Browsing University of Alaska Fairbanks by Subject "seedlings"
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Bringing broader impacts to the community via university K-12 partnerships: growth in and seed quality of Betula neoalaskana SargentBetula neoalaskana Sargent is the most abundant birch species in Alaska. All parts of the tree can be used in creating timber and non-timber products, and birch stands provide high-value ecosystem services for ecotourism and outdoor recreational purposes. For these reasons, the OneTree Alaska program of the University of Alaska Fairbanks uses Interior Alaska white birch as the centerpiece of its work. This M.S. thesis is a contribution to OneTree Alaska's goal of raising the public's understanding of the effects of Interior Alaska's lengthening growing season on the growth and reproduction of the local birch resource. Specifically, the thesis relates to the growth and reproduction of the offspring of the original "one trees" harvested on Nenana Ridge in October 2009. The saplings have been growing in the Generation OneTree Research Plot in the T-field, north of the Smith Lake on the University of Alaska Fairbanks campus, since June 2011 and represent half-sibling families reared from the seed of 8 maternal trees. As seedlings, they were reared for growing seasons of variable length, both by students at the Watershed Charter School of the Fairbanks North Star Borough and by OneTree personnel in a University of Alaska Fairbanks growth chamber. Prior to this study, end of year measurements had been taken of the young trees in the T-field for all but one year and established that the length of the first growing season persistently affected the number of stems and the diameter at breast height (DBH) of the main stems. New findings in this thesis show that the elevation difference among trees impacts the number of infructescences and germination rates but not the number of male catkins. At least for the 2018 seed crop, seeds from trees planted at higher elevations in the T-field showed higher germination rates than those planted at lower elevations, while they produce fewer infructescences at up slope. Other findings demonstrate that sibling family does not have an effect on either vegetative or reproductive growth. Instead, the length of the first growing season provides for a diversity of canopy shapes across sibling families. The most significant finding is the effect of elevation on female reproductive growth: It suggests a number of next steps, tools, and analysis to better understand environmental variables that work alongside elevation in determining growth and reproductive success. Soil moisture and pH (H2O), Carbon/Nitrogen ratio, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to determine micronutrient composition, sensors to capture wind speed/direction and solar radiation, photosynthetic traits, and chlorophyll concentration measurements could all be valuable in further elucidating the hypotheses being advanced by this research regarding the interactions between changing environment and reproduction.
Seedling recruitment, genetic diversity, and secondary growth of deciduous shrubs in Arctic tundra disturbed by retrogressive thaw slump thermokarst on Alaska's North SlopeSince the 1970s, Arctic temperatures have risen by 2.7 °C, more than twice that of lower latitudes. Productivity of tundra vegetation is historically nutrient-limited, largely due to low rates of decomposition in soils underlain by permafrost, where cold temperatures limit nutrient uptake by plants. However, climate warming is implicated in the recent expansion of tall (≥ 0.5 m) deciduous woody shrubs across the Arctic. Among the largest tundra plants, deciduous shrubs exert strong controls on hydrology, heat balance, nutrient cycling, and food webs. These shrubs may be key players in carbon storage and re-stabilization of thaw-deformed permafrost landscapes (thermokarst), however, shrub-climate feedbacks are complex and their magnitude remains uncertain. Warming associated with recent thermokarst activity includes large (≥ 1 ha) de-vegetated depressions on hillslopes caused by mass soil thaw, known as retrogressive thaw slumps (RTS). RTS have increased on Alaska's North Slope by two-thirds since the 1980s. Within a few decades, some RTS near Toolik Lake support tall willow (Salix spp.) and dwarf birch (Betula nana) colonies. This study quantified three aspects of plant response in RTS of different ages (chronosequences) at two North Slope lakes: 1) recruitment (seedlings m⁻² and percent germination of soil seedbanks), 2) clonal (asexual) growth of dominant vegetation (willow), and 3) secondary growth (annual rings) of dwarf birch and willow. I hypothesized that conditions in RTS support greater recruitment, genetic diversity, and growth than conditions in undisturbed moist acidic tussock tundra, and that the climate signal (June mean temperature) is amplified in RTS shrub ring widths. The study found higher seedling density and seedbank viability associated with warm, nutrient-rich bare soil in recent RTS. Willow species richness was higher in RTS than in undisturbed tundra, but all willows showed high heterozygosity and low clonal spread regardless of disturbance. Ramets (branches) within clones were more widely spaced in RTS, suggesting that RTS can fragment and disperse asexual propagules. Shrub rings in RTS were wider than in undisturbed tundra, but climate sensitivity to warmer temperatures was not amplified in the growth rings of most RTS shrubs. Most RTS shrubs had wider rings associated with greater September precipitation in the previous year, while shrubs growing outside of RTS did not, which suggests protective effects of early snow accumulations in RTS depressions. These results demonstrate that some North Slope RTS support greater seedling recruitment and shrub growth than undisturbed tundra and may enhance tundra shrub growth.