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  • Boreal forest regeneration dynamics: Modeling early forest establishment patterns in interior Alaska

    Rupp, Terry Scott; Yarie, John (1998)
    Ecological processes are responsible for vegetation trajectory within the boreal forest landscape of interior Alaska. The reproductive response of boreal forest to disturbance controls vegetation trajectory. Boreal forest reproduction dynamics are influenced by both biotic and abiotic factors, acting upon the spatio-temporal dynamics of the landscape. Understanding these factors and how the boreal forest responds, both spatially and temporally, is critical for the development of accurate models of regional and global vegetation dynamics. I developed a geographic model of the early post-disturbance seedling regeneration pattern of upland white spruce ecosystems in interior Alaska. The model was developed and runs within a geographic information system (GIS). The model simulates the establishment patterns of white spruce, paper birch, and aspen across the landscape following fire. Seed production and dispersal, disturbance effects upon the seedbed, and the early establishment of both seedlings and vegetative stems are simulated. The model was used to simulate a 6 yr period (1983-1988) of seedling establishment at the Bonanza Creek Experimental Forest near Fairbanks, following the Rosie Creek fire. Correlation values between predicted and established seedlings were high, demonstrating the model's ability to simulate general establishment patterns. Sensitivity analysis revealed seed production, seed source location and orientation, and seedbed "receptivity" as important controls upon the early establishment success of white spruce seedlings following disturbance. Establishment patterns between a hypothetical clearcut, strip-cut, and residual tree islands cut were simulated and compared. Distance from the seed source was identified as a major limitation to adequate stocking levels in the clearcut. The residual islands cut provided the highest stocking levels, followed by the strip-cut and clearcut. The results suggest large clearcuts are not an efficient harvesting method in interior Alaska for successful natural regeneration and stocking levels. The model results warrant further development and identified a "real" potential use as a forest management tool.
  • Structure and dynamics in mixed forest stands of interior Alaska

    Youngblood, Andrew (1992)
    This study examines aspects of stand development in young mixed hardwood-conifer forests on upland sites in interior Alaska, with the goal of refining concepts of plant community succession. Specific objectives were: (i) describe the structural characteristics of young mixed hardwood-conifer stands, including composition, horizontal and vertical arrangement and component size; (ii)define common stand development patterns; (iii) compare juvenile height and diameter growth increments for the different species; (iv) correlate existing stand structure with stand-disturbing events; and (v) suggest considerations for manipulating stand structure and composition of mixed stands to maintain productivity and provide a variety of forest products. Techniques involve the study of disturbance events, establishment and growth patterns following disturbance and the resulting stand structure. Procedures used were: (i) develop a community type classification to partition the variability within the ecosystem into units having similar floristic features; (ii) determine the successional trends within each community type by reconstructing the growth patterns along a chronosequence; (iii) describe common structural attributes of the community types and relate these to stand dynamics; and (iv) develop height growth relationships and estimates of productivity by species within the community types. A total of 53 upland mixed communities were sampled and classified into five community types: Populus tremuloides/Arctostaphylos uva-ursi, Populus tremuloides/Shepherdia canadensis, Betula papyrifera-Populus tremuloides/Viburnum edule, Betula papyrifera-Populus tremuloides/Alnus crispa and Picea glauca-Betula papyrifera/Hylocomium splendens. Community types were described on the basis of distribution and physical environment, vegetation composition and structural features, successional relationships of stand development, productivity estimates and relationship to previously described vegetation units. Two stand development patterns were identified. The first pattern was rapid establishment of hardwoods, followed by prolonged establishment of conifers. This pattern describes development within the Populus tremuloides/Arctostaphylos uva-ursi and Populus tremuloides/Shepherdia canadensis community types. In contrast, a second pattern occurring most often in the remaining three community types was one of rapid concurrent establishment of hardwoods and conifers. Productivity of open-grown conifers was differentiated from that of stand-grown or suppressed conifers. Estimates of productivity are generally dissimilar to those for pure, even-aged and fully stocked stands.
  • Birch, Berries, And The Boreal Forest: Activities And Impacts Of Harvesting Non-Timber Forest Products In Interior Alaska

    Maher, Kimberley Anne C.; Juday, Glenn P.; Barber, Valerie; Gerlach, S. Craig; Watso, Annette (2013)
    Harvesting wild berries, firewood, and other non-timber forest products (NTFPs) from the boreal forest in Interior Alaska is a common activity amongst local residents. NTFPs are harvested for personal use, subsistence, and commercial purposes. While these activities contribute to informal household economies and livelihoods, harvest of NTFPs are not well documented in Alaska. Availability of these ecosystem services may be altered under changing management and climate regimes. This interdisciplinary dissertation takes a look at the activities and impacts of current NTFP harvesting practices. Survey results from a forest use survey provide insight into harvest activity in the Tanana Valley. Wild blueberries (38.5% of households with mean harvested amount of 7.7 quarts) and firewood (25.0% of households with a mean harvest amount of 4.7 cords) were reported harvested with greatest frequency, and harvesting activities were mostly concentrated around larger population centers. Interviews were conducted with personal use and subsistence NTFP harvesters from Interior Alaska. Participants enjoy harvesting from the forest, and that the importance of harvesting is a combination of both the intangible benefits from the activity and the tangible harvested items. Harvested NTFPs were seen as high-quality products that were otherwise unavailable or inaccessible. Birch syrup is a commercially available NTFP produced in Alaska by a small number of companies. Similar to maple syrup, producing birch syrup is a labor intensive process with marginal profits. Interviews were conducted with workers in the Alaskan birch syrup industry, who reported that they were seeking an alternative to the traditional employment. The effects from mechanical damage from tapping for spring sap on birch's vigor are of concern to birch syrup producers and natural resource managers. This study compared the annual increment growth of Alaskan birch trees, Betula neoalaskana, between tapped and untapped trees. No significant difference was detected from tapping, but annual variability in growth was strongly significant. A temperature index accounted for nearly two-thirds of the annual variability. Pairing this index with two climate scenarios, birch growth was extended out through the 21st century. As temperatures rise, birch in Interior Alaska are projected to face a critical threshold, which may limit or extinguish their ability to sustain growth and yield a sustainable sap resource. Integrating the survey, interview, and dendroclimatological data provides a richer picture of how NTFP harvesters actively use the forest and about the benefits derived. These findings can assist resource managers in balancing these needs with those of other forest uses on public land.
  • Anatomical And Mechanical Characteristics Of Woods Used To Manufacture Bassoons

    Levings, Carolyn K.; Barber, Valerie; Alix, Claire; Hulsey, Leroy; Keating, Richard; Rydlinski, George (2012)
    The purpose of this dissertation was three-fold -- 1) to determine if anatomical characteristics and mechanical characteristics derived from tapping (the act of striking an object lightly) can be used to more accurately describe bassoon resonant wood than the characters in use now, 2) to determine if any Alaska hardwoods can be used to construct bassoons, and 3) to produce lists of potential North American hardwoods and resonant bassoon wood characters. The bassoon resonant woods (Acer spp., Dalbergia melanoxylon, and Pyrus spp.) were compared to a known non-resonant bassoon wood (Juglans nigra). Vessel length and width, fiber length, and axial parenchyma width were measured in sectioned and macerated wood slides, along with the ratios of crystalline cellulose, lignin, pectin, and other aromatics in the cell wall. Partial frequencies created from tapping specimens on each longitudinal face were measured from melodic and peak partial spectrograms, as well as the spectrum obtained from the beginning of the sound. MANOVA and univariate ANOVA showed the resonant woods were significantly different from the non-resonant Juglans nigra using the characters measured. These characters were then used to compare two Alaska hardwoods (Alnus rubra and Betula neoalaskana) to the temperate resonant woods (Acer spp. and Pyrus spp.) and the non-resonant Juglans nigra using k-means clustering, MANOVA, and univariate ANOVA. Both Alaska hardwoods grouped with the non-resonant Juglans nigra. Lastly a list of potential North American hardwoods to be checked anatomically was compiled, as well as a list of characters that combine those used now as well as characters found in this study.
  • Diversity In The Boreal Forest Of Alaska: Distribution And Impacts On Ecosystem Services

    Young, Brian D.; Yarie, John; Chapin, F. Stuart; Greenburg, Josh; Huettmann, Falk; Verbyla, David (2012)
    Within the forest management community, diversity is often considered as simply a list of species present at a location. In this study, diversity refers to species richness and evenness and takes into account vegetation structure (i.e. size, density, and complexity) that characterize a given forest ecosystem and can typically be measured using existing forest inventories. Within interior Alaska the largest forest inventories are the Cooperative Alaska Forest Inventory and the Wainwright Forest Inventory. The limited distribution of these inventories constrains the predictions that can be made. In this thesis, I examine forest diversity in three distinct frameworks; Recruitment, Patterns, and Production. In Chapter 1, I explore forest management decisions that may shape forest diversity and its role and impacts in the boreal forest. In Chapter 2, I evaluate and map the relationships between recruitment and species and tree size diversity using a geospatial approach. My results show a consistent positive relationship between recruitment and species diversity and a general negative relationship between recruitment and tree size diversity, indicating a tradeoff between species diversity and tree size diversity in their effects on recruitment. In Chapter 3, I modeled and mapped current and possible future forest diversity patterns within the boreal forest of Alaska using machine learning. The results indicate that the geographic patterns of the two diversity measures differ greatly for both current conditions and future scenarios and that these are more strongly influenced by human impacts than by ecological factors. In Chapter 4, I developed a method for mapping and predicting forest biomass for the boreal forest of interior Alaska using three different machine-learning techniques. I developed first time high resolution prediction maps at a 1 km2 pixel size for aboveground woody biomass. My results indicate that the geographic patterns of biomass are strongly influenced by the tree size class diversity of a given stand. Finally, in Chapter 5, I argue that the methods and results developed for this dissertation can aid in our understanding of forest ecology and forest management decisions within the boreal region.
  • Hydrologic Controls On Carbon Cycling In Alaskan Coastal Temperate Rainforest Soils

    D'Amore, David V.; David, Valentine, (2011)
    The northern perhumid North American Pacific coastal temperate rainforest (NCTR) extends along the coastal margin of British Columbia and southeast Alaska and has some of the densest carbon stocks in the world. Northern temperate ecosystems such as the NCTR play an important role in the global balance of carbon flows between atmospheric and terrestrial pools. However, there is little information on key components of the forest carbon budget in this region. Specifically, the large pool of soluble carbon that is transferred from soils via streamwater as dissolved organic carbon (DOC) certainly plays a role in the total carbon balance in wet forests such as the NCTR. In order to address this information gap, I applied the concept of hydropedology to define functional landscape units based on soil type to quantify soil carbon fluxes and apply these estimates to a conceptual model for determining the carbon balance in three NCTR watersheds. The strong hydrologic gradient among ecosystems served as a template for constructing a conceptual design and approach for constraining carbon budget estimates in the watersheds. Replicated hydropedologic units were identified in three classes: sloping bogs, forested wetlands, and uplands. Estimates of annual soil respiration and DOC fluxes from the hydropedologic types were obtained through seasonal measurements combined with temperature-dependent models. Soil respiration fluxes varied significantly across the hydrologic gradient where soil respiration was 78, 178, and 235 g CO2 m -2 y-1 in sloping bogs, forested wetlands and uplands respectively. Average DOC flux was 7.7, 30.3, to 33.0 g C m-2 y-1 in sloping bog, forested wetland, and upland sites respectively. Estimates of carbon efflux from the terrestrial ecosystem was combined with values of net primary productivity from remote sensing to determine net ecosystem production (NEP). The average NEP estimated in three NCTR watersheds was 2.0 +/- 0.8 Mg C ha-1. Carbon loss as DOC was 10--30% of the total carbon flux from the watersheds confirming the importance of this vector of carbon loss in the NCTR. The watershed estimates indicate that forests of the NCTR serve as a carbon sinks consistent with the average worldwide rate of carbon sequestration in terrestrial ecosystems.
  • A Geobotanical Analysis Of Circumpolar Arctic Vegetation, Climate, And Substrate

    Raynolds, Martha K. (2009)
    The objective of the research presented in this dissertation was to better understand the factors controlling the present and potential future distribution of arctic vegetation. The analysis compares the Circumpolar Arctic Vegetation Map (CAVM) with circumpolar data sets of environmental characteristics. Geographical information system (GIS) software was used to overlay the CAVM with a satellite index of vegetation (normalized difference vegetation index, NDVI) and environmental factors that are most important in controlling the distribution of arctic vegetation, including summer temperature, landscape age, precipitation, snow cover, substrate chemistry (pH and salinity), landscape type, elevation, permafrost characteristics, and distance to sea. Boosted regression tree analysis was used to determine the relative importance of different environmental characteristics for different vegetation types and for different regions. Results of this research include maps, charts and tables that summarize and display the spatial characteristics of arctic vegetation. The data for arctic land surface temperature and landscape age are especially important new resources for researchers. These results are available electronically, not only as summary data, but also as GIS data layers with a spatial context ( The results emphasize the value and reliability of NDVI for studying arctic vegetation. The relationship between NDVI and summer temperatures across the circumpolar arctic was similar to the correlated increases in NDVI and temperature seen over the time period of satellite records. Summaries of arctic biomass based on NDVI match those based on extrapolation from ground samples. The boosted regression tree analysis described ecological niches of arctic vegetation types, demonstrating the importance of summer temperatures and landscape age in controlling the distribution of arctic vegetation. As the world continues to focus on the Arctic as an area undergoing accelerated warming due to global climate change, results presented here from spatially explicit analysis of existing arctic vegetation and environmental characteristics can be used to better understand plant distribution patterns, evaluate change in the vegetation, and calibrate models of arctic vegetation and animal habitat.
  • Interactions Among Climate, Fire, And Vegetation In The Alaskan Boreal Forest

    Duffy, Paul Arthur; Rupp, Scott (2006)
    The boreal forest covers 12 million kM2 of the northern hemisphere and contains roughly 40% of the world's reactive soil carbon. The Northern high latitudes have experienced significant warming over the past century and there is a pressing need to characterize the response of the disturbance regime in the boreal forest to climatic change. The interior Alaskan boreal forest contains approximately 60 million burnable hectares and, relative to the other disturbance mechanisms that exist in Alaska, fire dominates at the landscape-scale. In order to assess the impact of forecast climate change on the structure and function of the Alaskan boreal forest, the interactions among climate, fire and vegetation need to be quantified. The results of this work demonstrate that monthly weather and teleconnection indices explain the majority of observed variability in annual area burned in Alaska from 1950-2003. Human impacts and fire-vegetation interactions likely account for a significant portion of the remaining variability. Analysis of stand age distributions indicate that anthropogenic disturbance in the early 1900's has left a distinct, yet localized impact. Additionally, we analyzed remotely sensed burn severity data to better understand interactions among fire, vegetation and topography. These results show a significant relationship between burn severity and vegetation type in flat landscapes but not in topographically complex landscapes, and collectively strengthen the argument that differential flammability of vegetation plays a significant role in fire-vegetation interactions. These results were used to calibrate a cellular automata model based on the current conceptual model of interactions among weather, fire and vegetation. The model generates spatially explicit maps of simulated stand ages at 1 km resolution across interior Alaska, and output was validated using observed stand age distributions. Analysis of simulation output suggests that significant temporal variability of both the mean and variance of the stand age distribution is an intrinsic property of the stand age distributions of the Alaskan boreal forest. As a consequence of this non-stationarity, we recommend that simulation based methods be used to analyze the impact of forecast climatic change on the structure and function of the Alaskan boreal forest. To assess the impact climate change has on the Alaskan boreal forest, interactions among climate, fire and vegetation were quantified. This work shows that climatic signals exert the dominant influence on area burned. These results inform a simulation model to assess the historical and future states of the Alaskan boreal forest.
  • Mechanisms Of Soil Carbon Stabilization In Black Spruce Forests Of Interior Alaska: Soil Temperature, Soil Water, And Wildfire

    Kane, Evan S.; Valentine, David (2006)
    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 minuscule 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.
  • The Treeline Ecotone In Interior Alaska: From Theory To Planning And The Ecology In Between

    Wilmking, Martin; Juday, Glenn Patrick (2003)
    Treelines have been the focus of intense research for nearly a hundred years, also because they represent one of the most visible boundaries between two ecological systems. In recent years however, treelines have been studied, because changes in forest ecosystems due to global change, e.g. treeline movement, are expected to manifest first in these areas. This dissertation focuses on the elevational and latitudinal treelines bordering the boreal forest of interior Alaska. After development of a conceptional model of ecotones as three-dimensional spaces between ecosystems, we offer a historical perspective on treeline research and its broader impact in the Brooks Range, Alaska. Dendrochronological analysis of >1500 white spruce (Picea glauca (Moench [Voss])) at 13 treeline sites in Alaska revealed both positive and negative growth responses to climate warming, challenging the widespread assumption that northern treeline trees grow better with warming climate. Hot Julys decreased growth of ~40% of white spruce at treeline in Alaska, whereas warm springs enhanced growth of others. Growth increases and decreases appear at temperature thresholds, which have occurred more frequently in the late 20th century. Based on these relationships between tree-growth and climate as well as using landscape characteristics, we modeled future tree-growth and distribution in two National Parks in Alaska and extrapolated the results into the 21 st century using climate scenarios from five General Circulation Models. In Gates of the Arctic National Park, our results indicate enhanced growth at low elevation, whereas other areas will see changes in forest structure (dieback of tree-islands, infilling of existing stands). In Denali National Park, our results indicate possible dieback of white spruce at low elevations and treeline advance and infilling at high elevations. This will affect the road corridor with a forest increase of about 50% along the road, which will decrease the possibility for wildlife viewing. Surprisingly, aspect did not affect tree growth-climate relationships. Without accounting for opposite growth responses under warming conditions, temperature thresholds, as well as meso-scale changes in forest distribution, climate reconstructions based on ring-width will miscalibrate past climate, and biogeochemical and dynamic vegetation models will overestimate carbon uptake and treeline advance under future warming scenarios.
  • Linked disturbance interactions in South-Central Alaska: implications for ecosystems and people

    Hansen, Winslow D. (2013-05)
    Communities and ecosystems in the Alaskan boreal forest are undergoing substantial change. People contribute to this change. They are also impacted by the consequences. For example, wildfire and spruce bark beetle (Dendroctonus rufipennis) outbreaks have increased in frequency and severity due to warming trends, affecting the ecosystem and services important to people. I conducted a study to explore the social and ecological implications of changing natural disturbances. I evaluated how the occurrence of spruce bark beetle outbreak has altered the probability of wildfire between 2001 and 2009 on the Kenai Peninsula, Alaska. Modeling the effects of bark beetle outbreak on the probability of large wildfire (> 500 ha) and small wildfires (<500 ha), I found that the influence of the outbreak differed as a function of wildfire size. The occurrence and length of outbreak increased large wildfire probability. Small wildfires were mediated by human influence and less so by bark beetle outbreak. I also used spatial econometric techniques to estimate how wildfires and the bark beetle outbreak affected property values on the Kenai Peninsula in 2001 and 2010. I found that wildfires> 3.3 ha and the bark-beetle outbreak increased property values. Wildfires <3.3 ha decreased property values.
  • Developing fuel models for the Anchorage wildland-urban interface using a forest inventory

    Cheyette, Daniel Louis (2005-05)
    I inventoried the forests of the Anchorage wildland-urban interface and created a hierarchical classification of twenty forest types differentiated according to tree species, tree and basal area densities and degree of spruce bark beetle mortality. The inventory included the data necessary to parameterize NEXUS - a fire behavior model that integrates surface and crown fire initiation and spread algorithms. The twenty inventory forest types consolidated into eight custom fuel models and canopy attribute sets that correspond to the cover types identified by the Anchorage Wildfire Partnership. I assessed the models using NEXUS and completed a sensitivity analysis that identified the most influential model parameters and the forest attributes that managers should prioritize in future mitigation efforts. Results indicate that needleleaf low-density forests pose the largest hazard due to large 1-hour fuel loads and fuelbed depths, low crown-base-heights and high crown bulk-densities. Stands infested by the spruce bark beetle also pose a serious hazard due to the ecological/physiological changes that promote the growth of Calamagrostis canadensis, a flash fuel that dries quickly and readily burns. The forest inventory, fire behavior predictions and sensitivity analysis demonstrate that parts of Anchorage's wildland-urban interface are at risk under extreme weather and topographic conditions.
  • Duff moisture dynamics in black spruce feather moss stands and their relation to the Canadian forest fire danger rating system

    Wilmore, Brenda (2001-08)
    The Canadian Forest Fire Danger Rating System's Fire Weather Index (FWI) system models 3 levels of fuel moisture within the forest floor using simple environmental inputs. Wildland fire managers in interior Alaska have expressed concern that the FWI System does not take northern latitude factors such as long day lengths and permafrost into account. During the 1999 fire season destructive sampling methods were employed to monitor moisture content throughout the feather moss profile in 3 interior Alaska black spruce stands. Measured moisture contents were compared to the FWI System's fuel moisture predictions. The FWI System followed general trends of the seasonal fuel moisture within the feather moss profile. However, the short-term response of the interior Alaska moss profile is more dynamic than the FWI System's fuel moistrue code predictions. Hydraulic properties that have been linked to bulk density may be the causative agent for the observed short-term discrepancy.
  • Estimation of growing season length in northern Alaska with AVHRR NDVI bi-weekly satellite data

    Goldman, Heather Beth (2000-05)
    Twice-monthly AVHRR-derived NDVI were used to estimate growing season length across Alaska, north of the Alaska Range. An algorithm, based on the ratio of NDVI to annual maximum NDVI for each pixel, was used to represent percent of maximum greenness for each composite period. Greenup and senescence commenced when NDVI values rose above and fell below a selected percent of maximum greenness. Six different percent of maximum greenness threshholds, ranging from 25 to 50 percent, were evaluated. This algorithm eliminates complications of landscape-specific NDVI thresholds and year-to-year variability. The algorithm was tested against 1) air temperature data from 23 weather stations located in northern Alaska from 1991 to 1997, 2) observed greenup at two sites in Fairbanks, Alaska, from 1991 to 1997, and 3)phenology observations on the Seward Peninsula during the 1996-1997 growing seasons. Best results were obtained with NDVI values at 30% and 40% of maximum NDVI.
  • Production and quality of spring sap from Alaskan birch (Betula neoalaskana sargent) in Interior Alaska

    Maher, Kimberley Anne Camille (2005-05)
    Little is known about the specifics of spring sap production in Alaskan birch Betula neoalaskana Sargent. With an emerging industry in Alaska based on the harvest of birch sap, additional information is needed. This thesis is an exploratory study that investigates the production of sap during the 2002 and 2003 spring seasons in the Fairbanks region and characterizes the dissolved solid components of the sap harvested in 2003. April 2002 and 2003 had strongly contrasting weather patterns which affected sap yields. In general, trees yielded more sap in the wet, cool spring of 2002 than the dry, warm spring of 2003. Larger diameter trees yielded more sap in both years, and this correlation was stronger during the dry, warm spring. Stand location on the hillside and indicator species were also related to sap yield. Carbohydrate content of birch sap is mostly glucose (44%) and fructose (40.3-54.6%); sucrose and galactose are also present. The relative concentration of carbohydrates varied throughout the sap season. Macronutrients (Ca, K, and Mg) and micronutrients (Mn, Fe, Al, Na, Zn and Cu) are present in the sap; their concentrations increase throughout the season.
  • Fire in boreal black spruce (Picea mariana mill.) forests: respiration, temperature sensitivity, and bioavailability of soil organic matter

    Masco, Sarah (2005-05)
    Boreal forests store large quantities of carbon (C) and currently act as atmospheric C sinks; however, predicted increases in temperature and fire frequency may change the boreal forest from a net C sink to a net source. This study evaluates the response of organic soil C and nitrogen (N) mineralization, and the bioavailability of C and N to burning in non-permafrost upland black spruce stands in Interior Alaska. Two years after an experimental wildfire, burned soils were warmer than control soils at all depths measured, and decay of common substrates was greater in the burned than in the control soils. Burned soils had higher concentrations of total C, lignin, N, and mineral N, and lower concentrations of dissolved organic carbon (DOC) and soluble organic matter. However, apparent differences in organic matter quality did not correlate well with respiration metrics. In laboratory incubations, burned soils respired less than control soils, and this difference was entirely due to differences on the first day of the incubation. Mean Q₁₀ values ranged from 2.1 to 2.5 and were greater in the burned soils than in the control soils.
  • MODIS Satellite vegetation indices over partially vegetated pixels on the Arctic Coastal Plain of Alaska

    Macander, Matt (2005-08)
    The performance and response of the MODIS Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) were evaluated over the Arctic coastal plain of Alaska. At the 250-l000-m resolution of moderate resolution sensors, a substantial portion of this landscape is a mixture of vegetated and non-vegetated cover types. Single-date MODIS swath scenes were used because of the higher geolocation accuracy, lack of radiometric artifacts, and temporal specificity. A higher resolution earth cover classification was used to sample pixels with a mixture of vegetation, water, and barren ground. The MODIS NDVI and EVI were compared to aggregated Landsat ETM+ NDVI. The subpixel ETM+ NDVI was a good predictor of the MODIS EVI in all mixed pixels, and of the MODIS NDVI in mixed vegetation and barren ground pixels. In these cases a simple linear relationship between subpixel ETM+ NDVI and the MODIS vegetation indices was observed. In the mixed pixels with vegetation and water, the MODIS NDVI had a curvilinear response to the ETM+ NDVI and the performance decreased as the subpixel water fraction increased. Spectral mixture modeling was then applied to synthesize mixed pixel spectral values and plot the response of the MODIS vegetation indices to subpixel non-vegetated fractions. The MODIS NDVI had a highly variable response to subpixel fractions of different non-vegetated backgrounds, while the MODIS EVI was fairly insensitive to background type. The models also suggest that large changes in observed NDVI values could occur due to changes in the spectral characteristics of the non-vegetated portion of a pixel-in particular, the conversion of ice to water in subpixel water fractions.
  • Using GIS-based and remotely sensed data for early winter moose (Alces alces gigas) survey stratification

    Clyde, Karen J. (2005-05)
    Stratification of moose survey areas is a key step to reduce population estimation variance. In the Yukon and Alaska, use of fixed-area grids for early winter moose counts combined with the increasing availability of GIS and remotely sensed data provide the opportunity to develop standardized and repeatable habitat-based stratifications. I used univariate comparisons, stepwise regression and AIC modeling to describe moose distribution as a function of landscape level variables for an area in west central Yukon during 1998 and 1999. Results quantified early winter habitat use of upland shrub habitats and support previous observations for early winter moose habitat use in Alaska, Minnesota and Montana. Number of patches, in association with areas of alpine and shrubs, were found to be highly influential for survey blocks where moose are expected to be present and in high numbers. Overall, model performance based on relative abundance of moose was less predictive than for blocks where moose were present or absent. Spatial resolution of GIS and remotely sensed data used in this study (25 m grid cells) provided sufficient spatial detail to generate correlations between moose presence and habitat for a first level stratification.
  • Quantifying upland boreal forest successional pathways near Fairbanks, Alaska

    Kurkowski, Thomas Andrew (2005-08)
    Previous studies have suggested that post-fire forest succession in Interior Alaska can occur in two different ways. Self-replacement occurs when pre-fire dominant species immediately replace themselves as the canopy dominants after fire. Species-dominance relay occurs when, after simultaneously establishing themselves after fire, deciduous trees relinquish canopy dominance to conifer species as the stand ages. The relative importance of these different successional processes at landscape scales in Interior Alaska is unknown. To test for the importance of these two trajectories, we built a multinomial logistic regression model explaining the relationship between classified vegetation type and topographic variables. We also determined the relative occurrence of species-dominance relay by comparing aged stands to known successional patterns. The model correctly predicted 78% of spruce distribution, and the majority of stands are not following the species-dominance relay pattern, implying that most of the study area appears to be following a self-replacement trajectory with only a small proportion of sites capable of supporting both deciduous and spruce species. These results have important implications for modeling forest succession in Interior Alaska because of the importance of these dynamics in determining the fire regime, carbon storage, and global warming scenarios.
  • Remote sensing of burn severity and the interactions between burn severity, topography and vegetation in interior Alaska

    Epting, Justin Frederick (2004-08)
    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 elevation, presumably due to the strong control of elevation on vegetation type. 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.

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