Physiographic Province Research Articles

Comparison of runoff and river flow in two large northern basins

AbstractThe magnitude and timing of water delivery in two large northern basins are analysed to clarify where runoff is generated and how their rivers acquire comparable regimes (or seasonal rhythms) of flow. These two rivers, the Mackenzie in Canada and the Yenisei in Russia, traverse similar latitudes, physiographic provinces, vegetation zones and climatic regions. Within the basins, mountainous terrain and high-precipitation sections usually yield large runoff, but low runoff comes from the plains, low plateaus and areas of aridity. Winter runoff is commonly low and snowmelt is responsible for annual peak runoff in most parts of these basins, though rainfall is a prominent runoff source in southern Yenisei. Many rivers in the drainage networks display a seasonal pattern that suggests the dominance of snowmelt to produce a spring freshet followed by a general decline in summer that diminishes to winter low flows. Regulation of reservoir outflow greatly distorts the natural flow regime. Yet, along the main river downstream of the reservoirs, the influx of tributary discharge can dilute such human influence. To truly understand how water is produced and transferred in large northern rivers, the spatial and temporal complexity of flow-generation mechanisms and storage effects need to be unravelled.

Emerging Environmental Ethics for Living with Novel Fire Regimes in the Blue Ridge Mountains

This article focuses on anthropogenic fire as a form of disturbance that is having an unusually strong influence on landscapes in the Blue Ridge Physiographic Province of the Southern Appalachian Mountains. One series of significant disturbance incidents was the Blue Ridge Complex, which was a dense cluster of wildfires that occurred during the fall of 2016. This article contains ethnographic information that I collected when the Blue Ridge Complex fires were burning and thereafter through the use of participant observation at community gatherings, land management events, and recreational activities. I have also conducted one-on-one interviews with residents of the fire-affected region, land managers, and firefighters. In community gatherings and in conversations with others, people living in the Blue Ridge Complex zone produced a collective ethical assemblage for living in a burning and burned landscape. The spatial and temporal patterns of burning in the fall of 2016 were so distinct from previous years that they may have redefined the Blue Ridge bioregion’s fire regimes. The proliferation of wildfires during the fall of 2016 also generated occasions for people to formulate their values related to one another, to their nonhuman co-residents, to fire, and to the overall mountainous landscape.

Modeling wet headwater stream networks across multiple flow conditions in the Appalachian Highlands

AbstractDespite the advancement of remote sensing and geospatial technology in recent decades, maps of headwater streams continue to have high uncertainty and fail to adequately characterize temporary streams that expand and contract in the wet length. However, watershed management and policy increasingly require information regarding the spatial and temporal variability of flow along streams. We used extensive field data on wet stream length at different flows to create logistic regression models of stream network dynamics for four physiographic provinces of the Appalachian Highlands: New England, Appalachian Plateau, Valley and Ridge, and Blue Ridge. The topographic wetness index (TWI) was the most important parameter in all four models, and the topographic position index (TPI) further improved model performance in the Appalachian Plateau, Valley and Ridge, and Blue Ridge. We included stream runoff at the catchment outlet as a model predictor to represent the wetness state of the catchment, but adjustment of the probability threshold defining wet stream presence/absence to high values for low flows was the primary mechanism for approximating network extent at multiple flow conditions. Classification accuracy was high overall (> 0.90), and McFadden's pseudo R2 values ranged from 0.69 for the New England model to 0.79 in the Appalachian Plateau. More notable errors included an overestimation of wet stream length in wide valleys and inaccurate reach locations amid boulder deposits and along headwardly eroding tributaries. Logistic regression was generally successful for modeling headwater streams at high and low flows with only a few simple terrain metrics. Modification and application of this modeling approach to other regions or larger areas would be relatively easy and provide a more accurate portrayal of temporary headwaters than existing datasets. © 2018 John Wiley & Sons, Ltd.

Landscape influence on the local distribution of western pond turtles

AbstractSpatial and temporal scales are important for understanding habitat associations because organisms have neither unbounded mobility nor perfect knowledge of their environment, but still must make decisions on where to seek food, shelter, and mates. Semi‐aquatic turtles exemplify the need to evaluate potential habitat characteristics at a range of scales, because their ectothermy makes these animals particularly sensitive to local environmental conditions, yet their limited mobility spatially constrains selection of microsites. Microsite choice may also be sensitive to larger geographic context. We explored site occupancy and abundance of western pond turtles (Actinemys [Emys] marmorata) as a function of environmental variables over a range of spatial scales up to that of the entire watershed. We modeled occupancy at ponds and abundance at river sites using data from surveys conducted at 50 ponds and 58 river locations throughout the South Umpqua, Umpqua, and North Umpqua watersheds in western Oregon, USA in 1999–2000. The South Umpqua supported the greatest abundance of western pond turtles in rivers and the highest rates of occupancy in ponds. No turtles were detected in rivers of the North Umpqua, and only low numbers were detected in ponds in that watershed. Increasing amount of potential relative solar radiation was associated with increased probability of pond occupancy, particularly in the North Umpqua watershed. Pond turtle abundance in rivers increased with increasing distance to nearest pond, decreasing area of nearby ponds, and increasing area of nearby wetland habitat of all types, particularly in the Klamath Mountain and Coast Range physiographic provinces, which dominate the South Umpqua and Umpqua watersheds, respectively. Western pond‐turtle occupancy and abundance varied with both broad‐scale and fine‐scale habitat features, not solely to the fine‐scale features that are most often measured.

Nest trees of northern spotted owls (Strix occidentalis caurina) in Washington and Oregon, USA.

The northern spotted owl (Strix occidentalis caurina) is a federally-threatened subspecies in the United States associated with late-successional forests. In mesic forests it nests primarily in tree cavities, but also uses various types of external platform nests in drier forests. We describe 1717 northern spotted owl nests in 16 different tree species in five study areas in Washington and Oregon in the Pacific Northwest, USA. The vast majority of nests (87%) were in Douglas-fir (Pseudotsuga menziesii) trees, except on the Olympic Peninsula, Washington, where nests were about equally abundant in Douglas-fir, western red cedar (Thuja plicata), and western hemlock (Tsuga heterophylla) trees. Distribution of nests was 57.9% in top cavities of trees with broken tops, 20.3% in side cavities of hollow tree trunks, and 21.8% on external platforms of trees. Platforms were most common in the two driest study areas in the Eastern Cascades Physiographic Province, Washington (89% of nests), and the Klamath Province, Oregon (32%). The vast majority (89%) of nests were in trees with intact or declining crowns. Nests in dead trees were most common on the Olympic Peninsula. Nest trees with top and side cavities were larger and much more prevalent in study areas where annual precipitation was highest (Olympic Peninsula, Oregon Coast Range). Large nest cavities and platforms used by northern spotted owls occur almost exclusively in old forest. Managing for the retention of such forests and for their replacement is a significant challenge for land managers, especially in the face of climate change and an increasing human population, but will likely be required for the persistence of viable populations of northern spotted owls.

Run‐off processes from mountains to foothills: The role of soil stratigraphy and structure in influencing run‐off characteristics across high to low relief landscapes

AbstractThe critical zone features that control run‐off generation, specifically at the regional watershed scale, are not well understood. Here, we addressed this knowledge gap by quantitatively and conceptually linking regional watershed‐scale run‐off regimes with critical zone structure and climate gradients across two physiographic provinces in the Southeastern United States. We characterized long‐term (~20 years) discharge and precipitation regimes for 73 watersheds with United States Geological Survey in‐stream gaging stations across the Appalachian Mountain and Piedmont physiographic provinces of North Carolina. Watersheds included in this analysis had <10% developed land and ranged in size from 14.1–4,390 km2. Thirty‐four watersheds were located in the Piedmont physiographic province, which is typically classified as a low relief landscape with deep, highly weathered soils and regolith. Thirty‐nine watersheds were located in the Appalachian Mountain physiographic province, which is typically classified as a steeper landscape with highly weathered, but shallower soils and regolith. From the United States Geological Survey daily mean run‐off time series, we calculated annual and seasonal baseflow indices (BFI), minimum, mean, and maximum daily run‐off, and Pearson's correlation coefficients between precipitation and baseflow. Our results showed that Appalachian Mountain watersheds systematically had higher minimum daily flows and BFI values. Piedmont watersheds displayed much larger deviations from mean annual BFI in response to year‐to‐year variability in precipitation. A series of linear regression models between 21 landscape metrics and annual BFIs showed non‐linear and complex terrestrial–hydrological relationships across the two provinces. From these results, we discuss how distinct features of critical zone architecture, with specific focus on soil depth and stratigraphy, may be dominating the regulation of hydrological processes and run‐off regimes across these provinces.

A multi-factor approach for process-based seabed characterization: example from the northeastern continental margin of the Korean peninsula (East Sea)

This study investigates sediment transport and depositional processes from a newly collected dataset comprising sub-bottom chirp profiles, multibeam bathymetry, and sediment cores from the northeastern continental margin of Korea in the East Sea (Japan Sea). Twelve echo-types and eleven sedimentary facies have been defined and interpreted as deposits formed by shallow-marine, hemipelagic sedimentation, bottom current, and mass-movement processes. Hemipelagic sedimentation, which is acoustically characterized by undisturbed layered sediments, appears to have been the primary sedimentary process throughout the study area. The inner and outer continental shelf (<150 m water depth) have been influenced by shallow-marine sedimentary processes. Two slope-parallel canyons, 0.2–2 km wide and up to 30 km long, appear to have acted as possible conduits for turbidity currents from the shallower shelf into the deep basins. Bottom current deposits, expressed as erosional moats immediately below topographic highs, are prevalent on the southern lower slope at water depths of 400–450 m. Mass-movements (i.e., slides/slumps, debris flow deposits) consisting of chaotic facies characterize the lower slope and represent one of the most important sedimentary processes in the study area. Piston cores confirm the presence of mass-transport deposits (MTDs) that are characterized by mud clasts of variable size, shape, and color. Multibeam bathymetry shows that large-scale MTDs are chiefly initiated on the lower slope (400–600 m) with gradients up to 3° and where they produce scarps on the order of 100 m in height. Sandy MTDs also occur on the upper continental slope adjacent to the seaward edge of the shelf terrace. Earthquakes associated with tectonic activity and the development of fluid overpressure is considered as the main conditioning factor for destabilizing the slope sediments. Overall, the sedimentary processes show typical characteristics of a fine-grained clastic slope apron and change down-slope and differ within each physiographic province. Furthermore, the influence of geological inheritance (i.e., structural folds and faults) on geomorphology and sediment facies development is an important additional factor on the lower slopes. Together, these factors provide a rational basis for continental margin seabed characterization.

Caracterización de frijol ayocote (Phaseolus coccineus L.) del Eje Neovolcánico y la Sierra Madre Oriental

&#x0D; &#x0D; &#x0D; El frijol ayocote es originario de las zonas templadas del territorio mexicano. Las provincias fisiográficas del territorio nacional, más representadas en la colección de variedades nativas de frijol ayocote del banco de germoplasma del INIFAP son el Eje Neovolcánico y La Sierra Madre Oriental. En el ciclo Primavera-Verano 2009 se cultivaron 231 variedades nativas de ayocote en el Campo Experimental Valle de México en Chapingo, Estado de México. Se sembraron dos surcos el 30 de abril de 2009 bajo temporal con siete matas dentro de cada surco de 4 m. Se registraron los días a inicio de f loración y días a inicio de madurez. En octubre- noviembre se cosechó la semilla y se determinó en ocho repeticiones el peso de 100 semillas en gramos. Se corrió un análisis de componentes principales y otro de agrupamientos con el método “complete”. Los tres primeros componentes explicaron 73% de la variabilidad contenida en las 231 variedades. El primero se relacionó con la altitud y temperaturas mínima y máxima media anual de los sitios de colecta, el segundo con los días a floración y a madurez de la planta, y el tercero con el peso de 100 semillas, días a floración, y precipitación de los sitios de colecta. El dendograma asociació cuatro grandes grupos de acuerdo a su origen geográfico: el primero con accesiones de la subprovincia fisiográfica Chichonquiaco y los tres restantes de las subprovincias Eje Neovolcánico, Llanuras y Sierras de Querétaro e Hidalgo, Sur de Puebla, y Neovolcánica Tarasca. Los ayocotes de la Sierra Madre Oriental, subprovincia Chiconquiaco, se diferenciaron de los del Eje Neovolcánico por su ciclo de cultivo más corto y semilla pequeña. Los ayocotes del Eje Neovolcánico tuvieron ciclos de cultivo más largos con semilla de mayor tamaño. A su vez, los ayocotes del Eje Neovolcánico fueron diferentes en su plasticidad fenológica: algunos al alargar su período vegetativo, acortaron el período reproductivo disminuyendo así el tamaño de su semilla. En cambio otros, a pesar de venir de lugares muy altos y muy fríos, mantuvieron su ciclo de cultivo largo y su tamaño de semilla posiblemente por la capacidad de su raíz de “rebrotar” después de las heladas.&#x0D; &#x0D; &#x0D;

Anthropogenic dispersion of selected germplasm creates a geographic mosaic of contrasting maternal lineages in Crescentia cujete from Mesoamerica

The modification of the genetic/phenotypic composition of plant populations through artificial selection occurs both through time and space. We analyzed the role of human dispersal on the geographic distribution of maternal lineages of Crescentia cujete in Mesoamerica. We sampled 28 homegarden (224 individuals) and 12 wild populations (159 individuals). Semi-structured interviews provided information on the origin of cultivated trees. Six chloroplast microsatellites allowed for the identification of 21 haplotypes, four of them exclusively in 83% of homegarden trees. Wild haplotypes from local C. cujete and Crescentia alata were found at low frequencies (17%) under cultivation. Cultivated and wild haplotypes constituted two different haplogroups. Accordingly, barriers to seed dispersal were detected among neighboring cultivated and wild populations. Recorded events of human dispersal of cuttings and seeds attaining up to > 200 km agreed with homegardens’ lower diversity (Nei’s h = 0.55, dropping to 0.32 when excluding wild haplotypes). Wild populations displayed high diversity (h = 0.71) and isolation by distance, in agreement with physiographic provinces. Our results support the native status of wild C. cujete and a Pre-Columbian introduction of cultivated lineages that generated a novel genetic mosaic superimposed on native maternal lineages. The results reveal the active role of farmers in maintaining the identity of cultivated lineages through time, while chloroplast capture from local congeners has increased the diversity of maternal lineages under cultivation. Additional data are needed on the origins of cultivated lineages, but our results contribute new insights into tree domestication in this center of crop diversity.

Rare Earth Elements (REE) Deposits Associated with Great Plain Margin Deposits (Alkaline-Related), Southwestern United States and Eastern Mexico

W.G. Lindgren in 1933 first noted that a belt of alkaline-igneous rocks extends along the eastern edge of the Rocky Mountains and Basin and Range provinces from Alaska and British Columbia southward into New Mexico, Trans-Pecos Texas, and eastern Mexico and that these rocks contain relatively large quantities of important commodities such as, gold, fluorine, zirconium, rare earth elements (REE), tellurium, gallium, and other critical elements. In New Mexico, these deposits were called Great Plain Margin (GPM) deposits, because this north-south belt of alkaline-igneous rocks roughly coincides with crustal thickening along the margin between the Great Plains physiographic province with the Basin and Range (including the Rio Grande rift) and Rocky Mountains physiographic provinces, which extends into Trans-Pecos Texas and eastern Mexico. Since 1996, only minor exploration and development of these deposits in New Mexico, Texas, and eastern Mexico has occurred because of low commodity prices, permitting issues, and environmental concerns. However, as the current demand for gold and critical elements, such as REE and tellurium has increased, new exploration programs have encouraged additional research on the geology of these deposits. The lack of abundant quartz in these systems results in these deposits being less resistant to erosion, being covered, and not as well exposed as other types of quartz-rich deposits, therefore additional undiscovered alkaline-related gold and REE deposits are likely in these areas. Deposits of Th-REE-fluorite (±U, Nb) epithermal veins and breccias are found in the several GPM districts, but typically do not contain significant gold, although trace amounts of gold are found in most GPM districts. Gold-rich deposits in these districts tend to have moderate to low REE and anomalously high tungsten and sporadic amounts of tellurium. Carbonatites are only found in New Mexico and Mexico. The diversity of igneous rocks, including alkaline-igneous rocks, and associated mineral deposits along this boundary suggests that this region is characterized by highly fractionated and differentiated, multiple pulses of mantle-derived magmas evolving to lower crustal magmas related to the subduction of the Farallon plate. The differences in incompatible trace elements, including REE and beryllium, between the different granitic to rhyolite rocks are likely related to either differences in the crustal rocks that were assimilated during magmatic differentiation or by potential minor contamination from crustal sources and/or magma mixing. Deep-seated fracture systems or crustal lineaments apparently channeled the magmas and hydrothermal fluids. Once magmas and metal-rich fluids reached shallow levels, the distribution and style of these intrusions, as well as the resulting associated mineral deposits were controlled by local structures and associated igneous rock compositions.

Floodplain Trapping and Cycling Compared to Streambank Erosion of Sediment and Nutrients in an Agricultural Watershed

AbstractFloodplains and streambanks can positively and negatively influence downstream water quality through interacting geomorphic and biogeochemical processes. Few studies have measured those processes in agricultural watersheds. We measured inputs (floodplain sedimentation and dissolved inorganic loading), cycling (floodplain soil nitrogen [N] and phosphorus [P] mineralization), and losses (bank erosion) of sediment, N, and P longitudinally in stream reaches of Smith Creek, an agricultural watershed in the Valley and Ridge physiographic province. All study reaches were net depositional (floodplain deposition &gt; bank erosion), had high N and P sedimentation and loading rates to the floodplain, high soil concentrations of N and P, and high rates of floodplain soil N and P mineralization. High sediment, N, and P inputs to floodplains are attributed to agricultural activity in the region. Rates of P mineralization were much greater than those measured in other studies of nontidal floodplains that used the same method. Floodplain connectivity and sediment deposition decreased longitudinally, contrary to patterns in most watersheds. The net trapping function of Smith Creek floodplains indicates a benefit to water quality. Further research is needed to determine if future decreases in floodplain deposition, continued bank erosion, and the potential for nitrate leaching from nutrient‐enriched floodplain soils could pose a long‐term source of sediment and nutrients to downstream rivers.

Arsenic exposure and cancer risk reduction with local ordinance requiring whole-house dual-tank water treatment systems

ABSTRACTArsenic, a known human carcinogen, occurs naturally in groundwater in New Jersey and many other states and countries. A number of municipalities in the Piedmont, Highlands, and Valley and Ridge Physiographic Provinces of New Jersey have a high proportion of wells that exceed the New Jersey maximum contaminant level (MCL) of 5 µg/L. Hopewell Township, located in Mercer County and the Piedmont Province, has a progressive local ordinance which requires the installation of dual-tank, point-of-entry treatment systems on affected wells. This provided a unique study opportunity. Of the 55 homes with dual-tank POE treatment systems recruited into this study, 51 homes (93%) had arsenic levels under the MCL at the kitchen sink, regardless of years in service and/or maintenance schedule adherence. Based on the study participants’ water consumption and arsenic concentrations, we estimate that Hopewell's arsenic water treatment ordinance, requiring POE dual-tank arsenic treatment, reduced the incidence of excess lifetime (70-year) bladder and lung cancers from 121 (1.7 cancer cases/year) to 16 (0.2 cancer cases/year) preventing 105 lifetime cancer cases (1.5 cases/year). Because the high risk of cancer from arsenic can be mitigated with effective arsenic water treatment systems, this ordinance should be considered a model for other municipalities.

A Comparison of Simulated and Field-Derived Leaf Area Index (LAI) and Canopy Height Values from Four Forest Complexes in the Southeastern USA.

Vegetative leaf area is a critical input to models that simulate human and ecosystem exposure to atmospheric pollutants. Leaf area index (LAI) can be measured in the field or numerically simulated, but all contain some inherent uncertainty that is passed to the exposure assessments that use them. LAI estimates for minimally managed or natural forest stands can be particularly difficult to develop as a result of interspecies competition, age and spatial distribution. Satellite-based LAI estimates hold promise for retrospective analyses, but we must continue to rely on numerical models for alternative management analysis. Our objective for this study is to calculate and validate LAI estimates generated from the USDA Environmental Policy Impact Climate (EPIC) model (a widely used, field-scale, biogeochemical model) on four forest complexes spanning three physiographic provinces in Virginia and North Carolina. Measurements of forest composition (species and number), LAI, tree diameter, basal area, and canopy height were recorded at each site during the 2002 field season. Calibrated EPIC results show stand-level temporally resolved LAI estimates with R2 values ranging from 0.69 to 0.96, and stand maximum height estimates within 20% of observation. This relatively high level of performance is attributable to EPIC’s approach to the characterization of forest stand biogeochemical budgets, stand history, interspecies competition and species-specific response to local weather conditions. We close by illustrating the extension of this site-level approach to scales that could support regional air quality model simulations.

Trautvetteria fonticalcarea (Ranunculaceae: Ranunculeae), a new tassel rue species endemic to calcareous seepage habitats in Tennessee, USA

This paper describes a novel species of Trautvetteria as well as provide information on the newly characterized habitat in which it occurs. The discovery of morphologically distinct populations of Trautvetteria in a novel habitat has prompted an investigation of the habitat and resulted in the description and illustration of this novel species, T. fonticalcarea sp. nov. from the Powell River valley of northeast Tennessee, USA, North America. The morphology of T. fonticalcarea is discussed in comparison to the allopatric T. caroliniensis which occurs in physiographic provinces east and west of the new species. In addition, the floristic components of the habitat of T. fonticalcarea are discussed with six species reported as new to the state of Tennessee: Carex interior, C. tetanica, C. woodii, Nabalus albus, Patis racemosa and Triantha glutinosa, and another species, Rhynchospora capillacea, rediscovered in the state. Several other species present in the habitat reach their southernmost geographic distribution here and are also rare for the state. Not only the novel species, T. fonticalcarea, but also the habitat are sufficiently rare and distinctive that they should be a focus for conservation efforts.

Conservation genetics of eastern hellbenders Cryptobranchus alleganiensis alleganiensis in the Tennessee Valley

The eastern hellbender has declined across much of its range and is a candidate for listing under the Endangered Species Act. Some of the most viable remaining populations exist in the Southern Appalachian Region in the Tennessee Valley watershed; however these populations are highly isolated and fragmented, and occupy several physiographic provinces, suggesting they may exhibit significant levels of genetic differentiation. We investigated genetic and phylogeographic relationships among eastern hellbender populations across the Tennessee Valley, using nuclear microsatellite markers and mitochondrial sequence data. Our population genetic analyses of microsatellite data revealed a strong pattern of isolation by stream distance, and 4 genetically distinct populations. These four populations were mainly associated with major watersheds, although middle Tennessee samples were difficult to assign to any particular population. Our phylogeographic analysis of mtDNA resulted in a strongly supported monophyletic ingroup containing nine largely allopatric clades, which also largely corresponded to major watersheds. Our findings suggest that hellbenders from different watersheds in the Tennessee Valley should be recognized as genetically distinct populations, and care should be taken to balance the needs of rescuing declining populations with translocation or headstart programs, while also preserving genetic diversity across the region.

Endemic vascular plants of the Sierra Madre Oriental, Mexico

To aid in formulating conservation strategies for protection of species in mountainous regions, we studied the distribution of endemic vascular plants of northeastern Mexico’s Sierra Madre Oriental physiographic province, a massive mountain system in which different types of climate, vegetation, topography, and sedimentary soil converge. The information used in our five-year study was gathered from databases of national and international herbaria, as well as from botanical studies and floristic inventories conducted in the study area. We corroborated the nomenclature and geographical distribution of each species in the databases. A total of 1,135 species of endemic vascular plants from 369 genera and 88 families, including 177 infraspecific categories and one hybrid, were recorded in this study. The families with the most species and genera are Asteraceae (232 species, 75 genera), Cactaceae (170, 26), Fabaceae (66, 19) and Lamiaceae (66, 10). The genera with the most species are Mammillaria (43), Turbinicarpus (40), Agave (20), Salvia (20), Sedum (20) and Pinguicula (19). The families with the largest number of endangered species are Cactaceae, Zamiaceae, Pinaceae, and Fagaceae. Endemic species were most abundant in vegetation of temperate regions (554 endemic species) and in zones with dry climates or chalky soils (a total of 380 species for the two types of zones combined). The principal endemism-promoting attributes of the Sierra Madre Oriental may be its location, climate, physiography, soil types, geological age, karstic landscape, and wide range of elevations.

Lithospheric discontinuities beneath the U.S. Midcontinent – signatures of Proterozoic terrane accretion and failed rifting

Seismic discontinuities between the Moho and the inferred lithosphere–asthenosphere boundary (LAB) are known as mid-lithospheric discontinuities (MLDs) and have been ascribed to a variety of phenomena that are critical to understanding lithospheric growth and evolution. In this study, we used S-to-P converted waves recorded by the USArray Transportable Array and the OIINK (Ozarks–Illinois–Indiana–Kentucky) Flexible Array to investigate lithospheric structure beneath the central U.S. This region, a portion of North America's cratonic platform, provides an opportunity to explore how terrane accretion, cratonization, and subsequent rifting may have influenced lithospheric structure. The 3D common conversion point (CCP) volume produced by stacking back-projected Sp receiver functions reveals a general absence of negative converted phases at the depths of the LAB across much of the central U.S. This observation suggests a gradual velocity decrease between the lithosphere and asthenosphere. Within the lithosphere, the CCP stacks display negative arrivals at depths between 65 km and 125 km. We interpret these as MLDs resulting from the top of a layer of crystallized melts (sill-like igneous intrusions) or otherwise chemically modified lithosphere that is enriched in water and/or hydrous minerals. Chemical modification in this manner would cause a weak layer in the lithosphere that marks the MLDs. The depth and amplitude of negative MLD phases vary significantly both within and between the physiographic provinces of the midcontinent. Double, or overlapping, MLDs can be seen along Precambrian terrane boundaries and appear to result from stacked or imbricated lithospheric blocks. A prominent negative Sp phase can be clearly identified at 80 km depth within the Reelfoot Rift. This arrival aligns with the top of a zone of low shear-wave velocities, which suggests that it marks an unusually shallow seismic LAB for the midcontinent. This boundary would correspond to the top of a region of mechanically and chemically rejuvenated mantle that was likely emplaced during late Precambrian/early Cambrian rifting. These observations suggest that the lithospheric structure beneath the Reelfoot Rift may be an example of a global phenomenon in which MLDs act as weak zones that facilitate the removal of cratonic lithosphere that lies beneath.

Struthanthus ramiro-cruzii (Loranthaceae), a new species from Guerrero, Mexico

A new species of Struthanthus from the state of Guerrero, Mexico, is described and illustrated: Struthanthus ramiro-cruzii. It grows in oak and pine-oak forests, in the physiographic province of the Southern Coastal Range in the Guerrerense region. It is morphologically similar to S. deppeanus, but differs by having leaves with a subcordate to truncate base, a sessile central flower of the triad and a strongly convoluted style. A key to distinguish the new species from other species of the genus present in the state of Guerrero is included.

A test of the delayed oak dominance hypothesis at mid-rotation in developing upland stands

Abstract Red maple often dominates tree regeneration following the harvest of upland oak stands in eastern North America. An open question is whether the oak component of the new stands will eventually reassert dominance (delayed oak dominance hypothesis) or whether red maple will succeed as a major, new overstory component on these sites (red maple dominance hypothesis). We examined changes between the 3rd and 4th decades of growth (mean interval 13 years) in 46 stands on formerly oak-dominated sites in the Blue Ridge (BlRi), Ridge and Valley (RiVa), and Appalachian Plateau (ApPl) physiographic provinces of the central Appalachians. Almost without exception, the new stands in their 4th decade (mean age 38 yrs) had less oak and more red maple than did their predecessors. All ApPl stands had failed to develop a substantial component of oak early in stand development, and most were dominated by red maple in their 4th decade. Most BlRi stands had become dominated by oak by their 4th decade, and changes between the 3rd and 4th decades show that oak is progressively becoming more dominant by displacing the relatively minor component of red maple that remains. The success of oak was generally intermediate in the RiVa, where red maple retained an approximately co-equal position of dominance with oak between the 3rd and 4th decades and in some stands advanced in dominance against oak. We suggest a nuanced interpretation of delayed oak dominance as an emergent and contingent property of individual trees and their neighborhoods. Both this and red maple dominance accurately describe developmental trajectories that are co-occurring in most of our stands, with one predominating over the other depending upon physiographic region and site-related characteristics. In general, development favored oaks where growth rates were slower and where species composition was more xerophytic. Red maple was favored on better sites, where delayed oak dominance appears to be a longer and ultimately less successful process.

Relationships between physical‐geochemical soil properties and erodibility of streambanks among different physiographic provinces of Tennessee, USA

AbstractErosion of cohesive soils in fluvial environments is dependent on physical, geochemical and biological properties, which govern inter‐particle attraction forces and control detachment rates from stream beds and banks. Most erosion rate models are based on the excess shear stress equation where the soil erodibility coefficient (kd) is multiplied by the difference between the boundary hydraulic shear stress (τb) and the soil critical shear stress (τc). Both kd and τc are a function of soil properties and must be obtained through in situ field or laboratory testing. Many studies have generated predictive relationships for kd and τc derived from various soil properties. These studies typically were conducted in watersheds within a single physiographic region with a common surficial geology and/or investigated a limited number of soil properties, particularly geochemical properties. With widely reported differences in relationships between τc and soil properties, this study investigated differences in predictive relationships for τc among different physiographic provinces in Tennessee, USA. Erodibility parameters were determined in the field using a mini‐jet test device. Among these provinces, statistically four unique clusters were identified from a dataset of 128 observations and these data clusters were used to develop predictive models for τc to identify dominant properties governing erosion. In these clusters, 16 significant physical and geochemical soil properties were identified for τc prediction. Among these soil properties, water content and passing #200 sieve (percentage soil less than 75 μm) were the dominant controlling parameters to predict τc in addition to clay percentage (&lt; 2 μm), bulk density, and soil pore water chemistry. This study suggests that unique relationships exist for physiographic provinces that are likely due to soil physical‐geochemical processes associated with surficial geology that determine minerology of the cohesive soil. Copyright © 2017 John Wiley &amp; Sons, Ltd.