Browsing by Subject "Natural resources science & management"

Now showing 1 - 7 of 7
  • Thumbnail Image
    Item
    All cellulose composites prepared in an ionic liquid.
    (2010-12) Zhou, Lili
    The overall goal of this project was to investigate all-cellulose composites prepared in a “green” solvent – ionic liquid. The approach was to partially dissolve cellulose and subsequently convert it into a matrix domain embedding the reinforcement domain – the undissolved cellulose. Microcrystalline cellulose (MCC) was partially dissolved in 1-N-Butyl-3-methylimidazolium chloride (BMIMCl) ionic liquid. The dissolved portion of cellulose was precipitated by adding water, and the gels obtained were washed, dried, and pressed into films. The all-cellulose composite films were structurally characterized using x-ray diffraction (XRD) and scanning electron microscopy (SEM), while their properties were determined using tensile tests and dynamic vapor sorption (DVS) studies. XRD results verified that the crystallinity index and weight fraction of cellulose I in the composites can be controlled by controlling the soaking time and cellulose concentrations. The tensile test data revealed that the all-cellulose composite produced in this study had mean elastic moduli and strength of up to 4.4 GPa and 49 MPa, respectively, which are in the range of a randomly oriented biofiber-reinforced polymer composites. The tensile properties increased as a response to the composite density, which was found to increase as more cellulose II matrix (from increased dissolution) was present to presumably better fill the voids. This presumption was supported by SEM images of cryo-fractured surfaces. The sorption isotherms obtained from DVS studies showed a non-sigmoidal behavior at low relative humidity levels (<44%), while the equilibrium moisture content values at higher humidity levels closely correlated to the cellulose I crystallinity index of the composites. Overall, this study verified that dissolution of cellulose in ionic liquid can be controlled to control the properties of all-cellulose composites.
  • Thumbnail Image
    Item
    Canopy transpiration and water yield changes following forest canopy conversion in Northern Minnesota.
    (2011-03) Shannon, Joseph
    In 1980, the upland aspen (Populus tremuloides & P. grandidentata) portion of the S6 watershed of the Marcell Experimental Forest was clearcut and subsequently converted to red pine (Pinus resinosa) and white spruce (Picea glauca). Comparisons of water yield observed at S6 and that predicted using the aspen dominated S2 control watershed, suggest that streamflow from S6 has decreased over the past two decades as the conifers have matured. Granier-style thermal dissipation probes were used to quantify sap flux in 36 trees in S2 and S6 throughout the growing season to determine if transpiration rates differed between the two watersheds. Representative sample trees were selected according to factors which may cause sap-flux rates to differ: tree species, slope position, and slope aspect. Using forest inventory data, sap-flux rates were up-scaled to watershed canopy transpiration. Transpiration losses in the S6 watershed were 30% greater than those in S2 for the duration of the study period. Differences were primarily driven by a longer growing season in conifers and greater forest basal area in S6. By representatively sampling forest species it is possible to show that 40 - 50% of transpiration in each watershed is the result of one dominant species, red pine or aspen, in the experimental or control watersheds respectively. Future use of these data will include combination with concurrent interception and flow routing studies to better evaluate hydrologic impacts of similar management decisions in the future. Forest conversion is an ongoing management strategy that brings about long-term effects on streamflow. Understanding these effects allows better prediction of the effect of management on water resources.
  • Thumbnail Image
    Item
    Disturbance dynamics and carbon storage in southern boreal mesic aspen mixedwood forests of northern Minnesota, USA.
    (2011-05) Reinikainen, Michael Richard
    One emerging objective related to forest management is developing silvicultural systems that increase the levels of carbon storage so as to mitigate or offset atmospheric concentrations of carbon dioxide. Understanding the ecological factors and conditions that led to the development of forest stands with high levels of carbon storage can allow for the formulation of management prescriptions that emulate the frequency, timing, and severity of disturbances leading to these conditions. The aims of this thesis were to (1) generate an understanding of the factors affecting stand-level structural and compositional development in southern boreal mesic aspen mixedwoods (hereafter referred to as ‘aspen mixedwoods’), and (2) identify relationships between carbon storage, stand characteristics (e.g., composition and structure) and disturbance histories. Dendroecological methods were used to detail the mechanisms by which nine aspen mixedwood stands in northern Minnesota developed in terms of composition and structure over the last nine decades. With that knowledge and detailed plot-level measurements of forest carbon pools, relationships between patterns of carbon storage resulting from various disturbance histories and compositional mixtures were examined. Dendroecological reconstructions demonstrated that the development of mature aspen mixedwoods was strongly influenced by the defoliation of trembling aspen (Populus tremuloides) by forest tent caterpillar (FTC: Malacosoma disstria) and of balsam fir (Abies balsamea) by eastern spruce budworm (SBW: Choristoneura fumiferana), resulting in complex multi-aged forests. Notably, disturbance-induced structural and compositional changes began as early as 30 years after stand initiation. Concerning carbon storage, stands with a high proportion of aspen stocking resulted in greater total ecosystem (TEC) and tree carbon (TREEC) storage with an opposite trend observed with proportion of conifer, particularly balsam fir. However, in light of recent disturbance, stands containing a greater diversity of tree species and a greater proportion of conifer stems had higher rates of tree carbon increment over the last two decades than plots with a greater proportion of aspen. Furthermore, lower levels of TEC in plots that had experienced elevated rates of disturbance over the last three decades were documented. Collectively, these findings highlight the influence of low to moderate severity disturbances on the patterns of carbon storage and compositional and structural complexity within these systems. As such, regional patterns of natural disturbance present a challenge within the context of managing for highly productive mature aspen mixedwoods; however, the restoration of historically important species (i.e., Picea glauca, Pinus strobus and Thuja occidentalis), specifically long-lived species resistant to FTC and more importantly SBW, may offer a means to store large amounts of carbon for longer periods.
  • Thumbnail Image
    Item
    The influence of natural disturbance-based silviculture treatments on northern hardwood forests in Northeastern Minnesota, USA.
    (2010-12) Bolton, Nicholas William
    Natural disturbance-based silviculture (NDBS) has been suggested as an approach for promoting late-successional forest characteristics and maintaining native biodiversity in managed forests. Harvest gaps based on the natural disturbance patterns found in the upper Great Lakes (46 study gaps) were created throughout northern hardwood forests in northeastern Minnesota, USA, during the winters of 2002 and 2003. Gaps were measured 6- and 7-years post-treatment and subsequent analysis of these measurements was used to evaluate the success of these treatments at meeting structural and compositional objectives. Results indicated that these gaps have done little to increase tree diversity, including the recruitment of shade mid-tolerant species; however, the richness of herbaceous understory vegetation has responded positively to larger gap sizes. Herbaceous species increasing in harvest gaps included Actaea spp. L. (baneberry), Botrychium virginianum L. (rattlesnake fern), Mertensia paniculata Aiton (Northern bluebell), Rubus idaeus L. (red raspberry), Sanguinaria canadensis L. (bloodroot) and Cirsium arvense L. (Canada thistle). Results also indicated that subtle patterns were found among species spatial establishment within gaps (e.g., gap edge and gap center) and species that expressed no preference between the intact forest and harvest gaps. Levels of downed coarse woody debris (CWD) differed among gap size and all gaps had lower levels of CWD compared to the surrounding intact forest. Due to the historical importance of Betula alleghaniensis in these systems, the factors affecting the recruitment of this species were also investigated. Based on these investigations, it was found that B. alleghaniensis establishment was strongly related to highly decayed, large coniferous pieces of CWD with little recruitment occurring on the undisturbed forest floor. As such, providing appropriate seedbed conditions for shade mid-tolerant species and utilizing natural canopy gap sizes would improve the success of maintaining this species on the landscape.
  • Thumbnail Image
    Item
    The influence of stand stocking level on the growth and structure of managed old-growth northern hardwoods.
    (2010-09) Gronewold, Christopher Alan
    Summary abstract not available.
  • Thumbnail Image
    Item
    Response of Thuja occidentalis and Abies balsamea seedlings to stand manipulations in Northern Minnesota riparian forests.
    (2011-11) Haworth, Brooke Karen
    Northern white-cedar (Thuja occidentalis L.), a long-lived conifer closely associated with many riparian boreal forests of Minnesota, is an important species to riparian ecosystem health and to the forest products industry. Northern white-cedar is currently experiencing a decline in recruitment throughout much of its natural range, due primarily to herbivory by white-tailed deer (Odocoileus virginianus). Herbivory on northern white-cedar removes seedling and sapling size classes, and allows less browsed species (notably balsam fir (Abies balsamea (L.) Mill) to further displace the northern white-cedar forest component. This study examined practices that could encourage advance regeneration of northern white-cedar in the riparian setting. The role of partial overstory removal and forest floor microsite was tested on the development of planted 3-0 seedlings of northern white-cedar and the potentially competitive species of balsam fir. Seedlings were planted in mound, pit, and slash microsites (important to seedling germination and establishment) in partially harvested and unharvested riparian areas, and assessed for survival and growth over a four-year period. The test was duplicated inside and outside of fenced plots to evaluate the impact of deer browse and to more fully understand the current dynamic between species. Protected from herbivory, results indicated that partial harvest of the overstory contributed to significant seedling growth with both species demonstrating potential to recruit into taller height and larger basal diameter classes. Basal diameter growth rates were greater in northern white-cedar than balsam fir. Microsites of mound, pit, and slash did not contribute significantly to growth. Percent survival of northern white-cedar was greater than balsam fir, which experienced lower survival in controls. Due to seasonal flooding, pits had a significant negative effect on survival of both species. When protected from herbivory, planted northern white-cedar seedlings were shown to be good candidates for outplanting in a variety of riparian settings, particularly partial harvest areas, and were competitive with balsam fir seedlings for up to four years in the field. Percent browse frequency on unfenced seedlings was greater in harvest treatments and on mound microsites. Unfenced northern white-cedar seedlings were browsed at a significantly higher rate than balsam fir. Northern white-cedar showed significant mortality and no height increase in any treatments, with browse on seedlings overwhelming the benefits of overstory harvests. However, seedlings continued carbon allocation to basal diameter. In addition, northern white-cedar displayed survival resiliency, although reduced vitality, for the four years subjected to herbivory. Basal diameter increase and survival of browsed northern white-cedar seedlings are most likely due to their ability to replace browsed foliage in the current year. Unfenced balsam fir seedlings maintained growth responses to harvest treatments and did not experience significant mortality due to browse. Balsam fir seedlings exhibited the potential to recruit successfully into the overstory even under browse pressure, while northern white-cedar did not. Management activities that increase light availability while retaining some overstory structure, and selection of planting sites that limit or exclude browse, will result in the best chance for northern white-cedar seedlings to recruit into the sapling stage.
  • Thumbnail Image
    Item
    Selection of landscapes by male ruffed grouse during peak abundance.
    (2011-08) Kouffeld, Meadow Jean
    Most research on ruffed grouse (Bonasa umbellus) habitat selection has focused either on habitat structure within their activity centers or characteristics of forest stands containing activity centers. I studied the relationship between landscape configuration and density of male grouse during the high portion of their cycle. I located 290 and 230 male grouse during 2009 and 2010 respectively, on 30 landscapes encompassing 5,349 hectares. I used information theoretic model selection to examine two sets of a priori models. The top model in the first set was the null model (intercepts only), but a model representing Shannon‘s Evenness Index was competing. This competing model contained the second greatest cumulative weight (AICcwi = 0.203). Shannon‘s Evenness Index was positively correlated with male grouse density (R= 0.43). The effect of Shannon‘s Evenness Index within landscapes was difficult to interpret because it was confounded by cover type dominance in landscapes. The proportion of the aspen cover type was positively correlated (R= 0.55), and the proportion of the conifer cover type was negatively correlated (R= -0.79) with Shannon‘s Evenness Index. The top ranked model in my second set of models was based on road density and had the greatest cumulative weight (AICcwi= 0.52). Road density was negatively related to grouse density (R= -0.34), which could mean either that hunting pressure affects density or habitats were different in landscapes with higher road densities. The year only model indicated that male grouse density declined from 2009 to 2010 (βYear= -0.014, 95% CI = -0.024 to -0.005).