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At least 1,081 records · Page 60Linked to original sources

USGS2016

Forest structure of oak plantations after silvicultural treatment to enhance habitat for wildlife

During the past 30 years, thousands of hectares of oak-dominated bottomland hardwood plantations have been planted on agricultural fields in the Mississippi Alluvial Valley. Many of these plantations now have closed canopies and sparse understories. Silvicultural treatments could create a more heterogeneous forest structure, with canopy gaps and increased understory vegetation for wildlife. Lack of volume sufficient for commercial harvest in hardwood plantations has impeded treatments, but demand for woody biomass for energy production may provide a viable means to introduce disturbance beneficial for wildlife. We assessed forest structure in response to prescribed pre-commercial perturbations in hardwood plantations resulting from silvicultural treatments: 1) row thinning by felling every fourth planted row; 2) multiple patch cuts with canopy gaps of <1 0.25 – 2 ha; and 3) tree removal on intersecting corridors diagonal to planted rows. These 3 treatments, and an untreated control, were applied to oak plantations (20 - 30 years post-planting) on three National Wildlife Refuges (Cache River, AR; Grand Cote, LA; and Yazoo, MS) during summer 2010. We sampled habitat using fixed-radius plots in 2009 (pre-treatment) and in 2012 (post-treatment) at random locations. Retained basal area was least in diagonal corridor treatments but had greater variance in patch-cut treatments. All treatments increased canopy openness and the volume of coarse woody debris. Occurrence of birds using early successional habitats was greater on sites treated with patch cuts and diagonal intersections. Canopy openings on row-thinned stands are being filled by lateral crown growth of retained trees whereas patch cut and diagonal intersection gaps appear likely to be filled by regenerating saplings.

Conference Paper↗

USGS2011

Structure and dynamics of an upland old- growth forest at Redwood National Park, California

Many current redwood forest management targets are based on old-growth conditions, so it is critical that we understand the variability and range of conditions that constitute these forests. Here we present information on the structure and dynamics from six one-hectare forest monitoring plots in an upland old-growth forest at Redwood National Park, California. We surveyed all stems =20 cm DBH in 1995 and 2010, allowing us to estimate any systematic changes in these stands. Stem size distributions for all species and for redwood ( Sequoia sempervirens (D. Don) Endl.) alone did not appreciably change over the 15 year observation interval. Recruitment and mortality rates were roughly balanced, as were basal area dynamics (gains from recruitment and growth versus losses from mortality). Similar patterns were found for Sequoia alone. The spatial structure of stems at the plots suggested a random distribution of trees, though the pattern for Sequoia alone was found to be significantly clumped at small scales (< 5 m) at three of the six plots. These results suggest that these forests, including populations of Sequoia, have been generally stable over the past 15 years at this site, though it is possible that fire exclusion may be affecting recruitment of smaller Sequoia (< 20 cm DBH). The non-uniform spatial arrangement of stems also suggests that restoration prescriptions for second-growth redwood forests that encourage uniform spatial arrangements do not appear to mimic current upland old-growth conditions.

California↗

USGS2016

A management-oriented framework for selecting metrics used to assess habitat- and path-specific quality in spatially structured populations

Mobile species with complex spatial dynamics can be difficult to manage because their population distributions vary across space and time, and because the consequences of managing particular habitats are uncertain when evaluated at the level of the entire population. Metrics to assess the importance of habitats and pathways connecting habitats in a network are necessary to guide a variety of management decisions. Given the many metrics developed for spatially structured models, it can be challenging to select the most appropriate one for a particular decision. To guide the management of spatially structured populations, we define three classes of metrics describing habitat and pathway quality based on their data requirements (graph-based, occupancy-based, and demographic-based metrics) and synopsize the ecological literature relating to these classes. Applying the first steps of a formal decision-making approach (problem framing, objectives, and management actions), we assess the utility of metrics for particular types of management decisions. Our framework can help managers with problem framing, choosing metrics of habitat and pathway quality, and to elucidate the data needs for a particular metric. Our goal is to help managers to narrow the range of suitable metrics for a management project, and aid in decision-making to make the best use of limited resources.

Ecological Indicators↗

USGS2009

Engaging stakeholders for adaptive management using structured decision analysis

Adaptive management is different from other types of management in that it includes all stakeholders (versus only policy makers) in the process, uses resource optimization techniques to evaluate competing objectives, and recognizes and attempts to reduce uncertainty inherent in natural resource systems. Management actions are negotiated by stakeholders, monitored results are compared to predictions of how the system should respond, and management strategies are adjusted in a “monitor-compare-adjust” iterative routine. Many adaptive management projects fail because of the lack of stakeholder identification, engagement, and continued involvement. Primary reasons for this vary but are usually related to either stakeholders not having ownership (or representation) in decision processes or disenfranchisement of stakeholders after adaptive management begins. We present an example in which stakeholders participated fully in adaptive management of a southeastern regulated river. Structured decision analysis was used to define management objectives and stakeholder values and to determine initial flow prescriptions. The process was transparent, and the visual nature of the modeling software allowed stakeholders to see how their interests and values were represented in the decision process. The development of a stakeholder governance structure and communication mechanism has been critical to the success of the project.

Conference Paper↗

USGS2006

Structural equation modeling and natural systems

This book, first published in 2006, presents an introduction to the methodology of structural equation modeling, illustrates its use, and goes on to argue that it has revolutionary implications for the study of natural systems. A major theme of this book is that we have, up to this point, attempted to study systems primarily using methods (such as the univariate model) that were designed only for considering individual processes. Understanding systems requires the capacity to examine simultaneous influences and responses. Structural equation modeling (SEM) has such capabilities. It also possesses many other traits that add strength to its utility as a means of making scientific progress. In light of the capabilities of SEM, it can be argued that much of ecological theory is currently locked in an immature state that impairs its relevance. It is further argued that the principles of SEM are capable of leading to the development and evaluation of multivariate theories of the sort vitally needed for the conservation of natural systems.

Book↗

USGS2017

LANDFIRE 2015 Remap – Utilization of Remotely Sensed Data to Classify Existing Vegetation Type and Structure to Support Strategic Planning and Tactical Response

The LANDFIRE Program produces national scale vegetation, fuels, fire regimes, and landscape disturbance data for the entire U.S. These data products have been used to model the potential impacts of fire on the landscape [1], the wildfire risks associated with land and resource management [2, 3], and those near population centers and accompanying Wildland Urban Interface zones [4], as well as many other applications . The initial LANDFIRE National Existing Vegetation Type (EVT ) and vegetation structure layers, including vegetation percent cover and height, were mapped circa 2001 and released in 2009 [5]. Each EVT is representative of the dominant plant community within a given area. The EVT layer has since been updated by identifying areas of landscape change and modifying the vegetation types utilizing a series of rules that consider the disturbance type, severity of disturbance, and time since disturbance [6, 7]. Non-disturbed areas were adjusted for vegetation growth and succession. LANDFIRE vegetation structure layers also have been updated by using data modeling techniques [see 6 for a full description]. The subsequent updated versions of LANDFIRE include LANDFIRE 2008, 2010, 2012 , and LANDFIRE 2014 is being incrementally released, with all data being released in early 2017. Additionally, a comprehensive remap of the baseline data, LANDFIRE 2015 Remap , is being prototyped, and production is tentatively planned to begin in early 2017 to provide a more current baseline for future updates.

Earthzine↗

USGS1977

Topography, structure, and mare ridges in southern Mare Imbrium and northern Oceanus Procellarum

The gross topography in southern Mare Imbrium and northern Oceanus Procellarum correlates with the buried structure and deposits of the Imbrium Basin and its rim, and many of the mare slopes may be depositional and reflect the pre-existing major features of the basin. Post-depositional, local distortion of the mare surface, however, is present and in many places associated with mare ridges. Many mare ridges are concentric to the Imbrium Basin suggesting that they are influenced by basin structures. Morphologic diversity of mare ridges suggests that not all have the same origin, and volcanic activity took place along some of them. Most mare ridges are associated with faults. The faults could be reverse and associated with a shrinking of the moon, however, some ridges parallel slopes and could be interpreted as decollement thrust faults along gliding horizons or as vertical faults caused by differential gravitational settling along lines that separate areas that are thinly flooded on topographic highs from areas that are thickly flooded in adjacent lows.

Conference Paper↗

USGS2017

Food-web structure in canyon and slope-associated fauna revealed by stable isotopes

Food webs and associated trophic linkages among organisms are central themes in ecology that provide insight into the structure and function of ecosystems. In the deep sea, food webs rely on particulate flux raining from surface waters for energy (Klages et al. 2003), except for chemosynthetic communities, which rely on in situ production via chemosynthesis (Van Dover 2007). In general, the deep sea is a food limited environment because only a small percentage of organic carbon produced in surface waters settles to the seafloor (Gage and Tyler 1991, Klages et al. 2003, De La Rocha and Passow 2007). In contrast, relative to more quiescent slope environments, canyons can experience dynamic flow and turbulence. Internal tides can enhance turbulent mixing near the canyon seafloor leading to resuspension of sediments. Channeling of organic matter in deepsea canyons can enhance benthic productivity leading to high biodiversity (Vetter and Dayton 1998, 1999) and trophic complexity (Stefanescu et al. 1994, Cartes and Sorbe 1999). Thus, there may be a decoupling between the benthic-productivity relationships in canyon environments where food limitation may not be a driving factor influencing community structure. However, there have been only a few studies, often limited in depth range and spatial scale, that have examined the trophic pathways of deepsea canyons relative to adjacent slope environments (Duineveld et al. 2001, Fanelli et al. 2009, Cartes et al. 2010, Jeffreys et al. 2011).

OCS Study↗

USGS2018

Which geologic factors control permeability development in geothermal systems? The geologic structure of Dixie Valley

Geothermal systems occur where subsurface permeability and temperature are sufficiently high to drive fluid circulation. In the Great Basin region of the United States, which hosts ~20% of domestic geothermal electricity generation capacity and much of the projected undeveloped and undiscovered resource, crustal heat flow is relatively high, so permeability is the dominant factor controlling the occurrence or absence of a geothermal system. In the most general sense, fracture permeability along faults and/or networks of interconnected faults and fractures serves as a pathway for fluids upwelling from depth. Within the Great Basin, Dixie Valley hosts an anomalously high number of geothermal systems. It is unclear whether this relatively dense collection of systems is associated with regional strain or structural patterns, local structural or geological characteristics, basin hydrogeology, or some other factors. The relatively rich data-set available for Dixie Valley, and the well-studied nature of the area affords the opportunity to characterize the geologic and lithologic factors that control permeability development at the local scale. There are at least eleven distinct geothermal systems in Dixie Valley, NV. We utilize a wealth of existing data, which have been collected over several decades, to assess the geologic controls on geothermal fluid upwelling in these systems.

Geothermal Resources Council Transactions↗

USGS1993

Spectral reflectance and canopy structure characteristics of gulf coast wetland vegetation types

Field measurements of canopy structure and species composition are related to spectral reflectance measurements taken with a radiometer over a number of marsh sites. Marsh vegetation types are discussed in terms of their characteristic canopy structure and phenology; the influence of these characteristics on spectral reflectance will be examined. Vegetation types that are discussed include Panicum hemitomon (fresh marsh) Spartina patens (brackish marsh), Spartina alterniflora and Juncus roemerianus (saline marsh). This work is part of the high resolution component of a study to develop methods to spectrally discriminate and monitor the wetlands of the gulf coast.

Louisiana↗

USGS2020

Book review of "Plant anatomy—A concept based approach to the structure of seed plants"

Plant Anatomy: A Concept-Based Approach to the Structure of Seed Plants by Crang, Lyons-Sobaski, and Wise is a beautifully-illustrated, 600+ page textbook highlighting the wonderful diversity of anatomical form in plants. The layout of the chapters follows many traditional plant anatomy textbooks. Plant Anatomy begins with an overview of plant morphology and proceeds through evolutionary time and across systems (Chapter 1. The Nature of Plants) before zooming into the microscopic, internal world of plant structures and their function (Chapter 2. Microscopy and Imaging through Chapter 8. Phloem). Quite fortunately, historical context is described throughout these sections, highlighting seminal studies that have shaped the plant sciences over the past 300+ years.

Plant Science Bulletin↗

USGSDate not supplied

Relations between geological structure and aeromagnetic anomalies in central Nevada

An aeromagnetic survey of a 6000-km 2 area in central Nevada has been complied by the U.S. Geological Survey. An interpretation of the aeromagnetic data is developed to establish relations between near-surface geological features and structure extending to intermediate depths in the crust. A three-dimensional distribution of magnetized material is described which would reproduce approximately the observed aeromagnetic anomalies. Anomaly sources extend from the surface to depths exceeding 15 km and require values of magnetic moment per unit volume averaging more than 2000 × 10 −6 (cgs). Magnetic anomaly lineations were analyzed by two methods. The first involves digital fan filtering and subsequent autocovariance computations. This method is sensitive to amplitude of linear anomalies, and indicated a dominant north-northwest trend with approximately 80 percent of the anomaly trend power in an azimuth range of northwest to northeast. The second method involves preparation of rosettes from measured lengths and azimuths of lineations indicated by noses and flexures on the contoured map. This method is not sensitive to anomaly amplitude. The dominant N. 10°E. trend determined in this way is indicative of the effect of near-surface geological structure on the magnetic field. The dominant north-northwest-trending zone of magnetic anomalies is located along an alinement of windows through the Roberts Mountains thrust fault. This suggests that elongate doming of the Paleozoic sedimentary rocks associated with the thrust may be related to emplacement of magnetic anomaly source material, and implies that this has been a zone of recurring tectonic activity since late Paleozoic time. Analysis of stresses possibly associated with forceful injection of magnetic anomaly sources and possible shear deformation along this north-northwest-trending zone suggests that these factors may have had a secondary influence on azimuths of high-angle faults and dikes.

Nevada↗

USGS1975

Structure and Paleozoic stratigraphy of a complex of thrust plates in the Fish Creek Reservoir area, south-central Idaho

Permian, Pennsylvanian, Mississippian, Devonian, and Silurian marine rocks of diverse facies are brought together in a complex of six thrust sheets in the Fish Creek Reservoir area on the north edge of the Snake River Plain, Idaho. The lowest structural element, the parautochthon, is made of more than 450 m (1,500 ft) of folded and faulted Devonian miogeosynclinal carbonate rocks present in a 6.5-km 2 (2.5-mi 2 ) window. Along the east margin of the window, a sliver of continental margin transitional carbonate rocks of Early Devonian and Late Silurian age assigned to the Roberts Mountains Formation is thrust over the miogeosynclinal rocks. The window of middle Paleozoic rocks is overridden along the Fish Creek thrust fault by the flysch facies of the Copper Basin Formation, a turbidite-submarine-fan sequence more than 1,000 m (3,300 ft) thick, of Mississippian age. About 4.8 km (3 mi) southwest of the window, about 100 m (300 ft) of deepwater siliceous oceanic facies clastic rocks are exposed, which are assigned with question to the Milligen(?) Formation of Devonian age. These clastic rocks are interpreted to be thrust over the Copper Basin Formation. The highest structural elements are sequences more than 610 m (2,000 ft) thick of interbedded sandy and conglomeratic limestones, quartzites, and conglomerates and interbedded siltstones and argillites of the Wood River Formation of Middle Pennsylvanian to Early Permian age. The Wood River Formation is in thrust contact with the Milligen(?) Formation in the southwest part of the mapped area and with Copper Basin Formation along the west side of Fish Creek Reservoir. All the thrust sheets have moved eastward. The minimum distance moved is estimated from sedimentation models and facies reconstructions to range from perhaps several kilometres for the allochthon of the Roberts Mountains Formation to 48 km (30 mi) for the Milligen(?) Formation allochthon. The principal period of thrusting was post-Early Permian (post-Wood River Formation) and preEocene (pre-Challis Volcanics) and is of probable Sevier age. Middle Paleozoic rocks of the Milligen and Roberts Mountains Formations, however, also may have been involved in an earlier period of thrusting of latest Devonian to earliest Mississippian age related to the Antler orogeny. The thrust sheets were deformed into a northwest-trending dome in late Mesozoic time and were broken by basin-range faults during the Tertiary.

Idaho↗

USGS1978

Blue Ribbon Lineament, an east-trending structural zone within the Pioche mineral belt of southwestern Utah and eastern Nevada

The Blue Ribbon lineament is an east-west structural zone that is about 25 kilometers wide and passes through the Pioche mineral belt at about 38°10' N. It is best known in Utah, where it is at least 190 km long, and extends from the southern Sevier Plateau in the High Plateaus westward and across southern Mountain Home (Needle) Range in the Great Basin. It probably continues westward an additional 170 km into Nevada, where it connects with the eastern end of the 230-km Warm Springs lineament. The Blue Ribbon lineament is defined by range terminations and east-trending valleys, alinement of eruptive centers of middle Miocene (20 million years) to Pliocene(?) (5-1.8 m.y.) alkalic rhyolite, alinement of areas of middle Miocene to Pliocene mineralized rocks (mostly fluorine, uranium, tungsten) and hydrothermally altered rocks, east-trending magnetic highs and interruptions of magnetic anomalies, and east-striking basin-range faults of late Tertiary and Quaternary age. Mountains south of the lineament are topographically and structurally lower than those to the north. North-striking Quaternary basin-range faults, the Thermo hot springs area, several warm springs and former hot springs, and numerous dacitic to andesitic volcanic centers of early to middle Miocene age (26-20 m.y.) occur along the lineament. The Blue Ribbon lineament is believed to be a deep crustal fault zone dating from at least middle Miocene time and possibly much earlier. It thus developed generally coincident with northerly trending classical basin-range faults. Its fracture system was an important, long-lived conduit for mineralizing fluids, and it should be an attractive target for minerals exploration in the future. The lineament could be due to an east-trending warp in the subducting mantle plate, or it could be part of a past or present intracontinental transform fault that locally gets younger eastward and dies out eastward in the western Colorado Plateaus province.

Utah↗

USGS2016

Shifting patterns in SAV species diversity and community structure

This chapter examines the shifting patterns in Chesapeake SAV community structure and the potential environmental variables that explain variation in species composition patterns at both long and short time periods. Bay-wide species occurrence data sets are summarized. These data show that twenty-seven or more species of SAV are found within the tidal Chesapeake Bay. Seventeen of these are common, and four of those are non-native. The distributions of these SAV species are largely controlled by salinity, resulting in species associations along salinity gradients. There is higher species richness in low salinity SAV communities compared to medium and high salinity areas, but some of the species have wide salinity tolerances and are found in more than one community type. Most low salinity SAV species have expanded their distributions within the Bay, whereas the distributions of medium and high salinity species have either not changed or decreased. Two non-native species ( Hydrilla verticillata , Najas minor ) have increased their distributions, while the distributions of two nonnative species ( Myriophyllum spicatum , Potomogeton crispus) have not been observed to spread. Factors other than salinity that affect SAV community structure include water quality conditions, water movement, sediment quality, temperature, disease, water fowl herbivory, competitive interactions, propagule availability and shading from the invasive floating aquatic vegetation, Trapa natans . Historic declines in SAV abundances and diversity have largely been linked to anthropogenic impacts, although disease and storms have also contributed to episodic alterations to SAV communities.

Chesapeake Bay↗

USGS2025

Evaluating mountain goat population structure in Glacier National Park and Waterton Lakes National Park

Mountain goats are an iconic, climate-sensitive species across their North American alpine range. Among its nearly complete complement of native wildlife, no single species embodies Glacier National Park (GNP) more than the mountain goat. They play an important role as an alpine food source for many of the park’s carnivores including wolverines, mountain lions, and grizzly bears. Mountain goats face many increasing threats, particularly at the southern extent of their range. These include changes in precipitation and temperature, shifts in forage and fire frequency and intensity, and rapidly increasing visitation and recreation. Although the high latitude and elevations of GNP offer refugia, the mountain goat population likely declined between 2008 and 2019 and may also have a smaller distribution. In Montana, many other native mountain goat populations are also declining or have disappeared entirely. Using a combination of staff and citizen scientists, we collected fecal pellets across GNP in Montana, USA, and adjoining Waterton Lakes National Park (WLNP) in Alberta, Canada, between 2019 and 2023. We used genotypes of 6 to 19 loci microsatellites to identify individuals and assess isolation by distance, genetic structure, and genetic diversity. We found no evidence of genetic structure and only limited isolation by distance. This suggests that mountain goats in GNP and WLNP can be considered a single population, so samples can be combined across the area to estimate a single population size. Genetic diversity was similar to recent mountain goat studies conducted in other regions; allelic richness was 3.54 and inbreeding coefficients ( F IS ) ranged from 0.01–0.19, with values >0.11 only in the Livingston Range in the northwest of the study area. The high F IS in the Livingston Range suggests several closely related groups with little interchange, and perhaps a recent decrease in gene flow, both of which are consistent with a recent population decline in that area. We detected a high number of closely related individuals throughout our study area, consistent with the high adult survival, low reproductive success life history of goats, but also suggesting that we sampled much of the overall population.

Alberta, Montana↗

USGS2025

Relationship of basin structure and bedrock lithology to faulting in the 2019 Ridgecrest earthquake region, California, from gravity and aeromagnetic data

We investigate patterns of cumulative offsets on the faults that ruptured in 2019 and along the Garlock Fault in the Ridgecrest region, California using recently published gravity and aeromagnetic data. We also examine the relationship of basin structure and bedrock structure to the 2019 M7.1 Ridgecrest earthquake ruptures (Fig. 1A), which were primarily along a dextral northwest-striking fault system, and along a sinistral northeast-striking fault, which ruptured hours earlier with a M6.4 event.

California↗

USGS1974

Relationships between chemical structure and rat repellency. II. Compounds screened between 1950 and 1960

Over 4,600 compounds, chiefly organic types, were evaluated using both a food acceptance test (Part A) and a barrier penetration bioassay (Part B), to correlate relationships between chemical structure and rodent repellency.These chemicals are indexed and classified according to the functional groups present and to the degree of substitution within their molecular structures. The results of reduction in foot consumption for each compound appraised are calculated and their K values listed in Table I.The repellent activities of the functional groups represented, alone or in combinations, are expressed in Table II by a Functional Group Repellency Index. A ranking of these indices suggests that acyclic and heteroyclic compounds containing tri- or pentavalent nitrogen would be a parent compound of choice for synthesizing novel repellents. Other molecular arrangements, spatial configurations and combinations of functional groups are compared.There were 123 active, interesting or promising compounds included in the 699 having K values of 85 or greater, which were selected for the barrier appraisal study. These chemicals were formulated in selective solvents at several concentrations and applied to burlap. Small foot bags were fashioned using the fabric impregnated with the candidate formulation, and exposed to rodent attack following storage periods of varying intervals. The results of these tests are listed in Table III. Again, those compounds containing nitrogen in the functional groupings indicated a high order of effectiveness. Several commercial patents covering rodent repellents were issued using the data from the food acceptance and barrier studies.Organizations and cooperators which supplied samples for the program are listed in Appendix I. The Wiswesser cipher for compounds in Table I is used in Appendix II to facilitate location of chemicals by sample code number as they appear under the index headings, and for computer storage and analysis.

Report↗