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At least 739 records · Page 41Linked to original sources

Spatial patterns of large natural fires in Sierra Nevada wilderness areas

The effects of fire on vegetation vary based on the properties and amount of existing biomass (or fuel) in a forest stand, weather conditions, and topography. Identifying controls over the spatial patterning of fire-induced vegetation change, or fire severity, is critical in understanding fire as a landscape scale process. We use gridded estimates of fire severity, derived from Landsat ETM+ imagery, to identify the biotic and abiotic factors contributing to the observed spatial patterns of fire severity in two large natural fires. Regression tree analysis indicates the importance of weather, topography, and vegetation variables in explaining fire severity patterns between the two fires. Relative humidity explained the highest proportion of total sum of squares throughout the Hoover fire (Yosemite National Park, 2001). The lowest fire severity corresponded with increased relative humidity. For the Williams fire (Sequoia/Kings Canyon National Parks, 2003) dominant vegetation type explains the highest proportion of sum of squares. Dominant vegetation was also important in determining fire severity throughout the Hoover fire. In both fires, forest stands that were dominated by lodgepole pine (Pinus contorta) burned at highest severity, while red fir (Abies magnifica) stands corresponded with the lowest fire severities. There was evidence in both fires that lower wind speed corresponded with higher fire severity, although the highest fire severity in the Williams fire occurred during increased wind speed. Additionally, in the vegetation types that were associated with lower severity, burn severity was lowest when the time since last fire was fewer than 11 and 17 years for the Williams and Hoover fires, respectively. Based on the factors and patterns identified, managers can anticipate the effects of management ignited and naturally ignited fires at the forest stand and the landscape levels. ?? 2007 Springer Science+Business Media, Inc.

Landscape Ecology↗

Influence of landscape structure, topography, and forest type on spatial variation in historical fire regimes, central Oregon, USA

Context In the interior Northwest, debate over restoring mixed-conifer forests after a century of fire exclusion is hampered by poor understanding of the pattern and causes of spatial variation in historical fire regimes. Objectives To identify the roles of topography, landscape structure, and forest type in driving spatial variation in historical fire regimes in mixed-conifer forests of central Oregon. Methods We used tree rings to reconstruct multicentury fire and forest histories at 105 plots over 10,393 ha. We classified fire regimes into four types and assessed whether they varied with topography, the location of fuel-limited pumice basins that inhibit fire spread, and an updated classification of forest type. Results We identified four fire-regime types and six forest types. Although surface fires were frequent and often extensive, severe fires were rare in all four types. Fire regimes varied with some aspects of topography (elevation), but not others (slope or aspect) and with the distribution of pumice basins. Fire regimes did not strictly co-vary with mixed-conifer forest types. Conclusions Our work reveals the persistent influence of landscape structure on spatial variation in historical fire regimes and can help inform discussions about appropriate restoration of fire-excluded forests in the interior Northwest. Where the goal is to restore historical fire regimes at landscape scales, managers may want to consider the influence of topoedaphic and vegetation patch types that could affect fire spread and ignition frequency.

Landscape Ecology↗

Valleys of fire: Historical fire regimes of forest-grassland ecotones across the montane landscape of the Valles Caldera National Preserve, New Mexico, USA

Context Montane grasslands and forest-grassland ecotones are unique and dynamic components of many landscapes, but the processes that regulate their dynamics are difficult to observe over ecologically relevant time spans. Objectives We aimed to demonstrate the efficacy of using grassland-forest ecotone trees to reconstruct spatial and temporal properties of the historical fire regime in a complex landscape of montane forests and adjacent grasslands. Methods We sampled and crossdated fire-scarred trees along ecotones and compared variations in historical fire occurrence within and among nine adjoining valle basins in a 10,158 ha landscape. We analyzed fire year extensiveness, climate regulation, and the occurrence of consecutive fire years. Results The resulting tree-ring record covers 1240–2005 AD, with 296 trees recording 125 replicated fire years during the analysis period 1601–1902 AD . Mean fire intervals for all events recorded on two or more trees ranged from 4.7 to 13.6 years in individual valles , and a mean of 2.4 ± 1.7 (SD) years at the landscape scale. Between 1660 and 1902, extensive fires occurring in six or more valles occurred 15 times, on average at ~ 17-year intervals; 29 moderately widespread fires (3–5 valles ) occurred during this period, at 8.7 year intervals on average. Widespread events occurred in years with a significantly lower Palmer Drought Severity Index (PDSI) preceded by years of significantly positive PDSI, indicating conditions favorable for fine fuel production. Spatial reconstruction of fire extent revealed multiple occurrences of consecutive-year fires burning non-overlapping areas, associated with persistent low PDSI anomalies preceded by positive conditions in antecedent years. Conclusions A landscape spatiotemporal approach to reconstructing fire regimes of montane forest-grassland complexes provides a valuable baseline for guiding prescribed and natural fire management at large spatial scales.

New Mexico↗

Coal-to-liquids: Potential impact on U.S. coal reserves

The production of liquid fuels from coal will very likely become an important part of the hydrocarbon energy mix of the future, provided that technical and environmental obstacles are overcome economically. The coal industry should be able to handle a coal-to-liquids (CTL) industry of modest size, using 60-70 million short tons or 54-64 million metric tonnes of coal per annum, without premature depletion of the country's coal reserves. However, attempts to use CTL technology to replace all petroleum imports would deplete the nation's coal reserves by the end of the century. ?? 2009 U.S. Government.

Natural Resources Research↗

Global trends in mineral commodities for advanced technologies

The U.S. Geological Survey National Minerals Information Center (NMIC) is the U.S. Government agency tasked with the collection, analysis, and dissemination of information on the production, consumption, import, export, and other measures of the flows of non-fuel mineral commodities of importance to the U.S. economy and national security. The NMIC and its agency predecessors have maintained a database of this information, collected and published annually, dating back to the beginning of the twentieth century. Time series analysis of annual information from the NMIC provides the opportunity to identify trends in the supply chains of the minerals and metals which are increasingly in demand for advanced technologies. The identification of trends in data for net import reliance, country concentration of production, global demand, price volatility, and other measures, when combined with world governance indicators, can be used to focus attention on individual mineral commodities where supply chain restrictions may develop. Specific examples for U.S. net import reliance, global tantalum primary mining, and mineral criticality screening are presented to illustrate the utility of time series analysis of trends in mineral commodity supply and demand, the types of data required, and the limitations of currently available information.

Natural Resources Research↗

Biocrusts: The living skin of the Earth

Biological soil crusts (biocrusts) form a “living skin” at the soil surface in many low productivity ecosystems around the world including water- and cold-limited environments, and early successional seres (Belnap et al. 2003). They may be composed of any configuration of soil surface-dwelling cyanobacteria, eukaryotic algae, lichens, mosses or liverworts, and support assemblages of decomposers and a faunal food web (Belnap et al. 2003). These soil surface communities have global relevance, as it has been recently estimated that they cover about 12% of the terrestrial surface currently (Rodriguez-Caballero et al. 2018). Biocrust communities are perhaps an ideal subject for the journal Plant and Soil, because they are simultaneously plant-like, due to their dominance by autotrophs, yet biocrusts are also clearly a physical feature of the soil given that component organisms are enmeshed in, adherent to, or otherwise in direct contact with the soil surface. The activity of the organisms is what engineers the well-aggregated thin layer at the soil surface that we recognize as a biocrust (Belnap et al. 2003). The contributions of biocrusts to ecosystem function has fueled much research interest, initially in the observation of biocrusts’ soil aggregating and erosion-resisting nature, and later as a multifunctional, globally-relevant ecosystem element instrumental in: 1. building or otherwise altering soil nutrient stocks through N-fixation (Elbert et al. 2012), dust trapping (Reynolds et al. 2001) and nutrient cycling (Strauss et al. 2012), 2. influencing hydrological properties of soil such as the water balance (Chamizo et al. 2016), and 3. The thermal energy balance of the ecosystem (Coradeau et al. 2016, Rutherford et al. 2017).

Plant and Soil↗

Selection of the Mars Science Laboratory landing site

The selection of Gale crater as the Mars Science Laboratory landing site took over five years, involved broad participation of the science community via five open workshops, and narrowed an initial >50 sites (25 by 20 km) to four finalists (Eberswalde, Gale, Holden and Mawrth) based on science and safety. Engineering constraints important to the selection included: (1) latitude (&plusmn;30&deg;) for thermal management of the rover and instruments, (2) elevation (<-1 km) for sufficient atmosphere to slow the spacecraft, (3) relief of <100-130 m at baselines of 1-1000 m for control authority and sufficient fuel during powered descent, (4) slopes of <30&deg; at baselines of 2-5 m for rover stability at touchdown, (5) moderate rock abundance to avoid impacting the belly pan during touchdown, and (6) a radar-reflective, load-bearing, and trafficable surface that is safe for landing and roving and not dominated by fine-grained dust. Science criteria important for the selection include the ability to assess past habitable environments, which include diversity, context, and biosignature (including organics) preservation. Sites were evaluated in detail using targeted data from instruments on all active orbiters, and especially Mars Reconnaissance Orbiter. All of the final four sites have layered sedimentary rocks with spectral evidence for phyllosilicates that clearly address the science objectives of the mission. Sophisticated entry, descent and landing simulations that include detailed information on all of the engineering constraints indicate all of the final four sites are safe for landing. Evaluation of the traversabilty of the landing sites and target “go to” areas outside of the ellipse using slope and material properties information indicates that all are trafficable and “go to” sites can be accessed within the lifetime of the mission. In the final selection, Gale crater was favored over Eberswalde based on its greater diversity and potential habitability.

Space Science Reviews↗

Fundamental challenges to methane recovery from gas hydrates

The fundamental challenges, the location, magnitude, and feasibility of recovery, which must be addressed to recover methane from dispersed hydrate sources, are presented. To induce dissociation of gas hydrate prior to methane recovery, two potential methods are typically considered. Because thermal stimulation requires a large energy input, it is less economically feasible than depressurization. The new data will allow the study of the effect of pressure, temperature, diffusion, porosity, tortuosity, composition of gas and water, and porous media on gas-hydrate production. These data also will allow one to improve existing models related to the stability and dissociation of sea floor hydrates. The reproducible kinetic data from the planned runs together with sediment properties will aid in developing a process to economically recover methane from a potential untapped hydrate source. The availability of plentiful methane will allow economical and large-scale production of methane-derived clean fuels to help avert future energy crises.

Topics in Catalysis↗

Ecosystem services from converted land: the importance of tree cover in Amazonian pastures

Deforestation is responsible for a substantial fraction of global carbon emissions and changes in surface energy budgets that affect climate. Deforestation losses include wildlife and human habitat, and myriad forest products on which rural and urban societies depend for food, fiber, fuel, fresh water, medicine, and recreation. Ecosystem services gained in the transition from forests to pasture and croplands, however, are often ignored in assessments of the impact of land cover change. The role of converted lands in tropical areas in terms of carbon uptake and storage is largely unknown. Pastures represent the fastest-growing form of converted land use in the tropics, even in some areas of rapid urban expansion. Tree biomass stored in these areas spans a broad range, depending on tree cover. Trees in pasture increase carbon storage, provide shade for cattle, and increase productivity of forage material. As a result, increasing fractional tree cover can provide benefits land managers as well as important ecosystem services such as reducing conversion pressure on forests adjacent to pastures. This study presents an estimation of fractional tree cover in pasture in a dynamic region on the verge of large-scale land use change. An appropriate sampling interval is established for similar studies, one that balances the need for independent samples of sufficient number to characterize a pasture in terms of fractional tree cover. This information represents a useful policy tool for government organizations and NGOs interested in encouraging ecosystem services on converted lands. Using high spatial resolution remotely sensed imagery, fractional tree cover in pasture is quantified for the municipality of Rio Branco, Brazil. A semivariogram and devolving spatial resolution are employed to determine the coarsest sampling interval that may be used, minimizing effects of spatial autocorrelation. The coarsest sampling interval that minimizes spatial dependence was about 22 m. The area-weighted fractional tree cover for the study area was 1.85 %, corrected for a slight bias associated with the coarser sampling resolution. The pastures sampled for fractional tree cover were divided between ‘high’ and ‘low’ tree cover, which may be the result of intentional incorporation of arboreal species in pasture. Further research involving those ranchers that have a higher fractional tree cover may indicate ways to promote the practice on a broader scale in the region.

Urban Ecosystems↗

Manganese biogeochemistry in a central Czech Republic catchment

Mn biogeochemistry was studied from 1994 to 2003 in a small forested catchment in the central Czech Republic using the watershed mass balance approach together with measurements of internal stores and fluxes. Mn inputs in bulk deposition were relatively constant during a period of sharply decreasing acidic deposition, suggesting that the Mn source was terrestrial, and not from fossil fuel combustion. Mn inputs in bulk deposition and Mn supplied by weathering each averaged 13 mg m-2 year-1 (26 mg m -2 year-1 total input), whereas Mn export in streamwater and groundwater averaged 43 mg m-2 year-1. Thus an additional Mn source is needed to account for 17 mg m-2 year -1. Internal fluxes and pools of Mn were significantly greater than annual inputs and outputs. Throughfall Mn flux was 70 mg m-2 year-1, litterfall Mn flux was 103 mg m-2 year -1, and Mn net uptake by vegetation was 62 mg m-2 year-1. Large pools of labile or potentially labile Mn were present in biomass and surficial soil horizons. Small leakages from these large pools likely supply the additional Mn needed to close the watershed mass balance. This leakage may reflect an adjustment of the ecosystem to recent changes in atmospheric acidity. ?? 2007 Springer Science+Business Media B.V.

Water, Air, & Soil Pollution↗

Advances in estimation methods of vegetation water content based on optical remote sensing techniques

Quantitative estimation of vegetation water content (VWC) using optical remote sensing techniques is helpful in forest fire assessment, agricultural drought monitoring and crop yield estimation. This paper reviews the research advances of VWC retrieval using spectral reflectance, spectral water index and radiative transfer model (RTM) methods. It also evaluates the reliability of VWC estimation using spectral water index from the observation data and the RTM. Focusing on two main definitions of VWC—the fuel moisture content (FMC) and the equivalent water thickness (EWT), the retrieval accuracies of FMC and EWT using vegetation water indices are analyzed. Moreover, the measured information and the dataset are used to estimate VWC, the results show there are significant correlations among three kinds of vegetation water indices (i.e., WSI, NDII, NDWI 1640 , WI/NDVI) and canopy FMC of winter wheat ( n =45). Finally, the future development directions of VWC detection based on optical remote sensing techniques are also summarized.

Science China Technological Sciences↗

Variation in foraging patterns as reflected by floral resources used by male vs female bees of selected species at Badlands National Park, SD

Female and male bees forage for different reasons: females provision nests with pollen appropriate for larval development and consume nectar for energy while males need only fuel their own energetic requirements. The expectation, therefore, is that females should visit fewer floral resource species than males, due to females’ focus on host plant species and their tie to the nest location. We used pollen collected from bees’ bodies and the flowers they were collected on to infer floral resource use in 2010-2012 at Badlands National Park, SD, USA. We collected bees on 24 1-ha plots centered on particular plant species. We compared number of floral species and families (1) associated with individual female and male bees (via generalized linear mixed models) and (2) accumulated by each sex (using rarefaction); and (3) effect of variation between sexes in plant-bee interactions via modularity analyses. Analyses were restricted to bee species with > 5 individuals per sex. Contrary to expectation, female and male bees differed infrequently in the number of floral resources they had visited, both on single foraging bouts and collectively when accumulated across all males and females of a species. When males and females did differ, males visited fewer floral species than females. Generalist and specialist bee species did not differ markedly in floral resource use by females and males. When separated by sex, seven of eleven species occupied different modules than they did when analyzed as a species; most of the bee species were connectors, thus important for stability of the network during perturbations.

South Dakota↗

Sediment dynamics of a divergent bay–marsh complex

Bay–marsh systems, composed of an embayment surrounded by fringing marsh incised by tidal channels, are widely distributed coastal environments. External sediment availability, marsh-edge erosion, and sea-level rise acting on such bay–marsh complexes may drive diverse sediment-flux regimes. These factors reinforce the ephemeral and dynamic nature of fringing marshes: material released by marsh-edge erosion becomes part of a bay–marsh exchange that fuels the geomorphic evolution of the coupled system. The dynamics of this sediment exchange determine the balance among seaward export, deposition on the embayment seabed, flux into tidal channels, and import to the marsh platform. In this work, we investigate the sediment dynamics of a transgressive bay–marsh complex and link them to larger-scale considerations of its geomorphic trajectory. Grand Bay, Alabama/Mississippi, is a shallow microtidal embayment surrounded by salt marshes with lateral erosion rates of up to 5 m year −1 . We collected 6 months of oceanographic data at four moorings within Grand Bay and its tidal channels to assess hydrographic conditions and net sediment-flux patterns and augmented the observations with numerical modeling. The observations imply a divergent sedimentary system in which a majority of the suspended sediment is exported seaward, while a smaller fraction is imported landward via tidal channels, assisting in vertical marsh-plain accumulation, maintenance of channel and intertidal-flat morphologies, and landward transgression. These results describe a dynamic system that is responsive to episodic atmospheric forcing in the absence of a strong tidal signal and the presence of severe lateral marsh loss.

Alabama, Mississippi↗

Etiology of a fish kill, Including the endangered Tidewater Goby (Eucyclogobius newberryi), in a northeastern pacific coastal lagoon

Ecological disturbances such as fish kills can negatively impact ecosystem processes in coastal lagoons. To gain an understanding of factors causing fish kills, we examined conditions associated with a summertime fish kill in a northeastern Pacific coastal lagoon (Rodeo Lagoon, CA, USA). Examination of available data indicated the fish kill was likely caused by hypoxia involving the following etiology: (1) strong onshore winds (up to 12 m/s) mixed a stratified water column, (2) water column mixing transported nutrients from near the bed into the photic zone, (3) increased nutrient concentrations in the photic zone (> 200%) together with high solar irradiance fueled a phytoplankton bloom, (4) death and decomposition of phytoplankton (72% decrease in abundance) contributed to biological oxygen demand that led to (5) hypoxic conditions (as low as 0.6 mg/L) that caused the fish kill. The event resulted in the death of an estimated 3677 Tidewater Goby ( Eucyclogobius newberryi ), a species listed as endangered under the US Endangered Species Act, and numerous (but not enumerated) Threespine Stickleback ( Gasterosteus aculeatus ), unidentified sculpins (Cottidae), and macroinvertebrates (primarily Amphipoda). The processes contributing to the event are likely re-occurring phenomena responsible for observed periodic fish kills. Coastal lagoons with limited freshwater inflows and connection to the Pacific Ocean may retain nutrients and be susceptible to similar events.

California↗

Assessing the status and drivers of phytoplankton blooms along the riverine to freshwater-tidal continuum in a modified delta

Shifts in phytoplankton communities, from beneficial taxa that fuel food webs to harmful taxa that degrade water quality, are often linked to anthropogenic modifications to estuaries. We analyzed monitoring data from 2000 to 2023 in the heavily modified southern, landward portion of the Sacramento-San Joaquin Delta (California, USA) to determine the status and drivers of phytoplankton abundance and community composition along the riverine to freshwater tidal transition. Diatoms and green algae dominated the phytoplankton community, especially when chlorophyll a (chl- a ) concentrations exceeded 16 µg L − 1 . Common riverine diatoms (e.g., Cyclotella and Aulacoseira ) dominated upstream riverine stations, while taxa associated with tidally influenced conditions (e.g., colonial cyanobacteria, cryptophytes) were more prevalent in western, freshwater tidal stations. The potentially toxigenic cyanobacterium, Microcystis , was present each summer, but was not associated with elevated chl- a or cyanotoxins (microcystins were detected in 12% of samples with a maximum concentration of 3.9 µg L − 1 ). A Bayesian ordinal regression showed that mean prior week water speeds below 0.18 m s − 1 and water temperatures above 22 ˚C were associated with the presence of Microcystis. Random forest modeling to assess factors associated with phytoplankton blooms (chl- a > 16 µg L − 1 ) found that mean prior week turbidity, inflows from the San Joaquin River, region, and mean prior week water temperature were important drivers of blooms. These modeling results emphasize the importance of hydrodynamics in controlling phytoplankton dynamics in lowland rivers and tidal deltas, offering insights for how anthropogenic impacts on flow regimes may affect the base of estuarine food webs.

California↗

Drivers of ecosystem metabolism in an anthropogenically modified delta

Estuaries are under threat globally from a wide range of stressors, with rates of ecosystem metabolism – respiration (R), gross primary production (GPP), and net ecosystem metabolism (NEM) – representing a way for resource managers to quantify their impacts. In this study, we assessed how natural and anthropogenic stressors have altered metabolism within the extensively modified Sacramento-San Joaquin Delta (“Delta”) in California, USA. Metabolism was estimated using a diel open-water technique utilizing dissolved oxygen measurements from a high frequency (15 min) water quality monitoring array, and spanned 6 sites across 11 years (2014–2025). Our analyses were driven by a conceptual model of Delta carbon (C) cycling focused on 1) Invasive aquatic vegetation (IAV), 2) Phytoplankton, 3) Wastewater treatment plant (WWTP) upgrades, 4) Large-scale flow alterations, and 5) Wet vs. dry years. We found that allochthonous C fuels net heterotrophy in the outer riverine sections of the Delta, while the heavily vegetated central Delta produces autochthonous C remineralized elsewhere in the system. IAV were the dominant primary producers, with low phytoplankton production except during a historic bloom. WWTP upgrades imparted negligible changes to metabolism, with low chlorophyll a (< 5 µg L −1 ) both before and after. Introduction of a flow barrier – a management response to drought – hydrodynamically isolated deep-water channels from nearby shallow areas, resulting in decreased metabolism indicative of changes to C transport. Contrary to past research, low rainfall years were associated with increased metabolism. This study demonstrates how multi-sensor arrays can be used to quantify ecosystem responses to major environmental stressors.

California↗

The development of China’s monopoly over cobalt battery materials

While previous resource conflicts have often been linked to fuel minerals such as oil, future resource conflict may revolve around nonfuel minerals that enable strategic emerging technologies. During a 2010 diplomatic dispute, China reportedly blocked exports of rare earth elements to Japan, thereby leveraging China’s near-monopoly to threaten Japanese manufacturers of advanced technologies including batteries and permanent magnets. Although this caused significant concern for manufacturers outside China, China’s control over other critical minerals has yet to be studied comprehensively. Besides rare earth elements, perhaps no mineral has received more attention for its supply risks than cobalt. Here Chinese control is estimated for each cobalt material at each stage of the cobalt supply chain from 2000 through 2022. The results show that from mining, to refining, consumption, recycling, stocks, and trade, China dominates the cobalt materials that feed lithium-ion battery cathode production. Specifically, the results show that in 2022 Chinese firms had control over 62% of cobalt mine materials primarily used for cobalt chemical refining, 95% control of refined commercial-grade cobalt chemicals, 92% control of battery-grade tricobalt tetroxide, 85% control of battery-grade cobalt sulfate, and 91% control of nickel–cobalt-manganese cathode precursor materials. China’s monopoly over cobalt battery materials may imply a serious supply risk to non-Chinese battery producing and consuming industries—especially given rising geopolitical tensions and the reemergence of critical mineral export restrictions including gallium for semiconductors, germanium for solar panels, graphite for lithium-ion batteries, and (again) rare earth elements.

Mineral Economics↗

Drought and fire in the western USA: Is climate attribution enough?

Purpose of Review I sought to review the contributions of recent literature and prior foundational papers to our understanding of drought and fire. In this review, I summarize recent literature on drought and fire in the western USA and discuss research directions that may increase the utility of that body of work for twenty-first century application. I then describe gaps in the synthetic knowledge of drought-driven fire in managed ecosystems and use concepts from use-inspired research to describe potentially useful extensions of current work. Recent Findings Fire responses to climate, and specifically various kinds of drought, are clear, but vary widely with fuel responses to surplus water and drought at different timescales. Ecological and physical factors interact with human management and ignitions to create fire regime and landscape trajectories that challenge prediction. Summary The mechanisms by which the climate system affects regional droughts and how they translate to fire in the western USA need more attention to accelerate both forecasting and adaptation. However, projections of future fire activity under climate change will require integrated advances on both fronts to achieve decision-relevant modeling. Concepts from transdisciplinary research and coupled human-natural systems can help frame strategic work to address fire in a changing world.

Current Climate Change Reports↗