Una aproximación ecológica a la silvicultura del roble:síntesis de 50 años de investigación en ecosistemas de roble en Norteamérica

Oak (Quercus L.) is an abundant and widely distributed genus in eastern North America. A history of periodic ire, grazing, canopy disturbance and timber harvesting has favored oak's dominance. But, changes in this regime toward much less ire or complete ire suppression, and selective cutting are causing the successional replacement of oak. High populations of forest herbivores such as whitetailed deer (Odocoileus virginianus), invasive species such as gypsy moth (Lymantria dispar), or dominance of native lora such as mountain laurel (Kalmia latifolia) can also inhibit oak regeneration and add to its loss within a region. Successful oak regeneration is dependent on having an adequate number of large oak advance reproduction before stand regeneration. However, this prerequisite is often lacking in eastern oak forests. Many oak stands have either few or no oak advance reproduction, and when present, it is small and noncompetitive. These common situations can be addressed through silviculture. The lack of oak seedlings in older, mature stands is addressed with a three-stage shelterwood method that promotes acorn production and site preparatory burning that increases acorn germination success. In younger, i.e., sapling and pole stands, crop tree thinning to release co-dominant oaks promotes crown development and future acorn production. The lack of competitive-sized oak reproduction is addressed with a two ­ or three ­ stage shelterwood sequence because this method is very useful for providing adequate light to foster root development of the shade intolerant oak seedlings. Application of the shelterwood method often includes herbicides or prescribed ire to control competing vegetation either before or after the inal overstory removal. When adequate oak advance reproduction is present, then clearcutting is a viable option, but measures may be needed after harvesting to control competing vegetation. Prescribed ire applied several times after inal removal of the shelterwood, or clearcutting is proving a useful tool to favor oak. These silvicultural practices generally have either no or positive impacts on non-target communities of herbaceous plants, mammals, birds, and herpetofauna.Los encinos constituyen un género (Quercus L.) abundante y ampliamente distribuido en los bosques del este de Norte América. La dominancia de los encinos se debe, en gran parte, a una historia de frecuentes disturbios que incluyen fuegos, herbivoría por mamíferos y explotación forestal. Alteraciones a estos regímenes de disturbios históricos hacia disturbios con menos frecuencia e intensidad, y la supresión de fuego, han ocasionado un remplazo gradual de los encinos. El aumento de poblaciones de herbívoros mamíferos (por ejemplo, Odocoileus virginianus), de insectos invasivos (por ejemplo, Lymantria dispar), o la dominancia de arbustos nativos (por ejemplo, Kalmia latifolia) impiden la regeneración de los encinos y contribuyen a su deterioro dentro de una región. La regeneración exitosa de los encinos depende de obtener un nivel adecuado de regeneración avanzada antes de que se inicien los cortes inales. La producción de bellotas puede incrementarse en rodales jóvenes con la aplicación de raleos para estimular el desarrollo de los doseles, o en rodales maduros utilizando una serie de cortes de protección para estimular la producción de semillas. Los cortes de protección suelen estimular el desarrollo de especies helióilas como los encinos, porque aumentan la luminosidad en el sotobosque. Estos cortes usualmente se aplican en conjunto con procedimientos para controlar la vegetación en el sotobosque que compite con los encinos, como el uso de herbicidas o quemas prescritas. Si existe una cantidad adecuada de regeneración avanzada, el uso de la tala raza es apropiado, pero usualmente requiere el control de la competencia (por ejemplo, de malezas) que puede desarrollarse después de la cosecha. La quema prescrita, aplicada una o varias veces después de los cortes de protección o de la tala raza, es una práctica viable que favorece a los encinos. Todas estas intervenciones generalmente ocasionan una respuesta relativamente neutra o positiva a las comunidades de otros grupos de organismos como plantas herbáceas, aves, mamíferos, y la herpetofauna

Challenges facing gap-based silviculture and possible solutions for mesic northern forests in North America

Gap-based silvicultural systems were developed under the assumption that richness, and diversity of tree species and other biota positively respond to variation in size of harvest-created canopy gaps. However, varying gap size alone often does not meet diversity objectives and broader goals to address contemporary forest conditions. Recent research highlights the need to consider site factors and history, natural disturbance models, within-gap structure and recruitment requirements in addition to light resources for desired tree diversity. This synthesis brings together silvicultural developments and ecological literature on gap-based management, highlighting interactions with other factors such as microsite conditions, non-tree vegetation and more. We pose a revised concept for managers and researchers to use in prescriptions and studies focused on integrated overstory and understory manipulations that increase structural complexity within and around canopy openings

Long-Term exercise intervention in patients with McArdle disease: clinical and aerobic fitness benefits

Introduction: The long-term effects of exercise in patients with McArdle disease—the paradigm of ‘exercise intolerance’—are unknown. This is an important question as the severity of the disease frequently increases with time. Purpose: To study the effects of a long-term exercise intervention on clinical and fitness-related outcomes in McArdle patients. Methods: Seventeen patients (exercise group: N=10, 6 male, 38±18yrs; control: N=7, 4 male, 38±18yrs) participated in a twoyear unsupervised intervention including moderate-intensity aerobic (cycle-ergometer exercise for 1h) and resistance (high load-low repetition circuit) training on 5 and 2-3 days/week, respectively. Patients were assessed at baseline and postintervention. Besides safety, outcomes included clinical severity (e.g., exercise intolerance features) on a 0-3 scale (primary outcome), and aerobic fitness, gross muscle efficiency, and body composition (total/regional fat, muscle, and bone mass) (secondary outcomes). Results: The exercise program was safe and resulted in a reduction of one point (-1.0, 95% confidence interval -1.6—-0.5, p=0.025) in clinical severity vs. the control group, with 60% of participants in the exercise group becoming virtually asymptomatic and with no functional limitation in daily life activities. Compared with controls, the intervention induced significant and large benefits (all p<0.05) in the workload eliciting the ventilatory threshold (both in absolute (watts, +37%) and relative units (watts·kg-1 of total body mass or of lower-limb muscle mass, +44%)), peak oxygen uptake (ml·kg-1 ·min-1 , +28%) and peak workload (absolute (+27%) and relative units (+33%)). However, no significant changes were found for muscle efficiency nor for any measure of body composition. Conclusions: A two-year unsupervised intervention including aerobic and resistance exercise is safe and induces major benefits in the clinical course and aerobic fitness of patients with McArdle disease

Decision Support Systems for Weed Management

Editors: Guillermo R. Chantre, José L. González-Andújar.Weed management Decision Support Systems (DSS) are increasingly important computer-based tools for modern agriculture. Nowadays, extensive agriculture has become highly dependent on external inputs and both economic costs, as well the negative environmental impact of agricultural activities, demands knowledge-based technology for the optimization and protection of non-renewable resources. In this context, weed management strategies should aim to maximize economic profit by preserving and enhancing agricultural systems. Although previous contributions focusing on weed biology and weed management provide valuable insight on many aspects of weed species ecology and practical guides for weed control, no attempts have been made to highlight the forthcoming importance of DSS in weed management. This book is a first attempt to integrate 'concepts and practice' providing a novel guide to the state-of-art of DSS and the future prospects which hopefully would be of interest to higher-level students, academics and professionals in related areas

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Ten millennia of hepatitis B virus evolution

Hepatitis B virus (HBV) has been infecting humans for millennia and remains a global health problem, but its past diversity and dispersal routes are largely unknown. We generated HBV genomic data from 137 Eurasians and Native Americans dated between ~10,500 and ~400 years ago. We date the most recent common ancestor of all HBV lineages to between ~20,000 and 12,000 years ago, with the virus present in European and South American hunter-gatherers during the early Holocene. After the European Neolithic transition, Mesolithic HBV strains were replaced by a lineage likely disseminated by early farmers that prevailed throughout western Eurasia for ~4000 years, declining around the end of the 2nd millennium BCE. The only remnant of this prehistoric HBV diversity is the rare genotype G, which appears to have reemerged during the HIV pandemic

Stochastic and deterministic processes regulate spatio-temporal variation in seed bank diversity

Question: Seed banks often serve as reservoirs of taxonomic and genetic diversity that buffer plant populations and influence post-disturbance vegetation trajectories; yet evaluating their importance requires understanding how their composition varies within and across spatial and temporal scales (α- and β-diversity). Shifts in seed bank diversity are strongly governed by the deterministic role of differential seed longevities. Nevertheless, spatio-temporal variability in propagule depletion from and recruitment into seed banks may alter both α- and β-diversity. Here, we ask to what degree deterministic seed exhaustion, stochasticity in recruitment and mortality, or both, shape α- and β-diversity? Location: Temperate hardwood forest stands of varying ages in northern Pennsylvania, USA. Methods: We surveyed the seed bank and herbaceous vegetation communities at 39 sites and examined whether the species richness, abundance and composition of either community differs among and within sites of increasing age ranging from 43 to 106 yr old. We explored how α-diversity (species richness) and abundance (percentage cover, seed density) varied across the chronosequence age using regression analyses. We analyzed differences in β -diversity (community composition) using permutational multivariate analyses (i.e. PERMANOVA, PERMDISP). Finally, we tested whether community composition of the herbaceous layer and seed bank communities exhibited nestedness, where nestedness refers to the degree to which less species-rich sites are a non-random subset of more species-rich sites. Results: We found seed bank α-diversity and abundance consistently declined across a gradient of increasingly older sites. Moreover, nestedness analyses indicated species composition at older sites represented a subset of the species found at younger sites characterized by species with persistent seeds. Nevertheless, seed bank communities demonstrated divergent compositional trajectories, whereby older sites were increasingly dissimilar, not only from younger sites, but also from each other. Conclusions: Our results suggest that even in assemblages strongly structured by deterministic forces, such as seed banks, minor stochastic differences in colonization and extinction events may increase β-diversity over time. Therefore, we argue deterministic and stochastic processes are complementary factors governing post-disturbance turnover in species assemblages, and suggest that seed banks contribute to species’ persistence and overall forest community diversity across space and time

Soil feedback and pathogen activity in \u3ci\u3ePrunus serotina\u3c/i\u3e throughout its native range

1. Oomycete soil pathogens are known to have a negative effect on Prunus serotina seedling establishment and to promote tree diversity in a deciduous forest in Indiana, USA. Here, we investigate whether negative feedbacks operate widely in its native range in eastern USA. 2. In laboratory experiments, soil sterilization was used to test the net effect of soil biota (pathogens and mutualists) and fungicide treatments to test the effects of soil pathogens (oomycetes) on survival of P. serotina seedlings in soils from 22 P. serotina populations throughout the eastern USA. 3. In soil associated with P. serotina trees, there was a significant positive effect of both soil sterilization and fungicide on seedling survival. The two effects were positively correlated, suggesting that oomycetes were responsible for the observed mortality of seedlings in untreated soils relative to sterilized soils. 4. We determined the host-specificity of these interactions by comparing the effects of the soil biota associated with conspecific and heterospecific trees. There was no interaction between the effects of soil origin and soil sterilization, or of soil origin and fungicide, on seedling survival, although an effect of soil origin on the relative oomycete effect suggested that soil pathogens associated with conspecifics had a more negative influence than those from heterospecifics. 5. Fungicide treatment decreased pre-emergence mortality of P. serotina seedlings at two of three field sites in the northern USA. 6. The overall consistency between the laboratory experiments and the field experiment strongly suggests that oomycete soil pathogens have a negative effect on the survival of P. serotina seedlings throughout its native range in the eastern USA. 7. Soil-borne pathogens therefore appear to regulate the densities of a common tree species (P. serotina) at larger geographical scales than previously described, providing additional evidence of the important role that soil biota play in regulating plant populations and structuring plant communities