Theses and Dissertations at Montana State University (MSU)
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/732
Browse
4 results
Search Results
Item Hydrothermal influences on the Holocene environmental history of central Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2020) Schiller, Christopher Michael; Chairperson, Graduate Committee: Cathy Whitlock; Cathy Whitlock, Kathryn L. Elder, Nels A. Iverson and Mark B. Abbott were co-authors of the article, 'Erroneously old radiocarbon ages from terrestrial pollen concentrates in Yellowstone Lake, Wyoming, USA' in the journal 'Radiocarbon' which is contained within this dissertation.; Rosine Cartier, Cathy Whitlock and Lisa A. Morgan were co-authors of the article, 'Multi-proxy record of Holocene paleoenvironmental conditions from Yellowstone Lake, Wyoming, USA' submitted to the journal 'Quaternary science reviews' which is contained within this dissertation.; Cathy Whitlock, Sabrina R. Brown and Petra Zahajska were co-authors of the article, 'Holocene geo-ecological evolution in Lower Geyser Basin, Yellowstone National Park' submitted to the journal 'Geological Society of America bulletin' which is contained within this dissertation.; Cathy Whitlock, Mio Alt and Lisa A. Morgan were co-authors of the article, 'Vegetation responses to Quaternary volcanic and hydrothermal disturbances in the northern Rocky Mountains and Greater Yellowstone Ecosystem' in the journal 'Palaeogeography, Palaeoclimatology, Plaeoecology' which is contained within this dissertation.The postglacial vegetation history of Yellowstone National Park is well established by past paleoecological studies, but the role of hydrothermal activity--pervasive in areas of the park--in that history is poorly understood. To address this unknown, pollen and charcoal records were examined from lake sediment cores at multiple sites in central Yellowstone National Park to reconstruct Holocene vegetation. First, radiocarbon ages obtained from pollen concentrates were compared with other age controls at Yellowstone Lake, revealing ages that were up to 4300 cal years too old. Erroneous ages were due to either old carbon contamination from magmatic or hydrothermally degassed CO 2 or old pollen reworked from an unknown source. Second, Holocene vegetation and fire history were reconstructed from a Yellowstone Lake sediment core. The record was characterized by gradually increasing closure or extent of Pinus contorta forest and increasing fire activity to the present, consistent with reduced summer insolation creating cooler, effectively wetter conditions in central Yellowstone National Park. No impact of hydrothermal activity was detected in the regional Holocene-long vegetation and fire histories. Third, Holocene vegetation and fire history were studied at Goose Lake in Lower Geyser Basin, an area with abundant modern hydrothermal activity. The vegetation and fire history diverged from the regional trend at 3800 cal yr BP, synchronous with geochemical indicators indicating reorganization of hydrothermal activity in the basin, suggesting an abrupt ecological response to shifting hydrothermal activity. Finally, a variety of volcanic and hydrothermal processes were investigated as disturbances in the Northern Rocky Mountains and Yellowstone National Park through high-resolution pollen analysis. Hydrothermal explosion deposits were found to be synchronous with conifer morality, in some records, indicating that the effects of hydrothermal explosions are local and short-lived. At a regional scale, it is evident that vegetation changes were chiefly responding to millennial-scale, insolation-driven climate change. However, the impacts of hydrothermal activity were locally important where pervasive, as in Lower Geyser Basin, and in areas recently affected by hydrothermal explosions.Item Disentangling anthropogenic and natural drivers of change in vegetation and fire history along the forest-grassland ecotones of the central United States and Patagonia(Montana State University - Bozeman, College of Letters & Science, 2020) Nanavati, William Parashar; Chairperson, Graduate Committee: Cathy Whitlock; Eric C. Grimm was a co-author of the article, 'Humans, fire, and ecology in the southern Missouri Ozarks' in the journal 'The holocene' which is contained within this dissertation.; Cathy Whitlock, Valeria Outes and Gustavo Villarosa were co-authors of the article, 'A holocene history of Araucaria araucana in northernmost Patagonia' submitted to the journal 'Journal of biogeography' which is contained within this dissertation.; Cathy Whitlock, Virginia Iglesias and Maria Eugenia de Porras were co-authors of the article, 'Postglacial vegetation, fire, and climate history along the eastern Andes, Argentina and Chile (lat. 41-55°S)' in the journal 'Quaternary science reviews' which is contained within this dissertation.Disentangling anthropogenic and natural drivers of vegetation and fire history at different spatiotemporal scales is a fundamental challenge in Earth Systems science. To better understand the role of past human ignition in altering long-term ecosystem dynamics, we rely on the anthropogenic fire regime conceptual model proposed by Guyette et al. (2002) in the central U.S. Ozarks. The synthesis of new and existing pollen and charcoal records, and their integration with archaeological, ethnographic, and independent paleoclimate records is used to test the anthropogenic fire regime conceptual model at a longer time scale in the central U.S. Ozarks. Following its validation, this conceptual model is applied to the forest-steppe ecotone east of the Patagonian Andes (38-55°S) for the first time. Although it is well established that Patagonian vegetation and fire history for most of the postglacial period was governed by the strength and position of the Southern Westerly Wind (SWW) storm tracks, the influence of land use since the arrival of American Indians to the region ~12,000 years ago remains unclear. From the late glacial to early Holocene, region-wide increases in fire were associated with aridity while the SWW were weakened and south of their present position. Between ~7000-4000 cal yr BP, increased arboreal taxa and decreased fire throughout Patagonia suggest wet conditions as the SWW moved northward to their present position. After ~4000 cal yr BP, a combination of increased land use and greater climate variability, led to spatially heterogeneous but generally rising fire activity along the forest-steppe ecotone. When trends in the vegetation and fire history of individual sites are compared to each other and to the archaeological record, however, it becomes apparent that American Indians may have served as an important source of ignition, locally increasing landscape heterogeneity since their arrival. During the last 100 years, increased Euro-American settlement and land clearance in Patagonia led to native forest loss, more disturbance, and the spread of introduced taxa along the eastern flanks of the Andes. These ecological changes in the recent century far outweigh thousands of years of American Indian influence on fire and vegetation history.Item Late Holocene climate, fire, and vegetation history on the northern range, Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2019) Firmage, David Samuel; Chairperson, Graduate Committee: Cathy WhitlockYellowstone National Park is an iconic natural landscape that encompasses unique geologic features as well as a diverse and ecologically important flora and fauna. The ecological resilience of the Northern Range of the park, home to the park's ungulate herds, faces an uncertain future with a projected warming climate over the next century. Understanding the variability of vegetation organization in response to past changes in climate can help park managers plan for future climate scenarios. Lake sediment cores from two lakes were collected, analyzed for pollen type, charcoal accumulation and lithological components, and compared with other studies to highlight commonalities in fire-histories and vegetation trends across the Northern Range over the past 4000 cal yr BP. Foster Lake the records suggest fire-episodes and changes to lake productivity and between ~3500-2900 cal yr BP, large intense fire-episodes between ~2500-2150 cal yr BP, ~1000 cal yr BP and frequent large fire episodes from ~700 cal yr BP to the present day. Floating Island Lake records between ~4000-3000 cal yr BP suggest the site experienced infrequent, large fire episodes concurrent with periods of protracted drought and decreases in water level. Between ~3000-1500 low intensity fire episodes were common, punctuated by infrequent large fire episodes at ~2900, ~2250, ~2050 and ~1880 cal yr BP. During the last ~1ka two fire episodes were recorded at Floating Island Lake, at ~1030 cal yr BP coincident with the Medieval Climate Anomaly, and 270~ cal yr BP during the Little Ice Age. A comparison of fire histories from studies spanning the Northern Range shows that during periods of protracted drought large fire episodes are common across the landscape, and that during periods of moderate climate fire size and severity is likely modulated by local site controls such as topography and vegetation structure. This study shows that fire episodes in the Northern Range have occurred as a spatial and temporal mosaic, and are likely to continue to do so. Additionally, this study increases our understanding of how vegetation structure and fire regimes in the Northern Range have varied as a result of a range of climate conditions in the past. Such baseline information helps us anticipate some of the ecological responses that may occur in the decades ahead with global warming.Item Ecosystem response to Holocene fire and climate change at Hobart Lake, southwestern Oregon(Montana State University - Bozeman, College of Letters & Science, 2014) White, Alicia Lauren; Chairperson, Graduate Committee: Cathy Whitlock; Cathy Whitlock and Christy E. Briles were co-authors of the article, 'Ecosystem response to Holocene fire and climate change at Hobart Lake, southwestern Oregon' submitted to the journal 'Quaternary paleoecology' which is contained within this thesis.Oregon's southern Cascade Range contains one of the world's most biologically diverse forests. Past ecosystem responses to fire and climate change have been well studied in the Coast Range, the eastern Cascade Range, and the Klamath Mountains but the ecological and environmental histories of the southern Cascade Range are poorly understood. Therefore, an 8000-year-long record from Hobart Lake (42.09935°N, 122.48170°W, 1458m), Oregon in the southern Cascade Range was examined to better understand past changes in vegetation and fire activity, conifer biogeographic distributions, and regional climate variability. Hobart Lake is exceptional in that it has an unusually fast sedimentation rate, resulting in a detailed vegetation and fire records based on pollen and macroscopic charcoal data. From 8000 to 3500 cal yr BP, the dominance of xerophytic species, such as Pinus and Cupressaceae, and the high frequency of fires are consistent with a climate that was warm and dry. Late-Holocene vegetation from 3500 cal yr BP to the present day was characterized by an abundance of mesophytic taxa, such as Abies and Pseudotsuga, and the decline of xerophytic taxa such as Pinus. These changes, along with reduced fire frequency, suggest that the climate became cooler and wetter. In addition to the Hobart Lake record, changes in the abundance of Abies and Pseudotsuga pollen at multiple sites throughout Oregon and northern California were examined. Abies was abundant during the late glacial, its range and/or abundance contracted during the early Holocene, and it gradually became more widespread and abundant during the mid- and late-Holocene. Pseudotsuga became more abundant at northern low-elevation sites during the warm dry conditions of the early Holocene and then flourished in more southern mid-elevation sites when the climate became cooler and wetter in the late Holocene. The vegetation history at Hobart Lake and other sites is consistent with large-scale variations in regional climate related to slowly varying changes in the seasonal insolation cycle and the indirect effects of insolation on the size and strength of the northeastern Pacific subtropical high-pressure system.