Browsing by Subject "Phenology"

Now showing 1 - 10 of 10
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    The life history of Anax junius (Drury) in Minnesota: Determining instars, growth development pathways, emergence phenology, and the effect of temperature on development (Odonata: Aeshnidae)
    (2019-12) Thompson, Ami
    This dissertation is a report based on careful observations of Anax junius, the common green darner dragonfly. Odonatology, the study of dragonflies and damselflies, is presently at a delightful stage of maturity. The basics of odonate life history are well understood but the details of how different species express variations in their development and reproduction, in response to different evolutionary drivers, is ripe for exploration. These variations can only be discovered through field observations executed with thoughtful experimental design and then the observational data collected must be interpreted with appropriate statistical and analytical tools. For a naturalist with a patient and inquisitive mind this kind of research is exceptionally rewarding. Chapters 1, 2, and 3 focus on these goals. Observational data on A. junius growth and emergence were collected over a period of two years at Crow-Hassan Park Reserve, near Minneapolis, Minnesota. Severe winter conditions are the largest constraint influencing dragonfly life histories in Minnesota. Odonata must both survive the winter, and time their emergence and reproduction so that they occur during the short growing season. This research was designed to explore how northern A. junius have adapted to survive winter. Chapter 1 demonstrates the application of a statistical tool that identifies the number of instars in a field-collected sample of nymphs: a need for interpreting observed growth and development data. This mixed distribution analysis has been used in other fields of entomology, but this is the first time (to the author’s knowledge) that it has been applied to dragonflies. Chapter 2 maps nymph growth over time and identifies different A. junius growth pathways that are associated with two different overwintering strategies. Chapter 3 summarizes observations of A. junius emergence phenology via exhaustive exuviae collection, and reveals that cold temperatures and stochastic events are the greatest constraints on emergence duration. Northern ectoderms, like dragonflies, with life histories that are constrained by severe winters are impacted by climate change. The implications of the changing climate on dragonfly natural history are of increasing conservation interest. Rare and threatened niche species of Odonata could be at risk of extinction if their habitat conditions are altered beyond to what they can adapt to. However, A. junius is a common and abundant dragonfly and is of conservation interest for different reasons. Extremely common species are the skeletons of ecosystems; they make up most of the biomass and provide structure and support for all the other components. A change in the geography or abundance of A. junius could have wide-ranging and cascading effects. Models based on known temperature thresholds are required to predict ectoderm response to the changing climate. Chapter 4 describes an experiment that defined these threshold temperatures for the northern winter growth pathway of A. junius. Development duration and rate were measured for nymphs reared in different temperature-controlled chambers, and the base and optimum growth temperatures were calculated for the last two nymph development stages. These values can now be used in models to predict the impact of climate change on the phenology of A. junius development and emergence. Note: Some materials and methods descriptions, figures, and tables are repeated in this dissertation because each chapter was written with the intent to be published individually.
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    Mapping oak wilt disease from space using land surface phenology
    (Remote Sensing of Environment, 2023-12-01) Guzmán, Jose A; Pinto-Ledezma, Jesús N; Frantz, David; Townsend, Philip A; Juzwik, Jennifer; Cavender-Bares, Jeannine
    Protecting the future of forests relies on our ability to observe changes in forest health. Thus, developing tools for sensing diseases in a timely fashion is critical for managing threats at broad scales. Oak wilt —a disease caused by a pathogenic fungus (Bretziella fagacearum)— is threatening oaks, killing thousands yearly while negatively impacting the ecosystem services they provide. Here we propose a novel workflow for mapping oak wilt by targeting temporal disease progression through symptoms using land surface phenology (LSP) from spaceborne observations. By doing so, we hypothesize that phenological changes in pigments and photosynthetic activity of trees affected by oak wilt can be tracked using LSP metrics derived from the Chlorophyll/Carotenoid Index (CCI). We used dense time-series observations from Sentinel-2 to create Analysis Ready Data across Minnesota and Wisconsin and to derive three LSP metrics: the value of CCI at the start and end of the growing season, and the coefficient of variation of the CCI during the growing season. We integrate high-resolution airborne imagery in multiple locations to select pixels (n = 3872) from the most common oak tree health conditions: healthy, symptomatic for oak wilt, and dead. These pixels were used to train an iterative Partial Least Square Discriminant (PLSD) model and derive the probability of an oak tree (i.e., pixel) in one of these conditions and the associated uncertainty. We assessed these models spatially and temporally on testing datasets revealing that it is feasible to discriminate among the three health conditions with overall accuracy between 80 and 82%. Within conditions, our models suggest that spatial variations among three CCI-derived LSP metrics can identify healthy (Area Under the Curve (AUC) = 0.98), symptomatic (AUC = 0.89), and dead (AUC = 0.94) oak trees with low false positive rates. The model performance was robust across different years as well. The predictive maps were used to guide local stakeholders to locate disease hotspots for ground verification and subsequent decision-making for treatment. Our results highlight the capabilities of LSP metrics from dense spaceborne observations to map diseases and to monitor large-scale change in biodiversity.
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    Modeling the phenological response to climate change and its impact on carbon cycle in Northeastern U.S. forests
    (2015-03) Xu, Hong
    By controlling the timing of leaf activities, vegetation phenology plays an important role in regulating photosynthesis and other ecosystem processes. As driven by environmental variables, vegetation phenology has been shifting in response to climate change. The shift in vegetation phenology, in turn, exerts various feedbacks to affect the climate system. The magnitude of phenological change and the feedbacks has yet been well understood. The goal of this dissertation is to use phenological model with remote sensing and climate data to quantify historical and future trends in leaf onset and offset in northeastern U.S. forests, and use a dynamic ecosystem model, Agro-IBIS, to quantify the impact of phenological change on terrestrial carbon balance. This dissertation has three major parts. First, six phenological metrics based on remotely sensed vegetation index were evaluated with ground phenological observation in Agro-IBIS. Second, a modified phenological metric was used to parameterize a set of phenological models at regional scale; one model for each of leaf onset and offset were selected to examine historical trends; Agro-IBIS simulations were run to quantify the impact of phenological trends on ecosystem productivities. Finally, downscaled climate projections from global climate models under two emission scenarios were used to drive phenological models to predict the trends in leaf onset and offset in the 21st century; and the impact of photoperiod on leaf onset were particularly examined. The results of this study suggest that remotely sensed phenological metrics can be used to improve phenological models with evaluation and adjustment; advancement of leaf onset and delay of leaf offset in the past have increased productivities and could potentially mitigate the warming temperature in the future; lack of physiological understanding of the driving factors of phenology such as photoperiod could result in large uncertainties in phenological projections.
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    Phenological responses of herbaceous plants, shrubs, and tree seedlings to experimental climate change conditions in northern Minnesota
    (2016-08) Rice, Karen
    Changing climate has been linked to changes in phenology, the timing of biological events such as leaf out and flowering. Phenological changes of herbaceous plants and shrubs remain less studied and thus less understood. This study takes place within the Boreal Forest Warming at an Ecotone in Danger (B4WarmED) project in Minnesota, examining phenological responses of herbaceous plants, shrubs, and tree seedlings to warming and reduced rainfall over. Warming extended the growing season, primarily through earlier leaf unfolding in the spring. Flowering advanced under warming, though more so for fall blooming species than for spring blooming species. Warming did not alter senescence for most species, though several species did delay senescence with warming. Community level phenological responses of the groundlayer and tree seedlings were not altered by rainfall treatments. Fall blooming species altered flowering phenology to rainfall manipulation. Two species diverged in flowering time in the warmest, driest treatment.
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    Phenology data for watermilfoil taxa Myriophyllum spicatum, M. sibiricum, and M. spicatum x M. sibiricum in Minnesota, USA, 2017 - 2018
    (2021-11-15) Glisson, Wesley J; Larkin, Daniel J; wjglisson@gmail.com; Glisson, Wesley; Minnesota Aquatic Invasive Species Research Center (MAISRC)
    In North America, the hybrid aquatic plant Myriophyllum spicatum × Myriophyllum sibiricum (hybrid watermilfoil, HWM) is a cross between non-native invasive Eurasian watermilfoil (M. spicatum, EWM) and native northern watermilfoil (M. sibiricum, NWM). We compared HWM to its parental taxa, EWM and NWM, by examining the amount and timing of: 1) flowering, 2) surface cover, and 3) biomass (using stem counts as a proxy). We conducted repeat surveys of Myriophyllum beds at eight lakes (2–3 lakes/taxon) in the Minneapolis-St. Paul Metropolitan area (Minnesota, USA) between June 2017 and November 2018. To sample biomass without destroying plants, we developed a novel sampling device that uses underwater video to measure Myriophyllum stems; we validated the utility of this device by comparing Myriophyllum stem counts and biomass collected from the same locations. The data from these studies are provided and documented here.
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    Responses of two understory herbs, Maianthemum canadense and Eurybia macrophylla, to experimental forest warming: early emergence is the key to enhanced reproductive output
    (Botanical Society of America, 2015) Jacques, Marie-Hélène; Lapointe, Line; Rice, Karen; Montgomery, Rebecca A; Stefanski, Artur; Reich, Peter B
    Understory herbs might be the most sensitive plant form to global warming in deciduous forests, yet they have been little studied in the context of climate change. A field experiment set up in Minnesota, United States simulated global warming in a forest setting and provided the opportunity to study the responses of Maianthemum canadense and Eurybia macrophylla in their natural environment in interaction with other components of the ecosystem. Effects of +1.7° and +3.4°C treatments on growth, reproduction, phenology, and gas exchange were evaluated along with treatment effects on light, water, and nutrient availability, potential drivers of herb responses. Overall, growth and gas exchanges of these two species were modestly affected by warming. They emerged up to 16 (E. macrophylla) to 17 d (M. canadense) earlier in the heated plots than in control plots, supporting early-season carbon gain under high light conditions before canopy closure. This additional carbon gain in spring likely supported reproduction. Eurybia macrophylla only flowered in the heated plots, and both species had some aspect of reproduction that was highest in the +1.7°C treatment. The reduced reproductive effort in the +3.4°C plots was likely due to reduced soil water availability, counteracting positive effects of warming. Global warming might improve fitness of herbaceous species in deciduous forests, mainly by advancing their spring emergence. However, other impacts of global warming such as drier soils in the summer might partly reduce the carbon gain associated with early emergence.
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    Role of leafing phenology in the invasion of forest ecosystems by Rhamnus cathartica
    (2015-04) Pretorius, Andrew
    Buckthorn breaks bud earlier in the spring and holds leaves later in the fall compared to co-occurring native understory species and the forest canopy. This phenology may allow buckthorn to take advantage of high light levels prior to canopy closure in spring and after leaf drop in fall. We hypothesized that this unique phenology is one mechanism that facilitates invasion of the forest interior by buckthorn. To test our hypothesis, we experimentally shaded buckthorn seedlings, reducing high light levels in the spring and fall to simulate intact canopy conditions. We measured spring and fall leafing phenology, light availability and seedling survival and growth. After a year and half of shading little mortality was observed but individuals receiving shading treatments had significantly decreased growth. Supporting our hypothesis that access to phenology-induced high light levels in the spring and autumn is one mechanism for buckthorn success in closed canopy forests.
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    Stewarding Floodplain Forests in a Changing Climate: Assisted Migration and Spring Tree Phenology in an Urban Climate Change Experiment and Monitoring for Floodplain Tree Regeneration
    (2024) Daniel, Abby
    As climate change continues to affect the world’s ecosystems, land managers seek to determine the best actions to maintain or adapt their forests to the current and projected climatic shifts. Floodplain forests are an ecosystem of interest for mitigating the effects of climate change, primarily through increased critical habitat and biodiversity, reduced nutrient input in riverine systems, and carbon sequestration. These unique forests are critical in climate action plans, but they are also facing increasing stressors due to severe weather events, nonnative species, and landscape alterations, resulting in the need to support these forests through a changing climate. Chapter 1 of this thesis focuses on the spring phenology of trees planted in an urban floodplain forest climate change experiment in Saint Paul, MN. Specifically, we examined the bud break and leaf out of trees in the Adaptive Silviculture for Climate Change (ASCC) project to determine if resident tree species, southern tree species, and populations of trees from USDA Hardiness Zones 4, 5, and 6 differed in the timing of these phenophases. We found that novel southern tree species who were moved northward via assisted species migration and range expansion leafed out significantly later than all other species. We did not find many significant differences among trees within the same species who were sourced from different hardiness zones, with the exception of eastern cottonwood (Populus deltoides) trees from hardiness zone 5 breaking bud and leafing out later than those from zone 4. Our findings suggest that the movement of species northward from outside of their natural range may have implications for their successful growth and survival due to the potentially altered timing in key leaf phenological events and subsequent mismatch with the growing season at the site of relocation. Chapter 2 is focused on a collaboration with Prairie Island Indian Community to monitor floodplain forests to support the Tribe’s reforestation efforts. The overarching goal of monitoring was to support healthy and resilient floodplain forests through providing information that will assist in identifying successful tree planting locations for diverse and climate-resilient tree species derived from the “Resilience” management approach of the ASCC project. Planting of diverse tree species in canopy openings was desired to maintain a forest canopy and other ecosystem services after the removal of green ash (Fraxinus pennsylvanica) trees impacted by the nonnative insect emerald ash borer (Agrilus planipennis). We developed a monitoring plan to sample the understory vegetation and overstory light levels at sites deemed a priority for planting or for management actions to reduce reed canary grass (Phalaris arundinacea) abundance. While specific results and management recommendations will not be shared in this published thesis, we assessed the potential success of enrichment plantings as well as the impacts of reed canary grass in 19 canopy gaps. These included gaps where ash were harvested, where ash will be harvested, and pre-existing canopy gaps. We identified suitable sites and locations within gaps to plant a diverse set of floodplain tree species that will create and maintain forest canopy, provide habitat, and potentially increase resilience to the impacts of climate change.
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    Water yield in the southern Appalachian Mountains.
    (2011-05) Kove, Katherine Marie
    With over 55% forest cover, the southern Appalachians (SA) are a main water resource for the surrounding areas. These water resources are at risk due to changing climate and precipitation regimes as well as changes in forest cover. Understanding the implications of these risks will help to develop management strategies for an increasingly valuable resource. Evapotranspiration (ET), the combination of plant transpiration and surface evaporation, can vary across space and time, and is a significant component of the hydrological cycle in densely forested regions. Quantifying ET is critical to understanding the available water resource, especially in the SA. In the SA, ET averages 50% of annual precipitation in forested watersheds and can climb to 85%. However, ET is among the most difficult and complex component of the water cycle to measure and model. This dissertation addresses these complexities by investigating the ability of sap flow models to estimate ET and examining the impact of potential temperature and compositional shifts on water yield. We also examined sap flow input variables to determine the best methods for the SA including the spatial estimation of climatological variables, phenological dates, and leaf area index (LAI) estimates all of which would particularly enhance the development of our hydrological models.
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    Wild rice geochemistry and reproductive life stage data from experimental pots amended with sulfate, 2016
    (2019-10-24) LaFond-Hudson, Sophia L; Johnson, Nathan W; Pastor, John; Dewey, Brad; lafo0062@d.umn.edu; LaFond-Hudson, Sophia L
    Wild rice, an annual aquatic plant produces fewer, smaller seeds with less nitrogen when exposed to sulfide, but does not produce decreased vegetative biomass. We compared the timing and duration of reproductive life stages in sulfate-amended plants to unamended plants to see how sulfide affects reproductive phenology. We recorded the life stage of plants starting with initiation of reproduction until senescence and measured seed count, mass and nitrogen content. Additionally, we sampled the geochemistry of porewater, sediment, and root surfaces to understand how plant life stage may control sediment redox conditions relevant to sulfide.