Browsing by Subject "fire ecology"

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    Human impacts on how savanna plants interact through fire, resources, and microclimate
    (2015-08) Wragg, Peter
    Grasslands and savannas harbor immense plant biodiversity. This biodiversity is threatened by land transformation. Moreover, the biodiversity of even intact ecosystems is affected by widespread human impacts on environmental factors-- particularly resources, fire, and climate-- that underlie interactions among plant species and structure plant communities. This dissertation examines how plants interact by affecting, and responding to, their environment. Much research has examined how plants interact by depleting shared limiting resources such as nitrogen (i.e., resource competition), and how increasing nitrogen deposition causes biodiversity loss; this research has been mainly north-temperate. To widen understanding of this issue, I examined the roles of multiple nutrients in structuring endemic-rich grasslands of conservation concern on highly weathered soils in South Africa, as part of the globally distributed Nutrient Network experiment. It is less clear how plants interact through fire and microclimate. I investigated how grasses differ from other herbaceous plants (forbs) in their effects on fire behavior and resource availability, and how fire and resources in turn affected savanna tree establishment, in a 16-year biodiversity experiment. I also investigated how plant diversity and composition interacted with experimentally simulated global warming to determine microclimate and resource availability, and how microclimate and resource availability in turn affected seedling establishment of 32 savanna herb and tree species. This research on the multiple ways in which plants interact by influencing their environment sheds light on how human actions alter grassland and savanna biodiversity.
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    Impacts of multiple fires and wind disturbance on forest community composition, succession and diversity in the Boundary Waters Canoe Area Wilderness.
    (2018-01) Anoszko, Elias
    Under a warming climate, the Boundary Waters Canoe Area Wilderness (BWCAW) of Northern MN is expected to see an increase in the frequency of disturbances including wildfires and severe windstorms. While boreal forests such as those of the BWCAW are generally considered disturbance adapted, it is uncertain how changing disturbance regimes will impact these forests. We used a series of recent disturbances in the BWCAW ranging from areas affected by wind or fire only, to areas affected by wind followed by fire, or multiple fires, to examine how predicted changes in boreal disturbance regimes are likely to impact these forests. We found that multiple disturbances typically had greater cumulative disturbance severity than single disturbance events and in the case of wind+fire combinations also tended to burn with greater intensity, and fire severity relative to areas affected by a single fire only. While diversity-severity relationships varied in shape, we found that diversity was generally lower at high disturbance severity relative to moderate severities. Multiple disturbances had modestly reduced diversity relative to single disturbances, but this relationship varied depending on the spatial scale of inquiry. Despite only modest impacts on diversity, multiple disturbances did have a pronounced impact on succession and composition. Regardless of pre-disturbance composition, multiple disturbances resulted in succession to aspen and paper birch, with birch being more dominant in areas burned in late season fires and aspen more dominant in areas burned by early season fires. Stands subjected to single disturbance events exhibited multiple successional pathways and mix of forest types. Our results suggest that predicted changes in boreal disturbance regimes are likely to have minor impacts on woody plant diversity, but could adversely affect disturbance adverse species, and alter the age structure and composition of forests by reducing long-lived boreal conifers and increasing the dominance of aspen and paper birch.
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    A Tree-Ring Fire History Of The Upper Bois Brule River, Northwest Wisconsin
    (2019-01) Martin, Liam
    The Bois Brule River is a 44-mile-long, northward flowing Wisconsin waterway. From 1650 – 1830 the river served as part of a popular fur trade route, used by the Ojibwe, the British, and the French, that connected Lake Superior to the Mississippi River. The route eventually reached such prominence that it was termed “The Historic Highway”. I developed fire histories at three discrete sites along the Upper Bois Brule River in Northwest Wisconsin in order to (A) determine the rate of historic fire along the Upper Bois Brule River, (B) provide fire history information within the context of changes in Native American and European American land use, (C) investigate the influence of seasonal drought patterns on fire occurrence and (D) provide crucial and necessary baseline information to be used in land management decision-making. The fire history is comprised of 60 fire scarred trees, 344 individual fire scars and 68 unique fire years. The mean fire interval ranged from 15.7 – 22.4 and the mean fire interval for the entire region was 5.1. The rate of fires began to slow in the early 1900s, before eventually ceasing in 1918. There was no consistent relationship between fire events and regional climate patterns when each site was considered individually. When all fire years were considered in aggregate there was a significant relationship between the event year and regional drought. Results suggest that lighting, as a lone ignition source, cannot fully explain the reconstructed fire regime. It seems likely that human land use activities may have influenced the rate of fire along the Upper Bois Brule River. These findings have important implications for future land management and can be used as a guide to achieve site specific goals.