• 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.
    • Mapping landscape values and forest uses on the Tongass National Forest

      Schroeder, Britta; Verbyla, David; Brinkman, Todd; Fix, Peter (2014-05)
      Throughout the world, humans are often faced with the challenge of sustaining economic development while also promoting environmental stewardship. Such is true for the management history of the Tongass National Forest, where the U.S. Forest Service is transitioning away from harvesting old-growth and moving towards a more economically and environmentally sustainable approach. To measure the preferences of local community members affected by this transition, I conducted an interdisciplinary case study on the Wrangell Ranger District in Southeast Alaska. Community members from Wrangell mapped landscape values, acceptable and unacceptable forest uses. By assessing these landscape values and forest uses with respondents' attitudes towards forest management alternatives, I identify spatial locations of conflicting timber harvest uses and recommend forest management objectives for the district. Through public participation, communities can provide spatially explicit input during the planning process, which creates opportunities for managers to incorporate community needs and better prioritize management objectives.
    • 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.
    • 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.
    • The potential of lodgepole pine in Alaska

      Cushing, Alina (2005-08)
      The introduction of non-native trees should be informed by various perspectives. In the case of forestry in high-latitude regions, managers face the challenge of finding cold-hardy species adequately adapted to harsh climatic environments; Lodgepole pine (Pinus contorta Dougl. Ex. Loud.) has been introduced to three regions at or above its natural northern latitudinal extent; Alaska, Iceland, and northern Sweden. Analysis of interviews in each region revealed the structure of common arguments, including underlying assumptions and perceptions of the natural world. Results of a mail-out-survey to the Alaskan public indicate that a considerable portion of the public is concerned about the possibility for adverse ecological effects on the native ecosystem. However, acceptance of non-native trees increased under certain circumstances; e.g. small-scale ornamental plantings, and when economic benefit is demonstrated. In comparisons of twenty-year growth data of lodgepole pine in Alaska with native white spruce (Picea glauca), lodgepole pine achieved greater height, diameter, and volume. The response of lodgepole pine in all three regions to scenarios of climate change was predicted using tree-ring analysis. Results indicate a negative response (reduced growth) in the Fairbanks area, a positive response (increased growth) in Delta and Glennallen, and a positive response at all but one Icelandic site and both Swedish sites. Overall, lodgepole pine appears relatively well-adapted to the present and modeled future environments of interior Alaska, Iceland, and northern Sweden.
    • 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.
    • 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.
    • Soil surface organic layers in the Arctic foothills: development, distribution and microclimatic feedbacks

      Baughman, Carson A.; Mann, Daniel; Verbyla, David; Valentine, David (2013-12)
      Accumulated organic matter at the ground surface plays an important role in Arctic ecosystems. These soil surface organic layers (SSOLs) influence temperature, moisture, and chemistry in the underlying mineral soil and, on a global basis, comprise enormous stores of labile carbon. Understanding the dynamics of SSOLs is a prerequisite for modeling the responses of arctic ecosystems to climate changes. Here we ask three questions regarding SSOLs in the Arctic Foothills of northern Alaska: 1) What environmental factors control their spatial distribution? 2) How long do they take to form? 3) What is the relationship between SSOL thickness and mineral soil temperature during the growing season? Results show that the best predictors of SSOL thickness and distribution are duration of direct sunlight during the growing-season, upslope-drainage-area, slope gradient, and elevation. SSOLs begin to form within decades but require 500-700 years to reach steady-state thicknesses. SSOL formation has a positive feedback on itself by causing rapid soil cooling. Once formed, mature SSOLs lower the growing-season temperature and mean annual temperature of underlying mineral soils by 8° and 3° C, respectively, which reduces growing degree days by 78%. How climate change in northern Alaska will affect the region's SSOLs is an open and potentially crucial question.
    • 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.
    • Surface water dynamics of shallow lakes following wildfire in boreal Alaska

      Altmann, Garrett L.; Verbyla, Dave; Fox, John; Yoshikawa, Kenji (2013-12)
      Wildfire is ubiquitous to interior Alaska and is the primary large-scale disturbance regime affecting thawing permafrost and ecosystem processes in boreal forests. Since surface and near surface hydrology is strongly affected by permafrost occurrence, and wildfire can consume insulating organic layers that partially control the thickness of the active layer overlying permafrost, changes in the active layer thickness following fire may mark a distinct change in surface hydrology. In this study, we examined surface area dynamics of lakes following wildfire in four regions of Interior Alaska during a 25-year period from 1984 - 2009. We compared the surface water dynamics of lakes in burned areas relative to lakes in adjacent unburned (control) areas. Lake area changes in the short-term (0-5 years), mid-term (5-10 years), and long-term (>10 years) were analyzed. Burn severity, as a function of radiant surface temperature change, was also explored. Surface water changes were greatest during the short-term (0-5 years) period following fire, where burn lakes increased 10% and control lakes decreased -8% (P=0.061). Over the 5-10 year post-fire period, there was no significant difference in lake dynamics within burned areas relative to control unburned areas. On average, there was an 18 percent decrease in surface water within burned areas over the >10 year post fire time period, while unburned control lakes averaged a 1 percent decline in surface water. The long term declining trend within burned areas may have been due to talik expansion and/or increased evapotranspiration with revegetation of broadleaf plants. Fire had the greatest effect on radiant surface temperature within two years of a fire, where radiant temperatures increased 3-7°C in the most severely impacted areas. Temperature differences between burn and control areas remained less than 1°C as vegetation reestablished. There was no correlation between radiant temperature change and decreasing lake area change. Conversely, there was a trend between lake area differences increasing in size and increases in temperature. While fire displayed the greatest effect on lake area in the short-term, a combination of fire, climate, and site-specific conditions dominate long-term lake area dynamics in Alaska boreal forest.
    • 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.
    • 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.