• A dendroclimatological study of long-term growth patterns of yellow-cedar trees in Southeast Alaska

      Sink, Scott E. (2006-08)
      Yellow-cedar is a very long-lived, commercially important tree species found along the coasts of Southeast Alaska and also in small populations in Prince William Sound. However, this is the first study of the tree's annual ring growth patterns in the region. Tree cores were collected from over 400 trees across a large latitudinal gradient and cross-dated using standard dendrochronological techniques. Radial tree-ring growth was measured and compared to reconstructed weather station data to gain a better understanding of the climatic conditions favoring yellow-cedar growth. We found consistent, significant positive correlations between ring widths and mean monthly temperatures in August, previous January, and previous December, and negative relationships with May and December precipitation. Climate indices we created using these variables explain approximately 25% of growth variability in five distinct yellow-cedar populations. Long-term growth patterns in tree populations going back three centuries were similar across all sites, specifically the sustained below mean growth during the 1800s. Yellow-cedar at the northern limits of its distribution shows a common growth signal which may indicate the influence of larger pressure anomalies, such as EI Nino-Southern Oscillation (ENSO), on the climate factors affecting the trees.
    • 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.
    • 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.
    • 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.
    • An evaluation of fuels conversion treatments in Interior Alaska

      St. Clair, Thomas Barton (2006-05)
      The study site was a permafrost-free upland site with an east-northeast aspect, west/northwest of Fairbanks at mile 10 on the Cache Creek road in a mixed hardwood/spruce stand of Betula neoalaskana Sarg., Populus tremuloides Michx., Populus balsamifera L., Picea glauca (Moench) Voss, and Picea mariana (Mill.) BSP. In treatments designed to encourage hardwood growth, four different methods were used for removing vegetation (shearblading, masticating head, drum-crusher, and chainsaw thinning), resulting material was then left in place, burned, or chunked and removed. Treatments were evaluated using man/machine hour and dollar cost data and Permanent Sample Plot (PSP) data. PSPs were installed within six different fuels conversion treatments and a control for monitoring purposes. A pilot study revealed that debris pile burning changed soil color (more red) and soil water repellency properties. All treatments that had one full growing season showed hardwood regeneration. Shearblading and leaving material on site was the least labor-intensive treatment and least costly. Burning windrows was the least labor-intensive and least costly method of removing material from the site.
    • 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.
    • Freeze-thaw effect on soil microbial activity with biochar application in subarctic soils

      Castillo, Sunny M.; Soria, Juan Andres; Ping, Chien Lu; Michaelson, Gary; Leigh, MaryBeth (2013-08)
      Alaska has limited agricultural production due to extreme climatic conditions and weakly developed soils, which affect productivity. In higher latitudes, freeze-thaw cycles are common and influence soil biology and nutrient dynamics, offering a unique opportunity to investigate the use of soil amendments like biochar to enhance native biota and soil's intrinsic properties. Biochar for this study was produced from locally harvested black spruce (Picea mariana), using a fixed bed pyrolysis unit. The production of biochar was electronically controlled with temperatures kept at 550°C, and residence times manipulated by a mechanical auger, in order to yield five distinct biochar products. Chemical analyses showed differences among the biochar samples, including cation exchange capacity (CEC), micronutrients and pH. To evaluate the influence of each biochar on higher latitude native soils and biota, a response surface model was employed to design a set of experiments that measured CO₂ accumulation during a 15-day freeze -thaw cycle. Microbial activity during this experimental phase was monitored before and after freeze-thaw. Results of this study demonstrated that cultivated soils amended with biochar showed higher microbial activity before and after freeze-thaw. Forest soil on the contrary showed no significant results when amended with biochar. These results on different microbial activity were likely due to the amounts of organic carbon present in each soil type. The study serves as an evaluative tool for determining the impact that biochar may have in subarctic regions of the US that have limited agricultural potential as a result of climatic and native soil conditions.
    • Growth and Yield of Black Spruce, Picea mariana (Mill.) B.S.Pl., in Alaska

      Rosner, Carolyn; Packee, Edmond; Ping, Chien-Lu; Maich, John C. (University of Alaska Fairbanks, School of Natural Resources and Agricultural Sciences, 2004-08)
      Black spruce, Picea mariana (Mill.) B.S.P., is largely overlooked in Alaska because of its small size and slow growth. Growth and yield information is therefore limited or nonexistent. Presented here are the first polymorphic site index (height-age) curves and height-diameter functions for predicting height and volume for Alaska black spruce. Models are accurate for trees up to 50 feet in height and 8 inches DBH. Predicted stem volumes range from 0.006 ft3 to 21.8 ft3 for trees between 0.5 and 11.5 inches DBH Sampled tree dimensions range from 5.5 to 78.0 feet tall and from 0.4 to 11.0 inches DBH. Sampled breast-height ages range from 49 to 257 years; average age-to-breast-height is 26 years. This research, although limited, also characterizes general stand-level structure and community composition for Alaska black spruce. 60 Permanent Sample Plots (PSPs) representing 20 stands were established throughout the Tanana Valley, with stand inventory conducted according to a consistent protocol. Stand densities range from 137 to 2,907 trees per acre; stand volumes ranged from 8 to 2,507 ft3 per acre. Stand density index values range from 6 to 453. Periodic remeasurement of PSPs will yield valuable information about stand evolution and community type change.
    • Growth response of lutz spruce saplings to the removal of a herbaceous competitor and the application of fertilizer in Southeast Alaska

      Dickson, Emily; Barber, Valerie; Sparrow, Stephan; Harris, Norman (2014-08)
      Herbaceous competitor species such as fireweed can impact future survival and growth of Lutz (Picea x lutzii Little, Pinaceae) spruce saplings. Fertilizer is applied to crop trees in order to supply more nutrients to promote growth. However, fertilizer benefits competitor species as well. Literature regarding the impacts of competition for resources between fireweed and spruce saplings are lacking, but the impacts of resource competition on seedling growth and fireweed are documented as significant. Seedlings are distinguished from saplings by differences in height and/or diameter. In order to test the influence of both competitor species and added fertilizer, we analyzed growth response of Lutz spruce saplings to fireweed removal and applied fertilizer through treatments and controls using a two by two factorial experiment. Results revealed that fireweed removal had a positive effect on sapling growth response, while added fertilizer alone showed no effect on sapling growth response. I found a strong, positive correlation between soil moisture and fireweed cover. I also found a strong, positive relationship between sapling growth and soil moisture as well as sapling growth and fireweed cover. This study demonstrates that spruce saplings positively responded to fireweed removal compared to the application of fertilizer. More importantly, the overall conclusion is that when saplings are not N limited soil, moisture is the driving factor in sapling height growth. The long-term effects of harvesting an efficient nitrogen competitor species are not well known and could be detrimental to future site fertility.
    • 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.
    • 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.
    • 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.