Browsing by Subject "Quercus macrocarpa"

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    Consequences of plant function for species distributions, fitness, and community assembly across latitudinal and altitudinal gradients
    (2024-05) Rea, Lucy
    Understanding which adaptations are beneficial in different climates is a question that has intrigued plant ecologists for centuries. Alexander von Humboldt is one of the first to document how plant communities change with elevation in the Ecuadorian Andes in 1824 (Humboldt, 1805). Such altitudinal or latitudinal gradients are still useful to ecologists today to address a broad swatch of ecological and evolutionary questions, including how environmental conditions shape community assembly and interspecific diversity, by learning how species function in different environments. Understanding how plants function in different environments allows us to predict the distribution and range of a species and identify the filters that lead to plant communities. With climate change ongoing, understanding of the abiotic processes that shape ecological communities and species ranges is especially critical. As the Earth’s climate warms, cooler climates are expected to shift to higher latitudes and elevations. There is evidence that species ranges are already shifting, for example much of the new growth of North American trees is further north than older members of the species, indicating a shift northward in the populations (Woodall et al., 2009). My overall research goal is to understand how plant function varies across environmental gradients and how that affects species distributions and community assembly. To this end, I have conducted field-based research on plants across latitudinal and altitudinal gradients.
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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.