Garrett Altmann
M.S. Candidate

Start date:
Advisor: D. Verbyla
Co-Advisors: J. Fox, K. Yoshikawa,

Increases in fire frequency and severity have resulted from a warming climate in boreal Alaska. These changes alter the successional trajectories of plant species, facilitate permafrost degradation, and have the potential to cause changes in ecosystem state. Using GIS and Landsat TM/ETM+ satellite imagery, my research examines how fire affects pond dynamics in areas of discontinuous permafrost. Through a multi-temporal examination of pond sizes related to fire occurrence, my research goal is to determine if high severity fires create successional conditions that facilitate permafrost degradation in the form of thermokarsting (lake surface area expansion) or talik drainage (lake surface area reduction). Determining how these changes vary with topography, soils, and disturbance regime can produce rules for predicting where threshold changes in hydrology are most likely.

Mike Anderson
Ph.D. Candidate

Start date:
Advisor: R. Ruess
Co-Advisors: L. Taylor, C. Mulder,

Becky Baird
M.S. Candidate

Start date: 01-Aug-07
Advisor: T. Hollingsworth
Co-Advisors: D. Verbyla, J. Kidd,

Climate has warmed substantially in boreal Alaska since the mid-1970s. The direct effects of rising temperatures on sub-Arctic ecosystems are already being seen in the form of drought stress, increased fire frequency and severity, and increased frequency and severity of herbivorous insect outbreaks. These effects of climate change should have a direct impact on the vegetation of the boreal forest and can lead to a decreased remotely sensed vegetation index. The vegetation index, NDVI, is an effective proxy for plant photosynthesis on a landscape scale, and therefore, an appropriate measure to examine landscape-scale changes in vegetation due to climate change effects. The overarching goal of my research is to assess the change in vegetation at Bonanza Creek Experimental Forest, and partition these changes into a) expected changes through successional processes, and b) unexpected changes which could be due to climate change. Once I have assessed these changes using a combination of remote sensing and field sampling, I will examine associated patterns on a hierarchical scale from landscape level changes to differences in vegetation patches and finally by examining trends in individual vegetation stands.

Andres Baron Lopez
M.S. Candidate

Start date: 17-Aug-09
Advisor: T. Schuur
Co-Advisors: , ,

Todd Brinkman
Ph.D. Candidate

Start date:
Advisor: T. Chapin
Co-Advisors: , ,

Robert Burgess
Ph.D. Candidate

Start date: 01-Aug-08
Advisor: M.B. Leigh
Co-Advisors: L. Taylor, ,

Decomposition of soil organic matter (SOM) is an important process that determines rates of CO2 release, and is mediated exclusively by soil microbes. The response of these microbes to climate change is unknown, as is the identity of most active soil microbes that break down lignocellulose, a major component of SOM. A recently developed technique, stable isotope probing (SIP), allows the identification of microbes performing specific functions. The proposed research will use SIP to identify microbes that degrade lignocellulose in boreal forest soils, and will use this information to determine their abundance and distribution in response to the simulated climate change scenario of long-term snow exclusion. In addition, SIP will be combined with metagenomics to find genes responsible for the breakdown of lignocellulose. Information from this research can be used to scale-up the small-scale processes responsible for CO2 release, thus increasing the accuracy of climate change modeling. In addition, the discovery of novel genes may be applicable to the biotechnological production of cellulosic bio-ethanol.

Cameron Carroll
M.S. Candidate

Start date: 01-Sep-07
Advisor: K. Kielland
Co-Advisors: P. Doak, Terry Chapin, K. Kellie

The importance of moose as a subsistence food to many Alaskans is indisputable. Impacts of a changing climate upon those resources are therefore of great concern for wildlife managers. Increasing global temperatures have been linked to increases in fire frequency and fire severity at northern latitudes where there is a related shifting toward a more deciduous dominated landscape. In contrast to previous models of boreal forest successional dynamics, this modeling project explores the link between fire severity and moose population responses. It examines the intricacies of response in non-predator-limited moose populations and the paradox that their rapid ability to respond to available forage puts these populations at greater risk of decline in years of extreme environmental events. The model simulates population dynamics of a moose population where fire severity and available browse inputs inform a matrix population model, and explores the interactions between browse production and consumption in response to fire severity, where a supposed linear function becomes non-linear due to the multiplicative effects of both a functional and numerical response.

Amber Churchill
M.S. Candidate

Start date: 18-Jan-09
Advisor: A.D. McGuire
Co-Advisors: M. Turetsky, ,

Remote sensing in interior Alaska has shown that major wetland complexes are drying, likely due to better drainage induced by permafrost thaw and/or increased evapotranspiration with warming (Riordan et al 2006). However, in other areas, permafrost thaw and groundwater upwelling is leading to flooding due to thermokarst and peat subsidence (Osterkamp and Romanovsky 1999). Thus, Alaskan peatlands could become drier or wetter under future climate regimes depending on landscape position, permafrost stability, and climate change. These changes will increase the variability of CO2 uptake across peatland landscapes in central Alaska, and may ultimately change whether the region acts as a source or sink for atmospheric CO2. At the Alaskan Peatland Experiment, located near the Bonanza Creek Experimental forest in interior Alaska, we are examining the effects of changing water availability on ecosystem processes across a range of peatland types. These peatland types include a moderate rich fen, a thermokarst/collapse scar and a forested peatland with intact surface permafrost. At the rich fen, a large-scale manipulation of water table position (control, lowered, raised) has been ongoing since 2005. The permafrost peatland and adjacent collapse scar represent a natural gradient from dry surface peat (permafrost bog) to inundated conditions (collapse scar bog). CO2 flux measurements at the rich fen from 2005-2008 show that the lowered water table treatment had lower rates of gross primary productivity (GPP) than the control plot. Across all three sites, 2008 CO2 fluxes show that the rich fen and collapse scar sites had similar magnitudes of GPP, but exhibited different seasonal patterns of C uptake (Figure 1). Our continuing research is focusing on understanding how water and nutrient availability influences rates of plant C uptake (GPP and NPP) across the APEX sites. Specifically our goals are to evaluate the effects of water table manipulations (at the rich fen) and permafrost thaw on the growth of plant functional groups and their competition for light, water, and nitrogen. This information will help to identify how various plant functional groups may respond to climate change and drive potential changes in ecosystem structure and function in interior Alaska.

La'ona DeWilde
Ph.D. Candidate

Start date:
Advisor: T. Chapin
Co-Advisors: , ,

Jason Fellman
Ph.D. Candidate

Start date:
Advisor: R. Boone
Co-Advisors: , ,

My dissertation research will explore the role of terrestrial ecosystems in influencing the quantity and quality of stream DOM in southeast Alaska. I will attempt to use DOM characterization as a watershed tracer to evaluate the biogeochemical coupling between soils and streams on the watershed scale. I will further attempt to document that terrestrial ecosystems are a source of labile DOM to aquatic ecosystems.

Brian Heitz
Ph.D. Candidate

Start date:
Advisor: B. Sveinbjornsson
Co-Advisors: R. Ruess, ,

Rebecca Hewitt
Ph.D. Candidate

Start date: 01-Aug-08
Advisor: T. Chapin
Co-Advisors: T. Hollingsworth, ,

Understanding the complex mechanisms controlling treeline advance or retreat in the arctic has important implications for projecting ecosystem response to direct and indirect effects of global environmental change. Changes in landcover due to a treeline biome shift would alter climate feedbacks (carbon storage and energy exchange) and other ecosystem services such as wildlife and berry habitat, impacting subsistence users. In the boreal forest climate-induced changes in the fire regime may be a more critical driver of landscape processes than the direct effects of warming. Currently modeling of a dynamic arctic treeline may overlook critical factors influencing tree seedling establishment in previously unforested sites. Soil microbes are key drivers of ecosystem processes, yet their role in regulating landscape-scale vegetation change is not known. Comprehensive studies of treeline position have noted that ectomycorrhizal fungi (EMF) may be an important factor delineating the boundary between forest and tundra. Yet, these critical plant-fungal symbioses are sensitive to wildfires. My research examines the role of EMF in mediating biome shifts at arctic treeline using a suite of laboratory and field experiments. Through my experiments I will develop rules for previously developed frame based models (ALFRESCO) to relate wildfire-induced changes in tree establishment at treeline with landscape patterns of treeline movement. I will model treeline expansion as a function of fire severity, mycorrhizae availability, and postfire tree and understory cover. This research integrates plant-microbial symbioses with landscape processes to address the linkages between climate change, fire ecology, and ecosystem processes in two innovative ways: (1) exploring the importance of plant-microbial interactions to vegetation dynamics by linking fungal genomics to community-scale processes and (2) investigating the role of seedling establishment to biome shifts by linking community-scale processes to globally significant trends. Boreal and treeline research done to date suggests that fire and mycorrhizal inoculum availability are important to plant community composition. This research is a critical step in placing these observations into a predictive framework.  

Caitlin Hicks
Ph.D. Candidate

Start date: 25-Aug-07
Advisor: T. Schuur
Co-Advisors: , ,

Permafrost soils store almost 1700 Pg carbon (C)—C that is at risk of being respired to the atmosphere as the climate warms and permafrost thaws. Because loss of permafrost soil C is a positive feedback to climate change, we need to understand how thaw affects both autotrophic and heterotrophic components of C cycling in order to improve future climate predictions. The goals of this proposed study are to understand how warming affects which ecosystem components are driving ecosystem C flux in both a natural gradient of permafrost thaw and an experimental tundra warming experiment. While measuring C fluxes indicates whether an ecosystem is a source or a sink, it cannot explain why the ecosystem is a source or a sink. Partitioning can answer why, such as if an ecosystem is a source because respiration of newly-fixed C from plants is increasing or because deep soil respiration is increasing. I will use both ?13C and ?14C to partition ecosystem respiration into four sources: aboveground plant structures, belowground plant structures, surface soil, and deep soil. 13C separates sources based on plant parameters (type, structure, tissue), while 14C separates sources based on organic C age. I will sample the ?13C and ?14C of sources using incubations and the ?13C and ?14C of ecosystem respiration using field measurements. This study will utilize an established gradient of permafrost thaw and a warming experiment near Healy, Alaska where soil parameters and C fluxes are already being measured. I have tested the dual isotope approach at the thaw gradient and shown the four sources are distinctly separated allowing for constrained calculations of source contribution ranges. I will apply this method to calculate which sources drive differences in ecosystem respiration that have been measured in the thaw gradient and are hypothesized to occur with experimental warming. I will determine whether old, previously stored C is being respired in response to warming—a positive feedback to climate change. | The goals of this study are to understand how climate and vegetation have affected C balance, as measured by C accumulation rates, throughout the Holocene and during modern times and to test the potential of plant communities as proxies for C accumulation. Modern vegetation and soil moisture relationships will be determined so that past changes in vegetation can be connected to changes in soil moisture. Stratigraphic macrofossil analyses will show how vegetation communities changed in each core. Radiocarbon dating of the soil profile at the depths of vegetation change will be used to calculate the age of each distinct plant community. Carbon accumulation rates for each plant community will be determined in soils by measuring C contents, using 14C dates, and mathematical models. Holocene climate records from nearby lakes in Interior Alaska (e.g. Anderson et al. 2001) will be used to determine whether past changes in climate are connected to plant community transitions or changes in C accumulation rates.

Hanna Lee
Ph.D. Candidate

Start date: 23-Aug-04
Advisor: T. Schuur
Co-Advisors: , ,

One of the biggest potential feedbacks to global climate change from high latitude ecosystems may come from thawing of permafrost, which stores more than 50% of the total global terrestrial soil carbon. Thawing of permafrost may accelerate decomposition of soil organic matter and increase carbon dioxide (CO2) emissions. When permafrost thaws in ice-rich areas, it creates localized topographical surface subsidence called thermokarst, which can induce variations in soil abiotic properties. Also, depending on the location of thermokarst formation it can create anaerobic conditions in soil. By altering multiple resources in soil, thermokarst can change C-cycling in high latitude ecosystems beyond simple increases in temperature alone. My research was conducted at a subarctic tundra site near Healy, Alaska (Latitude: 63.7ºN), where permafrost thaw and thermokarst development have been observed and monitored for two decades. I established soil gas wells to explain how thermokarst affects soil respiration and to determine which depth in the soil profile has the greatest soil CO2 flux. I also established plot- scale studies to determine how thermokarst affects ecosystem C exchange by measuring above ground CO2 fluxes using clear chambers. Then I collected permafrost soils with different substrate qualities and incubated them at 15°C under aerobic and anaerobic conditions to observe C loss and climate forcing in different environments after permafrost thaw. I found that there was an increase in soil CO2 production where thermokarst development progressed; this was mostly driven by surface soil layer CO2 production rather than deeper soil layer CO2 production This was likely due to changes in the environment such as soil temperature, moisture, and vegetation. I was able to estimate the annual ecosystem carbon balance using surface subsidence created by thermokarst development, thaw depth, and plant biomass. Permafrost soil incubation showed that carbon loss was 3 times greater under aerobic conditions, but climate forcing was 1.15 times greater under anaerobic conditions due to methane emissions. Therefore, permafrost thaw and thermokarst development may stimulate soil CO2 production, ecosystem carbon exchange, but will affect climate warming more under anaerobic conditions.

Collin Macheel
M.S. Candidate

Start date: 01-Aug-08
Advisor: D. Misra
Co-Advisors: A. D. McGuire, R. Daanen, M. Darrow

Peatlands store an estimated one quarter of the Earth's terrestrial soil carbon. Predominantly found within northern latitudes, peatlands contribute an estimated 17-28% of global methane emissions and therefore play an important role in the global carbon cycle. The application of models attempting to accurately represent the energy and hydrologic mass transfer in peatlands have been limited by crude numerical representations and over generalizations when considering variable saturation. Variably saturated hydrology and energy transfer processes are important for regulating the oxidation and reduction of methane and the production of carbon dioxide. Here, we capitalize on environmental data that has been collected since 2004 at the Alaska Peatland Experiment (APEX), a heavily instrumented fen located in interior Alaska, in which water table position and soil temperatures have been manipulated in situ. The key goal of this research is to develop numerical simulation models of complex energy transfer and multiphase hydrologic processes and to apply them to organic variably saturated soils in peatlands, with the application to other climatic treatments at the APEX manipulation sites. More complex representations of the unsaturated subsurface and energy transfer within organic soils has the potential to provide insight on the dynamics of subterranean microbiological processes associated with carbon transformations, atmospheric emissions of greenhouse gases, and hydrologic transport. Finite element and volume analysis that use contemporary numerical codes account for seasonal variations of mass and energy transport. The application of a modified van Genuchten equation for variably saturated flow has been used to account for all hydrologic and energy transport processes. The results show that the water table has a distinctive non-linear effect on heat transfer and phase change. This study will contribute to the development of coupled biogeochemical-hydrologic models that are capable of simulating the dynamics of methane, carbon dioxide, and dissolved organic carbon in northern peatlands.

Kimberley Maher
Ph.D. Candidate

Start date:
Advisor: G. Juday
Co-Advisors: , ,

Jordan Mayor
Ph.D. Candidate

Start date: 20-Aug-05
Advisor: T. Schuur
Co-Advisors: M. Mack, ,

Measuring the ratio of heavy to light stable isotopes of nitrogen (15N:14N, expressed as d15N relative to a standard) provides unique information regarding the nitrogen (N) cycle in forested ecosystems. This is important because the productivity and ecosystem dynamics of many terrestrial and aquatic ecosystems are limited by N availability. Because anthropogenic change can increase N availability through deposition, or alter N mineralization rates through climate warming and landscape modification, monitoring ecosystem responses to shifts in N availability is a research priority. However, to be confident in the interpretation of foliar d15N, mechanistic processes must be better understood. Across 46 plots in interior Alaska, black spruce trees were found to exhibit a wide range of foliar d15N values. This is likely due to one of two main processes in the N cycle known to significantly alter the ratio of 15N:14N in plants. These include the degree of N-dependency on root associated symbiotic fungi (mycorrhizae) and changes to the 15N:14N of soil N sources caused by soil fertility influencing the soil N cycle. This project uses a detailed method for measuring the d15N values of soil N to determine if changing sources of N can alone explain black spruce variability in d15N or if integrating fungal activity will better explain observed patterns. A mechanistic understanding of foliar ?15N is required to fully understand N cycling and to refine the use of ?15N as a proxy of ecosystem N cycling.

Nicole McConnell
M.S. Candidate

Start date: 01-Aug-09
Advisor: M. Turetsky
Co-Advisors: A.D. McGuire, ,

Jonathan O'Donnell
Ph.D. Candidate

Start date: 01-Jan-07
Advisor: A.D. McGuire
Co-Advisors: J. Harden, V. Romanovsky, E. Hood

The Alaskan interior contains enormous carbon reserves in vegetation and soils. As a result of changing temperatures, we anticipate enhanced releases of carbon dioxide, methane, and dissolved organics to streams and ocean waters. How carbon responds to changing climate will affect carbon dynamics and will likely depend on interactions with soil moisture and permafrost extent, which are quite variable in Alaskan landscapes. To better understand these interactions, I am studying the implications of permafrost degradation on soil carbon (C) accumulation and loss from boreal ecosystems. The primary questions of his research are (1) How does water influence the stability of permafrost in upland and wetland ecosystems, (2) What is the net effect of permafrost degradation on C storage across a range of boreal ecoystems, and (3) What controls C loss from ecosystems where permafrost has degraded?

Jenny Rhors-Richey
Ph.D. Candidate

Start date: 01-Sep-04
Advisor: C. Mulder and B. Roy
Co-Advisors: R. Ruess, D. Bret-Harte, L. Winton

Interests: physiology of Alnus fruticosa subsp viridis, susceptibility of drought stressed A. viridis to pathogens and herbivores, pathogens affecting water-relations in A. viridis

Amanda Rineharrt
Ph.D. Candidate

Start date:
Advisor: J. Jones
Co-Advisors: , ,

Katie Shea
M.S. Candidate

Start date: 15-Jan-09
Advisor: M. Turetsky
Co-Advisors: H. Maherali, A. Gordon,

High latitude ecosystems are expected to be among the regions most severely affected by global climate change. In particular, melting permafrost may seriously alter the landscape, ecology and climate forcing potential of northern regions. Since northern peatlands are known to contain approximately one third of global soil carbon, they have the potential to act as large sources of both carbon dioxide (CO2) and methane (CH4) which are known greenhouse gases. Therefore, understanding the impacts of climate change on these sensitive ecosystems is of the utmost importance. My overall research goal is to examine the controls and mechanisms of CH4 production and release pathways from Alaskan peatlands along a gradient of permafrost integrity. Specific objectives are 1) quantification of CH4 flux from intact permafrost, melting permafrost and non-permafrost peatlands and 2) identification of physical and biological controls on CH4 production and release including soil properties, local hydrology and microclimate and plant and microbial community activities. To address these objectives, I will use ecosystem and plant chambers to measure CH4 emissions and plant transport, respectively, and gas capture funnels to measure ebullition, or bubbling, in the three permafrost settings. I will relate these data to soil climate and vegetation community data already being collected through the Bonanza Creek Long Term Ecological Research (LTER) sites that use soil warming and water table manipulations to study the effects of climate change on vegetation and nutrient cycling.

Aditi Shenoy
Ph.D. Candidate

Start date: 01-Sep-07
Advisor: J. Johnstone
Co-Advisors: K. Kielland, ,

Colin Tucker
M.S. Candidate

Start date:
Advisor: D. Bret-Harte
Co-Advisors: , ,

Delia Vargas Kretsinger
M.S. Candidate

Start date:
Advisor: K. Kielland
Co-Advisors: , ,

Betsy Young
M.S. Candidate

Start date:
Advisor: T. Chapin
Co-Advisors: , ,

Amy Angell
M.S. Candidate

Start date: 01-Sep-05
Advisor: K. Kielland
Co-Advisors: C. Mulder, J. Fox,

The boreal forest ecosystem is one of the largest terrestrial biomes in the world spanning northern Europe, North America, and Russia. Interior Alaska is dominated by boreal forest consisting of Black Spruce (Picea mariana), White Spruce (Picea glauca), Paper Birch (Betula papyrifera), and Poplar (Populus sp.) Boreal forests along the Tanana and Yukon River Floodplains are a result of primary floodplain succession developing into mature Black Spruce stands after 200-300 years (Viereck et al.,1993). Moose herbivory of early succession willow species favors the formation of White Spruce or Black Spruce trees, which are likely to become important timber species in Alaska (Bryant and Chapin, 1986, Kielland et al., 1997). I am researching how browsing on willow may have indirect impacts on seedling establishment of later primary succession species. Plausible factors that could be influenced by moose browsing are an increase in photosynthetically active radiation (PAR), an increase in soil temperature, potential increase in nutrient availability, and increase in evaporation. While many of these appear to be positive for seedling establishment, the climate extremes of interior Alaska floodplain communities exacerbate these features leading to salt crust formation on the soil surface, excessive leaf heating, and increased water stress. All of these factors could inhibit seedling photosynthesis and growth. I will address several potential ways that moose herbivory can effect seedling growth by assessing the following factors along the terrace age gradient: 1) changes in canopy structure and light regimes surrounding the seedlings, 2) collecting microclimate data, 3) analyzing the soil ion chemistry, 4) obtaining seedling photosynthesis levels, 5) performing stable isotope analyses to look at carbon and nitrogen shifts coupled with seedling water use efficiency, and 6) performing vegetation cover analysis and plant identification to obtain information concerning the local flora inside and outside of the moose exclosures.

Kelly Balcarczyk
M.S. Candidate

Start date: 01-Sep-05
Advisor: J. Jones
Co-Advisors: R. Boone, D. White,

In northern boreal forests the presence or absence of permafrost has a large effect on catchment hydrology and vegetation, and consequently impacts the quantity and quality of dissolved organic carbon (DOC) transported to streams. Catchments with permafrost are dominated by black spruce, mosses and sedges with flow through the organic layer delivering high amounts of DOC to the streams. Catchments without permafrost consist of birch, white and black spruce, willow and alder with flow delivering lower concentrations DOC to the streams. Differences in DOC quality cause variation in stream bacterial activity which affects the amount and rate at which carbon is supplied to higher trophic levels and lost downstream. Discontinuous permafrost is thawing with climate warming, which will impact the biogeochemistry of high latitude watersheds and influence the movement of dissolved nutrients from upland soils to streams. In order to understand the influence of permafrost and vegetation on DOC my research will address: 1. the input rate of DOC from different source waters, 2. the composition/quality of DOC in streams and source waters and 3. factors controlling the bioavailability of DOC in streams. The research will be conducted in four subcatchments of Caribou-Poker Creeks Research Watershed with varying degrees of permafrost and differences in vegetation.

Mike Balshi
M.S. Candidate

Start date:
Advisor: A.D. McGuire
Co-Advisors: , ,

Colin Beier
Ph.D. Candidate

Start date:
Advisor: T. Chapin
Co-Advisors: , ,

Emily Bernhardt
M.S. Candidate

Start date: 01-Sep-05
Advisor: T. Hollingsworth and T. Chapin
Co-Advisors: C. Mulder, ,

The main objective of this research is to determine how fire severity and site moisture affects the density, species composition, and functional properties of black spruce forests in interior Alaska. I propose to address this in two ways; by comparing the species composition of sites pre/post fire, and by looking at the changes in functional diversity for each site. Pre-fire vegetation composition and soil characteristics collected across a broad range of black spruce forest types will be used in conjunction with burn severity, post-fire plant community composition and site moisture data to address changes in community composition. A functional survey of flora pre / post fire in interior Alaska black spruce forests in regards to two aspects of functional types; response types (tolerance, disturbance response), and effect types (flammability, formation of permafrost, nitrogen fixation) will be conducted in an effort to determine the effects of fire on the functional diversity of black spruce forests.

Emma Betts
M.S. Candidate

Start date:
Advisor: J. Jones
Co-Advisors: , ,

In boreal forest catchments of interior Alaska, discontinuous permafrost has a large effect on groundwater flowpaths and consequently regulates dissolved organic matter (DOM) and nutrient fluxes to streams. Streams in catchments with large extents of permafrost typically have high DOM and low nutrient concentrations, whereas streams in catchments with less permafrost receive reduced DOM and greater nutrient inputs. Within streams, sediment microorganisms are integral for DOM processing and facilitate the transfer of terrestrially derived DOM into aquatic food webs. Regions of discontinuous permafrost are very sensitive to temperature change. Reduction in the extent of permafrost is likely to have significant effects on watershed hydrology and the inputs of DOM and nutrients into streams, A full understanding of how catchment hydrology governs DOM and nutrient fluxes into streams is integral to understanding how stream food webs and ecosystem functioning may respond to climatic change. The objectives of my research are: 1) Quantify flow rates and DOM fluxes from the major ground/source waters in catchments with differing extents of permafrost; 2) Determine the proportion of DOM from each source water that is readily decomposed by stream microorganisms; 3) Assess how the differences in DOM inputs due to differences in catchment hydrology regulate stream metabolism; 4) Determine the physical and chemical factors controlling metabolism. Research will be conducted in four subcatchments of the Caribou-Poker Creeks Research Watershed, in interior Alaska. DOM fluxes from the major source waters will be determined using field sampling and by using an end member mixing analysis. The labile proportion of DOM will be quantified using laboratory mesocosms. Stream dissolved oxygen concentration will be continuously measured and used to calculate whole stream rates of metabolism. Lastly, monthly mesocosm manipulations will be conducted to determine how labile DOM, nutrient concentrations and temperature regulate stream metabolism.

Leslie Boby
M.S. Candidate

Start date:
Advisor: M. Mack
Co-Advisors: , ,

Bob Bolton
Ph.D. Candidate

Start date:
Advisor: L. Hinzman
Co-Advisors: , ,

My research involves studying the hydrologic processes and moisture dynamics in areas of discontinuous permafrost. I am also interested in studying how disturbances, such as wildfire, affect these processes. Permafrost plays an important role in the hydrology of sub-arctic watersheds. Ice-rich conditions at the permafrost table do not allow significant infiltration, resulting in decreased response time to precipitation events (including snowmelt), limited subsurface, and low base flows between precipitation events. I am applying a process based, spatially distributed model to the Caribou-Poker Creeks Research Watershed, located Northeast of Fairbanks, Alaska, with the aim of quantifying the hydrologic processes in the sub-arctic environment.

Andrew Borner

Start date:
Advisor: K. Kielland
Co-Advisors: , ,

Lem Butler

Start date:
Advisor: K. Kielland
Co-Advisors: , ,

Hannah Clilverd
M.S. Candidate

Start date: 01-Jul-04
Advisor: J. Jones
Co-Advisors: R. Boone, K. Kielland,

My research examines the interaction between the hydrology of the Tanana River and nitrogen dynamics of the hyporheic zone, with emphasis on denitrification. This project expands upon current Bonanza Creek LTER research on hyporheic flow as a source of nitrogen to early to mid-successional stands of floodplain vegetation such as: willow, alder and balsam poplar. This research will address: 1) the effect of trajectory and rate of hyporheic flow on the spatial variation of subsurface biogeochemistry, and 2) the effect of temporal variation of river discharge on the biogeochemistry and nitrogen flux of the hyporheic zone.

Bjorn Flora

Start date:
Advisor: K. Kielland
Co-Advisors: , ,

Nancy Fresco
Ph.D. Candidate

Start date:
Advisor: T. Chapin
Co-Advisors: A.D. McGuire, ,

Ian Herriott
M.S. Candidate

Start date: 01-Sep-05
Advisor: Lee Taylor
Co-Advisors: , ,

Soil microbial activity does not cease during winter in many alpine and arctic ecosystems, and winter CO2 efflux can make a significant contribution to annual C budgets. In addition to exhibiting activity, recent investigations have shown that microbial communities of fungi can also undergo significant seasonal changes in species composition, and previously unreported lineages of deep branching clades have been recently discovered in alpine winter soils. No studies have tested for seasonal changes in boreal forest fungal communities; whether and how they may respond to the temperature regime of subarctic winter is unknown. The need to understand fungal community dynamics is great if we are to predict capacity for resilience and adaptation to climate change, and concomitant biogeochemical feedbacks. To address these shortcomings in our current understanding, I have designed a study to be conducted during the fall, winter, and spring of 2004-2005 at Tanana River floodplain sites of the Bonanza Creek LTER. Soil cores from a spatially explicit and replicated sampling design will be pooled. DNA and RNA will be extracted and followed by PCR, the community amplicons will be profiled using terminal restriction fragment length polymorphism (TFRLP). The following questions will be addressed. Will fungal community species composition and functional guilds (ectomycorrhizae vs. saprotrophs) change throughout the “winter” season in Alaska? What shifts in fungal community composition will be imposed by experimental manipulations of snow depth? To test these questions I will compare community profiles generated by TRFLP. How will individual members of the community adjust their metabolic activity with changes in seasonal and experimental parameters? To test this I will use an rRNA based TRFLP approach. Comparison of profiles of the existing community (DNA presence) and the active community (rRNA presence) will provide unique views on cold-tolerant and cold-active species adaptations respectively.

Evan Kane
Ph.D. Candidate

Start date: 01-Aug-02
Advisor: D. Valentine
Co-Advisors: T. Chapin, S. Rupp, J. Harden

It is widely accepted that positive feedbacks exist between the increasing atmospheric concentration of CO2 and global warming (e.g., Keeling et al. 1996, Chapin et al. 2000), and therefore the ability of soil to accumulate and preserve mineralizeable organic matter has received growing interest. The stabilization of Soil Organic Carbon (SOC) in the boreal forest biome, which harbors the world’s second largest SOC stock, is of marked concern because climate warming is projected to be greatest in high latitudes (McGuire et al. 2000) and temperature is the cardinal determinant of soil C mineralization. To determine how the complex interplay between stand production, nutrient mineralization, and soil temperature affects soil C stabilization, we investigated total SOC along four replicate gradients in black spruce productivity and climate in interior Alaska. Research focuses on three main problem areas: 1) How stand production and temperature affect soil organic C stocks and lability, 2) how the chemistry and quantity of dissolved organic C affect SOC stability, and 3) fire as a mechanism of soil C stabilization in the boreal forest: charcoal accumulation along climate and productivity gradients.

Prathap Kodial
M.S. Candidate

Start date:
Advisor: H. Toniolo
Co-Advisors: L. Hinzman, K. Yoshikawa,

My research focuses on the rapid thermokarst evolution in the Caribou Poker Creeks Research Watershed (CPCRW). It is a relatively new feature in this predominantly discontinuous permafrost region. The thermokarst was initiated by permafrost degradation and precipitated by the rain event that occurred in July 2003. The primary objective of this research is to assess the role of sediment transport processes in the spatial and temporal evolutions of a thermokarst located in the Caribou-Poker Creeks Research Watershed (CPCRW). A major focus of the study is to better understand the possible effects of the accelerated growth of the thermokarst on the local topography.

Nick Lisuzzo
M.S. Candidate

Start date:
Advisor: K. Kielland
Co-Advisors: , ,

Methods for calculating nitrogen availability in terrestrial ecosystems are well established for most terrestrial ecosystems. However, the understanding of the dynamics between plant communities and hydrologic processes occurring within riparian areas is limited, and may invalidate some of the underlying assumptions of traditional methodsof study. The early successional stands located on the sub-arctic Tanana River’s floodplain are potential examples of ecosystems where hydrologic processes control ecosystem productivity. Traditional measurements of nitrogen availability can only account for about 10% of the annual nitrogen requirement for these stands. Interactions between the terrestrial environment and the hyporheic zone potentially explain this discrepancy. A system of groundwater wells was installed to characterize the hydrologic processes occurring in these ecosystems, and establish the chemical composition of the hyporheic zone throughout the growing season. Simple mathematically models based upon Darcy’s Law were than used to calculate the potential supply of nitrogen via capillary rise and lateral subsurface flow. To empirically determine if hyporheic was being assimilated by the plant communities, 15N labeled NH4NO3 was injected into the water table at a depth below the rooting zone. The foliage of willows (Salix spp.)growing downstream of the injection point, relative to subsurface flow paths, was then collected after 14 days. The label was clearly evident in the collected foliage confirming that plants are assimilating groundwater nitrogen. Based on our calculations hydrologic processes contribute approximately twice as much nitrogen as in situ microbial processes and can supply 20-25% of the ecosystem’s annual nitrogen requirement in a single pulse of nutrients that corresponds with a late summer spike in stream discharge. Although together both microbial and hydrological supplies of nitrogen still fail to balance the nitrogen budgets of these sites, our findings suggest that subsurface hydrology plays a greater role than nitrogen mineralization, and fixation in these stands.

Rachel Lord
M.S. Candidate

Start date: 01-Sep-05
Advisor: K. Kielland
Co-Advisors: F. Huettmann, K. Hundertmark, T. Paragi

Forest fires are the dominant disturbance factor in boreal forests and with global climate change may increase in severity, with decreased return interval times. The spatial heterogeneity following fires over the landscape may exert long-term influence on the quantity and quality of moose winter foraging habitat. Post-fire succession within the Rosie Creek Burn (1983, covering part of the Bonanza Creek Experimental Forest, appx. 20 miles SW of Fairbanks, AK) is spatially heterogeneous with underlying distribution patterns, in part related to initial fire severity. I hypothesize that moose utilization of this area is spatially related to the successional patterns within the burn, as measured by spatial distribution of forage composition and nutrient availability. I intend to examine what current patterns exist within the Rosie Creek Burn area in terms of forage distributions in terms of quantity and quality as well as moose utilization by using remote sensing, GIS, and ground-based field data. A better understanding of the fine-scale response of moose to burned forests will assist in management plans concerning improving moose habitat in the boreal forest.

Isla Myers-Smith
M.S. Candidate

Start date:
Advisor: A. D. McGuire
Co-Advisors: J. W. Harden, F. S. Chapin,

The Alaskan interior contains large carbon reserves stored in poorly drained ecosystems. With warming, these areas of the boreal forest may experience more frequent or extensive stand replacing fires, and thus change the primary factors controlling carbon emissions. We have investigated the interactions between fire and hydrology in controlling landscape evolution and carbon exchange in a recent burn on the Tanana Flood Plain adjacent to the Bonanza Creek LTER. Historical changes in vegetation, hydrology and fire were tracked through macrofossil, charcoal and diatom analysis of peat cores. The paleoecological record reveals a pattern of expansion of collapse features after fire. Spatial and temporal variations in fluxes were examined to identify the controls on carbon exchange in this ecosystem. We hypothesize that, after fire, lowland areas become wetter. This leads to high NEP, greater inputs of labile carbon, and increased CH4 efflux. However, if interior Alaska experiences more abnormally warm and dry summers like that of 2004, future CH4 production may be suppressed by the changing climate.

Dana Nossov
M.S. Candidate

Start date: 01-Jan-06
Advisor: R. Ruess
Co-Advisors: T. Hollingsworth, ,

Thinleaf alder (Alnus tenuifolia) is extremely important in the floodplain ecosystems of interior Alaska because of its ability to form actinhorizal symbioses and thereby fix large quantities of nitrogen, greatly enriching floodplain soils. The goals of my research are to characterize the spatial and temporal patterns of Alnus tenuifolia population structure and plant growth across a broad reach of the Tanana River floodplain, and to assess the implications of these patterns for ecosystem nitrogen balance.

Jonathan O'Donnell
M.S. Candidate

Start date: 01-Sep-02
Advisor: J. Jones
Co-Advisors: K. Kielland, L. Hinzman,

In the boreal forest, the presence of permafrost is an important feature controlling watershed hydrology and stream chemistry. In interior Alaska, stream export of nitrogen often exceeds atmospheric input in watersheds underlain by discontinuous permafrost. Poor retention of fixed nitrogen is one potential explanation that could account for this pattern of nitrogen loss. Two research questions were addressed in this study: 1) how does riparian zone nitrogen retention vary in watersheds with varying extents of permafrost, 2) what is the contribution of denitrification to riparian zone nitrogen retention? Nitrogen retention was examined in the riparian zone of two watersheds underlain by discontinuous permafrost using two approaches. First, groundwater chemistry was analyzed using an end-member mixing model to provide an estimate of the contribution of the riparian zone to watershed nitrogen retention. Second, field denitrification assays were conducted to assess the importance of denitrification as a mechanism of nitrogen retention. Based on estimates from the mixing model, nitrogen retention averaged 8.9 and 5.7 mgN m-2 d-1 in the low and high permafrost watersheds, respectively. In the absence of riparian zone nitrogen retention, stream export would increase by 10-12% in each watershed. Denitrification accounted for a small proportion of total nitrogen retention, averaging 3% in both watersheds, although denitrification measurements were likely underestimated in this study. The riparian zone appears to be an effective site for retaining nitrogen in watersheds with varying extents of permafrost.

Sarah Runck
M.S. Candidate

Start date: 01-Jan-05
Advisor: D. Valentine
Co-Advisors: J. Yarie, T. Chapin,

Empirical evidence from the past 30 years supports the prediction that high latitude ecosystems will experience the most pronounced effects of climate change. The net effect of reduced precipitation on boreal forest carbon (C) balance remains unclear, largely because the source-sink balance depends on the degree of moisture sensitivity of soil decomposition relative to that of net primary production. Studies examining the long-term effects of precipitation reduction on boreal soils and vegetation are necessary for a clearer understanding of the relationship between boreal forest processes and climate. The objective of this project is to determine how experimentally reduced summer precipitation (ongoing since 1989) has affected the C balance of boreal forests in interior Alaska. Specifically, I am addressing long-term changes in soil organic C (SOC) storage, root depth distribution, and decomposition through soil analyses, root biomass measurements, and a common substrate decomposition experiment. If throughfall exclusion results in a soil environment that reduces decomposition of a common substrate, then under a drier future climate, we may expect reduced turnover rates of soil C contained at or near the soil surface in boreal forests. If throughfall exclusion results in C allocation further down in the soil profile, where mean annual moisture and temperature differ from that near the soil surface, then we might expect reduced summer precipitation to alter belowground SOC distribution, thereby possibly influencing the sink-source strength of boreal forest soils. This information can assist the development of models capable of (1) predicting how potential climate changes will affect the productivity of high-latitude forests and (2) aiding policy makers in determining appropriate management strategies of CO2 emissions.

Blaine Spellman
M.S. Candidate

Start date: 01-Sep-05
Advisor: T.Wurtz
Co-Advisors: J. Fox, J. Conn,

Non-native white sweetclover (Melilotus alba Medikus) has recently been found growing in dense mono-specific patches along several rivers in Alaska. While there is currently no research regarding the affect of sweetclover on floodplain plant communities, this invasive has the potential to threaten the ecological integrity of riparian areas within Alaska. Addressing the lack of research regarding the invasion of sweetclover in Alaska is the overall goal of my Master’s thesis research. My research involves studying the affect sweetclover has on the colonization success of native riparian plant species. Since the rate of colonization plays a pivotal role in the determination of plant community composition, a reduction in this rate could result in natives being reduced or eliminated from the floodplain vegetative assembly. I hypothesize that sweetclover can reduce the colonization success of native species through the limitation of light (PAR) and through interspecific competition. These hypotheses will be addressed through descriptive, removal, competition, and light manipulation experiments. I hope the findings from this research will assist land managers in making complex decisions regarding the control of sweetclover in Alaska.

Horacio Toniolo
Ph.D. Candidate

Start date:
Advisor: L. Hinzman
Co-Advisors: , ,

Katie Villano
M.S. Candidate

Start date: 01-Sep-05
Advisor: C. Mulder
Co-Advisors: T. Hollingsworth, ,

A warming climate has increased fire disturbance in interior Alaska and the likelihood of invasive plant success. My study aims to assess black spruce forest susceptibility to invasive species colonization in wildfire burn areas. I will evaluate invasive plant germination, growth and reproductive success in burns of varying severity and age. The research will make use of previously studied burn sites along the Alaskan highway system, including sites burned in 2004 that span a gradient of burn severity and sites that span a fire chronosequence beginning in 1915. Three high-risk species from three plant families (Bromus inermis ssp. inermis, Hieracium aurantiacum, and Melilotus alba) will be used to investigate susceptibility to invasion. The relationships between burn severity, burn age and susceptibility to invasion can then be used by land managers to focus invasive plant monitoring and prevention efforts.

Nan Werdin-Pfisterer
M.S. Candidate

Start date:
Advisor: K. Kielland
Co-Advisors: R. Boone, ,

Naturally occurring soil amino acids have been shown to be important sources of organic nitrogen for plant nutrition, yet few studies have examined which amino acids are most prevalent in the soil. In this study, we examined soil amino acid composition, concentration and seasonal patterns across a primary successional sequence encompassing a natural gradient of plant productivity and soil physio-chemical characteristics. Soil cores were collected from five stages encompassing the floodplain successional sere (willow, alder, balsam poplar, white spruce and black spruce) in the Bonanza Creek Experimental Forest Long Term Ecological Research sites on the Tanana River in interior Alaska. Water-extractable amino acid composition and concentration were determined by HPLC. We found that later coniferous successional stages generally had five times the amino acid concentration of the early deciduous-dominated stages. Amino acid concentrations in organic horizons (forest floor and buried organic horizons) were an order of magnitude greater than in mineral horizons. Across all successional stages, the amino acid pool was dominated by glutamic acid, glutamine, aspartic acid, asparagine, alanine, and histidine. These six amino acids accounted for approximately 80% of the amino acids found. Amino acid concentration generally decreased across the growing season, with highest values in early June and lowest values in late September. The similar amino acid composition across the successional stages suggests a common amino acid origin and that simple parameters such as vegetation type, soil pH, or organic matter content are poor predictors of amino acid composition. These results further demonstrate the biogeochemical diversity of nitrogen forms in boreal forests.

Stephen Winslow
M.S. Candidate

Start date: 01-Sep-06
Advisor: G.Juday
Co-Advisors: Clair Alix, Dave Verbyla,

People living in the Kuskokwim River Basin often rely on wood to heat their homes and are considering wood-fueled 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 (Picea glauca (Moench) Voss) and 77 black spruce and black spruce (Picea mariana (Mill.)B.S.P.) trees sampled along 370 km of the Kuskokwim River, Alaska to mean monthly temperatures (MMT) and total monthly precipitation (TMP) at McGrath. 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 wood-fueled energy generation.