Browsing by Subject "Disturbance"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Assessing the impacts of forest disturbances on stand and individual tree growth in the Lake States
    (2016-06) Glasby, Mack
    Forest disturbances cause changes in site conditions and forest structure which in turn influences the species composition of the site. This study utilized Forest Inventory and Analysis (FIA) annual plot data collected between 1999 and 2014, in Michigan, Minnesota, and Wisconsin to analyze the impacts of disturbance across the region. The study also analyzed the accuracy of the Forest Vegetation Simulator- Lake States (FVS-LS) diameter growth equation in disturbed and non-disturbed forests. Results showed that animal and weather disturbances were the most common disturbance agents in the region, while human-caused disturbance (excluding timber harvesting) resulted in the largest losses in live and standing dead tree basal area. Results indicated that the FVS-LS diameter growth equations performed well on average, but when the data were grouped by species or disturbance, the model equation was rarely validated using equivalence tests. Findings highlight the importance of incorporating forest disturbance into tree and stand growth and yield projections.
  • Thumbnail Image
    Item
    Multiple Disturbances and the Turbulent Forest
    (2023-08) Reed, Samuel
    I have always been drawn to change, whether I liked it or not. As a kid, I was obsessed with dinosaurs and their extinction, all while having to move constantly as a Navy brat. As an adult, I am devoted to understanding how and why systems change, likely inspired by the unending change of my childhood. However, as I matured, I realized that change is almost never spurred by a single event, but rather a multitude of shocks to the system. This dissertation focuses on the complexity of multiple ecological disturbances and highlights their importance in the world. Using several multi-disturbance experiments, I explore a wide variety of disturbance interactions in the temperate deciduous forest. The first chapter of this dissertation focuses on how deer and canopy gaps influence invasive earthworms, shedding new light on how aboveground events can change belowground communities. The second chapter builds upon the first and tests how combined deer and canopy gaps influence understory regeneration over 15 years, with some reference to invasive earthworms. Lastly, the third chapter explores how combined fire, deer, and canopy gaps change the seed bank over 13 years. Each of the aforementioned disturbances are common and influential in eastern forests, although they are not often studied together. In each chapter we find that community responses vary depending on the disturbances in question. This dissertation is meant to highlight how little we know about the many ways in which multiple disturbances change ecosystems and how critical it is that we start to study these complex drivers of change, particularly as the climate warms and disturbances become more frequent on the landscape.
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    Winter-emerging chironomidae (Insecta: Diptera) in Minnesota trout streams
    (2012-12) Anderson, Alyssa Mae
    The Chironomidae (Diptera) is among the few aquatic insect families with species that are reliably able to grow, develop, and emerge as fully functional adults throughout the cold winter months that characterize the midwestern United States. However, few studies document their role in trout streams during this time of year. The intent of this dissertation is to enhance the field of Chironomidae research by focusing on the winter dynamics of these insects, including their response to severe flood events, their incorporation in the winter diet of trout, and the morphological and molecular description of three new cold-adapted Chironomidae species. The resistance and resilience of the winter chironomid community was assessed following a severe flood that impacted many streams in southeast Minnesota during the late summer of 2007. Methodology included collections of chironomid surface-floating pupal exuviae from 18 southeast Minnesota streams; streams were selected to include representation of localities that incurred moderate to extreme levels of flooding disturbance. These data were compared to data from the same localities during prior winters. Significantly more taxa emerged during the winter after late-summer flooding as compared to historic collections, and the number of species emerging in winter was positively correlated with rainfall severity, indicating the winter-active Chironomidae are resistant to late summer spates. This indicates that chironomids are an available winter food resource to stream trout recovering from devastating floods. In attempt to examine the importance of Chironomidae and other winter-active aquatic insects to the winter diet of brown trout (Salmo trutta L.), stomach contents were collected from trout inhabiting three southeast Minnesota streams; these data were compared to organisms collected in the stream drift and benthos. Results indicated that trout diets differ by stream and by fish size, with larger trout feeding heavily on Trichoptera and Physella, and smaller fish relying more on Gammarus and Chironomidae larvae. Stomach contents were more similar to the benthos than the drift, indicating a greater reliance on benthic feeding during winter. Trout in all streams selected Trichoptera and Chironomidae over other prey, and appeared to maintain sizeselective predation throughout winter. Winter-emerging Chironomidae appear to enhance the trout diet in all streams, and chironomid larvae were particularly dominant in the diet of one trout population. Three new chironomid species within the genus Micropsectra, a genus commonly found in the winter trout diet, were discovered from a study of five Minnesota streams. These species, Micropsectra neoappendica, n. sp., Micropsectra penicillata, n. sp., and Micropsectra subletteorum, n. sp., were described using morphological and molecular methods, along with one additional species, Micropsectra xantha Roback, which was redescribed. Two of the new species initially appeared identical to species known from the Palearctic, however molecular data indicated they are genetically distinct. Subsequently, reexamination of morphological characters revealed slight, but consistent diagnostic differences. These results emphasize the importance of using molecular tools in conjunction with traditional morphological techniques when studying Chironomidae diversity, especially when relying on diagnoses from other regions. The culmination of these studies sheds light on the dynamics of winter-emerging Chironomidae in southeastern Minnesota trout streams, their distribution and abundance, and the larger role they play in stream communities.