Urgent, Comprehensive Federal Action Needed To Stem Mortality and Medicare Costs Associated With Antimicrobial Resistance

This paper is a call to action for the policies necessary to reduce the burden of antimicrobial resistance, including federal investments in antibiotic stewardship, antibiotic innovation, surveillance, research, diagnostics, infection prevention, the infectious diseases workforce, and global coordination.

A large database supports the use of simple models of post-fire tree mortality for thick-barked conifers, with less support for other species

Background Predictive models of post-fire tree and stem mortality are vital for management planning and understanding fire effects. Post-fire tree and stem mortality have been traditionally modeled as a simple empirical function of tree defenses (e.g., bark thickness) and fire injury (e.g., crown scorch). We used the Fire and Tree Mortality database (FTM)—which includes observations of tree mortality in obligate seeders and stem mortality in basal resprouting species from across the USA—to evaluate the accuracy of post-fire mortality models used in the First Order Fire Effects Model (FOFEM) software system. The basic model in FOFEM, the Ryan and Amman (R-A) model, uses bark thickness and percentage of crown volume scorched to predict post-fire mortality and can be applied to any species for which bark thickness can be calculated (184 species-level coefficients are included in the program). FOFEM (v6.7) also includes 38 species-specific tree mortality models (26 for gymnosperms, 12 for angiosperms), with unique predictors and coefficients. We assessed accuracy of the R-A model for 44 tree species and accuracy of 24 species-specific models for 13 species, using data from 93 438 tree-level observations and 351 fires that occurred from 1981 to 2016. Results For each model, we calculated performance statistics and provided an assessment of the representativeness of the evaluation data. We identified probability thresholds for which the model performed best, and the best thresholds with either ≥80% sensitivity or specificity. Of the 68 models evaluated, 43 had Area Under the Receiver Operating Characteristic Curve (AUC) values ≥0.80, indicating excellent performance, and 14 had AUCs <0.7, indicating poor performance. The R-A model often over-predicted mortality for angiosperms; 5 of 11 angiosperms had AUCs <0.7. For conifers, R-A over-predicted mortality for thin-barked species and for small diameter trees. The species-specific models had significantly higher AUCs than the R-A models for 10 of the 22 models, and five additional species-specific models had more balanced errors than R-A models, even though their AUCs were not significantly different or were significantly lower. Conclusions Approximately 75% of models tested had acceptable, excellent, or outstanding predictive ability. The models that performed poorly were primarily models predicting stem mortality of angiosperms or tree mortality of thin-barked conifers. This suggests that different approaches—such as different model forms, better estimates of bark thickness, and additional predictors—may be warranted for these taxa. Future data collection and research should target the geographical and taxonomic data gaps and poorly performing models identified in this study. Our evaluation of post-fire tree mortality models is the most comprehensive effort to date and allows users to have a clear understanding of the expected accuracy in predicting tree death from fire for 44 species.

Wind and seed: a conceptual model of shape-formation in the cushion plant Azorella Selago

Aims The sub-Antarctic cushion plant, Azorella selago, is usually hemispherical when small but frequently crescent-shaped when larger. Spatial variation in wind speed and in air-borne seed and sediment deposition is examined to determine if wind scouring and deposition patterns could contribute to the development of non-hemispherical shapes in cushion plants. Methods Computational fluid dynamic analyses were conducted for hemispherical and crescent-shaped cushion plants parameterizing models with data from A. selago habitats on Marion Island. Numerical data were contextualized with field observations to arrive at a conceptual model for shape development. Results Airflow modelling showed that both wind scouring and seed deposition of the commonly co-occurring grass Agrostis magellanica are greater on the windward side of the plant. By contrast, heavier sediment particles are predominantly deposited on the leeward side of plants, leading to burial of lee-side A. selago stems. This sediment accumulation may initiate the development of the crescent-shape in hemispherical plants by increasing stem mortality on the plant’s leeward edge. Once developed, the crescent-shape is probably self-reinforcing because it generates greater air recirculation (and lower air velocities) which enhances further deposition and establishment of A. magellanica grasses in the lee of the crescent. The conceptual model consists therefore of three stages namely, (1) negligible air recirculation, (2) sediment deposition and grass establishment, and (3) differential cushion growth. Conclusion This conceptual model of plant shape development may explain the occurrence and orientation of crescent-shaped cushion plants and highlights how predicted changes in wind patterns may affect vegetation patterns.

Drought-induced Amazonian wildfires instigate a decadal-scale disruption of forest carbon dynamics

Drought-induced wildfires have increased in frequency and extent over the tropics. Yet, the long-term (greater than 10 years) responses of Amazonian lowland forests to fire disturbance are poorly known. To understand post-fire forest biomass dynamics, and to assess the time required for fire-affected forests to recover to pre-disturbance levels, we combined 16 single with 182 multiple forest census into a unique large-scale and long-term dataset across the Brazilian Amazonia. We quantified biomass, mortality and wood productivity of burned plots along a chronosequence of up to 31 years post-fire and compared to surrounding unburned plots measured simultaneously. Stem mortality and growth were assessed among functional groups. At the plot level, we found that fire-affected forests have biomass levels 24.8 ± 6.9% below the biomass value of unburned control plots after 31 years. This lower biomass state results from the elevated levels of biomass loss through mortality, which is not sufficiently compensated for by wood productivity (incremental growth + recruitment). At the stem level, we found major changes in mortality and growth rates up to 11 years post-fire. The post-fire stem mortality rates exceeded unburned control plots by 680% (i.e. greater than 40 cm diameter at breast height (DBH); 5–8 years since last fire) and 315% (i.e. greater than 0.7 g cm −3 wood density; 0.75–4 years since last fire). Our findings indicate that wildfires in humid tropical forests can significantly reduce forest biomass for decades by enhancing mortality rates of all trees, including large and high wood density trees, which store the largest amount of biomass in old-growth forests. This assessment of stem dynamics, therefore, demonstrates that wildfires slow down or stall the post-fire recovery of Amazonian forests. This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.

Short-term stem mortality of 10 deciduous broadleaved species following prescribed burning in upland forests of the Southern US

In upland forests of the Southern US, management is increasingly focussed on the restoration and maintenance of resilient structures and species compositions, with prescribed burning being the primary tool used to achieve these goals and objectives. In this study, we utilised an extensive dataset comprising 91 burn units and 210 plots across 13 National Park Service lands to examine the relationships between the probability of stem mortality (P(m)) 2 years after prescribed fire and stem size and direct fire effects for 10 common deciduous broadleaved species. Post-fire stem mortality ranged from 6.9% for Quercus alba to 58.9% for Sassafras albidum. The probability of stem mortality was positively associated with maximum bole char height (CHAR) and inversely related to diameter at breast height (DBH) for all 10 deciduous broadleaved species. Model goodness-of-fit varied, with the poorest fit generally associated with fire-tolerant species and best fit generally associated with fire sensitive species. The information presented contributes to our understanding of post-fire stem mortality and may contribute to the development of fire-related stem mortality models following prescribed burning for eastern tree species. Models should be validated with independent datasets across upland forests types to test for spatial relationships before widespread application.

Post-fire response variability in Mediterranean Basin tree species in Portugal

Fire is the most important natural disturbance driving vegetation dynamics in the Mediterranean Basin. However, studies relating fire-induced tree responses to both fire severity and plant traits are still scarce in this region. We aimed to investigate such relationships further and to develop simple models that could help improve forest management in these fire-prone ecosystems. We compiled data from 16 fire sites in different regions and used models to relate post-fire responses of 4155 trees from 14 species with fire severity indicators and tree characteristics. The influence of several spatiotemporal factors at the site level was also considered. Results showed that pine mortality was usually high and mainly determined by fire severity, whereas plant traits played a minor role. In contrast, mortality of broadleaved trees was usually low, even for high-severity fire, but most trees were top-killed. Stem mortality increased with fire severity and decreased with bark thickness and tree size. The models for predicting individual mortality of pines and stem mortality of broadleaves showed very good performance, including when validated against independent datasets. Our results suggest that it is possible to accurately predict the most common post-fire responses of Mediterranean species based on simple fire and tree characteristics.