Tree-ring records collected from living mountain hemlock trees in the southern British Columbia Coast Mountains have been used to provide insights into the character of historical climatic fluctuations and the behaviour of individual climate forcing mechanisms. The relatively short-duration of these records limits, however, their ability to describe climate variability and atmospheric processes that change gradually or undergo long-term regime shifts. The objectives of this research were to extend the duration and quality of proxy climate information extracted from mountain hemlock tree-ring chronologies. In coastal British Columbia most existing mountain hemlock tree-ring chronologies extend from ca. AD 1600 to present. To extend the duration of these chronologies, coarse woody debris recovered from the bottom of M Gurr Lake, a high-elevation lake in the vicinity of Bella Coola, British Columbia, was cross-dated to nearby living chronologies surrounding M Gurr lake and increment core samples of ancient trees at Mt Cain on northern Vancouver Island. From this, a regional continuous 917-year long record of radial growth was constructed. The resulting regional chronology was used to construct a 785 year-long proxy record of gridded air temperature anomalies displaying periods of cooler and warmer than average regional air temperatures that contained century-long low frequency trends. Cross-dating and tree morphological evidence of snow avalanche activity displayed within living trees surrounding the lake, and within the coarse woody debris, revealed that low-magnitude avalanches occurred in the winter months of AD 1713-1714, 1764-1765, 1792-1793, 1914-1915, 1925-1926, and 1940-1941. High magnitude avalanche events occurred in the winter months of AD 1502-1502 and 1868-1869. A second objective of the thesis was to investigate the radial growth response of mountain hemlock trees to subseasonal climate variables using standardized ring-width and densitometric analyses. Mountain hemlock chronologies from M Gurr Lake, Cyprus Provincial Park, and Mount Arrowsmith were used to describe the inherent climate-growth trends. Maximum annual tree-ring density values provided a robust data series for constructing site-specific proxy records of late-summer temperature. Annual tree-ring width measurements provided independent proxies of spring snowpack trends. Regionally-derived proxy models indicated that intervals of cooler-than-average and higher-than-average air temperatures correspond to years of higher-than-average average and cooler-than-average snowpacks, respectively. Of note were the significant decreases in air temperature and increases in snowpack depths during the early-1700s and early-1800s coinciding with documented glacier advances in the Coast Mountains. Identification of these subseasonal climate signals within the tree-rings of mountain hemlock trees demonstrates the value of incorporating investigations of multiple tree-ring parameters. / Graduate

Thesis (Ph. D. - Geosciences)--University of Arizona, 1983. / Includes bibliographical references (leaves 168-177).

Thesis (M.Env.Sc.)--Memorial University of Newfoundland, 1999. / Bibliography: leaves 50-52.

Thesis (Ph. D.)--West Virginia University, 2010. / Title from document title page. Document formatted into pages; contains vii, 102 p. : ill. (some col.), maps (some col.). Vita. Includes abstract. Includes bibliographical references.

This thesis presents an empirical study of dendroclimatology, with the purpose of contributing to a wider understanding of the way scientists generate knowledge about climate change. Dendroclimatology is a science that produces knowledge about past climates from the analysis of tree growth. For two years, I have studied the work of a group of dendroclimatologists, joining them on fieldwork and sampling expeditions in the Scottish Highlands, observing how they generate data from tree samples to reconstruct past temperatures in Scotland and examining how they have mobilised a Scottish temperature reconstruction in a scientific debate over historical changes in climate. This thesis develops two parallel narratives about the practice of making dendroclimatological knowledge and the roles of trust and scepticism in this process. In describing how dendroclimatologists work to extract information about past climates from trees, I identify the importance of trust relationships and scepticism at each stage of their work. I conduct a symmetrical analysis of both trust and scepticism in science. In the past, scholars studying science have emphasised the critical role of either trust or scepticism in the construction of scientific knowledge, and have paid relatively little attention to examining the relationship between the two. In my study, I demonstrate that scepticism is part of the ordinary practice of dendroclimatology, and that scepticism in normal science (which I call “civil scepticism”) is fundamentally dependent (or “parasitic”) on existing trust relationships established through a variety of means. Dendroclimatologists engage in intimate interactions and mutual scrutiny of each other’s competence throughout the work they do in the field and in the laboratory, and they build upon and expand these trust relationships to create and defend climate reconstructions. I show that dendroclimatologists sustain trust relationships in part by demonstrating that they are competent sceptics (which I call “sceptical display”) and, in part by provisionally suspending their scepticism to permit agreement on what constitutes valid dendroclimatological knowledge. I also analyse how these internal practices of scepticism and agreement are influenced by sceptical challenges from actors external to the dendroclimatology community, including challenges grounded in similar trust relationships (a further instance of civil scepticism) and challenges that are not (which I call “uncivil scepticism”). I conclude that dendroclimatological knowledge is only possible as a result of contingent social negotiations over the distribution of trust and the boundaries of a trusting community.

Hemlock woolly adelgid (Adelges tsugae Annand) is causing defoliation and mortality of eastern hemlock (Tsuga canadensis (L.) Carrière) in the eastern United States. The objectives of this study were to quantify changes in tree-ring width and wood anatomy for trees that survived adelgid infestation, and to contrast dendroclimatic relationships across a latitudinal gradient. Six sites spanning the current range of hemlock woolly adelgid (HWA) infestation were selected. At each site, 23 infested eastern hemlocks were cored and two trees were felled at the Virginia site and thin-sectioned using a sliding microtome for analysis of wood anatomy. Tree cores were cross-dated and ring widths were measured. For each site, t-tests were used to determine if there was a difference in radial growth pre- and post-HWA arrival. To compare differences in pre- and post-HWA cell properties, t-tests were used. For dendroclimatic analysis, Pearson correlation coefficients were calculated between radial growth and monthly climate variables. Three sites showed significant suppression in radial growth after HWA arrival and latewood produced post- HWA arrival had significantly smaller cells with reduced cell-wall thickness than latewood produced before HWA arrival. This indicates that HWA can reduce a tree's photosynthate production. The relationship between hemlock growth and climate also varied with latitude and site, with trees growing further south or on shallower soils being more sensitive to moisture levels. This sensitivity to drought can also partially explain the variation in hemlock response to adelgid feeding, as trees affected by moisture stress tend to be more sensitive to insect attack. / Master of Science

Annual tree-ring width of Southwestern conifers growing on dry sites exhibits sensitivity to variation in climatically created moisture stress. Douglas-fir, ponderosa pine, and pinyon in the eastern San Juan Basin in northwestern New Mexico and southwestern Colorado were sampled at four sites to investigate covariation of climate with intra-annual anatomy. The sites possessed characteristics that created different amounts of physiological stress in trees. Increment borer samples were glued into wooden mounts and machined to approximately 1.0 mm thickness by a special router-planer. All samples were crossdated by comparing climatically controlled synchronous patterns of ring widths. Moving slit X-ray densitometry (at Forintek Canada Corporation Western Forest Products Laboratory, Vancouver, British Columbia) objectively defined the earlywood zone (large, low density cells) and latewood zone (smaller, denser cells formed late in the growing season) in each ring. The densitometer measured eight parameters for each ring: ring, earlywood, and latewood width, minimum and maximum density, and mean ring, earlywood, and latewood density. Individual radial series were standardized (i.e, transformed to indices with 1.0 mean and homogeneous variance) by fitting curves and dividing annual values by the corresponding curve values. Density series proved more difficult to standardize than widths and usually correlated more poorly among individual radii of the same data data type. Statistical characteristics of site summary density chronologies differed from width chronologies. Response functions using monthly mean temperature and total precipitation showed climate influenced all data types. Low moisture stress increased ring, earlywood, and latewood width and ring, maximum, and latewood density. High moisture stress increased minimum and early— wood density. No width or density type consistently covaried more than any other with climate. Linkage of climatic variation with density parameters differed considerably from that reported in the literature for conifers growing in wetter, cooler climates. Southwestern conifers posed unique densitometric technical difficulties. Selection of sites that caused moderate physiological stress and samples with few missing rings proved critical. Acquisition of density data required much more time and effort than optical measurement of ring width, but yielded valuable intra—annual data. Intra—annual densitometric data hold great promise for reconstruction of seasonal paleoclimate.

The tree-ring characteristics of material used in a 35-tree, 265-year modern oak chronology from a site in North Wales are discussed. Three methods of standardisation are compared and temporal variation in chronology statistics examined. A response function using rainfall data from a station very close to the tree site related 45% of the chronology variance to climate and 73% to climate plus prior growth.

A pilot investigation of 11 trees from London parks has shown that elm (Ulmus) is suitable for dendrochronology and dendroclimatological analysis. Ten trees are shown to crossdate well and form the basis of a London group elm chronology for the years 1900-1971; chronologies derived from fewer trees cover the period 1840-1971. Correlations with monthly climatic variables and seasonal rainfall and soil moisture totals are described. Response functions for the relationship between the London elm chronology and precipitation and temperature recorded at Kew demonstrate the direct relationship between ring width and precipitation during the growing season and during the previous autumn and early winter (September to December), an inverse relationship to rainfall the previous summer; above average temperature during the previous autumn leads to above average ring width but there is an inverse relation between ring width and temperature during March and April at the commencement of the growing season.

Six modern oak tree-ring chronologies from Ireland are presented. All are from planted or from disturbed-natural woodland of Quercus petrea. The final chronologies were tested for climate content by the response function method. The results range from 5% to 52% of the chronology variance explained by temperature and precipitation of a 14 month period during and prior to the growing periods. The relationship between these figures and the site and chronology details are examined. The relationship of the individual chronologies to each other is examined and the hypothesis put forward that Ireland can be considered as a single tree-ring area from a dating viewpoint.