Time filter

Source Type

Ellis, WI, United States

Johnson S.E.,University of Wisconsin - Madison | Johnson S.E.,Northland College | Waller D.M.,University of Wisconsin - Madison
Canadian Journal of Forest Research | Year: 2013

Floodplain and swamp forests are undergoing extensive changes due to altered flow regimes, invasive species, logging, and various land use changes. These changes often go unnoticed due to the absence of adequate baseline data and monitoring. Using a data set from 55 years ago, we resampled 50 lowland forest stands in southern Wisconsin to assess changes in forest overstory composition, structure, diversity, and dominant species abundances. We also applied univariate and multivariate analyses to determine whether these changes varied between dam-regulated and unregulated rivers, tree species with different flooding tolerances, the presence of logging, and variations in edaphic and hydrologic variables. Although these forests display various types of resilience, their forest canopies are substantially different from 55 years ago, reflecting shifts in hydrology and the impacts of disease. On average, these forests have retained the same local (alpha) diversity but have converged in species composition (declined in beta diversity). They are now composed of more and smaller trees. Along the unregulated rivers, colonizing species have declined while later successional flood-tolerant species have increased. In the aftermath of Dutch elm disease, Ulmus spp. have greatly declined in abundance and size. Species with less flooding tolerance have generally increased across sites, especially along dam-regulated rivers. Because they are subject to chronic disturbances that reset succession, floodplain forests may respond more readily to shifts in disturbances regimes. Such forests may therefore serve as sentinels for forecasting the types of change that we can expect to unfold more gradually in upland forests. Source

Garcia-Berthou E.,University of Girona | Carmona-Catot G.,University of Girona | Merciai R.,University of Girona | Ogle D.H.,Northland College
Reviews in Fish Biology and Fisheries | Year: 2012

The growth of many organisms is seasonal, with a dependence on variation in temperature, light, and food availability. A growth model proposed by Somers (Fishbyte 6:8-11, 1988) is one of the most widely used models to describe seasonal growth. We point out that three different formulae (beyond numerous typographical errors) have been used in the literature referring to Somers (Fishbyte 6:8-11, 1988). These formulae correspond to different curves and yield different parameter estimates with different biological interpretations. These inconsistencies have led to the wrong identification of the period of lowest growth rate (winter point) in some papers of the literature. We urge authors to carefully edit their formulae to assure use of the original definition in Somers (Fishbyte 6:8-11, 1988). © 2012 Springer Science+Business Media B.V. Source

Therizinosaurs represent a highly unusual clade of herbivorous theropods from the Cretaceous of North America and Asia. Following descriptions of the basicrania of the North American therizinosaurs Falcarius utahenisis and Nothronychus mckinleyi, the craniocervical musculature in both taxa is reconstructed using Tyrannosaurus, Allosaurus, and some extant birds as models. These muscles are subdivided into functional groups as dorsiflexors, lateroflexors, and ventroflexors. Lateroflexors and dorsiflexors in Nothronychus, but not Falcarius , are reduced, from the plesiomorphic theropod condition, but are still well developed. Attachments in both genera are favorable for an increase in ventroflexion in feeding, convergent with Allosaurus fragilis. Falcarius and Nothronychus are both characterized by a flat occipital condyle, followed by centra with shallow articular facets suggesting neck function very similar to that of an ostrich Struthio camelus. Neck movement was a combined result of minimal movement between the individual cervical vertebrae. © 2015 David K. Smith. Source

Courtwright J.,Northland College | Courtwright J.,James Madison University | Findlay S.E.G.,Cary Institute of Ecosystem Studies
Wetlands | Year: 2011

Hudson River freshwater tidal swamps have dynamic flooding and oxygenation regimes due to daily tidal flushing. Microtopography, small scale differences in elevation, adds even more complexity to inundation patterns and may have important implications for nutrient flow and wetland plant communities. The objective of this study was to determine if differences in inundation between microtopographic features were sufficient to alter physical, chemical, and biological attributes. Microtopography significantly affected flooding duration and redox conditions. Hummocks had lower concentrations of soluble phosphate in their porewater probably due to differing depths of iron oxidation. Hummocks also had lower porewater ammonium concentrations which could be explained by higher plant uptake of nitrogen on hummocks or less ammonium being nitrified and subsequently denitrified in hollows due to lack of oxygen. Decomposition rates were slower in hollows perhaps due to lack of oxygen due to flooding or differing decomposer communities. Fewer herbaceous plant species were found in hollows compared to hummocks perhaps because of hollow's anoxic soils. Microtopography affects freshwater tidal swamp ecosystem function by affecting oxygen penetration, nutrient availability, rates of decomposition, and herbaceous plant species distributions. © Society of Wetland Scientists 2011. Source

Johnson S.E.,Northland College | Mudrak E.L.,Iowa State University | Waller D.M.,University of Wisconsin - Madison
Journal of Vegetation Science | Year: 2014

Questions: Changes in land use, altered flow regimes, invasions by pests and pathogens, and climate change are, separately and together, altering ecological dynamics of floodplain forests. The complex changes these forces impose often go unnoticed due to a lack of reliable baseline data. Using historical data from the 1950s and re-survey data on floodplain forest understories, we ask: (1) what is the direction, magnitude and nature of changes in local and regional diversity; (2) have these floodplain communities become more homogenous in composition due to losses of native species and increases in non-natives; (3) has the relationship between the ground layer and overstorey community weakened over time; and (4) are changes in local and regional diversity among these floodplain forests more or less pronounced than in nearby upland forests? Location: Floodplain forests throughout southern Wisconsin, USA. Methods: We quantified composition of vegetation in the understorey and overstorey of 40 sites and compared these data with data from the 1950s using a combination of uni- and multivariate analyses. We focus on changes in local vs regional diversity. Results: Although average site-level diversity has increased by 18.5%, sites are now 30% more similar to each other, reflecting a pronounced decline in among-site (beta) diversity. Although exotic species have increased in site occupancy and abundance, increases in native woody plants (+30%), graminoids (+24%) and forbs (+16%) drive most of these changes in local and regional diversity. Sites have experienced an average species turnover rate of 39% since the 1950s, and understories are now 39% more correlated with canopy composition than in the 1950s. Biotic homogenization among these floodplain forests since the 1950s is 23.3% higher than the increase in similarity observed in nearby upland forests. Conclusions: Vegetation changes in floodplain understories differ from changes previously documented in nearby upland forests. Floodplain forests have experienced a faster rate of biotic homogenization. Unlike upland forests the homogenization trend in these floodplain forests is accompanied by increases in site-level diversity. These may reflect widespread colonization by certain native species. Both trends may also reflect relatively high connectivity among floodplain forests and control of hydrologic fluctuations via dams. © 2013 International Association for Vegetation Science. Source

Discover hidden collaborations