The influence of defects of the fatigue resistance of butt and girth welds in A106B steel

This three-phase study was directed at developing a fitness for service defect acceptance criteria for welds with defect indications. The study focussed on A106 Gr. B steel pipe. The first phase involved a literature search and critical review to develop the preliminary acceptance criteria to the extent permitted by the data. The second phase developed data for flat plate, wall segment, and vessel specimens containing artificial or natural planar or volumetric defects. The final phase developed acceptance criteria from the test data

Evaluating lethal toxicant doses for the largest individuals of an invasive vertebrate predator with indeterminate growth

The brown treesnake (Boiga irregularis) was accidentally introduced to Guam and caused severe ecological and economic damages. Acetaminophen is an effective, low-risk oral toxicant for invasive brown treesnakes, and an automated aerial delivery system (ADS) has been developed for landscape-scale toxic bait distribution. A fixed dose of 80 mg of acetaminophen within a tablet inserted into a dead neonatal mouse (DNM) was lethal for all brown treesnakes in previous trials; however, these trials did not include very large individuals which are difficult to acquire for testing. Because most reptiles continue to grow throughout their lifespan, a small number reach much greater than average body sizes. Here, we tested effectiveness of 80 mg acetaminophen DNM baits for unusually large brown treesnakes as they became available. Our results confirmed that an 80 mg dose is lethal for the vast majority of snakes on Guam, but efficacy starts to diminish around 200 g of body mass. We also tested an alternative mouse bait configuration with 160 mg of acetaminophen that could be incorporated into the ADS to improve control of unusually large snakes. The 160 mg dose is expected to be effective for nearly all female snakes; males grow much larger and additional methods will be needed for extraordinarily large individuals. We describe a full dose-response curve for brown treesnakes to acetaminophen tablets and estimate the LD90 at 299 mg/kg and the LD99 at 578 mg/kg. To our knowledge, this is the first published dose-response curve for an invasive vertebrate with indeterminate growth

Diet and Foraging Behaviors of Timber Rattlesnakes, Crotalus horridus, in Eastern Virginia

During a 17-yr telemetry study, we examined the diet and ambush behavior of a population of Crotalus horridus in southeastern Virginia. Forty dietary items were identified from 37 fecal samples. We documented 722 instances of snakes in an ambush posture, 61 of which were in a vertical-tree posture, as if hunting arboreal prey at the base of a tree. The most common prey items were Eastern Gray Squirrels (Sciurus carolinensis), which accounted for 45 of all dietary items and represented an estimated 78 of total biomass consumed by C. horridus. Prey was not consumed in proportion to availability, based on small mammal surveys. Our analysis provides indirect evidence that the vertical-tree foraging behavior is adopted to target arboreal Eastern Gray Squirrels. Further, we provide support for the hypothesis that C. horridus alters ambush behavior to forage selectively for specific prey types

Focus on changing fire regimes: interactions with climate, ecosystems, and society

Fire is a complex Earth system phenomenon that fundamentally affects vegetation distributions, biogeochemical cycling, climate, and human society across most of Earth’s land surface. Fire regimes are currently changing due to multiple interacting global change drivers, most notably climate change, land use, and direct human influences via ignition and suppression. It is therefore critical to better understand the drivers, patterns, and impacts of these changing fire regimes now and continuing into the future. Our review contributes to this focus issue by synthesizing results from 27 studies covering a broad range of topics. Studies are categorized into (i) Understanding contemporary fire patterns, drivers, and effects; (ii) Human influences on fire regimes; (iii) Changes in historical fire regimes; (iv) Future projections; (v) Novel techniques; and (vi) Reviews. We conclude with a discussion on progress made, major remaining research challenges, and recommended directions

Diet and Foraging Behaviors of Timber Rattlesnakes, \u3ci\u3eCrotalus Horridus\u3c/i\u3e, in Eastern Virginia

During a 17-yr telemetry study, we examined the diet and ambush behavior of a population of Crotalus horridus in southeastern Virginia. Forty dietary items were identified from 37 fecal samples. We documented 722 instances of snakes in an ambush posture, 61% of which were in a vertical-tree posture, as if hunting arboreal prey at the base of a tree. The most common prey items were Eastern Gray Squirrels (Sciurus carolinensis), which accounted for 45% of all dietary items and represented an estimated 78% of total biomass consumed by C. horridus. Prey was not consumed in proportion to availability, based on small mammal surveys. Our analysis provides indirect evidence that the vertical-tree foraging behavior is adopted to target arboreal Eastern Gray Squirrels. Further, we provide support for the hypothesis that C. horridus alters ambush behavior to forage selectively for specific prey types

Forest Composition Change and Biophysical Climate Feedbacks Across Boreal North America

Deciduous tree cover is expected to increase in North American boreal forests with climate warming and wildfire. This shift in composition has the potential to generate biophysical cooling via increased land surface albedo. Here we use Landsat-derived maps of continuous tree canopy cover and deciduous fractional composition to assess albedo change over recent decades. We find, on average, a small net decrease in deciduous fraction from 2000 to 2015 across boreal North America and from 1992 to 2015 across Canada, despite extensive fire disturbance that locally increased deciduous vegetation. We further find near-neutral net biophysical change in radiative forcing associated with albedo when aggregated across the domain. Thus, while there have been widespread changes in forest composition over the past several decades, the net changes in composition and associated post-fire radiative forcing have not induced systematic negative feedbacks to climate warming over the spatial and temporal scope of our study

Impacts of Climate and Insect Herbivory on Productivity and Physiology of Trembling Aspen (Populus tremuloides) in Alaskan Boreal Forests

Climate change is impacting forested ecosystems worldwide, particularly in the Northern Hemisphere where warming has increased at a faster rate than the rest of the globe. As climate warms, trembling aspen (Populus tremuloides) is expected to become more successful in northern boreal forests because of its current presence in drier areas of North America. However, large-scale productivity decline of aspen has recently been documented throughout the United States and Canada as a result of drought and insect outbreaks. We used tree ring measurements (basal area increment (BAI) and stable carbon isotopes (δ 13C)) and remote sensing indices of vegetation productivity (NDVI) to study the impact of climate and damage by the aspen epidermal leaf miner (Phyllocnistis populiella) on aspen productivity and physiology in interior Alaska. We found that productivity decreased with greater leaf mining and was not sensitive to growing season (GS) moisture availability. Although productivity decreased during high leaf mining years, it recovered to pre-outbreak levels during years of low insect damage, suggesting a degree of resilience to P. populiella mining. Climate and leaf mining interacted to influence tree ring δ 13C, with greater leaf mining resulting in decreased δ 13C when GS moisture availability was low. We also found that NDVI was negatively associated with leaf mining, and positively correlated with BAI and the δ 13C decrease corresponding to mining. This suggests that NDVI is capturing not only variations in productivity, but also changes in physiology associated with P. populiella. Overall, these findings indicate that the indirect effects of P. populiella mining have a larger impact on aspen productivity and physiology than climate under current conditions, and is essential to consider when assessing growth, physiology and NDVI trends in interior Alaska

Brown Treesnake Mortality After Aerial Application of Toxic Baits

Quantitative evaluation of control tools for managing invasive species is necessary to assess overall effectiveness and individual variation in treatment susceptibility. Invasive brown treesnakes (Boiga irregularis) on Guam have caused severe ecological and economic effects, pose a risk of accidental introduction to other islands, and are the greatest impediment to the reestablishment of extirpated native fauna. An aerial delivery system for rodent‐based toxic baits can reduce brown treesnake abundance and heterogeneity among individuals may influence bait attraction or toxicant susceptibility. Previous baiting trials have either been simulated aerial treatments or relied on slightly different bait capsule compositions and the results of aerial delivery of toxic baits under operational conditions may not be directly comparable. We monitored 30 radio‐tagged adult snakes (990–1,265 mm snout‐vent length) during an aerial baiting operation in a 55‐ha area using transmitters equipped with accelerometers and receivers programed to display a status code indicating mortality if a snake failed to move for \u3e24 hours. We used known‐fate models to estimate mortality and evaluate a priori hypotheses explaining differences in mortality based on size, sex, and treatment effects. Eleven radio‐tagged snakes died in the aerial baiting treatment period (0.37, 95% CI=0.21–0.55) and no individuals (0.00, 95% CI=0.00–0.04) died during the non‐treatment period. Our data provide strong evidence for an additive size‐based treatment effect on mortality, with smaller adults (0.59, 95% CI=0.35–0.80) exhibiting higher mortality than larger snakes (0.14, 95% CI=0.02–0.37) but did not support a sex effect on mortality. The high mortality of snakes during the treatment period indicates that aerial baiting can reduce brown treesnake abundance, but further refinement or use in combination with other removal tools may be necessary to overcome size‐based differences in susceptibility and achieve eradication. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society

Bottom-up drivers of future fire regimes in western boreal North America

Forest characteristics, structure, and dynamics within the North American boreal region are heavily influenced by wildfire intensity, severity, and frequency. Increasing temperatures are likely to result in drier conditions and longer fire seasons, potentially leading to more intense and frequent fires. However, an increase in deciduous forest cover is also predicted across the region, potentially decreasing flammability. In this study, we use an individual tree-based forest model to test bottom-up (i.e. fuels) vs top-down (i.e. climate) controls on fire activity and project future forest and wildfire dynamics. The University of Virginia Forest Model Enhanced is an individual tree-based forest model that has been successfully updated and validated within the North American boreal zone. We updated the model to better characterize fire ignition and behavior in relation to litter and fire weather conditions, allowing for further interactions between vegetation, soils, fire, and climate. Model output following updates showed good agreement with combustion observations at individual sites within boreal Alaska and western Canada. We then applied the updated model at sites within interior Alaska and the Northwest Territories to simulate wildfire and forest response to climate change under moderate (RCP 4.5) and extreme (RCP 8.5) scenarios. Results suggest that changing climate will act to decrease biomass and increase deciduous fraction in many regions of boreal North America. These changes are accompanied by decreases in fire probability and average fire intensity, despite fuel drying, indicating a negative feedback of fuel loading on wildfire. These simulations demonstrate the importance of dynamic fuels and dynamic vegetation in predicting future forest and wildfire conditions. The vegetation and wildfire changes predicted here have implications for large-scale changes in vegetation composition, biomass, and wildfire severity across boreal North America, potentially resulting in further feedbacks to regional and even global climate and carbon cycling

Bottom-Up Drivers of Future Fire Regimes in Western Boreal North America

Forest characteristics, structure, and dynamics within the North American boreal region are heavily influenced by wildfire intensity, severity, and frequency. Increasing temperatures are likely to result in drier conditions and longer fire seasons, potentially leading to more intense and frequent fires. However, an increase in deciduous forest cover is also predicted across the region, potentially decreasing flammability. In this study, we use an individual tree-based forest model to test bottom-up (i.e. fuels) vs top-down (i.e. climate) controls on fire activity and project future forest and wildfire dynamics. The University of Virginia Forest Model Enhanced is an individual tree-based forest model that has been successfully updated and validated within the North American boreal zone. We updated the model to better characterize fire ignition and behavior in relation to litter and fire weather conditions, allowing for further interactions between vegetation, soils, fire, and climate. Model output following updates showed good agreement with combustion observations at individual sites within boreal Alaska and western Canada. We then applied the updated model at sites within interior Alaska and the Northwest Territories to simulate wildfire and forest response to climate change under moderate (RCP 4.5) and extreme (RCP 8.5) scenarios. Results suggest that changing climate will act to decrease biomass and increase deciduous fraction in many regions of boreal North America. These changes are accompanied by decreases in fire probability and average fire intensity, despite fuel drying, indicating a negative feedback of fuel loading on wildfire. These simulations demonstrate the importance of dynamic fuels and dynamic vegetation in predicting future forest and wildfire conditions. The vegetation and wildfire changes predicted here have implications for large-scale changes in vegetation composition, biomass, and wildfire severity across boreal North America, potentially resulting in further feedbacks to regional and even global climate and carbon cycling