• 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.