Browsing by Subject "stand dynamics"

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    Effects of Eastern Spruce Dwarf Mistletoe (Arceuthobium Pusillum Peck) Infestation in Lowland Black Spruce (Picea Mariana (Mill.) B. S. P.) at Multiple Scales
    (2022-05) Gray, Ella
    Forests are shaped by stand dynamics and disturbances. Knowledge of the effects and interactions of these dynamics is important for understanding the processes that determine forest structure and composition and inform management decision making. Our understanding of the role of disturbances in stand dynamics has shifted over time, with the view that they are important components of forest development, rather than an external influence. This view has influenced management actions, with an increase in disturbance-based silvicultural prescriptions. For these prescriptions to be effective in mimicking post-disturbances conditions, the effects of the disturbance of interest should be well understood across multiple scales. Here, I investigated the effects of a native, morality-causing disturbance agent, eastern spruce dwarf mistletoe (Arceuthobium pusillum Peck; hereafter ESDM), on lowland black spruce (Picea mariana (Mill.) B. S. P.) forests of Minnesota. Using a combination of observational field studies and statistical modeling of publicly available large-scale datasets, effects of ESDM infestations across multiple scales were quantified and their influence on stand dynamics and management were assessed. Results show ESDM to be a complex disturbance agent, with effects manifesting differently at the tree, stand, and landscape scales. ESDM infestations result in increased species diversity and structural heterogeneity at sub-stand scales, with implications for landscape-scale diversity. As forestry continues to implement disturbance-based forest management, the management of black spruce in the presence of ESDM should reflect these complex effects, by assessing the trade-offs of infestation to different ecosystem services.
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    Prescribed fire in oak savanna: Fire frequency effects on stand structure and dynamics
    (2001) Peterson, David W; Reich, Peter B
    Although it is well known that fire can exert strong control on stand structure, composition, and dynamics in savannas and woodlands, the relationship between fire frequency and stand structure has been characterized in few of the world's savanna and woodland ecosystems. To address this issue in temperate oak-dominated ecosystems, we studied the effects of fire frequency on stand structure and dynamics in oak savanna and woodland stands that had been burned 0–26 times in 32 yr, in the Anoka Sand Plain region of Minnesota (USA). Seedling densities declined with increasing fire frequency, but differentially, for northern pin oak (Quercus ellipsoidalis), black cherry (Prunus serotina), serviceberry (Amelanchier sp.), and red maple (Acer rubrum). Bur oak (Q. macrocarpa) seedling density was not sensitive to fire frequency. Frequent burning (at least three fires per decade) prevented development of a sapling layer and canopy ingrowth. Low-frequency burning (fewer than two fires per decade) produced stands with dense sapling thickets. Reductions in overstory density and basal area from 1984 to 1995 were observed for all stands burned two or more times during that period. Basal area declined by 4–7% per year, and density declined by 6–8% per year in stands burned four or more times. Mortality rates in burned stands were higher for northern pin oak (50%) than for bur oak (8%). Northern pin oak mortality was highest for small trees (< 20 cm dbh) and lowest for mature trees (30–40 cm dbh); mortality increased with fire frequency. Bur oak mortality declined with increasing fire frequency. Attempts to preserve and maintain savannas as a viable ecosystem type in this region will require a long-term commitment to restoration-based management, with prescribed fire as a central tool. Burn frequency treatments with four or more fires per decade produce similar reductions in stem density and stand basal area but may lead to unsustainable oak tree populations. Within this general range, fire frequencies at a decadal scale should be chosen to address other management objectives, including suppressing shrubs and promoting increased cover of grasses and other herbaceous species. Fire management with a long-term view may also require periodic respites to allow for new cohorts of mature oak trees.