climatological, ecological and archaeological questions by applying den-drochronology. This study will therefore provide a new endeavor in tropical dendrochronology of South Asian moist tropical forests.
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South American Dendroecological Fieldweek 2016: Exploring Dendrochronological Research In Northern PatagoniaThe South American Dendroecological Fieldweek (SADEF) associated with the Third American Dendrochronology Conference was held in El Bolson, Argentina, in March 2016. The main objective of the SADEF was to teach the basics of dendrochronology while applying specific knowledge to selected research questions. The course included participants and instructors from six different countries. This report describes activities of the course and briefly summarizes exploratory group projects. The Introductory Group developed an Austrocedrus chilensis chronology from 1629-2015 and documented a persistent decline in growth since 1977 which supports the fact that the current severe drought is the most severe in the 386-year record. Based on regional A. chilensis chronologies from 32. to 39. S Latitude, the Stream Flow Reconstruction Group developed a regional 525 year-long reconstruction from Rio Chubut and found the most severe drought episodes from 1490 to the present occurred from 1680-1705, 18131828, 1900-1920, 1993-2002, and from 2011 to the present. The Drought Reconstruction Group used A. chilensis annual tree-ring width chronologies to develop preliminary spatial field reconstructions of the Palmer Drought Severity Index spanning the Central Andes region. The reconstructions explain up to 81% of the 1907-1975 PDSI variance, indicating this tree species is powerful for informing on historical drought especially in very arid domains. The Dendroecology Group documented three spreading fires since the 1850s with a 12-year return interval but lack of fire for the last 94 years; they also documented a persistent decline in their chronologies in recent years, dating back to 1965.
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Millennium-Long Tree-Ring Chronology Reveals Megadroughts on the Southeastern Tibetan PlateauMillennium-aged trees are rare in natural forests. Here we present an 1184-year-long tree-ring width chronology from living juniper trees in the Biru area on the southeastern Tibetan Plateau. Growth-climate response analysis shows that the Biru chronology is significantly and positively correlated with late-spring (May-June) Standardized Precipitation Evaporation Index (SPEI) (r = 0.67, n = 53, p < 0.01). The tree-ring chronology explains 44.5% of the total variance of SPEI during the period AD 81957-2010. Reconstruction of May-June SPEI shows that there was a two-century-long megadrought during the late 13th to late 15th Centuries, and a seven-decade-long megadrought during AD 1630s to 1690s. Comparisons with other moisture records in the region suggest that the two-century megadrought identified in our reconstruction might be a widespread phenomenon most likely reflecting a stage of reduced Southwest Asian Summer Monsoon. Our results provide new evidence on the megadrought events on the Tibetan Plateau for the last millennium. © 2017 by The Tree-Ring Society.
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Assessing the Potential of Pinyon Pine for Climate Reconstructions in Eastern CaliforniaThis paper documents a pilot study investigating the potential use of pinyon pine (Pinus monophylla Torr. & Frem) growing in the White Mountains of eastern California for climate reconstructions. The single-leaf pinyon pine from this study exhibit a significant and stable relationship with annual (August-July) precipitation over the instrumental record (r = 0.69). This relationship is stronger than that of the lower forest border bristlecone pine (Pinus longaeva) growing nearby. Spatially, the climate-growth relationship remains strong beyond this localized region, extending over Southern California. Although pinyon pine is not as long lived as the bristlecone pine, these results indicate that the strength of the climate-growth relationship makes this species valuable in developing climate reconstructions in the future. Additionally, the presence of persistent remnant wood at all sampling sites offers an opportunity to extend pinyon records further back in time. Furthermore, the close proximity of pinyon pine to bristlecone pine at these sites presents the possibility of developing multi-species reconstructions using both species. © 2017 by The Tree-Ring Society.
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Crossdating Dead Trees: Does Sampling Height Influence Results?In trees experiencing stress prior to death, growth may be partially or totally suppressed, or may occur only in the upper part of the boles. This may induce inaccuracies when retrospectively crossdating dead trees. In this study, we investigated the occurrence and range of time lags between year of last ring production (YOLRP) in crossdated discs collected at the base, at breast height (BrH), and in the upper part (UP) of the boles of 145 snags and logs of four boreal species. We also assessed the influence of tree age and growth prior to death. When comparing YOLRP in the upper and lower part of trees, more than half the time lags departed from zero. Mean lags ranged from 0.6 to 4.6 years according to species, with lags up to 14 years. Negative time lags, i.e. ring production occurring in the lower part of boles while it has stopped in the upper part, were also observed in up to 26% of cases. We suggest that when reconstructing fine patterns of mortality where accuracy must be optimized, sampling entire discs at BrH should be considered, as well as sampling a disc in the UP when sampling old or slowly declining trees. © 2017 by The Tree-Ring Society.
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Dendroclimatic Responses of Sugar Maple Tapped for Maple Syrup: A Case Study from PennsylvaniaMaple syrup is a regional, non-timber forest product in the United States that depends upon healthy, mature sugar maple (Acer saccharum Marshall). We examined whether tapping for maple syrup altered the dendroclimatic response of sugar maple. Ring width indices from two sites (tapped and reference) in central Pennsylvania were correlated with regional temperature, precipitation, and Palmer Drought Severity Index (PDSI). Both sites had significant correlations between summer and fall PDSI and radial growth. Spring PDSI was significantly correlated with growth at the reference site, but not at the tapped site. Both tapped and reference trees experienced below-average growth during years with dry spring conditions (PSDI < 0), but tapped trees had a higher percentage of years (27%) with below-average growth during years with moist spring conditions (PDSI > 0) compared to reference trees (15%). These results indicate that tapping for maple syrup may have altered the dendroclimatic response of sugar maple to moisture availability during the spring months. © 2017 by The Tree-Ring Society.
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Dendrochronological Field Methods for Fire History in Pine Ecosystems of the Southeastern Coastal PlainFew tree-ring based fire-history studies have been completed in pine ecosystems of the Southeastern Coastal Plain, in part because of difficulties in finding old fire-scarred material. We propose specialized field methods that improve the likelihood of locating fire scars in dead trees (i.e. stumps, snags, and logs). Classic fire-history field methods developed in the southwestern United States involve targeting only trees with evidence of repeated external scarring, but we have found this approach to be less effective in our region given that trees without any external scarring may contain an abundance of buried scars. The buried scars occur primarily near the ground surface and can be sampled by collecting full cross-sections from the bases of old dead trees. We hope our insights foster further fire-history research in the Southeastern Coastal Plain. © 2017 by The Tree-Ring Society.
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Updating the Czech Millennia-Long Oak Tree-Ring Width ChronologyIn recent years, a millennia-long oak tree-ring width chronology, consisting of 3194 samples from 387 locations, was developed in the Czech Republic. Despite the collection of such a huge dataset, the replication in the 19th Century was very low and the natural oak distribution in the Czech Republic was insufficiently covered by recent samples, especially in Western Bohemia. This study aimed to remove these weaknesses, which have limited the paleoclimatic potential of this dataset, and to determine the number of sapwood rings, which is crucial for dendrochronological dating. Therefore, new recent samples were randomly collected at numerous sawmills along the Czech-German border. The historical material was usually sampled using a Pressler borer from church belfry constructions traditionally made from oak. In total, 252 recent and 90 historical tree-ring width series were incorporated into the chronology. The newly built chronology cumulatively consists of 3536 series, which covers the continuous period of A.D. 352-2014. The resulting tree-ring width record shows robust signal strength and homogeneous coverage of the territory. We show that the number of sapwood rings is constant over time. Therefore, we recommend using an estimate of 5-24 sapwood rings for a more precise dating of historical wood findings in the Czech Republic. © 2017 by The Tree-Ring Society.