Browsing by Subject "fire"
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Item Butterfly Responses To Management Of Disturbance-Dependent Ecosystems In North America And Australia.(2021-09) Leone, JuliaFire and grazing are primary sources of natural disturbance in grasslands and savannas worldwide, but they are also shaped by human impacts and decision-making. Appropriate management is therefore an essential goal for biodiversity conservation in disturbance-dependent landscapes. The butterflies which inhabit these ecosystems are reliant on the disturbances necessary for grassland and savanna persistence. Regular fire, herbivory, and drought shape and maintain these ecosystems, keeping woody plants from dominating. How, then, do butterflies persist and respond to disturbance in their chosen habitats? What management regimes are required in human-altered landscapes to conserve grassland and savanna butterfly biodiversity? I examine butterfly responses to management of disturbance-dependent ecosystems in North American and Australian using both taxonomic and functional trait lenses. In Chapter 1, I assess the impacts of current fire and grazing management regimes on butterfly communities in Minnesota tallgrass prairie and compare butterfly and bee responses to management. In Chapter 2, I assess the impacts of these same fire and grazing regimes on monarch butterflies (Danaus plexippus) and their milkweed host plants in Minnesota tallgrass prairie. In Chapter 3, I examine butterfly and butterfly resource responses to fire regimes in Australian tropical savanna, and in Chapter 4, I demonstrate the utility of trait-based ecology to explain global and mechanistic patterns in butterfly responses to fire by presenting and comparing butterfly traits associated with fire regimes in U. S. temperate prairie and Australian tropical savanna. I present findings that butterfly and bee abundances in tallgrass prairie are significantly negatively correlated. Butterfly abundance, but not species richness, is nearly twice as high at tallgrass prairie sites managed with fire compared to grazing, and prairie-associated grass-feeding butterflies are more abundant at sites with higher plant species richness. I find that monarch butterflies are also more abundant at tallgrass prairie sites managed with fire than with grazing, and that this association is not related to milkweed or forb frequencies, which are similar between burned and grazed prairies. In Australian tropical savanna, I find that recent, early dry season burning promotes butterfly diversity and abundance by increasing the supply of nectar resources in tropical savanna fire treatments. In my evaluation of butterfly traits associated with fire, diapause strategy, host plant specificity, wingspan, voltinism, and flight period are all associated with at least one fire treatment, but trait associations are not shared across Australian tropical savanna and U.S. temperate prairie. In tallgrass prairie, land managers and conservation practitioners interested in promoting butterfly abundance and diversity may consider increasing plant species richness and maintaining fire in the landscape. Because species composition differs between sites managed with fire and grazing and among sites managed for different numbers of years, I suggest a variety of management strategies is required to support the entire suite of butterfly species. In tropical savanna, land managers and conservation practitioners can ensure some areas of recent, early-season fire are maintained and focus on additional actions that will promote floral resource abundance and diversity, which will benefit butterflies as well as many other animal taxa. Trait-based ecology methods can help us understand the role of traits such as diapause strategy, host plant specificity, wingspan, voltinism, and flight period in explaining general patterns in butterfly responses to fire. However, to inform good conservation and management, trait-based findings should be tied back to the local species and landscapes being managed. The second chapter of this dissertation is published in Frontiers in Ecology and Evolution (Leone et al. 2019) and the first chapter is currently under review with the Journal of Insect Conservation. As a reflection of the collaborative nature of the work I present, I will use the first-person plural voice “we” throughout the rest of this dissertation.Item Data supporting: Century-scale wood nitrogen isotope trajectories from an oak savanna with variable fire frequencies(2020-09-09) Trumper, Matthew L; Griffin, Daniel; Hobbie, Sarah E; Howard, Ian M; Nelson, David M; Reich, Peter B; McLauchlan, Kendra K; trump022@umn.edu; Trumper, Matthew L; University of Minnesota Griffin Research LabFire frequency exerts a fundamental control on productivity and nutrient cycling in savanna ecosystems. A single fire event often increases short-term nitrogen (N) availability to individual plants, but repeated burning causes ecosystem carbon and N losses and can ultimately decrease soil organic matter and N availability. However, these effects remain poorly understood due to limited long-term biogeochemical data. Here, we leveraged one of the longest running prescribed burn experiments (established in 1964) to evaluate how fire frequency and changing vegetation composition influenced wood stable N isotopes (δ15N) across space and time. We developed multiple δ15N records across a burn frequency gradient from precisely dated Quercus macrocarpa tree-rings in an oak savanna at Cedar Creek Ecosystem Science Reserve, Minnesota, USA. Sixteen trees were sampled across four treatment stands that varied in temporal onset of burning and burn frequency, but were consistent in overstory species representation, soil characteristics, and topography. Burn frequency ranged from an unburned control stand to a high fire-frequency stand that burned in four of every five years during the past 55 years. Because N stocks and net N mineralization rates are currently lowest in frequently burned stands, we hypothesized that wood δ15N trajectories would have declined over time in all burned stands, but at a rate proportional to fire frequency. We found that wood δ15N records within each stand were remarkably coherent in their mean state and trend through time. A gradual, temporally synchronous decline in wood δ15N occurred in the mid 20th century in the no-, low-, and medium-fire stands, whereas there was no trend in the high-fire stand. The decline in the three stands did not systematically coincide with the onset of prescribed burning. Thus, we found limited evidence for variation in wood δ15N that could be attributed directly to long-term fire frequency in this prescribed burn experiment in temperate oak savanna. Our wood δ15N results may instead reflect decadal-scale changes in vegetation composition and abundance due to early to mid 20th century fire suppression.Item Ectomycorrhizal fungal communities of oak savanna are distinct from forest communities(2009) Dickie, I A; Dentinger, B T M; Avis, P G; McLaughlin, D J; Reich, Peter BOak savanna is one of the most endangered ecosystems of North America, with less than 0.02% of its original area remaining. Here we test whether oak savanna supports a unique community of ectomycorrhizal fungi, a higher diversity of ectomycorrhizal fungi or a greater proportional abundance of ascomycete fungi compared with adjacent areas where the absence of fire has resulted in oak savanna conversion to oak forest. The overall fungal community was highly diverse and dominated by Cenococcum geophilum and other ascomycetes, Cortinarius, Russula, Lactarius and Thelephoraceae. Oak savanna mycorrhizal communities were distinct from oak forest communities both aboveground (sporocarp surveys) and belowground (RFLP identification of ectomycorrhizal root tips); however total diversity was not higher in oak savanna than oak forests and there was no evidence of a greater abundance of ascomycetes. Despite not having a higher local diversity than oak forests, the presence of a unique fungal community indicates that oak savanna plays an important role in maintaining regional ectomycorrhizal diversity.Item Evaluating Landscape and Local Drivers of Pollination in Melittophilous Tallgrass Prairie Forbs: Effects of Surrounding Land-use on Pollen Limitation of Chamaecrista fasciculata & Prescribed Burning on Flowering and Pollination of Dalea purpurea(2020-01) Ritchie, AlanTallgrass prairies are one of the most endangered ecosystems in North America. Habitat loss and degradation of remaining prairies threaten both the biodiversity and functioning of these ecosystems. At the landscape scale, loss and fragmentation of existing prairie may limit regional pools of species and abundance of individuals, hampering movement of plants and animals between suitable habitats. At the local scale, degradation of prairies has been exacerbated by loss of native grazers and suppression of fire, the major ecological forces that historically shaped prairie species and communities. While the impacts of these factors on biodiversity in prairies is well-established, little is known about the role of these factors on plant-pollinator interactions, an important ecological process for many prairie forbs. As restoration of prairie habitats is one of the chief means of protecting prairie habitats and biodiversity, evaluating the roles of these factors in mediating ecological processes such as pollination will be critical to their reconstruction. Within this thesis, I explore how two important aspects of habitat restoration management, landscape context and prescribed burning, influence pollination in two common, widespread prairie forbs reliant on insects, namely bees, for pollination. The findings of these studies serve as initial assessments of two under-explored topics with relevance to tallgrass prairie conservation: how placement of a restoration effects recruitment of pollinators and the pollination they provision a habitat, and how animal-mediated pollination influences prescribed burning’s effects on plant reproduction.Item Fire Affects Ecophysiology and Community Dynamics of Central Wisconsin Oak Forest Regeneration(1990) Reich, Peter B; Abrams, Marc D; Ellsworth, David S; Kruger, Eric L; Tabone, Tom JIn order to understand better the ecophysiological differences among competing species that might influence competitive interactions after, or in the absence of, fire, we examined the response to fire of four sympatric woody species found in intermediatesized gaps in a 30-yr-old mixed-oak forest in central Wisconsin. Selected blocks in the forest were burned in April 1987 by a low-intensity controlled surface fire. The fire had significant effects during the following growing season on community structure, foliar nutrient concentrations, and photosynthesis. Acer rubrum seedling density declined by 70% following the fire, while percent cover increased several-fold in Rubus allegheniensis. In general, leaf concentrations of N, P, and K were increased by the fire in all species, although the relative enhancement decreased as the growing season progressed. Daily maximum photosynthetic rates were 30-50% higher in burned than unburned sites for Prunus serotina, Quercus ellipsoidalis, and R. allegheniensis, but did not differ between treatments for A. rubrum. Mean sunlit photosynthetic rates and leaf conductances were stimulated by the burn for all species, with the greatest enhancement in photosynthesis measured in Q. ellipsoidalis. Leaf gas exchange in R. allegheniensis was most sensitive to declining leaf water potential and elevated vapor pressure gradient, with Q. ellipsoidalis the least sensitive. Fire had no discernable effect on water status of these plants during a year of relatively high rainfall. In comparison with other species, A. rubrum seedlings responded negatively after fire-both in terms of survival/reproduction (decline in the number of individuals) and relative leaf physiological performance. Fire enhanced the abundance of R. allegheniensis and the potential photosynthetic performance of R. allegheniensis, P. serotina, and particularly Q. ellipsoidalis. We conclude that post-fire stimulation of net photosynthesis and conductance was largely the result of enhanced leaf N concentrations in these species.Item Impacts of Prescribed Burns and Severe Weather Events on Oak Wilt Transmission in Central Minnesota(2020-12) Ostlie, JamesEcological disturbances of a region shape the landscape and influence ecosystem structure and function. However, in a rapidly changing world, newly introduced disturbances such as diseases and pests interact with historical disturbance regimes in unknown ways. The purpose of this thesis was to identify relationships between oak wilt, a catastrophic disease of oak trees introduced to Minnesota in the 1940s, and two historical disturbances of central Minnesota: low intensity fires and severe weather events. 1. The relationship between fire frequency and oak wilt occurrence was explored using a prescribed burning program at Cedar Creek Ecosystem Science Reserve. Using data collected from a census of 1,700 oak trees located on 28 different burn plots, two descriptive models were created: a logistic regression model to describe the probability of oak wilt presence and a Poisson regression model to describe density of stems with oak wilt. High fire frequency plots had lower oak wilt probability and oak wilt stem density than low fire frequency plots. Oak wilt presence was lower in high fire frequency plots than low fire frequency plots as well. These results suggest there is a relationship between high fire frequency and reduced probability of oak wilt presence and oak wilt stem densities. This relationship provides preliminary support for the use of prescribed burning as a possible management tool in conjunction with existing control measures. 2. The relationship between severe weather events (wind speeds > 50 knots and/or recorded hail amounts) and new oak wilt infection site was examined using NOAA’s severe weather events database and Minnesota DNR oak wilt aerial surveys for Anoka County. New oak wilt pocket formation occurred more frequently in areas where a severe weather event occurred the previous year. These results suggest severe weather events increase the probability of aboveground transmission of oak wilt via insect vectors and the likelihood of new oak wilt pocket formation. This relationship can be used to prioritize recently storm-damaged areas for more focused surveying in order to increase the success of early oak wilt detection. The relationships between fire frequency, severe weather events, and oak wilt presented within this thesis provide a framework for future adaptations and research to further inform oak wilt detection and management practices.Item Post-Fire Associations Of Butterfly Behavior, Occupancy, And Abundance With Environmental Variables And Nectar Sources In The Sierra Nevada, California(2015-12) Pavlik, DavidFire can alter the quality of habitat for butterflies. Fire also affects environmental attributes associated with the distribution, abundance, and reproduction of butterflies. The effects of fire on butterfly occupancy, and on environmental attributes that are associated with butterfly occupancy, are largely unknown. In 2014 and 2015, we conducted butterfly and vegetation surveys within the Rim Fire boundary in California. We analyzed sugar and sucrose masses, and proportion of sucrose, in 20 nectar sources. We found no evidence that intensity of use was associated with sugar mass, mass of sucrose, or the relative proportion of sucrose. We found that environmental attributes associated with occupancy of some species were also associated with the abundances of those species. Burn severity affected environmental attributes that were associated with butterfly occupancy and abundance. Understanding how fire affects environmental attributes associated with occupancy and abundance can inform use of prescribed fire or management following wildfire.Item Recovery of grassland plant communities after cessation of nutrient enrichment(2020-08) Portales Reyes, Maria CristinaDiversity is declining in many ecosystems, resulting in rates of extinction much greater than what is expected based on the fossil record. Species declines can be attributed to human activities drastically changing ecosystems by increasing rates of nutrient inputs, altering precipitation and disturbance regimes, destroying habitat, and reducing landscape connectivity. If we are to preserve a considerable fraction of the species in our planet and our ability to enjoy the benefits we derive from them, direct and immediate action informed by science is necessary. My dissertation research investigates a small piece of this large puzzle. Here, I present results from three long-term nutrient addition and cessation experiments where I study barriers for the recovery of grassland plant diversity after cessation of long-term nutrient inputs, and explore strategies to prevent further species losses. First, I study the role of potential reinforcing feedbacks involving soil microbial communities and plant mutualists that could prevent the recovery of plant diversity after cessation of nutrient enrichment. I then explore the effectiveness of common restoration strategies that aim to further reduce nutrient inputs, increase light availability, and reduce recruitment limitation. Finally, I evaluate whether prescribed burning can slow rates of species loses and promote recovery of diversity after reducing nutrient inputs. While unassisted recovery of diversity might be impossible or slow, my dissertation provides experimental evidence that ecosystem management can help maintain local diversity. In particular, seed addition and prescribed burning are both useful strategies for promoting the recovery of grassland plant diversity following reductions in nutrient inputs.Item Supporting data for The hidden value of trees: Quantifying the ecosystem services of tree lineages and their major threats across the contiguous US(2021-06-29) Cavender-Bares, Jeannine; Nelson, Erik; Meireles, Jose Eduardo; Lasky, Jesse R; Miteva, Daniela A; Nowak, David; Pearse, William D; Helmus, Matthew; Zanne, Amy E; Fagan, William; Mihiar, Christopher; Muller, Nicholas Z; Kraft, Nathan; Polasky, Stephen; cavender@umn.edu; Cavender-Bares, JeannineTrees provide critical contributions to human well-being. They sequester and store greenhouse gasses, filter air pollutants, and provide wood, food, and other products, among other benefits. These benefits are threatened by climate change, fires, pests and pathogens. We show that the value of ecosystem services generated by US trees in forests, orchards, and plantations across five key services for which we had adequate data is $114 billion per annum (low: $85 B; high: $137 B; 2010 USD). The non-market ‘hidden’ ecosystem services of trees from carbon storage (51% of total value) and air pollution removal (37%) far exceed their commercial value from wood products and food crops (12%). The most valuable US tree species and lineages are also among those most threatened by known pests and pathogens, and the species most valuable for carbon storage are most at risk from increasing fire threat. Different species and lineages in different regions contribute to carbon storage and air pollution removal, which is distinct from tree crops that are often provided by the same species and lineages in different regions.