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Amy Angell ( send email )
M.S. Graduate
Advisor: K. Kielland
Co-Advisors: C. Mulder, J. Fox,
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THESIS :
Angell, Amy. 2007. Effects of moose browsing on the establishment and growth of white spruce seedlings on the Tanana River floodplain. M.S. Thesis, University of Alaska Fairbanks, 85 pages
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Kelly Balcarczyk ( send email )
M.S. Graduate
Advisor: J. Jones
Co-Advisors: R. Boone, D. White,
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THESIS ABSTRACT :
We examined the influence of permafrost on dissolved organic matter (DOM) in Caribou Poker Creeks Research Watershed (CPCRW). We analyzed long-term data from watersheds underlain with varying degrees of permafrost, sampled springs and thermokarsts to capture the range of DOM concentration and quality, used fluorescence spectroscopy to examine DOM composition, and measured DOM bioavailabity. Permafrost hydrology influenced DOM patterns, with the stream draining the high permafrost watershed having the highest dissolved organic carbon and nitrogen (DOC and DON) concentrations, higher DOC:DON, and greater specific ultraviolet absorbance (SUVA). Streams, springs, and thermokarsts exhibited a wide range of DOC and DON concentrations (1.5 – 37.5 mgC/L and 0.14 – 1.26 mgN/L), DOC:DON (7.08 – 42.8), and SUVA (1.5 – 4.7 L mgC-1 m-1). All sites had fluorescence index values (1.3 – 1.4) consistent with DOM derived from terrestrial sources. Principal components analysis revealed distinct groups in our fluorescence data determined by diagenetic processing and DOM source. Bioavailability of DOM ranged from 2 – 35% and was correlated with the proportion of tyrosine and tryptophan. Our results indicate that the degradation of permafrost in CPCRW will result in a decrease in DOC and DON concentrations, a decline in DOC:DON, and a reduction in SUVA, accompanied by a change in bioavailability.
THESIS :
Balcarczyk, K.L. 2008. Dissolved organic matter bioavailability and composition in stream draining catchments with discontinuous permafrost. M.S. Thesis. University of Alaska, Fairbanks, Fairbanks, AK, USA. 71 pages.
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Mike Balshi ( send email )
M.S. Graduate
Advisor: A.D. McGuire
Co-Advisors: Dave Verbyla, T. Chapin, R. Ruess
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THESIS ABSTRACT :
The boreal forest contains large reserves of carbon, and across this region wildfire
is a common occurrence. To improve the understanding of how wildfire influences the
carbon dynamics of this region, methods were developed to incorporate the spatial and
temporal effects of fire into the Terrestrial Ecosystem Model (TEM). The historical role
of fire on carbon dynamics of the boreal region was evaluated within the context of
ecosystem responses to changing atmospheric CO2 and climate. These results show that
the role of historical fire on boreal carbon dynamics resulted in a net carbon sink;
however, fire plays a major role in the interannual and decadal scale variation of
source/sink relationships. To estimate the effects of future fire on boreal carbon
dynamics, spatially and temporally explicit empirical relationships between climate and
fire were quantified. Fuel moisture, monthly severity rating, and air temperature
explained a significant proportion of observed variability in annual area burned. These
relationships were used to estimate annual area burned for future scenarios of climate
change and were coupled to TEM to evaluate the role of future fire on the carbon
dynamics of the North American boreal region for the 21st Century. Simulations with
TEM indicate that boreal North America is a carbon sink in response to CO2 fertilization,
climate variability, and fire, but an increase in fire leads to a decrease in the sink strength.
While this study highlights the importance of fire on carbon dynamics in the boreal
region, there are uncertainties in the effects of fire in TEM simulations. These
uncertainties are associated with sparse fire data for northern Eurasia, uncertainty in
iv
estimating carbon consumption, and difficulty in verifying assumptions about the
representation of fires that occurred prior to the start of the historical fire record. Future
studies should incorporate the role of dynamic vegetation to more accurately represent
post-fire successional processes, incorporate fire severity parameters that change in time
and space, and integrate the role of other disturbances and their interactions with future
fire regimes.
THESIS :
Balshi, M.S. 2007. The role of fire in the carbon dynamics of the boreal forest. Ph.D. Thesis, University of Alaska, Fairbanks, Fairbanks, AK, USA. 193 pages.
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Colin Beier ( send email )
Ph.D. Graduate
Advisor: T. Chapin
Co-Advisors: A.D. McGuire, ,
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THESIS ABSTRACT :
Complex systems of humans and nature often experience rapid and unpredictable change that results in undesirable outcomes for both ecosystems and society. In circumpolar regions, where multiple converging drivers of change are reshaping both human and natural communities, there is uncertainty about future dynamics and the capacity to sustain the important interactions of social-ecological systems in the face of rapid change. This research addresses this uncertainty in the region of Southeast Alaska, where lessons learned from other circumpolar regions may not be applicable because of unique social and ecological conditions. Southeast Alaska contains the most productive and diverse ecosystems at high latitudes and a human population almost entirely isolated and embedded in National Forest lands; these qualities underscore the importance of the region’s climate and federal management systems, respectively. This research presents a series of case studies of the drivers, dynamics, and outcomes of change in regional climate and federal management, and theoretically grounds these studies to understand the regional resilience to change.
Climate change in Southeast Alaska is investigated with respect to impacts on temperate rainforest ecosystems. Findings suggest that warming is linked to emergence of declining cedar forests in the last century. Dynamics of federal management are investigated in several studies concerning the origins and outcomes of national conservation policy, the boom-bust history of the regional timber economy, and the factors contributing to the current “deadlock” in Tongass National Forest management. Synthesis of case study findings suggests both emergent phenomena (yellow-cedar decline) and cyclic dynamics (timber boom-bust) resulting from the convergence of ecological and social drivers of change. Adaptive responses to emergent opportunities appear constrained by inertia in management philosophies. Resilience to timber industry collapse has been variable at local scales, but overall the regional economy has experienced transition while retaining many of its key social-ecological interactions (e.g., subsistence and commercial uses of fish and wildlife). An integrated assessment of regional datasets suggests a high integrity of these interactions, but also identifies critical areas of emergent vulnerability. Overall findings are synthesized to provide policy and management recommendations for supporting regional resilience to future change.
THESIS :
Beier, Colin M.. 2007. Regional Climate, Federal Land Management and the Social-Ecological Resilience of Southeastern Alaska
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Emily Bernhardt ( send email )
M.S. Graduate
Advisor: T. Hollingsworth and T. Chapin
Co-Advisors: C. Mulder, ,
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THESIS ABSTRACT :
In interior Alaska black spruce forest succession and vegetation properties are
tightly linked to fire disturbance, partly due to the functional properties of species.
Climatically induced changes in the fire regime could negatively affect some
functional groups and potentially lower the functional diversity of stands through
changes in fire severity and site moisture. In addition, there is little information
regarding the relationship between pre- and post-fire community composition in black
spruce communities of interior Alaska. To contribute to our knowledge regarding
post-fire plant community dynamics, I investigated how post-fire community
properties in relation to fire severity and site moisture: 1) species composition, in
which pre- and post-fire community composition was compared to determine changes
in species richness and functional diversity and 2) the functional traits of species.
Pre-fire species composition in black spruce forests was dominated by latesuccessional
understory species and was most similar in species composition to low
severity burned sites (regardless of stand age). Site moisture did not appear to affect
the change in species composition post-fire in the first two years following fire.
Functional groups that showed significant changes post-fire were bryophytes, lichen
and evergreen shrubs. When each species was deconstructed into a set of functional
traits, I observed that these traits were tightly linked to fire severity. These results
have large implications under projected climate scenarios that predict increasing fire
extent and severity in the boreal forest because high severity fire changes the species
iv composition and associated functional traits of black spruce post-fire communities in
interior Alaska.
THESIS :
Bernhardt, E.L.. 2008. The effects of fire severity and site moisture on species composition and functional properties of black spruce forests in interior Alaska. MS Thesis, University of Alaska Fairbanks, Fairbanks, AK. 124 pages.
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Emma Betts ( send email )
M.S. Graduate
Advisor: J. Jones
Co-Advisors: , ,
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THESIS ABSTRACT :
In the boreal forest of interior Alaska, both permafrost and wildfire impact stream solute concentrations, but their effect on stream function is unknown. This research focused on the effects of wildfire and permafrost on stream nutrient dynamics and metabolism in the Caribou Poker Creeks Research Watershed (CPCRW) in interior Alaska. Wildfire impact on chemistry was determined through comparison of pre- and post-fire stream chemistry in a control and a burned watershed. We predicted that increased nutrient and decreased dissolved organic carbon (DOC) delivery to streams after fire would stimulate gross primary productivity (GPP) and reduce ecosystem respiration in burned watersheds. Fire resulted in higher stream nitrate, sulfate, and cation concentrations, and lower DOC concentration, at the burned site than at the control site. Streams draining burned watersheds had higher summer GPP (2.4 gO2 m?2 day?1) than the unburned sites (1.2 gO2 m?2 day?1). Respiration was also higher in burned than unburned watersheds (3.9 and 3.0 gO2 m?2 day?1, respectively). Metabolism was not correlated with the increased nutrient concentrations observed after fire. Instead, we suggest GPP was stimulated through increased soluble reactive phosphorus availability after fire, whereas respiration was likely controlled by pre-existing differences in stream physical or chemical characteristics.
THESIS :
Betts, E.F.. 2006. Permafrost and Wildfire Influences on Stream Nutrient Dynamics and Metabolism in Boreal Forest Watersheds of Interior Alaska. M.S. Thesis, University of Alaska Fairbanks
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Leslie Boby ( send email )
M.S. Graduate
Advisor: M. Mack
Co-Advisors: , ,
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THESIS :
. .
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Bob Bolton ( send email )
Ph.D. Graduate
Advisor: L. Hinzman
Co-Advisors: , ,
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THESIS :
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Andrew Borner ( send email )
M.S. Graduate
Advisor: K. Kielland
Co-Advisors: , ,
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THESIS :
Borner, Andrew. 2006. Plant phenology and seasonal nitrogen availability in arctic snowbed communities. M.S. Thesis, University of Alaska Fairbanks, 47 pages
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Todd Brinkman ( send email )
Ph.D. Graduate
Advisor: T. Chapin
Co-Advisors: , ,
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THESIS :
. .
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Lem Butler ( send email )
M.S. Graduate
Advisor: K. Kielland
Co-Advisors: , ,
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THESIS :
Butler, L.G. 2003. The role of mammalian herbivores in primary succession of the Tanana River floodplain, interior Alaska. M.S. Thesis. University of Alaska Fairbanks. Fairbanks, AK, USA.
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Hannah Clilverd ( send email )
M.S. Graduate
Advisor: J. Jones
Co-Advisors: R. Boone, K. Kielland,
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THESIS ABSTRACT :
The aquatic-terrestrial interface is an active site of biogeochemical transformation, regulating the flux of nutrients between ecosystems. I addressed the hydrologic controls on nitrogen biogeochemistry in the hyporheic zone of a glacially fed river. I measured hyporheic concentrations of solutes and gases along subsurface flowpaths on two islands. Denitrification was quantified using an in situ ?15-NO3 push-pull technique. Nitrate concentration was consistently greater in river than in hyporheic water. Denitrification ranged from 1.9 – 29.4 mgN kg sediment-1 day-1. Hotspots of methane partial pressure, averaging 50,000 ppmv, were found in densely vegetated areas with low oxygen concentration (< 0.5 mgO L-12). Hyporheic flow was an important source of nitrogen to microbes and vegetation, transporting on average 0.41 gNO-3-N m-2 day-1 through surface sediments. Results suggest that denitrification is a major sink for river nitrate in boreal forest floodplain soils, particularly at the river-sediment interface. The stability of the river hydrograph is a key factor regulating anaerobic metabolism in the hyporheic zone.
THESIS :
Clilverd, Hannah. 2007. Surface-subsurface hydrologic exchange and nutrient dynamics in the hyporheic zone of the Tanana River. M.S. thesis. University of Alaska Fairbanks. 66 pages
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Dorte Dissing ( send email )
Ph.D. Graduate
Advisor: D.Verbyla
Co-Advisors: , ,
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THESIS ABSTRACT :
The relationship between lightning strike density, vegetation, and elevation was investigated at three different spatial scales: (i) interior Alaska (~630 000 km2), (ii) six longitudinal transects (~100 000 km2), and (iii) 17 individual physiographic subregions (~50 000 km2) within Alaska. The data consisted of 14 years (1986–1999) of observations by the Alaska Fire Service lightning strike detection network. The best explanation for the variation in lightning strike density was provided by a combination of the areal coverage of boreal forest and elevation. Each of these factors has the potential to influence the convective activity. Our study suggests that in a region that is climatically favorable for air-mass thunderstorms, surface properties may enhance local lightning storm development in the boreal forest. Lightning strikes were found to occur frequently both in mountainous areas and at river flats, which is contrary to results from previous Alaskan studies.
THESIS :
. .
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Justin Epting ( send email )
M.S. Graduate
Advisor: D. Verbyla
Co-Advisors: , ,
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THESIS ABSTRACT :
A variety of single-band, band ratio, vegetation index, and multivariate algorithms were evaluated for mapping burn severity using Landsat TM and ETM+ imagery across four burns in interior Alaska. The Normalized Burn Ratio (NBR) outperformed all algorithms, both when tested as a single post-fire value and when tested as a differenced (prefire – postfire) value. The NBR was then used to map burn severity at a historical burn near Yukon-Charley Rivers National Preserve and a time-series of images from 1986 to 2002 was analyzed to investigate interactions between vegetation, burn severity, and topography. Strong interactions existed between vegetation and burn severity, but the only topographic variable that had a significant relationship with burn severity was evelation, presumably due to the strong control of elevation on forest cover. The highest burn severity occurred in spruce forest, while the lowest occurred in broadleaf forest. Areas with high burn severity experienced disproportionately more shifts toward spruce woodland and shrub classes, while areas with low to moderate severity were less likely to change vegetation type. Finally, vegetation recovery, estimated using a remotely-sensed vegetation index, peaked between 8-14 years post-fire, and recovery was highest for areas with the highest burn severity.
THESIS :
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Jason Fellman ( send email )
Ph.D. Candidate
Advisor: R. Boone
Co-Advisors: , ,
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THESIS :
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Bjorn Flora ( send email )
M.S. Graduate
Advisor: K. Kielland
Co-Advisors: , ,
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THESIS :
Flora, B.K. 2002. Comparison of snowshoe hare populations in Interior. M.S. Thesis. University of Alaska Fairbanks. Fairbanks, AK, USA.
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Nancy Fresco ( send email )
Ph.D. Graduate
Advisor: T. Chapin
Co-Advisors: A.D. McGuire, ,
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THESIS ABSTRACT :
Northern ecosystems and those who rely upon them are facing a time of unprecedented rapid change. Global boreal forests will play an important role in the feedback loop between climate, ecosystems, and society. In this thesis, I examine forest carbon dynamics and the potential for carbon management in Interior boreal Alaska in three distinct frameworks, then analyze my results in the context of social-ecological resilience. In Chapter 1, I analyze comparative historical trends and current regulatory frameworks governing the use and management of boreal forests in Russia, Sweden, Canada, and Alaska, and assess indicators of socio-ecological sustainability in these regions. I conclude that low population density, limited fire suppression, and restricted economic expansion in Interior Alaska have resulted in a 21st-century landscape with less compromised human-ecosystem interactions than other regions. Relative wealth and a strong regulatory framework put Alaska in a position to manage for long-term objectives such as carbon sequestration. In Chapter 2 I model the landscape-level ecological possibilities for sequestration under three different climate scenarios and associated changes in fire and forest growth. My results indicate that Interior Alaska could act as either a weak carbon source or as a weak sink in the next hundred years, and that management for carbon credits via fire suppression would be inadvisable, given the associated uncertainty and risks. In Chapter 3 I perform a social, ecological, and economic analysis of the feasibility of switching from fossil fuels to wood energy in Interior Alaska villages. I demonstrate that this is a viable option with the potential benefits of providing lower-cost power, creating local employment, reducing the risk of catastrophic wildfire near human habitation, and earning marketable carbon credits. Finally, in Chapter 4, I assess how each of the above factors may impact social-ecological resilience. My results show some system characteristics that tend to bolster resilience and others that tend to increase vulnerability. I argue that in order to reduce vulnerability, management goals for Alaska’s boreal forest must be long-term, flexible, cooperative, and locally integrated.
THESIS :
Fresco, Nancy. 2006. Carbon Sequestration in Alaska's Boreal Forest: Planning for resilience in a changing landscape. PhD Thesis, University of Alaska Fairbanks. Fairbanks, AK, USA
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Ian Herriott ( send email )
M.S. Graduate
Advisor: Lee Taylor
Co-Advisors: , ,
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THESIS :
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Jill Johnstone ( send email )
Ph.D. Graduate
Advisor: T. Chapin
Co-Advisors: , ,
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THESIS ABSTRACT :
Because of the key role played by fire in structuring boreal forest ecosystems, interactions between vegetation and fire regime may be an important and dynamic control of forest response to climate change. This research uses a series of field observations and experiments in boreal forests to examine the nature of several potential fire and vegetation interactions, and how such interactions may influence forest response to climate change. Long-term observations of post-fire succession provide information on the timing of tree establishment and the effects of early establishment on subsequent successional trajectories. The role of competitive interactions in driving patterns of early establishment was tested with experimental manipulations of aspen (Populus tremuloides) cover after fire. This research demonstrated that competition by aspen resprouts may reduce the success of conifer establishment and favor long-term dominance by deciduous trees. The effects
of fire severity on successional trajectories were tested in a series of field experiments that contrasted patterns of seedling establishment across differences in depth of the post-fire organic layer. All species in the experiment responded negatively to decreased fire severity, but deciduous trees were more sensitive in their response than conifers. Thus, variations in burn severity are likely to mediate deciduous establishment in organic-rich stands. Observations of natural tree regeneration in stands that burned at different ages also indicate that a decrease in fire interval can influence the relative abundance of deciduous and coniferous species by reducing conifer establishment. Over longer time scales, changes in biota caused by species migration may influence fire and vegetation interactions. Observations of post-fire regeneration at the current distribution limits of lodgepole pine (Pinus contorta) indicate that continued range expansion of pine could initiate rapid shifts in dominance from spruce to pine within a single fire cycle. Together, these results provide insight into the dynamic feedbacks between fire and vegetation that can lead to high levels of system resilience, while also promoting rapid responses when threshold conditions are crossed. A more complete understanding of these interactions will improve our ability to manage and predict boreal ecosystem responses to a changing climate.
THESIS :
Johnstone, J.F. 2003. Fire and successional trajectories in boreal forest: Implications for response to a changing climate. Ph.D. Dissertation. University of Alaska Fairbanks. Fairbanks, AK, USA.
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Evan Kane ( send email )
Ph.D. Graduate
Advisor: D. Valentine
Co-Advisors: T. Chapin, S. Rupp, J. Harden
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THESIS ABSTRACT :
The likely direction of change in soil organic carbon (SOC) in the boreal forest biome, which harbors roughly 22% of the global soil carbon pool, is of marked concern because climate warming is projected to be greatest in high latitudes and temperature is the cardinal determinant of soil C mineralization. Moreover, the majority of boreal forest SOC is harbored in surficial organic horizons which are the most susceptible to consumption in wildfire. This research focuses on mechanisms of soil C accumulation in recently burned (2004) and unburned (~1850-1950) black spruce (Picea mariana [Mill.] BSP) forests along gradients in stand productivity and soil temperature. The primary research questions in these three chapters address: 1) how the interaction between stand production and temperature effect the stabilization of C throughout the soil profile, 2) the quantity and composition of water soluble organic carbon (WSOC) as it is leached from the soil across gradients in productivity and climate, and 3) physiographic controls on organic matter consumption in wildfire and the legacy of wildfire in stable C formation (pyrogenic C, or black carbon). Soil WSOC concentrations increased while SOC stocks decreased with increasing soil temperature and stand production along the gradients studied. Stocks of BC were miniscule in comparison to organic horizon SOC stocks, and therefore the C stabilizing effect of wildfire was small in comparison to SOC accumulation through arrested decomposition. We conclude that C stocks are likely to be more vulnerable to burning as soil C stocks decline relative to C sequestered in aboveground woody tissues in a warmer climate. These findings contribute to refining estimates of potential changes in boreal soil C stocks in the context of a changing climate.
THESIS :
Kane, Evan S.. 2006. Mechanisms of soil carbon stabilization in black spruce forests of interior Alaska: soil temperature, soil water, and wildfire. PhD thesis. University of Alaska Fairbanks. Fairbanks, Alaska, USA. 152p.
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Prathap Kodial ( send email )
M.S. Graduate
Advisor: H. Toniolo
Co-Advisors: L. Hinzman, K. Yoshikawa,
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THESIS :
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Nick Lisuzzo ( send email )
M.S. Graduate
Advisor: K. Kielland
Co-Advisors: , ,
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THESIS :
Lisuzzo, Nick . 2005. Physical controls over nitrogen supply in early successional riparian ecosystems along the Tanana River, Alaska. MS thesis, University of Alaska, Fairbanks, 80p.
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Patricia Loomis ( send email )
M.S. Candidate
Advisor: R. Ruess
Co-Advisors: , ,
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THESIS ABSTRACT :
We studied spatial and temporal patterns of soil nitrogen pools and fluxes at treeline and forested sites within three Alaskan mountain ranges along a latitudinal transect of 785 km during 2001- 2002. We measured soil temperatures, pools of soil mineral (ammonium and nitrate) and organic (amino acid and microbial biomass) nitrogen, in situ rates of net mineralization, net nitrification, and net amino acid production, conducted a decomposition experiment at all sites using common litter, and studied soil carbon turnover in a laboratory incubation experiment. Soils at treeline were colder than forested soils, particularly during fall and over winter, and had reduced rates of nitrogen cycling and litter decomposition relative to soils in forested stands. During incubation, treeline soils had lower respiration rates per unit carbon, suggesting lower soil organic matter quality relative to forested soils. 70% of annual net nitrogen mineralization occurred from August — May, suggesting that fall and winter are critical periods for soil nitrogen transformations in forested and treeline ecosystems. Among mountain ranges, nitrogen pools and fluxes were similar, despite variation in growing season length and mean annual temperatures. Soil moisture and organic matter quality may have stronger effects on variation in nitrogen cycling than temperature at our sites.
THESIS :
Loomis, P.F.. 2005. Nitrogen cycling at treeline: latitudinal and elevational patterns across a boreal landscape. M.S. thesis, University of Alaska Fairbanks, 65 pages.
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Rachel Lord ( send email )
M.S. Graduate
Advisor: K. Kielland
Co-Advisors: F. Huettmann, K. Hundertmark, T. Paragi
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THESIS ABSTRACT :
Over 1 million hectares burn annually across interior Alaska’s boreal forest,
altering the composition and distribution of vegetation communities that provide critical
winter habitat for Alaskan moose (Alces alces gigas). Within a burn, fire severity (the
amount of residual soil organic matter following a fire event) is spatially variable and
drives the trajectories of post-fire succession. I examined the response of moose to
patterns of regeneration resulting from variable fire severity within two burns in interior
Alaska. I found significantly higher production of forage biomass (kg/ha) in high fire
severity sites than in low severity sites. Proportional removal of forage biomass by
moose was 36% higher on sites with higher fire severity compared with low severity
sites. I used multiple regression models to examine the role of forage distribution
following fire on proportional removal. The overall explanatory power of any landscape
descriptors was moderate at best. Winter forage is a limiting factor for moose
reproductive potential, especially in areas with low predation rates. Changes in moose
habitat potential is easily measured using remote sensing and GIS techniques and should
be assessed to combine field-based knowledge of moose response to variations in
regeneration to large-scale patterns of vegetation regeneration following wildfires.
THESIS :
Lord, R.E.. 2008. Variable fire severity in Alaska's boreal forest: implications for forage productions and moose utilization patterns. M.S. Thesis, University of Alaska Fairbanks, Fairbanks, Alaska, 107 pages.
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Jack McFarland ( send email )
Ph.D. Student
Advisor: R. Ruess
Co-Advisors: , ,
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THESIS :
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Jen Mitchell ( send email )
M.S. Candidate
Advisor: R. Ruess
Co-Advisors: , ,
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THESIS ABSTRACT :
Patterns of and controls over N2 fixation by green alder (A. viridis) were studied in post-fire, mid-succession, and white spruce upland forests in interior Alaska during 1997-2000, focusing on the hypothesis that ecosystem-level nitrogen (N) inputs decrease with successional development. Across all stands, alder created islands of elevated soil N and carbon, depleted soil phosphorus (P), and more acidic soils, effects which translated to the stand-level in response to greater alder stem density. Rates of N2 fixation (measured by acetylene reduction = ARA) closely tracked plant phenology during the 1997 (a drought year) and 1998 (a year of normal precipitation) growing seasons. During 1998, stands with higher maximum ARA had higher %N in the O, A, and C soil horizons. N2-fixation rates were influenced by soil P, as evidenced by the findings that maximum ARA was positively correlated with foliar N:P ratios, and with subcanopy %P in the O and A soil horizons. During the drought year, alder leaf %P and leaf N resorption were lower and leaves were thinner when compared to 1998. Drought effects were most pronounced in mid-succession where alder exhibited reduced ARA (-76%), leaf %P (-14%), leaf thickness (-40%), and lower leaf resorption of P (-66%) and N (-78%). Although ARA and nodule biomass did not differ among stand types, increases in alder densities with successional time translated to increasing ecosystem-level N inputs across the chronosequence. These results contradict established theory predicting a decline in N2-fixation rates and N2-fixer abundance during successional stand development.
THESIS :
Mitchell, J. S.. 2006. Patterns of and controls over N inputs by green alder (Alnus viridis ssp. fruticosa) to a secondary successional chronosequence in interior Alaska. M.S. University of Alaska, Fairbanks. 82 pages.
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Isla Myers-Smith ( send email )
M.S. Graduate
Advisor: A. D. McGuire
Co-Advisors: J. W. Harden, F. S. Chapin,
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THESIS ABSTRACT :
With warming, the wetlands of Interior Alaska may experience more frequent or extensive stand-replacing fires and permafrost degradation, and thus change the primary factors controlling carbon emissions. I measured carbon exchange along a moisture transect from the center of a Sphagnum-dominated bog into the surrounding burn scar (2001 Survey Line Fire) during the growing season of 2004. Both the bog and the surrounding burn were sinks for CO2, and the bog was a CH4 source in the abnormally dry summer of 2004. Thermokarst and subsiding soils were observed on the margin of the Sphagnum bog in the three years since the fire, increasing the anaerobic portion of the soil landscape. It was in this portion of the transect where I observed the greatest variation in carbon fluxes, indicating that permafrost collapse is altering the pattern of emissions from this landscape. I tracked historic changes in vegetation, hydrology and fire at this site through macrofossil, charcoal and diatom analysis of peat cores. The paleoecological record suggests that fire mediates collapse in this system. This study suggests that future changes in temperature and precipitation will likely change carbon cycling and vegetation patterns across this landscape.
THESIS :
Myers-Smith, I. H.. 2005. Carbon exchange and permafrost collapse: Implications for a changing climate. M.S. University of Alaska Fairbanks, Fairbanks, AK.
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Dana Nossov ( send email )
M.S. Graduate
Advisor: R. Ruess
Co-Advisors: T. Hollingsworth, ,
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THESIS ABSTRACT :
This study describes the community, population, and growth dynamics of Alnus
tenuifolia (thinleaf alder) and implications for nutrient cycling on the Tanana River
floodplains. Through symbiotic N-fixation inputs, alder contributed to soil N
accumulation with time. N-fixation itself was likely limited by soil P. Soil N was
positively related to alder stem density in early successional stands. Community structure
varied along a temporal gradient of changing environmental characteristics, but variations
in successional patterns were found. Landscape scale alder recruitment varied temporally
and was apparently linked to interactions between geofluvial processes, seed production
and dispersal, and herbivory. A widespread stem canker outbreak has resulted in high
alder mortality and likely reductions in N-fixation inputs. Disease incidence and mortality
were positively related to stem density. Alder radial growth was sensitive to drought
during June and August. Alder growth was positively related to river level, suggesting
that fluctuation in hyporheic flow is important to alder water balance, especially on lower
terraces. The sensitivity of alder growth to meteorological drought was heightened with
increasing terrace elevation. Long-term climatic trends suggest that drought will become
more common and severe, resulting in reductions in alder-mediated ecosystem N inputs.
THESIS :
Nossov, D.R.. 2008. Community, population, and growth dynamics of Alnus tenuifolia: implications for nutrient cycling on an interior Alaskan floodplain. M.S. Thesis, University of Alaska Fairbanks, Fairbanks, Alaska. 99 pages.
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Jonathan O'Donnell ( send email )
M.S. Graduate
Advisor: J. Jones
Co-Advisors: K. Kielland, L. Hinzman,
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THESIS ABSTRACT :
Riparian zones function as important ecotones for reducing nitrate concentration in groundwater and inputs into streams. In the boreal forest of interior Alaska, permafrost confines subsurface flow through the riparian zone to shallow organic horizons, where plant uptake of nitrate and denitrification are typically high. Two research questions were addressed in this study: 1) how does riparian zone nitrogen retention vary in watersheds underlain by discontinuous permafrost, and 2) what is the contribution of denitrification to riparian zone nitrogen retention? To estimate the contribution of the riparian zone to watershed nitrogen retention, I analyzed groundwater chemistry using an end-member mixing model. To assess the importance of denitrification as a mechanism of nitrogen retention, I conducted field denitrification assays using the acetylene block technique. Nitrogen retention averaged 0.75 and 0.22 mmol N m-2 d-1 in low and high permafrost watersheds, respectively, over the summer. Compared with the fluvial export of nitrogen, the retention rate of nitrogen in the riparian zone is 10 – 15% of the loss rate in stream flow. Denitrification accounted for a small proportion (3%) of total nitrogen retention in the riparian zone. Variation in nitrogen retention between watersheds does not account for differences in stream nitrate concentration between watersheds.
THESIS :
O'Donnell, J.A.. 2005. Nitrogen retention in the riparian zone of watersheds underlain by discontinuous permafrost. M.S. Thesis. University of Alaska Fairbanks, Fairbanks, AK, USA.
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Jonathan O'Donnell ( send email )
Ph.D. Candidate
Advisor: A.D. McGuire
Co-Advisors: J. Harden, V. Romanovsky, E. Hood
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THESIS ABSTRACT :
High-latitude regions store large quantities of organic carbon (C) in permafrost soils and peatlands, accounting for nearly half of the global belowground C pool. Projected climate warming over the next century will likely drive widespread thawing of near-surface permafrost and mobilization of soil C from deep soil orizons. However, the processes controlling soil C accumulation and loss following permafrost thaw are not well understood. To improve our understanding of these processes, I examined the effects of permafrost thaw on soil C dynamics in forested upland and peatland ecosystems of Alaska’s boreal region. In upland forests, soil C accumulation and loss was governed by the complex interaction of wildfire and permafrost. Fluctuations in active layer depth across stand age and fire cycles determined the proportion of soil C in frozen or unfrozen soil, and in turn, the vulnerability of soil C to decomposition. Under present-day climate conditions, the presence of near-surface permafrost aids C stabilization through the upward movement of the permafrost table with post-fire ecosystem recovery. However, sensitivity analyses suggest that projected increases in air temperature and fire severity will accelerate permafrost thaw and soil C loss from deep mineral horizons. In the lowlands, permafrost thaw and collapse-scar bog formation resulted in the dramatic redistribution of soil water, modifying soil thermal and C dynamics. Water impoundment in collapse-scar bogs enhanced soil C accumulation in shallow peat horizons, while allowing for high rates of soil C loss from deep inundated peat horizons. Accumulation rates at the surface were not sufficient to balance deep C losses, resulting in a net loss of 26 g C m-2 y-1 from the entire peat column during the 3000 years following thaw. Findings from these studies highlight the vulnerability of soil C in Alaska’s boreal region to future climate warming and permafrost thaw. As a result, permafrost thaw and soil C release from boreal soils to the atmosphere should function as a positive feedback to the climate system.
THESIS :
O'Donnell, J. A.. 2010. The Effects of Permafrost Degradation on Soil Carbon Dynamics in Alaska's Boreal Region. Ph.D. Dissertation. University of Alaska Fairbanks. Fairbanks, AK, USA.
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Brian Riordan ( send email )
M.S. Graduate
Advisor: D. Verbyla
Co-Advisors: , ,
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THESIS ABSTRACT :
Over the past fifty years Alaska has experienced an increase in mean annual temperature. This warming may be causing significant changes in hydrology and permafrost dynamics. In recent decades, Native Americans and land managers have reported losses of water bodies and surface water area in interior Alaska. We conducted a study to determine the degree to which these informal observations were representative of a regional trend in surface water area loss. This study examines closed-basin water bodies in nine regions across Alaska: 1) Copper River Basin, 2) Talkeetna, 3) Tetlin National Wildlife Refuge, 4) Denali National Park, 5) Innoko Flats National Wildlife Refuge, 6) Minto Flats State Game Refuge, 7) Stevens Village, 8) Yukon Flats National Wildlife Refuge, and 9) Prudhoe Bay/Arctic Coastal Plain. The study included approximately 850,000 hectares and over 40,000 water bodies. To conduct such a large-scale study, GIS and Remote Sensing techniques were applied. Water body change detection was conducted over a fifty-year time period. A minimum of three time periods were used for each area. Imagery included black and white aerial photography (1950 -1957), color infrared aerial photography (1978 -1982), Landsat TM (1986 - 1995), and Landsat ETM+ (1999 - 2002). Based on these images, water body polygons were digitized for each time period. Area was calculated for each polygon and compared to corresponding ponds from images at later times. Of the nine regions, six showed substantial reductions in surface water area: Copper River Basin, Minto Flats, Innoko Flats, Yukon Flats, Stevens Village, and Denali National Park. The Innoko Flats and Copper River Basin regions showed the most loss at 31% and 28% respectively. There are several mechanisms possible for reductions of surface water in a warming climate including increased formation of taliks, increased soil water holding capacity, increased evapotranspiration, and terrestrialization.
THESIS :
Riordan, B. A.. 2005. Using Remote Sensing to Examine Changes of Closed-Basin Surface Water Area in Interior Alaska From 1950-2002. M. S. Thesis. University of Alaska Fairbanks. Fairbanks, AK, USA.
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Sarah Runck ( send email )
M.S. Graduate
Advisor: D. Valentine
Co-Advisors: J. Yarie, T. Chapin,
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THESIS ABSTRACT :
The objective of this study was to assess the effect of throughfall exclusion (1989-2005) on forest vegetation and soil in upland and floodplain landscape positions. In uplands, imposed drought reduced soil moisture at 5, 10, and 20 cm depths and increased soil C storage by slowing decomposer activity at the surface. In the drought plots, aboveground tree growth was reduced and root biomass in mineral soil was increased. In floodplains, imposed drought did not reduce soil moisture as strongly as it did in uplands, though near-surface soil C storage was still increased as a result of reduced decomposer activity. Floodplain vegetation response to imposed drought differed from that of uplands; imposed drought did not reduce aboveground tree growth but instead reduced root biomass in mineral soil. At both landscape positions, imposed drought accelerated the loss of understory vegetation. Overall, the results of the throughfall exclusion indicated that chronic soil drying is likely to increase forest C storage only in floodplains. In uplands, where soil moisture is more limited, forest C storage is not as likely to change because an increase in soil C may be offset by reduced tree growth.
THESIS :
Runck, S.. 2008. Sensitivity of boreal forest carbon dynamics to long-term (1989-2005) throughfall exclusion in interior Alaska. MS Thesis, University of Alaska Fairbanks. 78 pages.
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Blaine Spellman ( send email )
M.S. Graduate
Advisor: T.Wurtz
Co-Advisors: J. Fox, J. Conn,
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THESIS ABSTRACT :
Sweetclover, Melilotus alba, is an invasive legume that has formed dense and
extensive patches along several rivers in Alaska. The objective of my research was to
determine if sweetclover can impact native seedling recruitment in floodplain habitats.
To determine if sweetclover affects recruitment, I conducted a removal experiment along
two rivers in Alaska. When compared to areas where sweetclover was removed, areas
with sweetclover had 50% greater mortality of native seedlings. To determine if
sweetclover shading was a mechanism through which this impact occurred, I grew eight
floodplain plant species under a range of lighting conditions that were representative of
shading under sweetclover. Increases in shading stressed each species but did not lead to
mortality during the growing season. Competition for several resources, including light,
likely led to the increased mortality of seedlings in the removal experiment. To
determine if sweetclover is competitively superior to two native legumes, I conducted
two additive series competition experiments. Despite using high densities of seedlings,
there were few interactions between sweetclover and either native legume. The lack of
interactions may indicate that sweetclover and native legumes occupied separate niche
space. Together, these results provide a foundation for future research regarding the
impacts of invasive plants in Alaska.
THESIS :
Spellman, B.T. 2008. The impact of invasive sweetclover (Melilotus alba) in early-successional floodplain habitats of Alaska. M.S. Thesis, University of Alaska Fairbanks, 86 pages.
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Katie Spellman ( send email )
M.S. Graduate
Advisor: C. Mulder
Co-Advisors: T. Hollingsworth, ,
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THESIS ABSTRACT :
As the climate changes, Alaska’s boreal forest faces the simultaneous threats of rising
invasive plant abundances and increasing area burned by wildfire. Highly flammable and
widespread black spruce forest represents a boreal habitat that may be increasingly
susceptible to non-native plant invasion. In other biomes, non-native plant invasions are
generally greatest in high severity burns that are only a few years old. The relationship
between fire and non-native plant invasion has not been investigated in the northern
boreal forest. To assess the invasibility of burned black spruce forests, I used burned field
sites that spanned a gradient of burn severities, moisture levels, and burn ages. I
conducted both field surveys and a greenhouse experiment using soil taken from burn
sites. Contrary to generalizations from other biomes, I found soils from low severity
burns and burns between 10 and 20 years old support greater invasive plant growth in
black spruce forests than do high severity and more recent burns. In addition, regional
differences between burn complexes outweighed burn severity and site moisture in
determining the invasibility of burned black spruce sites. Finally, rebounding native
vegetation appears to offer burned areas a level of resistance to invasive plant
establishment.
THESIS :
Villano, K.L.. 2008. Wildfire burn susceptibility to non-native plant invasions in black spruce forests of interior Alaska. M.S. Thesis, University of Alaska Fairbanks, 112 pages.
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Nan Werdin-Pfisterer ( send email )
M.S. Graduate
Advisor: K. Kielland
Co-Advisors: R. Boone, ,
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THESIS :
Werdin-Pfisterer, Nancy. 2006. Soil amino acid composition across a boreal forest successional sequence. MS thesis, University of Alaska, Fairbanks, 135 p.
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Stephen Winslow ( send email )
M.S. Graduate
Advisor: G.Juday
Co-Advisors: Clair Alix, Dave Verbyla,
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THESIS ABSTRACT :
People living in the Kuskokwim River Basin often rely on wood to heat their homes, and
are considering wood biomass energy generation. To help inform community decisions,
we examined the growth history, climate sensitivity and growth potential of local tree
species. We compared ring-width growth of 188 white spruce and 77 black spruce trees
sampled along 370km of the Kuskokwim River, Alaska to mean monthly temperatures
(MMT) and total monthly precipitation (TMP) at McGrath. The mean growth
chronologies of both tree species were highly correlated with each other (r=0.84). White
spruce trees were either significantly negatively correlated (r= -0.62) with MMT of
August and June (-2) (two years prior to ring formation) or positively correlated (r=0.60)
with MMT of April (-2) and November (-2). Black spruce trees were either negatively
correlated (r= -0.64) with a warmth-dryness index composed of August and June (-1)
MMT minus TMP of August and June (-2), or positively correlated (r= 0.60) with
April (-1) and June (-1) MMTs. Negative growth responders predominate in eastern
(warmer and dryer) locations while positive responders predominate in western (cooler,
wetter) locations. The negative growth trend in interior white and black spruce decreases
the potential for biomass-fueled energy generation.
THESIS :
Winslow, S.E.. 2008. Tree growth history, climate sensitivity, and growth potential of black and white spruce along the middle Kuskokwim River, Alaska. M.S. Thesis, University of Alaska Fairbanks, Fairbanks, AK, 68 pages.
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