Browsing Theses (Agriculture and Horticulture) by Publication date
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Vegetation succession and pedogenesis on the Yukon-Kuskokwim Delta near St. Mary's, AlaskaArctic lowlands of Alaska are known to contain large stores of soil organic carbon (SOC) in organic-rich wetland systems and in the permafrost. Vegetation succession that follows floodplain and wetland development strongly affects the organic carbon stores and distribution of permafrost. Due to recent climate warming there has been losses of permafrost, and much of the SOC stored in Arctic lowlands is at risk for transfer within the global carbon budget. The vast Arctic lowland system in western Alaska is within the zone of discontinuous permafrost. It is anticipated to lose most of the permafrost within this century, yet it is inadequately studied due to the lack of road system connecting the region. This study is the first designed to explore the relationships between vegetation succession and soil development at different stages of sediment deposition. The study area is near St. Mary's at the north part of the Yukon-Kuskokwim Coastal Plain in western Alaska. Soil development is weak due to frequent flooding events and prolonged saturation. The irregular distribution of organic carbon and detritus, silt dominated particle size distribution, and nearly uniform composition of clay minerals with depth attest the alluvial deposition due to flooding events. Cryaquents were found in poor to very-poorly drained raised alluvial bars, Cryaquepts were found on somewhat poorly drained levees, Historthels were found on an abandoned floodplain, and Cryofibrists in very poorly drained depressions. Carbon stores range from 27.7 kg C m⁻² on raised alluvial bars and levees and 40.9 to 45.3 kg C m⁻² on oxbow depressions and the abandoned floodplain. It is crucial to have reliable measurements of SOC stores in order to estimate the potential impact of climate change on the global carbon budget. Soil development and nutrient level in response to vegetation succession are also reported for the area near St. Mary's, Alaska to add to the current understanding of soils in the region and the global carbon budget.
Utilizing pasture resources for sub-Arctic agriculture: sustainable livestock production in AlaskaIt is estimated that the globe must produce 100% more food in the next 50 years to meet growing demand while addressing the compounding challenge of climate change. One potential solution to this challenge is to produce more on existing agricultural lands and put more land into production. The extremely cold and dry climate that characterizes much of Alaska has all but removed the state from the state and national discussions of agricultural production and development. Yet despite this apparent incompatibility with traditional agricultural models, some of the largest wild herds of grazing ungulates are indigenous to Alaska - and thriving. This is both a testament to the resilience of grazing systems in general as well as a statement to the suitability of grazing systems specifically for Alaska. To shift the paradigm towards ecological and economic sustainability, we need to develop sustainable agricultural strategies that are specific to this unique ecosystem. A two-fold approach was used in this body of research: Is there an indigenous livestock species that could be economically feasible enterprise option? Is there a grazing management regime for subarctic Alaska that would improve ecosystem services and optimize pasture resources? I conducted an economic feasibility study of farming muskoxen (Ovibos moschatus), a uniquely adapted Arctic ungulate, to address the first question. An enterprise budget was used to estimate the fixed and variable costs and to model different revenue scenarios using six different combinations of qiviut, sold as raw fiber or value added yarn, and livestock sales to estimate the total economic potential of farming muskoxen at two scales, 36 and 72 muskoxen. Farming muskoxen was economically sustainable under several revenue scenarios. The most profitable scenario for either herd size was selling all the qiviut as value added yarn coupled with livestock sales. The enterprise was profitable at either scale assuming all the yarn sold at full retail price. If no livestock were sold, selling the total qiviut harvest as yarn was the only profitable option. When selling raw fiber alone, the break-even point was at a herd size of 124 muskoxen. Economies of scale accounted for a decrease in costs of approximately 21% overall, 30% in labor, and 23% in herd health, as the herd doubled in size. To address the need for grazing management strategies that are both environmentally and economically sustainable in Alaska, I conducted a study to evaluate the potential of intensively managed rotational grazing (IMRG) regimes on sub-arctic pasture. This regime is designed to mimic the short but intense grazing of wild, migratory ungulates that could enhance ecosystem function while optimizing pasture usage and forage growth. I conducted simulated grazing, applied using IMRG methodology, to evaluate above and below ground response to an IMRG regime and to gain insight on the role of grazing disturbance mechanisms on sub-arctic soil and plant health. A full factorial experiment of muskox dung/urine deposition (M), simulated trampling (T), and herbivory (H) (forage clipping), mimicking IMRG timing and intensity, was conducted at the Large Animal Research Station (LARS), UAF. I used a randomized block design with 96-1 m² plots in two established pastures with different soil types, over the 2014 and 2015 grazing seasons. I documented a treatment effect on soil parameters, forage growth, and percentage of bare soil (p<0.05). Soil nitrogen cycling and the Haney Soil Health Index both increased in plots that received a combination M and T or MT and H. The forage yield was consistently increased by MH, MTH, and H treatments. Although the MT and T treatments had a negative impact on forage yield, they had the largest reduction in the amount of bare ground. The data from this simulated study suggest that theories that underpin the IMRG method are potentially useful to producers, in the unique Alaskan subarctic environment.
Temporal and spatial variation of broadleaf forest flammability in boreal AlaskaThe boreal forest is a carbon reservoir containing roughly 40% of the world's reactive soil carbon, which is mainly cycled by wildland fires. Climate warming in boreal Alaska has changed the wildfire regime such that an increase in broadleaf forest relative to conifer forest is likely, which may reduce landscape flammability. However, the current and future flammability of broadleaf forest in a warming climate is not well understood. We used pre-fire and post-fire geospatial data to investigate the flammability of upland boreal forest patches in Interior Alaska in relation to summer weather conditions. Our objectives were to assess burning of broadleaf forest patches during "Normal" vs. "Large Fire Years", by week within a fire season, and by topographic position. Using 30-meter land-cover and fire-severity grids, we estimated the flammability of upland broadleaf forest patches during Large and Normal Fire Years. We then tested for topographic effects using a solar radiation index to eliminate potential deviations within the vegetation. Finally, Moderate Resolution Imaging Spectroradiometer (MODIS) hotspots were used to track the spatial extent of burns during the fire season by examining the periods of fire activity and intensity. Flammability of broadleaf forest patches varied both in time and space. Even during Normal Fire Years, broadleaf forest patches exhibited substantial flammability, with a mean of over 50% patch area burned. Patch flammability was significantly higher during Large Fire Years. Burning of broadleaf patches varied with topographic position and correlated with potential insolation. Broadleaf forest patches burned most frequently in late June-early July. Contrary to "conventional wisdom", broadleaf forest patches in boreal Alaska are susceptible to burning even during Normal Fire Years. With climate warming, the flammability of broadleaf forest is likely to increase due to more extreme fire weather events. Thus, although the frequency of broadleaf forest patches on the landscape is likely to increase with more frequent and severe wildfires, their effectiveness as a fire break may decrease in the future.