Browsing by Subject "oak savanna"

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    Content of leaf pigments of tree and grassland species collected at the Cedar Creek Ecosystem Science Reserve in 2015 and 2016
    (2020-09-01) Schweiger, Anna K; Fredericksen, Brett; Lapadat, Cathleen; Cavender-Bares, Jeannine; cavender@umn.edu; Cavender-Bares, Jeannine
    This data set contains the content of chlorophyll a, chlorophyll b, β-carotene, lutein, neoxanthin, violaxanthin, antheraxanthin and zeaxanthin pigments from tree and grassland species sampled at the Cedar Creek Ecosystem Science Reserve in East Bethel, MN. Mass- and area-based pigment contents were determined using high-performance liquid chromatography (HPLC). Data were collected as part of the Dimensions of Biodiversity project “Linking remotely sensed optical diversity to genetic, phylogenetic and functional diversity to predict ecosystem processes”. Samples were collected in or near the old fields chronosequence, the oak savanna, and the Forest and Biodiversity Experiment (FAB 1) plots. We used this data together with leaf-level spectral measurements to build partial least squares regression (PLSR) models for predicting leaf traits from spectra.
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    Fire suppression and ecosystem carbon storage
    (Ecological Society of America, 2000) Tilman, David; Reich, Peter B; Phillips, Hope; Menton, Mary; Patel, Ami; Vos, Erin; Peterson, David; Knops, J;
    A 35-year controlled burning experiment in Minnesota oak savanna showed that fire frequency had a great impact on ecosystem carbon (C) stores. Specifically, compared to the historical fire regime, fire suppression led to an average of 1.8 Mg·ha−1·yr−1 of C storage, with most carbon stored in woody biomass. Forest floor carbon stores were also significantly impacted by fire frequency, but there were no detectable effects of fire suppression on carbon in soil and fine roots combined, or in woody debris. Total ecosystem C stores averaged ∼110 Mg/ha in stands experiencing presettlement fire frequencies, but ∼220 Mg/ha in stands experiencing fire suppression. If comparable rates of C storage were to occur in other ecosystems in response to the current extent of fire suppression in the United States, fire suppression in the USA might account for 8–20% of missing global carbon.
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    Leaf carbon and nitrogen content of tree and grassland species collected at the Cedar Creek Ecosystem Science Reserve in 2015 and 2016
    (2020-09-01) Schweiger, Anna K; Lapadat, Cathleen; Cavender-Bares, Jeannine; cavender@umn.edu; Cavender-Bares, Jeannine
    This data set contains carbon and nitrogen content from combustion–reduction elemental analysis (TruSpec CN Analyzer, LECO) from tree and grassland species sampled at the Cedar Creek Ecosystem Science Reserve in East Bethel, MN. Data were collected as part of the Dimensions of Biodiversity project “Linking remotely sensed optical diversity to genetic, phylogenetic and functional diversity to predict ecosystem processes”. Samples were collected in or near the old fields chronosequence, the oak savanna, and the Forest and Biodiversity Experiment (FAB 1) plots. We used this data together with leaf-level spectral measurements to build partial least squares regression (PLSR) models for predicting leaf traits from spectra.
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    Leaf carbon fraction data from tree and grassland species collected at the Cedar Creek Ecosystem Science Reserve in 2015 and 2016
    (2020-08-12) Schweiger, Anna K; Lapadat, Cathleen; Kothari, Shan; Cavender-Bares, Jeannine; cavender@umn.edu; Cavender-Bares, Jeannine
    This data set contains results from carbon fraction analysis (Fiber Analyzer 200, ANKOM Technology), including non-structural carbohydrates, hemicellulose, cellulose, lignin, neutral detergent fiber, and acid detergent fiber contents in percent (%) from tree and grassland species sampled at the Cedar Creek Ecosystem Science Reserve in East Bethel, MN. The data was collected as part of the Dimensions of Biodiversity project “Linking remotely sensed optical diversity to genetic, phylogenetic and functional diversity to predict ecosystem processes”. Samples were collected in or near the old fields chronosequence, the oak savanna, and the Forest and Biodiversity Experiment (FAB 1) plots. We used this data together with leaf-level spectral measurements to build partial least squares regression (PLSR) models for predicting leaf traits from spectra.
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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.
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    A Resilience-Based Site Assessment Tool For Oak Savanna Restoration Practice
    (2020-06) Chien, Eric
    Practitioners of ecological restoration are faced with making sense of a wide range of information and generating conclusions about recovery potential that can inform effort and planning. In this thesis I use resilience theory to provide a framework for generating insights about ecological dynamics of ecosystems that tie directly to fundamental restoration assessment challenges. The design and function of resilience assessments needs to be informed by theory-based concepts as well as the needs and practice constraints of practitioners. There are few examples of resilience-based site assessments for restoration despite the theoretical link between resilience and fundamental practical restoration questions. Mid-continental North American oak savanna is introduced as a model system in which to design, test, and validate a resilience assessment for restoration practice. The objective was to create a tool that could reliably assess current condition of prospective restorations and diagnose recovery potential and dynamics. Beginning with defining the range of possible intact and altered states for a given ecosystem, this resilience assessment uses practically measurable attributes to gauge the recovery potential of a site. Resilience attributes include those that confer resistance to likely disturbances and regeneration ability for both desired and altered state features. The tool was initially designed through a process of rapid prototyping using academic and management literature and broad scoping of oak savanna restoration practitioners and projects. The design process included parameterizing the tool using field data from 47 oak savanna restoration projects. A refined, fully operational tool was then field tested by new and experienced practitioners for its usability, consistency, and validity. Results from tool testing showed the tool effectively supported consistent conclusions about site condition and recovery. Relative to using unstructured narrative site assessment, tool-supported practitioners used an expanded quantity of ecological information in site assessment, and the tool facilitated transparent decision-making with collected information. The validation approach was hampered by a limited ability to compare conclusions between tool-supported practitioners and unstructured expert assessments, as well as a lack of available pre-restoration starting condition information to retroactively populate the entire assessment tool using restoration case histories. With modifications to the validation approach, the process documented for the design and testing of a resilience-based site assessment of oak savannas has potential to serve as an effective model for expanding the development of similar tools for the restoration of other terrestrial ecosystems.
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    Shocks to the system: Community assembly of the oak savanna in a 40-year fire frequency experiment
    (Ecological Society of America, 2012) Cavender-Bares, Jeannine; Reich, Peter B
    Fire is a major force driving the evolution of plants and the structure and function of ecosystems globally. It thus likely operates as an important environmental filter that selects for species that have evolved to tolerate and depend on fire. Across a 40-year experimental fire gradient from frequently burned open savanna to unburned dense woodland in Minnesota, USA, we examined the relationships among community assembly, evolutionary history, and functional trait composition. Close relatives had similar abundance patterns across the fire gradient, providing evidence for phylogenetic conservatism in fire adaptation and highlighting the importance of shared ancestry in predicting species responses to fire. Phylogenetic beta diversity was greatest between the most extreme fire treatments across the gradient, indicating that species in the most contrasting fire regimes were most distantly related. Fire strongly influenced diversity, co-occurrence patterns, and leaf trait means and variances within communities. The most frequently burned communities had the highest species richness, exhibited the most resource-conservative leaf traits, and spanned the greatest number of phylogenetic lineages but harbored more close relatives within those lineages than other communities. In contrast, unburned communities had the lowest species diversity, the most acquisitive leaf traits, and the fewest phylogenetic lineages, but close relatives co-occurred less frequently. The largest difference in abundance between treatments occurred within the Rosales, Asteraceae, Vitaceae, and the Poaceae; woody Rosales were strongly selected for in unburned communities, while composites and grasses of the Poaceae were strongly selected for under frequent burning. A major climatic perturbation of consecutive hot, dry summers in the late 1980s prompted a significant shift in the functional and phylogenetic composition of communities. Greater than expected turnover in species composition occurred following the drought years, and then again during the subsequent five-year rebound period. Just after the drought year, turnover was greatest among recently diverged taxa, whereas during the rebound period turnover was greater among taxa that diverged deep in the phylogeny. The drought years also caused a short-term shift in functional traits, including declines in specific leaf area and leaf nitrogen content and an increase in leaf length. These results indicate that the phylogenetic and functional trait composition of communities are responsive both to fire gradients and to shocks to the system, such as climatic perturbation.