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Browsing by Subject "Aspen"

Now showing 1 - 6 of 6
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    Aspen Strip-Thinning Research Project: Summary Report
    (University of Minnesota Duluth, 1991-01) Berguson, William E; Buchman, Daniel
    Concern has been expressed by timber land managers, forest products industry representatives and the public, regarding the potential of Minnesota's aspen lands to supply sufficient raw material to meet anticipated demand. One way to address these concerns is to increase growth rates of natural aspen stands. Thinning has been shown to increase aspen productivity. Past research on manually-thinned aspen stands has demonstrated that reducing stand density by removing a portion of trees can accelerate growth rates of trees that are ultimately harvested. The goal of this project is to provide a cost-effective means to increase aspen supplies for the future. Thinning stands by hand is expected to be too expensive to justify widespread use. This research investigated the potential to increase growth rates of aspen stands through mechanical strip-thinning.
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    Impacts of woody biomass harvest on small mammals and plants in Northern Minnesota Aspen Forests
    (2014-05) Rentz, Michael S.
    Over the last decade, interest has grown in expanding the sources of energy produced in Minnesota, including burning wood alongside or in place of fossil fuels in commercial power plants. One possible source of this wood is through the harvest of residual material (hereafter "woody biomass harvest") left behind following traditional timber harvest. Although voluntary site-level harvest guidelines endorsed by the State initially called for the retention of residual material in the forest, the rules were modified in 2007 to allow for such harvest. It remained unclear, however, what, if any, ecological impacts woody biomass harvest could have in the region. I examined the immediate impacts of woody biomass harvest on small mammals and vegetation in 3 aspen (Populus spp) forests in northeast Minnesota. The study used of a "Before-After, Control-Impact" (BACI) design, with baseline surveys prior to treatment, follow up surveys after treatment, and a paired control that was not treated. I had two treatment categories: clearcut with slash left in situ (hereafter "slash-retention"), and clearcut with whole tree skidding and no replacement of residue (slash-removal). Each research site received a full complement of two treatments plus a control, giving me three replicates at each site.Prior to harvest, the stands contained an average coarse woody debris (CWD) density of 465 cm2/m2 (SE=49 cm2/m2). After harvest, the density of CWD increased in the slash-retention plots by an average of 422 cm2/m2, while slash-removal plots lost on average 29 cm2/m2. Prior to harvest there were no statistically significant differences in CWD density between treatments, but after logging CWD was higher in the retention than in the control plots, and higher in the control plots than in the removal plots.. In addition to gross changes in CWD area, the nature of the CWD in the harvested plots also shifted from initial conditions, with slash-retention plots gaining a disproportionate share of wood in less decayed conditions, while the slash-removal treatments shifted to a CWD base dominated by more decayed wood.Overall shrub stem counts increased similarly in both harvest treatments though more so in the slash-removal plots. Hazel (Corylus cornuta) stem counts increased by more than 3 stems/m2 in the slash-retention treatment, but stem counts were steady in the slash-removal treatment. Both treatments show a strong, similar regeneration of aspen stems after harvest (3-5 stems/m2).Both harvest types exhibited a decline in native forb species cover and an increase in bare ground, cover of non-native plants, and cover of graminoids compared to pre-existing conditions and associated control stands. Changes in native forb cover, non-native forb cover, and bare ground were greater in the slash-removal compared to the slash-retention treatment, but there was not a statistically significant difference between the plots for the increase in graminoid cover. Native species richness of survey plots 2 years post-harvest was not different from pre-harvest values for either treatment.In just over 29,000 trap nights I recorded 4,838 captures of 1,794 individual animals. I captured 15 mammal, 6 amphibian, and 1 snake species. Overall amphibian captures were low, but trended downward post-harvest in treatment plots. Population estimates of deer and white-footed mice (Peromyscus spp.) were little affected by treatment type or harvest status, while red-backed voles (Myodes gapperi) showed a positive response to harvest. Shrews (Sorex sinereus and Blarina brevicauda) and chipmunks (Tamias striatus) responded negatively to harvest of both types. The abundance of the communities overall (all individuals of all species lumped) were generally higher after treatment on the harvest sites than either before conditions or the adjacent controls, with slash-retention plots showing slightly greater gains than slash-removal plots.In conclusion, although many metrics responded similarly to either harvest type, in all cases where there were differences between the two treatments, the slash-removal treatment yielded a less favorable outcome for wildlife and a further shift from pre-treatment conditions than did the slash-retention treatment. This is especially true for the loss of native species cover, the increase in bare ground and non-native species cover, the loss of CWD, and the lower levels of C. cornuta. Although overall small mammal population sizes increased across both harvest types, increases were slightly greater for slash-retention treatments. Overall the results here do not warrant an avoidance of woody biomass harvest, but do argue for some caution, careful monitoring, and thoughtful siting. Future work should revisit these stands to assess longer term impacts.
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    Particleboard from Aspen Flakes and Sunflower Hulls
    (Minnesota Agricultural Experiment Station, 1972) Gertjejansen, R.O.; Haygreen, J.G.; French, D.W.
    Laboratory particleboards of 42 Ib/ft3 (pounds per cubic foot) nominal density were manufactured from sunflower hulls and 1/2" aspenflakes. Sunflower hull to aspen flake weight proportions were: 1:0 (all sunflower Hulls), 1:2, 2:1, and 0:1 (all aspen flakes). Although the addition of sunflower hulls reduced board strength and stability, Commercial Standard CS 236·66 minimum property requirements for modulus of rupture and modulus of elasticity were met by the 100% sunflower hull boards. However, the addition of approximately 50% aspen flakes would be required to meet the same minimum property requirements for internal bond strength and linear dimensional stability. Susceptibility to decay fungi increased with increasing sunflower hull content.
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    Productivity, recovery, diversity, and function of aspen-dominated forests vary in response to biomass harvest severity
    (2014-08) Curzon, Miranda Thomas
    Given uncertainty surrounding future climate and disturbance regimes, balancing objectives that include continuing to provide current forest products, meeting future resource demands, and maintaining ecosystem services presents a formidable challenge to forest managers. This research explored the short- and medium-term impacts of removing harvest residues for bioenergy feedstocks on aspen-dominated forests of the Lake States region. On sandy soils the removal of residues reduced standing biomass compared with stem-only harvest (SOH) 15 years after treatment, but no negative effect on aboveground biomass was observed following whole-tree harvest (WTH) on clayey or silty loam soils. Maximum diameter and the density of stems (> 5 cm diameter at breast height) declined on silty loam and sandy soils in response to increased severity in compaction and organic matter removal, respectively, indicating that structural development may be slowed. Although three species diversity measures and four functional diversity measures were used to assess community response to harvest disturbance, only indicator species analysis detected a functionally-relevant shift in community composition and structure that followed the most severe treatment combination on silty loam. This result highlighted the importance of employing multiple measures of diversity and composition to assess harvest impacts. Observations 2 years following bioenergy harvest with retention of aggregated overstory reserve trees indicate that both residue removal and overstory retention influence understory community composition. However, species diversity measures differed only between controls and disturbed areas (aggregates, SOH, WTH). Herbaceous plants considered interior forest obligates, such as Trientalis borealis, occurred in the aggregate understory, suggesting potential for small aggregates (0.1 ha) to serve as refugia for some species, at least in the short-term. Aspen sucker densities 0-5 m from the aggregate in the adjacent harvested areas were indistinguishable from densities 20 m from the aggregate edge, indicating ecological objectives might be achieved through aggregate retention without a trade-off in initial regeneration densities. Overall, results indicate that responses to the level of disturbance associated with harvest residue removal differ among sites, even when dominated by the same overstory species, but there is potential for severe disturbance to reduce standing biomass, shift community composition, and alter function and structure.
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    Stand Dynamics and Stand Development of Conventional and Mixedwood Aspen Systems in Northern Minnesota
    (2024-05) Semper, Chelsea
    In northern Minnesota, white spruce (Picea glauca (Moench) Voss) and aspen (Populus tremuloides Michx) mixedwood forests are important for timber production and ecological services. Traditionally grown in monoculture stands, little is known about the regeneration, growth, and yield of these species when managed in mixed compositions. 20 pure aspen and 20 mixedwood stands within a chronosequence of 0 – 23 years old in northern Minnesota were sampled to investigate stand differences. Forest inventory data were collected on seedlings, saplings, overstory trees, and non-tree understory cover, and forest modeling was conducted in Forest Vegetation Simulator (FVS) to simulate stand growth under different management scenarios. While aspen stands had higher density at regeneration and merchantable yield at harvest, mixedwoods maintained greater compositional and structural diversity throughout the rotation. Overall, white spruce-aspen mixedwood systems can provide opportunities for increased ecological services during early stand development without compromising on long-term timber-focused management goals.
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    Water Relations of the Aspens
    (Minnesota Agricultural Experiment Station, 1982) Sucoff, Edward