J. Anthony Stallins

Urban-induced thunderstorm modification in the Southeast United States

This study provides the first climatological synthesis of how urbanization augments warm-season convection among a range of cities in the southeastern U.S. By comparing the location of convection in these cities and adjacent control regions via high-resolution, radar reflectivity and lightning data, we illustrate that demographic and land-use changes feed back to local atmospheric processes that promote thunderstorm formation and persistence. Composite radar data for a 10-year, June–August period are stratified according to specific “medium” and “high” reflectivity thresholds. As surrogates for potentially strong (medium reflectivity) and severe (high reflectivity) thunderstorms, these radar climatologies can be used to determine if cities are inducing more intense events. Results demonstrate positive urban amplification of thunderstorm frequency and intensity for major cities. Mid-sized cities investigated had more subtle urban effects, suggesting that the urban influences on thunderstorm development and strength are muted by land cover and climatological controls. By examining cities of various sizes, as well as rural counterparts, the investigation determined that the degree of urban thunderstorm augmentation corresponds to the geometry of the urban footprint. The research provides a methodological template for continued monitoring of anthropogenically forced and/or modified thunderstorms.

Hydrological shifts and tree growth responses to river modification along the Apalachicola River, Florida

Shifts in the hydrologic regime of Florida’s Apalachicola River have been attributed to anthropogenic changes throughout its watershed, including local dam construction. To assess impacts of those shifts on floodplain forests, we reconstructed tree growth using dendrochronology and compared these trends with hydrological and climatic variables. Comparisons of stream-gage data before and after dam construction on the Apalachicola River revealed statistically significant mean declines in annual average stage. Mean minimum annual stages, rise rates, and fall rates also decreased, while hydrograph reversals increased. Growth in four tree species correlated strongly with site-specific inundation parameters. A wetter climate in the two decades following dam construction and fine-scale fluctuation of the hydrograph may have set the stage for positive growth releases. Logging and hurricane wind throw events may have also contributed. However, drier conditions in the last two decades are now exacerbated by stage-discharge declines that had been masked previously. Tree growth rates and recruitment have decreased and, in the absence of a major disturbance, the forest canopy is composed of an older cohort of individuals. Our findings highlight how hydrograph variability, climate change, and vegetation disturbance are all relevant for gaging and anticipating the range of impacts of river modification on floodplain forests.

Properties of dune topographic state space for six barrier islands of the U.S. southeastern Atlantic coast

Abstract Barrier island dunes are postulated to exhibit two states, or stability domains. In this model, transitions between domains can exhibit irreversibility. However, these transitions may also be bistable, whereby the topography of either domain can develop at a location. To infer evidence for these dynamical properties and link them to dune topography, statistical mapping of dune topographic state space was undertaken for six barrier islands of the southeastern U.S. Atlantic coast. Topographies for three to four plots per island were constructed from airborne LiDAR data. Elevation in each was quantified in terms of descriptive statistics, spatial autocorrelation and landscape patch structure. The state space derived from ordination of these data was not primarily structured by the domain model. Instead, positive and negative relief defined the major axis of topographic variability. Only the plot topographies intermediate of these extremes in relief and contained within a smaller window of elevations resembled those of the two-state model. Their emergence along the second axis of variability was correlated with the spatial autocorrelation of elevation and geographic factors related to wave and tidal energy. Topographies suggestive of irreversibility and bistability were distinguishable based on their position in state space relative to these two domains regions.

Resilience Theory and Thomas Vale's Plants and People: A Partial Consilience of Ecological and Geographic Concepts of Succession

Geography has discovered resilience theory, a body of thought about ecological change that initiated with C.S. Holling in the 1970s. We describe the similarities and differences between resilience theory and a geographical treatise, Thomas Vales (1982) book Plants and People. Vales work draws more from the tradition of field botany and plant succession than from the theoretical and mathematical ecology that prompted Hollings ideas. Yet like resilience theory, Vales model of ecological change emphasized multiple states, the threshold transitions between them, and their irreversibility. Each described how forests and rangelands can flip between stability domains in response to altered fire regimes, modified grazing pressures, and climate change. Plants and People also recognized the dual nature of stability encapsulated in Hollings formalization of engineering and ecological resilience. Although resilience theory predates Vales work and retains primacy through its citation record, we show how their partial consilience promotes a more critical understanding of resilience theory and the ways in which models, scale, and human values influence our comprehension of ecological change.

The Embeddedness of a North American Snake in the Wildlife Pet Trade and the Production of Assemblage Biogeographies

The wildlife pet trade has the potential to threaten the viability of free-ranging animal populations. Yet there are potential benefits from the informal biological knowledge produced by breeders and caretakers for these taxa. How the evolution of a species shapes and is shaped by its embeddedness in the unique and changeable spatialities of the pet trade is also of relevance. To convey these points, we invoke materialist approaches from human geography to construct an assemblage biogeography for hognose snakes (Heterodon spp.), one of several North American reptiles in the pet trade. Mixed methods delineated what aspects of hognose biology facilitate their trade, what social and economic sites define their commercialization, and how the snakes natural history is dynamically embedded within them. Interviews with breeders, participatory observations at reptile shows, and content analysis of herpetological Web sites indicated that one of three species of Heterodon, western hognose (H. nasicus), has characteristics desired by breeders and pet owners. Its smaller size, less dramatic displays of bluff aggression, variability in color, and flexible diet make it more suitable than eastern or southern hognose. The contingencies of dispersal and speciation leading to these life history traits for western hognose are embedded within transitory social networks of breeders operating under sharply contrasting state wildlife regulations. Although contextual, these legal asymmetries and situational social arrangements bootstrap the international trade in hognose. They demarcate a self-organizing horizontal assemblage with the potential to crowdsource production of information and skills of value for conserving a growing number of endangered organisms.

Beyond bivariate correlations: three‐block partial least squares illustrated with vegetation, soil, and topography

Ecologists, particularly those engaged in biogeomorphic studies, often seek to connect data from three or more domains. Using three-block partial least squares regression, we present a procedure to quantify and define bi-variance and tri-variance of data blocks related to plant communities, their soil parameters, and topography. Bi-variance indicates the total amount of covariation between these three domains taken in pairs, whereas tri-variance refers to the common variance shared by all domains. We characterized relationships among three domains (plant communities, soil properties, topography) for a salt marsh, four coastal dunes, and two temperate forests spanning several regions in the world. We defined the specific bi- and tri-variances for the ecological systems we included in this study and addressed larger questions about how these variances scale with each other looking at generalities across systems. We show that a system tends to exhibit high bi-variance and tri-variance (tight coupling among d...

Beyond binaries: Conservative Catholic visions and real estate in Ave Maria, FL

Ave Maria is a New Urban university town in rural southwest Florida that embodies a conservative Catholic world view. The way it responded to the recent housing market crash is a good example of how negotiations between religious and non-religious spheres are constantly spatialising new, and reinterpreting existing, values, landscapes and practices. At times, the outcome of these dynamics clearly articulates distinctions between religious and non-religious domains. However, there are also circumstances where the difference between religious and non-religious domains is a matter of degree rather than a binary. In Ave Maria, planned ‘religicity’ and its interplay with non-religious forces result in varying gradients of spatial sacralisation. This paper shows that planned religious developments ultimately rework the concept of belief in ways that cannot be fully controlled, open up new possibilities for spiritual practice and broaden the identification of influential agencies at work in the construction of urban settlements. Ave Maria exemplifies the productive power of religion to make things happen spatially, through dialectical relationships with the physical, economic, cultural and political forces.