In recent decades, there has been increased global concern about observed climate change; however for future climatic impacts and anthropogenic forcings of climate change to be realistically predicted, natural climate variability in the past needs to be better understood. The aim of this research is to develop quantifiable proxy records of past climate change through the calibration of isotope values in modern surface waters and tree ring cellulose with meteorological and atmospheric records. Terrestrial proxy records that utilize oxygen and hydrogen isotope values to reconstruct paleoclimatic and paleohydrologic conditions are limited by a paucity of data on the modification of surface water isotope values prior to sequestration into proxy material. To address this gap in our knowledge and determine the most appropriate study sites, this research focuses on isotopic records preserved in surface water reservoirs, precipitation, and tree-ring cellulose. In the first study, δD, δ18O, and deuterium-excess values were determined for lakes and rivers from Tasmania, southeastern Australia. <p> The second focus of this research was to calibrate the δ18O, δD, and δ13C values of tree-ring cellulose from North America with instrumental records. A new high-resolution sampling procedure that uses a robotic micromilling device to very precisely map and sample along growth rings in trees is discussed. Additionally, a seasonally resolved (early/late wood) 110-year record of δ18O values from tree-ring α-cellulose from spruce species (<i>Picea mariana</i> and <i>P. glauca</i>) from east-central Saskatchewan, Canada is compared to growing season precipitation δ18O values, temperature, and relative humidity. The δ18O time series from α-cellulose display a high correlation with growing season precipitation isotope values (r = 0.86). δ18O α-cellulose time series from a white spruce (<i>Picea glauca</i>) also records seasonal changes in atmospheric circulation associated with the position of the circumpolar vortex and dominate modes of atmospheric variability such as the North Atlantic Oscillation and Pacific Decadal Oscillation.

In recent decades, there has been increased global concern about observed climate change; however for future climatic impacts and anthropogenic forcings of climate change to be realistically predicted, natural climate variability in the past needs to be better understood. The aim of this research is to develop quantifiable proxy records of past climate change through the calibration of isotope values in modern surface waters and tree ring cellulose with meteorological and atmospheric records. Terrestrial proxy records that utilize oxygen and hydrogen isotope values to reconstruct paleoclimatic and paleohydrologic conditions are limited by a paucity of data on the modification of surface water isotope values prior to sequestration into proxy material. To address this gap in our knowledge and determine the most appropriate study sites, this research focuses on isotopic records preserved in surface water reservoirs, precipitation, and tree-ring cellulose. In the first study, δD, δ18O, and deuterium-excess values were determined for lakes and rivers from Tasmania, southeastern Australia. <p> The second focus of this research was to calibrate the δ18O, δD, and δ13C values of tree-ring cellulose from North America with instrumental records. A new high-resolution sampling procedure that uses a robotic micromilling device to very precisely map and sample along growth rings in trees is discussed. Additionally, a seasonally resolved (early/late wood) 110-year record of δ18O values from tree-ring α-cellulose from spruce species (<i>Picea mariana</i> and <i>P. glauca</i>) from east-central Saskatchewan, Canada is compared to growing season precipitation δ18O values, temperature, and relative humidity. The δ18O time series from α-cellulose display a high correlation with growing season precipitation isotope values (r = 0.86). δ18O α-cellulose time series from a white spruce (<i>Picea glauca</i>) also records seasonal changes in atmospheric circulation associated with the position of the circumpolar vortex and dominate modes of atmospheric variability such as the North Atlantic Oscillation and Pacific Decadal Oscillation.

The role of fire in determining the structure and composition of many forested ecosystems is well documented (e.g. North American boreal forests; piñon-juniper woodlands of the western US). Fire is also believed to be important in temperate forests of eastern North America, but the processes acting here are less clear, particularly in xerophytic forests dominated by yellow pine (Pinus, subgenus Diploxylon Koehne) and oak (Quercus L.). In this study, I use dendroecological techniques to investigate fire history and vegetation dynamics of mixed pine-oak forests in the central Appalachian Mountains of Virginia. The study addresses three objectives: (1) develop a lengthy fire chronology to document fire history beginning in the late presettlement era and extending throughout the period of European settlement, industrialization and modern fire exclusion; (2) explore fire-climate relationships; and (3) investigate vegetation dynamics in relation to fire occurrence. The study was conducted on three study sites within the George Washington National Forest. I used fire-scarred cross-sections from yellow pine trees to document fire history. Fire-climate relationships were investigated for each study site individually and all sites combined using superposed epoch analysis (SEA). Fire-history information was coupled with dendroecological data on age structure to explore stand development in relation to fire occurrence. Results of fire history analysis reveal a long history of frequent fire with little temporal variation despite changes in land use history. Mean fire intervals (MFI) ranged from 3.7–17.4 years. The most important change in the fire regime was the initiation of fire suppression in the early twentieth century. Results of SEA show that periodic droughts may be important drivers of fire activity. Drought the year of fire was important at two of the three study sites and when all sites were combined. Results of age structure indicate that vegetation development was clearly influenced by fire. Frequent burning maintained populations of yellow pine throughout the period of study until fire suppression allowed fire-sensitive hardwood trees and shrubs to establish. It is clear from this study that continued fire suppression will likely result in fire-tolerant pines and oaks being replaced by more mesophytic trees and shrubs.

Interactions among site conditions, disturbance events, and climate determine the patterns of forest species recruitment and mortality across landscapes. Forests of the American Southwest have undergone significant changes over a century of altered disturbance regimes, human land uses, and changing environmental conditions. This study reconstructs the interactions between fire, spruce beetle outbreaks, climate, and anthropogenic factors and their influence on the species composition, spatial extent, and structure of four upper elevation forest types. We found that fire-climate associations changed following fire exclusion and recent high-severity fires occurred during less severe conditions than in several larger, lower severity fires in the historical record. Contemporary fires are burning with higher severity than similarly-sized historical fires, suggesting a shift toward higher-severity fire as a result of changes to forest structure and fuels over much of the upper elevation forest. In high elevation forests, the area occupied by Engelmann spruce and corkbark fir doubled in size over the four decades following fire exclusion. The increase in spruce beetle outbreak size and severity in the 20th century appears to be linked to significant expansion of host extent, accelerated growth of spruce in mixed-conifer forest, and incidence of anomalously warm summer temperatures followed by up to a decade of low precipitation. Trends toward warming, drying conditions are expected to increase the risk of future high-severity outbreaks, especially in locations of recent spruce population expansion. Forest conversion from disturbance-adapted to competition-adapted species following fire exclusion was a function of site productivity. Species assemblages in the lowest and highest productivity sites were the most stable over the century following fire exclusion. Frequent low severity fires maintained the stocking of forests in moderate productivity sites below their biological potential, conferring a degree of resistance to drought, insect outbreaks, and high-severity fire prior to fire exclusion. Current forests located on moderate productivity sites are now the most vulnerable to drought and future disturbance. Aggressive action to restore historical species composition, stocking and fire component of these forests may return resilience to this system in the face of projected changes to fire and climate dynamics.

In the southwestern United States, the North American monsoon (NAM) is the main driver of severe weather and accounts for nearly half the annual precipitation. How the monsoon has behaved in the past and how it will change in the future is a question of major importance for natural resource management and infrastructural planning. In this dissertation, I present the results of three studies that have investigated North American monsoon variability and change from the perspective of paleoclimate records, future climate change projections, and simulation of the low-frequency variability with the longest retrospective atmospheric reanalysis. In the first study, a monsoon-sensitive network of tree-ring chronologies is evaluated within its ability to reproduce NAM variability during the past four centuries. Matrix methods are used to detect the low-frequency spatiotemporal variability. The treering chronologies can reasonable characterizes the dominant modes of NAM climate variability. The monsoon tree-ring network is able to reproduce the interannual variability of cool and warm season precipitation, in a manner similar to the period of the instrumental record. Earlywood and latewood adjusted chronologies reveal low frequency climate variability at decadal and longer timescales that is beyond the ability of the instrumental record to temporally well resolve. This low-frequency climate variability seems to be part of a much larger cycle that coincides with the occurrence of multiyear persistent droughts. In the second study, we consider the modes of natural climate variability identified in the previous study to objectively assess the degree of physical uncertainty in climate change projections for NAM from Regional Climate Models (RCMs) used in the North American Regional Climate Change Assessment Program (NARCCAP). Climate change projection models are evaluated mainly on their ability to represent warm season driven by quasi-stationary Rossby wave trains and El Niño Southern Oscillation – Pacific Decadal Variability (ENSO-PDV). It is concluded that use of the NARCCAP model ensemble mean for NAM climate projections is probably not suitable. NARCCAP RCMs are largely a slave to their driving global models and their error in the specification of large-scale atmospheric circulation. Only one out of eight NARCCAP RCMs has a reasonable representation of the seasonal cycle of monsoon precipitation and ENSOdriven interannual variability in both the 20th and 21st centuries. No decadal variability was observed in any of the NARCCAP RCMs. In the third study, the low-frequency drought signal found with tree-ring chronologies is further explored within the framework of a regional climate modeling. Version 2 of the Twentieth-Century Reanalysis (DD-20CR) is dynamically downscaled over a contiguous U.S.-Mexico domain. Statistic analysis of the DD-20CR suggests that the low-frequency drought signal in the Southwest is driven by atmospheric circulation changes on global to continental scales that affect precipitation in Central American as well. DD-20CR reproduces the spatial patterns of precipitation associated with climate variability at decadal and longer timescales in a manner that compares well with observational records and tree-ring chronologies. Low-frequency climate variability is therefore likely responsible for the multiyear persistent droughts in the last four centuries, as independently evaluated from the tree-ring monsoon-sensitive network.

Examination of the relationship between wood properties such as density, cell diameters and climate provides the opportunity to develop long-term climate and mass balance proxies, and is a key component to understanding when and how wood develops through time. This research sought to: create multi-proxy models to represent long-term changes in the climate-mass balance relationships at Place Glacier, and to describe glaciological changes in Mount Revelstoke and Glacier National Parks, British Columbia; use multiple wood properties to develop intra-annual climate records for tree-ring sites from the southern and northern interior regions of British Columbia; and, use climate as an indicator of wood quality by identifying historical climate impacts on wood development over time. Tree-ring samples from hybrid interior spruce (Picea glauca (Moench) Voss x engelmannii (Parry)) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were collected in north-central British Columbia; interior spruce, Douglas-fir, and subalpine fir (Abies lasiocarpa (Hooker) Nuttall) were collected from trees in the Pemberton area of British Columbia, and Engelmann spruce (Picea engelmannii Parry ex. Engelmann), subalpine fir, and mountain hemlock (Tsuga mertensiana Bongard Carrière) were collected from trees located within Glacier and Mt. Revelstoke National Parks. Tree-ring chronologies were constructed using standard ring width measurement techniques, densitometric methodologies, and using SilviScan technology. Relationships among the regional climate, snowpack, mass balance and various wood chronologies were identified and used as a basis for reconstructing proxy climate and mass balance data. A proxy snowpack record for Tatlayoko Lake was reconstructed using mean density and ring width chronologies. Maximum density and ring width chronologies were used to reconstruct winter and summer mass balance records for Place Glacier. Place Glacier was found to respond negatively to continental summer temperature regimes and positively to winter coastal precipitation events. A proxy record of maximum summer temperature was reconstructed for Revelstoke using maximum density and ring width chronologies; while maximum cell-wall thickness was used to reconstruct total August precipitation, and February snowpack from Golden was reconstructed from subalpine fir and mountain hemlock ring-width chronologies. Mass balance for glaciers in the Columbia Mountains was reconstructed using a combination of ring width, maximum density and maximum cell-wall thickness chronologies. The proxy mass balance reconstruction shows a general decline in ice mass over the time span of the net balance reconstruction. Two intra-annual proxy climate records were created for northern British Columbia. Mean June and mean July-August temperature chronologies were reconstructed for Smithers using ring width and maximum density, and for Fort St. James total May-June and July-August precipitation records were reconstructed using ring width, minimum density, and maximum cell-wall thickness. Wood parameters, including density, cell-wall thickness, microfibril angle, and cell diameter in Douglas-fir and interior spruce were reconstructed at five sites across British Columbia using temperature and precipitation data from local climate stations. Maximum cell-wall thickness was shown to be one of the most robust wood parameters to predict using temperature variables. Using a variety of tree-ring characteristics for time series reconstruction provides an opportunity to create multivariate models with greater predictive capabilities that correspond more closely to observed data sets, thereby allowing dendroclimatologists to predict climate data trends more robustly. Because individual wood parameters form at different times throughout the growing season in response to distinct seasonal climates, multiple proxy models allow for the development of intra-annual proxy climate and glaciological records. / Graduate

Exploring how drought influences growth, performance, and survival in different species is crucial to understanding the impacts of climate change on forest ecosystems. Here, we investigate the responses of two co-occurring pines (Pinus nigra and Pinus sylvestris) to interannual drought in east-central Spain by dendrochronological and wood anatomical features integrated with isotopic ratios of carbon (delta C-13) and oxygen (delta O-18) in tree rings. Our results showed that drought induces both species to allocate less carbon to build tracheid cell-walls but increases tracheid lumen diameters, particularly in the transition wood between early and latewood, potentially maximizing hydraulic conductivity but reducing resistance to embolism at a critical phase during the growing season. The thicker cell-wall-to-lumen ratio in P. nigra could imply that its xylem may be more resistant to bending stress and drought-induced cavitation than P. sylvestris. In contrast, the higher intrinsic water-use efficiency (iWUE) in P. sylvestris suggests that it relies more on a water-saving strategy. Our results suggest that narrower cell-walls and reduced growth under drought are not necessarily linked to increased iWUE. At our site P. nigra showed a higher growth plasticity, grew faster and was more competitive than P. sylvestris. In the long term, these sustained differences in iWUE and anatomical characters could affect forest species performance and composition, particularly under increased drought stress.

Better understanding and prediction of tree growth is important because of the many ecosystem services provided by forests and the uncertainty surrounding how forests will respond to anthropogenic climate change. With the ultimate goal of improving models of forest dynamics, here we construct a statistical model that combines complementary data sources, tree-ring and forest inventory data. A Bayesian hierarchical model was used to gain inference on the effects of many factors on tree growth-individual tree size, climate, biophysical conditions, stand-level competitive environment, tree-level canopy status, and forest management treatments-using both diameter at breast height (dbh) and tree-ring data. The model consists of two multiple regression models, one each for the two data sources, linked via a constant of proportionality between coefficients that are found in parallel in the two regressions. This model was applied to a data set of similar to 130 increment cores and similar to 500 repeat measurements of dbh at a single site in the Jemez Mountains of north-central New Mexico, USA. The tree-ring data serve as the only source of information on how annual growth responds to climate variation, whereas both data types inform non-climatic effects on growth. Inferences from the model included positive effects on growth of seasonal precipitation, wetness index, and height ratio, and negative effects of dbh, seasonal temperature, southerly aspect and radiation, and plot basal area. Climatic effects inferred by the model were confirmed by a den-droclimatic analysis. Combining the two data sources substantially reduced uncertainty about non-climate fixed effects on radial increments. This demonstrates that forest inventory data measured on many trees, combined with tree-ring data developed for a small number of trees, can be used to quantify and parse multiple influences on absolute tree growth. We highlight the kinds of research questions that can be addressed by combining the high-resolution information on climate effects contained in tree rings with the rich tree-and stand-level information found in forest inventories, including projection of tree growth under future climate scenarios, carbon accounting, and investigation of management actions aimed at increasing forest resilience.

L’Hémisphère Sud, et plus précisément le sud de l’Amérique du Sud, sont très sous-représentés dans les reconstitutions climatiques globales du fait d’un manque de données paléoclimatiques robustes. Mes travaux de thèse ont donc porté sur l’évaluation de l’archive naturelle cernes d’arbre, abondante le long de la Cordillère des Andes, comme traceur paléoclimatique. Je me suis ainsi appliquée à étudier la réponse régionale de deux espèces d’arbre (Fitzroya cupressoides et Nothofagus pumilio) natives du nord de la Patagonie (41°S, Argentine) aux forçages climatiques externes en analysant leurs différents paramètres physiques. Pour cela, j’ai commencé par déterminer l’influence du climat local et de grande échelle sur leur croissance en étudiant les variations temporelles de leurs largeurs de cerne, puis j’ai essayé d’extraire le signal climatique enregistré dans la composition isotopique de l’oxygène et du carbone de la cellulose de ces cernes. Deux résultats majeurs de ma thèse ont émergé: j’ai mis en évidence (1) des réponses non-linéaires de la croissance au cours du temps liées aux changements de régimes climatiques et, (2) le fort potentiel du delta18O et delta13C de la cellulose pour enregistrer les variations de température d’été-automne sur une large région aux latitudes moyennes de l’Amérique du Sud (35°-55°S). Du fait des relations fortes qui les lient aux températures, les outils isotopiques peuvent être utilisés pour reconstituer des chronologies de température mais aussi des modes climatiques tels que l’Oscillation Antarctique. / The Southern Hemisphere, and particularly southern South America, are very under-represented in global climate reconstructions due to a lack of robust paleoclimatic data. My thesis was therefore focused on the evaluation of the tree-ring archive, which is widespread along the Andes, as a paleoclimatic tracer. I studied the regional response to external climate forcing of two native species (Fitzroya cupressoides and Nothofagus pumilio) in northern Patagonia (41°S, Argentina), by analysing their different physical tree-ring parameters. In this perspective, I analysed the temporal variations of the width and of the oxygen and carbon isotopic compositions of the cellulose of their rings and related them to local and large-scale climate variations. Two major results of my thesis have emerged: I highlighted (1) non-linear growth responses over time related to shifts in climate regimes and, (2) the potential of cellulose delta18O and delta13C to record summer-autumn temperature variations over a large area in the mid latitudes of South America (35°-55°S). As their variations are strongly linked to temperature the isotopic tools can be used to reconstruct chronologies of temperature but also of climate modes such as the Southern Annular Mode.

京都大学 / 新制・課程博士 / 博士(農学) / 甲第23523号 / 農博第2470号 / 新制||農||1087(附属図書館) / 学位論文||R3||N5354(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)准教授 岡田 直紀, 教授 神﨑 護, 教授 北島 薫 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM