Theses and Dissertations at Montana State University (MSU)
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Item Reconstructing large herbivore abundance and environmental interactions in postglacial North America(Montana State University - Bozeman, College of Letters & Science, 2023) Wendt IV, John Arthur Frederic; Chairperson, Graduate Committee: David B. McWethy; This is a manuscript style paper that includes co-authored chapters.Large herbivores drive critical ecological processes, yet their long-term dynamics and effects are poorly understood due to the limitations of existing paleoherbivore proxies. To address these shortcomings, long-term records of paleoherbivores were constructed by (i) applying new analytical techniques to existing bison fossil datasets; and (ii) examining fecal steroid data that characterize temporal changes in ungulate abundance and community composition. These paleoherbivore reconstructions were analyzed in relation to their environmental contexts to better understand herbivore-ecosystem interactions through time in three separate studies: First, spatiotemporal changes in postglacial bison distribution and abundance in North America were examined by summarizing fossil bison observations. Bison observations were compared with simulated climate variables in a distribution modeling framework to project probable bison distributions in 1000-year intervals from the Last Glacial Maximum to present in light of changing climatic drivers over time. Since the Bolling-Allerod Interstadial (14.7-12.9 ka) the geographic distribution of bison is primarily explained by seasonal temperature patterns. Second, Holocene records of bison abundance were compared to paleofire reconstructions spanning the midcontinental moisture gradient to determine the relative dominance of herbivores and fire as biomass consumers. Bison dominated biomass consumption in dry settings whereas fire dominated consumption in wetter environments. Historical distributions of herbivory and burning resemble those of Sub-Saharan Africa, suggesting a degree of generality in the feedbacks and interactions that regulate long-term consumer dynamics. Third, the utility of fecal steroids in lake sediments for reconstructing past herbivore abundance and identity was tested by (i) characterizing the fecal steroid signatures of key North American ungulates, (ii) comparing these signatures with multiproxy data preserved in lake sediments from the Yellowstone Northern Range, and (iii) comparing influxes of fecal steroids over time to historical records of ungulate biomass and use. Bison and/or elk were abundant at Buffalo Ford Lake over the past c. 2300 years. Ungulate densities in the watershed were highest in the early 20 th century and likely contributed to decreases in forage taxa and possibly increased lake production. These results demonstrate long-term ecological impacts of herbivores and highlight opportunities for continued development of paleoherbivore proxies.Item Late Holocene vegetation and fire history in subalpine forests of northwestern Montana(Montana State University - Bozeman, College of Letters & Science, 2020) Sly, Shelby Fulton; Chairperson, Graduate Committee: David McWethyMid-to high- elevation forests of the Northern Rocky Mountains are dynamic systems that change in time in response to climate, disturbance and human activities. Climate models suggest these ecosystems will experience warmer temperatures, decreased spring snowpack, drier summers, and longer fire seasons, highlighting a need to better understand how these systems respond to changing climatic conditions. Sediment cores were extracted from two lakes in the Mission and Reservation Divide Mountains of Montana and analyzed for pollen and macroscopic charcoal to reconstruct fire and vegetation histories. The records from Mud Lake and Three Lakes Peak span the last 5400 and 4600 years respectively, and highlight the long-term persistence and relative stability of closed, mixed conifer/subalpine forests. During the mid-Holocene (approx. ca. 5000 yr BP), Pinus pollen percentages increased, suggesting closed forests which then transitioned to mesic forest of Pinus, Abies, and Picea over the last ca. 4000 years. Modern forests established between 3500-3000 cal yr BP at both sites. Both sites experience elevated fire activity during the Medieval Climate Anomaly c. 1000-900 cal yr BP which is consistent with other sites in the region. While relatively infrequent (2-4 fires per millennia), wildfires played a role in maintaining early successional vegetation (Poaeceae, Alnus spp.) and taxa that benefit from post-fire reduction in competition such as five-needle pines. Paleoenvironmental records from these two sites indicate subalpine forests of northwestern Montana persisted with relative stability throughout the mid to late-Holocene. With projections for increased warming, longer fire seasons and the possibility for increased occurance of short-interval fires in higher elevation ecosystems of the Northern Rocky Mountains, subalpine forests may become vulnerable to rapid transitions to different forest types or even non-forest systems.Item Paleofire patterns in Tasmania: postglacial and Holocene record of fire and vegetation from Cradle Mountain-Lake St. Clair National Park, Tasmania, Australia(Montana State University - Bozeman, College of Letters & Science, 2017) Stahle, Laura Nicole; Chairperson, Graduate Committee: Cathy Whitlock; Cathy Whitlock was a co-author of the book chapter, 'Getting information from the past: paleoecological studies of terrestrial ecosystems' in the book 'Key methods in geography' which is contained within this thesis.; Cathy Whitlock and Simon G. Haberle were co-authors of the article, 'A 17,000-year-long record of vegetation and fire from Cradle Mountain National Park, Tasmania' submitted to the journal 'Frontiers in ecology and evolution' which is contained within this thesis.; Cathy Whitlock and Simon G. Haberle were co-authors of the article, 'The postglacial and holocene record of fire and vegetation from Cradle Mountain National Park, Tasmania, Australia' which is contained within this thesis.On centennial to millennial timescales fire regimes are driven by climate changes, vegetation composition, and human activities. In this study, I reconstructed the vegetation and fire history of Cradle Mountain-Lake St Clair National Park in northwestern Tasmania, and linked vegetation changes to variations in the fire regime, large-scale climate patterns, and anthropogenic activity. Postglacial vegetation and fire dynamics were inferred from five high-resolution pollen and charcoal records from lakes in the montane and subalpine zones of the National Park. Watershed-scale reconstructions of fire and regional trends in vegetation composition were compared to independent records of past climate and the regional archeological record to assess long-term climate-vegetation-fire-human linkages. Pollen and charcoal data indicate that during late-glacial period, the vegetation was largely open and fires were rare. During the Pleistocene-Holocene transition, rainforest taxa and subalpine woody shrubs began to increase in abundance. In the early Holocene, a fire activity maximum occurred at the three lower elevation sites while biomass burning remained low at the higher sites. The elevational differences and basin characteristics likely resulted in climate-controlled differences in vegetation and fuel flammability. The high biomass burning in the early Holocene occurred during the warmest interval of the Holocene as recorded by regional paleoclimate proxy records. The mid-Holocene period featured a multi-millennial phase of cool, temperate rainforest dominance at all sites. The relatively wet conditions of the mid-Holocene likely allowed the rainforest to reach its maximum extent. The late Holocene marks a regional shift toward open sclerophyll woodland associated with increased climate variability and decreased precipitation. A large fire episode occurred at all five sites during this period and hastened the shift in compositional balance from rainforest to a mosaic of sclerophyll woodlands and shrublands, rainforests, buttongrass moorlands, and alpine vegetation. Overall, the vegetation became substantially more open in the late Holocene. The human-fire linkages in Cradle Mountain are tenuous. There is no clear evidence that fire regimes or vegetation were extensively modified by humans prior to European settlement. Climate was the primary driver of fire activity over millennial timescales as explained by the close relationship between charcoal and climate proxy data.Item Postglacial vegetation and fire history of the southern Mission Valley, Montana(Montana State University - Bozeman, College of Letters & Science, 2017) Alt, Mio Hazel; Chairperson, Graduate Committee: Cathy WhitlockEcosystems shaped by mixed - severity fire regimes cover a large area of the Northern Rocky Mountains, yet relatively little is known about the historical variability and drivers of these ecosystems. The low - and mid - elevations of the Mission Range, Montana, are dominated by mixed conifer forests, and the area has been occupied by humans for at least 10,000 years, making it an ideal location for investigating how climate and humans may have affected vegetation and fire regimes during the late - glacial period through the Holocene. Pollen and charcoal records from lake sediment cores from a small closed - basin lake (Twin Lake) were used to reconstruct the vegetation and fire history of the southern Mission Valley, Montana, and compared to other sites in the region. During the late - glacial period, data show an abundance of Pinus (P. albicaulis or monticola) Artemisia, and Poaceae pollen prior to 13,000 cal yr BP, suggesting the site was dominated by an open landscape with shrubs and grass, cold relatively dry conditions, and minimal fire activity. Increased percentages of Pinus (P. Ponderosa or contorta), Picea, and Abies pollen at 13,000 cal yr BP mark the onset of a closed conifer forest, relatively cool and wet conditions and an increase in fire activity accompanying an increase in biomass. Large increases in Pseudotsuga/Larix and Artemisia pollen between 10,000 - 6000 cal yr BP suggest warmer and drier climatic conditions developed during this interval, consistent with other records from the northwestern U.S. Charcoal influx show this interval of warm and dry conditions led to low severity fires followed by high severity fires as forests of P. contorta or P. ponderosa became more dense between 7000 and 5000 cal yr BP. The mixed - conifer forests that dominate the site today began to develop ca. 6000 cal yr BP when fire frequency and severity became highly variable. Surprisingly, fire activity from ca. 5000 cal yr BP to present remained relatively high despite a cooling and wetting trend in the region. This departure of fire activity from climatic controls suggests other local factors influenced fire activity, and may suggest a greater role of human influence during the late Holocene.Item Paleoecological reconstruction of the Bridger Range, Montana, USA(Montana State University - Bozeman, College of Letters & Science, 2016) Benes, James Victor; Chairperson, Graduate Committee: Cathy WhitlockThe postglacial vegetation and fire history of the Greater Yellowstone Ecosystem (GYE) is poorly known immediately outside of the Yellowstone and Grand Teton national parks due to the scarcity of pollen and charcoal records. The paleoecological record of the Bridger Range near the northwestern GYE boundary provides new information on the ecological history of the region. A 5-m-long sediment core was taken from Fairy Lake (45°54'16.00"N, 110°57'29.00"W, 2306 m elev) to reconstruct the regional vegetation, fire, and climate history. Pollen analysis reveals shifts in vegetation from tundra-steppe to early Picea with Pinus parkland, and open forest of Pinus, Pseudotsuga, Abies, and Picea and finally closed forest over the last ca. 15,000 years, similar to other regional pollen records in the GYE. Fluctuations in different conifer species are interpreted as a response to regional climate changes. Wetter, cooler periods are associated with expansion of Picea. Warmer periods of time are associated with more open landscapes, and more frequent burning, but with less biomass burnt due to the more open landscape. Changes in the ratio of arboreal pollen to non-arboreal pollen were studied through time from sites spanning a west-to-east transect across the Northern Rocky Mountains (NRM), with Fairy Lake, and other records from the northern GYE in the center. Arboreal pollen is higher in the west, where annual/seasonal rainfall (or available moisture during the growing season) is greater. Charcoal records from the NRM were also compared to Fairy Lake's charcoal record in an effort to distinguish Fairy Lake from other NRM sites. The Fairy Lake fire record is similar to some NRM sites in the late-glacial and late Holocene with increased fire activity along with increases in available biomass. Archeological remains in the Fairy Lake watershed suggest some level of human activity in recent centuries, although the extent of human influence on vegetation change is not easily distinguished from climatic controls.Item Snow accumulation and ablation under fire-altered lodgepole pine forest canopies(Montana State University - Bozeman, College of Letters & Science, 1994) Skidmore, Peter BrooksItem Holocene climate-vegetation-fire linkages along the Patagonian forest/steppe ecotone (41 - 43°S)(Montana State University - Bozeman, College of Letters & Science, 2013) Iglesias, Virginia; Chairperson, Graduate Committee: Cathy Whitlock; Cathy Whitlock, Maria Martha Bianchi, Gustavo Villarosa, and Valeria Outes were co-authors of the article, 'Holocene climate variability and environmental history at the Patagoanian forest/steppe ecotone: Lago Mosquito (42 29'37.89"S, 71 24'14.57"W) and Laguna del Condor (42 20'47.22"S, 71 17'07.62"W)' in the journal 'The Holocene' which is contained within this thesis.; Cathy Whitlock, Maria Martha Bianchi, Gustavo Villarosa, and Valeria Outes were co-authors of the article, 'Climatic and local controls of long-term vegetation dynamics in northern Patagonia (Lat. 41°S)' in the journal 'Quaternary research' which is contained within this thesis.; Cathy Whitlock was a co-author of the article, 'Climate-vegetation-fire linkages at local to regional scales along the Patagonian forest-steppe ecotone (41 - 43°S)' which is contained within this thesis.Patagonian vegetation has dramatically changed in composition and distribution since the Last Glacial Maximum. Although patterns of vegetation change are relatively clear, our understanding of the processes that produce them is limited. In this study, I reconstructed the vegetation and fire history of the North Patagonian forest-steppe ecotone (lat. 41 - 43°S) and linked vegetation changes to variations in the fire regime, large-scale synoptic controls of climate, and human activity. Postglacial vegetation and fire dynamics were inferred from seven high-resolution pollen and charcoal records from lakes located along the forest-steppe ecotone. Regional trends in vegetation composition and biomass burning were compared to independent records of climate to assess longterm climate-vegetation-fire linkages. Pollen data indicate that late-glacial steppe was replaced by parkland in the early Holocene and by shrubland and forest in the middle and late Holocene. Fire activity was lowest during the late-glacial/early-Holocene transition and gradually increased throughout the Holocene. Based on current knowledge of human settlement in the area, there is no evidence that indicates that increased aboriginal population densities resulted in higher biomass burning at regional scales. Instead, results show that climate was the main driver of Holocene ecological change, either by its direct effects on vegetation or its indirect effects on fire. Watershed vegetation flammability explains much of the fine-scale variability in the fire regime, which, in turn can amplify or override the direct influence of climate on ecotone composition. During the late Holocene, in particular, oscillations in forest dominance were largely driven by changes in humidity, possibly associated with the onset or strengthening of ENSO. At intermediate-moisture levels fire became an important control of community composition. These findings emphasize the importance of biophysical feedbacks in ecosystem dynamics and suggest that these relations must be understood in the context of millennial-scale climate variations that shape broad patterns of vegetation and fire in the region.Item Fire and vegetation history of the last 2000 years in Jackson Hole, Grand Teton National Park, Wyoming(Montana State University - Bozeman, College of Letters & Science, 2007) Jacobs, Karen Marie; Chairperson, Graduate Committee: Cathy WhitlockFire is an important natural disturbance in the western U.S., and information on how fire occurrence has varied in the past is critical to understanding modern ecosystem processes and their link to climate change. Long-term fire and vegetation histories are obtained from charcoal and pollen records preserved in lake sediments. Most charcoalbased fire-history studies have been conducted in middle- and high-elevation forest ecosystems, where glacial and other natural lakes are abundant. We have almost no information on the long-term fire history of low-elevation forest and steppe. The last 2000 years is of particular interest because it encompasses both human-induced and natural environmental change. Pollen and high-resolution macroscopic charcoal records obtained from three lakes in Jackson Hole were studied to reconstruct the vegetation and fire history over the last 2000 years in low-elevation ecosystems.