Browsing by Subject "Dendroecology"

Now showing 1 - 4 of 4
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    Dynamics of old-growth forests of Minnesota.
    (2009-08) Rauchfuss, Julia
    Disturbances are an essential part of almost every ecosystem. I studied disturbances in three different old growth forests in Minnesota. These old-growth remnants include the white and red pine forest of the Lost 40 in northern Minnesota, the balsam fir and white spruce forest at Itasca State Park in northern Minnesota, and the hardwood forest of the Big Woods in south-central Minnesota. In the Lost 40, white and red pine are not regenerating and shade-tolerant trees are abundant in the understory and canopy. This lack of regeneration is probably due to the lack of a disturbance like fire. If a management plan were to be implemented, the advancement of the shade-tolerant species into the canopy and the shifting climate space of white and red pine need to be taken into consideration. The white and red pines in Itasca State Park are actively managed, but not the fir-spruce forest. Now, mature fir-spruce forest is dying because of a recent spruce budworm outbreak. Spruce budworm, a defoliating insect that prefers balsam fir and spruce, has been in the park before the most recent outbreak. Before the two outbreaks that were reconstructed, the climate was wet, whereas other studies found dry conditions before an outbreak of the spruce budworm. In reconstructing canopy disturbances of eight remnants, I tested several methods for evaluating canopy disturbance in closed canopy forests. The sequential t-test (regime shift) method had best results when reconstructing canopy disturbances of these forests. I then used the sequential t-test method to reconstruct the canopy-disturbance history. Although a drought-disturbance relationship was detected by other authors, I did not find a consistent relationship in my data. I studied three different old-growth forests in Minnesota. In these stands, disturbances are an integral part. Methods of disturbance-history reconstructions were tested and one (sequential t-test) subsequently used. I made contributions to reconstructing canopy disturbances using release and suppression periods in tree rings of forest types that previously had not been studied this way. The information that I gathered could now be used to inform a management plan, to apply a possibly more precise method to reconstruct a canopy-disturbance history, and to inform the public.
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    Mixed-Silver Maple Forests Of The Upper Mississippi River Floodplain: Variations In Composition, Structure, And Growth Along Environmental Gradients
    (2020-05) Nielsen, Daniel
    Floodplain forests of the Upper Mississippi River are characterized by complex interactions between biota and the physical environment, specifically aspects of hydrology. The role of environmental variation in overstory composition, structure, and growth is not well documented. Goals of this study were to 1) characterize current stand conditions along gradients of inundation and relative elevation, and 2) describe growth patterns of silver maple (Acer saccharinum L.) trees, and their relationship to hydrological patterns. Patterns of forest composition and structure were more similar for plots comprising similar environmental conditions than plots within a stand, suggesting that current methods of stand delineation do not capture the full extent of within-stand environmental variation. I found evidence that growth patterns of silver maple had positive relationships to hydrology at a plot-level and a stand-level. These results suggest that forest managers may need to “rethink” how they summarize stand condition and develop silvicultural prescriptions.
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    Structure, dynamics, and climate sensitivity of range-margin jack pine forests in central Minnesota
    (2014-12) Gill, Kyle Gregory
    Species' ranges are expected to shift in response to changes in climate and disturbance regimes. Individuals and populations along the edge of their range are expected to be most affected because of their proximity to climatically limiting factors and the unique dynamics relative to non-marginal portions of their range. However, limited empirical knowledge exists concerning the historic range of ecological variability in range-margin populations and systems.Jack pine (Pinus banksiana) reaches its southwestern range limit in central Minnesota where it displays traits, including low-levels of cone serotiny, that differ from other portions of its range. However, the stand dynamics (establishment, age structures, and disturbance regimes) and linkages with climate have never been documented for these populations. Our aim was to quantify the natural range of variability of stand dynamics and climate relationships to establish reference conditions for monitoring future climate impacts, informing refinement of forest ecosystem models, and assisting in the development of management decisions for conservation.Our results indicate that jack pine stands in this region are structurally complex even and un-even aged systems that follow a variety of developmental pathways. These patterns are attributed to the non-serotinous cones of jack pine in this region, which allow for both episodic and extended recruitment patterns over time. Annual growth and recruitment were both significantly sensitive to moisture and temperature variables, especially during the winter-to-spring transition, yet the directionality of associations displayed much seasonal variation. Our results suggest that management and modeling practices should be broadened to account for the variety of structural conditions and developmental pathways that historically characterized these range-margin jack pine forests. Such changes will help to conserve jack pine forests for the short-term while promoting the propensity for long-term resilience and adaptability.
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    Tree rings detect earthworm invasions and their effects in northern Hardwood forests
    (2010) Larson, Evan R; Kipfmueller, Kurt F; Hale, Cindy M; Frelich, Lee E; Reich, Peter B
    Invasions of European earthworms into the forests of northern North America are causing dramatic changes in forest floor structure, vegetation communities, biogeochemical cycling, and site hydrology. However, long-term studies on the effects of invasive earthworms are limited because little data exist on the timing and rate of earthworm invasion at specific sites. We successfully used tree rings to identify the timing of earthworm invasions and the effects of earthworm activity on the Acer saccharum overstory of two recently invaded sites in northern Minnesota, thereby establishing a method to date earthworm invasions at other sites. In addition to identifying a tree-ring signature related to earthworm invasion, we found trees growing in invaded conditions were more sensitive to drought than trees growing in earthworm-free conditions. Increased drought sensitivity by A. saccharum has important implications for possible range shifts under climate change scenarios that include increasing drought frequency and severity.