What causes the density effect in young forest plantations?

In young forest plantations, trees planted at high densities frequently show more rapid height and diameter growth than those plants at lower densities. This positive growth response to density (the ''density effect'') often manifests long before seedlings are tall enough to shade one another, so it is not a simple response to shade. The mechanism(s) which trigger and sustain this growth enhancement are unknown. Our objectives were to document the temporal dynamics of positive growth response to increasing density in Douglas-fir plantations and to test two hypotheses as potential mechanisms for this response. The hypotheses are (1) a canopy boundary layer effect, and (2) alterations in the quality of light reflected from neighboring trees. The ''boundary layer'' hypotheses proposes that changes in atmospheric mixing occur in high-density plantations, promoting increased concentrations of CO{sub 2} and H{sub 2}O vapor during early morning hours, which in turn would enhance carbon assimilation. The ''light quality'' hypothesis proposes that the presence of neighbors alters the ratio of red to far red light in the canopy environment. Plant sensors detect this change in light quality, and growth and development is altered in response. We found that boundary layer conductance was higher, as we predicted, in low-density Douglas-fir stands than in high-density stands five years after planting. The changes in boundary conductance were accompanied by higher CO{sub 2} and H{sub 2}O vapor during early morning hours. However, we also found that the primary manifestation of the density effect in Douglas-fir occurs two to four years after planting, and we were not able to measure differences in boundary conductance in different densities at that time. Also, we found no difference in carbon isotope composition of wood cellulose formed in high- vs. low-density stands two to three years after planting. We conclude that although stand density may have a significant impact on boundary layer conductance in young stands, it does not account for the ''density effect''. Our tests of the light quality hypothesis were slowed due to poor plantation establishment in the early phase of this study. In a variable density experiment we detected significant changes in R:FR related to density. Also in that study we measured a significant enhancement of tree height at high density. However, after three years of growth, the study trees did not show significant differences in stem diameter related to density. Experimenters at Weyerhaeuser therefore decided not to harvest the trees at the end of the 3rd growth year, as originally planned. In a 1-year study of seedlings planted in raised beds subjected to different light quality treatments using transparent plastic film, we found that tree height but not diameter increased in response to decreased R:FR. At this point, we conclude that R:FR remains a viable hypothesis for the ''density effect'', but evidence is not conclusive. We expect that continued measurements in the variable density test plot at Weyerhaeuser will add more evidence in the future

Uso del agua y productividad de los bosques nativos e implantados en el NO de la Patagonia : aproximaciones desde la ecohidrología y la ecofisiología

Existe preocupación por el posible uso excesivo de agua de las forestaciones con especies exóticas de rápido crecimiento en comparación con las especies nativas a las cuales reemplazan en la región NO de la Patagonia. Debido a ello, se han realizado estudios de productividad, consumo y eficiencia en el uso del agua tanto en plantaciones de especies exóticas como en sistemas vegetales naturales en zonas con distintos niveles de déficit hídrico. Esto se llevó a cabo mediante aproximaciones ecohidrológicas y ecofisiológicas. El objetivo del presente trabajo fue analizar y sintetizar el nivel de avance logrado en el conocimiento hasta la fecha. Tanto a nivel de árbol individual como de bosques con cobertura total de dosel arbóreo, las especies exóticas [Pinus ponderosa (pino ponderosa) y Pseudotsuga menziesii (pino oregón)] poseen un mayor consumo de agua que los individuos-sistemas nativos que crecen en sitios similares [pastizal, bosque de ciprés de la cordillera (Austrocedrus chilensis) y bosque mixto de ñire (Nothofagus antarctica) y radal (Lomatia hirsuta), y otras especies leñosas, respectivamente), aunque en todos los casos también se verificó un aumento en la eficiencia en el uso del agua. Los resultados sugieren que las diferencias en productividad y uso de agua se relacionan principalmente con una mayor resistencia hidráulica tanto de flujos en estado líquido (menor conductividad de la madera) como en estado gaseoso (mayor sensibilidad estomática a la demanda atmosférica) en las especies nativas. En el caso de las plantaciones de pino ponderosa, es posible disminuir el consumo de agua mediante el manejo del área foliar (podas y densidad de plantación). A su vez, en el bosque mixto nativo es posible manejar la cantidad y la eficiencia en el uso del agua mediante la extracción selectiva de ciertas especies y tamaños de individuos. Por otro lado, las mayores diferencias en el consumo de agua se observaron entre los pastizales y los bosques densos de pino ponderosa, los que a su vez se ubican en las zonas más secas del área forestable. Por otro lado, la interceptación de lluvias en la zona más árida fue mayor en los bosques nativos que en los implantados, lo cual hizo similar la evapotranspiración total de ambos, aunque es levemente superior en los bosques exóticos en la zona de mayor precipitación anual. Esto pone de manifiesto la importancia de considerar la ubicación, la densidad y el tamaño de los parches forestados en situaciones en las que los recursos hídricos excedentes de las precipitaciones quieran ser aprovechados aguas abajo en otras actividades. En este tipo de situaciones se recomiendan plantaciones con una baja densidad arbórea. Por el contrario, dado los excedentes de agua en la zona más húmeda (de aptitud para el pino oregón), el mayor consumo de la especie exótica no redundaría en un impacto negativo sobre los recursos hídricos. Cabe destacar que dada la mayor eficiencia en el uso del agua de los sistemas exóticos, el costo en agua de la producción de madera de estos bosques es bastante menor al de los sistemas nativos.There is a concern about the potential excessive water used of forest plantations with fast growing exotic species compared to the native vegetation systems they replace in NW Patagonia. For this reason, several studies have being conducted focused on the productivity, water consumption and water use efficiency of the different systems, in areas with different precipitation levels. The studies were carried out from ecohydrological and ecophysiological approaches. The objective of this paper was to analyze and synthesize the available knowledge about these topics. Both at the individual tree level or at forest with complete cover systems, the exotic species (Pinus ponderosa and Pseudotsuga menziesii) have a higher water consumption than all native individual tree-vegetation systems they replace (grassland- Austrocedrus chilensis forests, and mixed forests with Nothofagus antarctica, Lomatia hirsuta, and other native woody species, respectively). However, in all cases, an increase in water use efficiency was observed in exotic species compared to native species. Our results suggest that differences in productivity and water use are mainly due to a higher resistance to water flow, both in liquid (lower wood conductivity) and vapor (higher stomatal sensitivity to vapor pressure deficit) phases in native species compared to exotic ones. At least in the case of ponderosa pine, water use of plantations may be decreased managing leaf area of the system by means of green pruning and thinning. Moreover, in the native mixed forest water use and water use efficiency are able to be managed through selective extraction of individuals of certain species and sizes. On the other hand, the higher differences in water use between native and exotic systems were observed in the most xeric areas, between native grasslands and high density ponderosa pine plantations. On the other hand, rain interception was higher in native forests than in forests plantations in the xeric area, resulting in similar whole evapotranspiration of both systems, whereas it was slightly higher in the forests plantations than in native systems in the humid area. This highlight the importance of considering the spatial distribution, density and size of plantation patches in those situations in which water surplus has to be used for other purposes. In these situations, it is recommended to install low density plantations. In contrast, due to the high water surplus in the more humid areas (with aptitude for Douglas-fir plantations), the higher water consumption of this exotic species compared to the native systems, would not lead to a negative impact on water resources. Finally, we highlight that, due to the high water use efficiency of exotic species, the wood production costs in terms of water are much lower using these species than native ones.Fil: Gyenge, Javier Enrique. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFernandez, Marí­a Elena. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Licata, Julián Andrés. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Concordia; ArgentinaFil: Weigandt, Mariana Noemi. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; ArgentinaFil: Schlichter, Tomas Miguel. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; Argentin

Progress in creating a joint research agenda that allows networked long-term socio-ecological research in southern South America : addressing crucial technological and human capacity gaps limiting its application in Chile and Argentina

Since 1980, more than 40 countries have implemented long-term ecological research (LTER) programs, which have shown their power to affect advances in basic science to understand the natural world at meaningful temporal and spatial scales and also help link research with socially relevant outcomes. Recently, a disciplinary paradigmatic shift has integrated the human dimensions of ecosystems, leading to a long-term socio-ecological research (LTSER) framework to address the world's current environmental challenges. A global gap in LTER/LTSER only exists in the latitudinal range of 40–60°S, corresponding to Argentina and Chile's temperate/sub-Antarctic biome. A team of Chilean, Argentine and US researchers has participated in an ongoing dialogue to define not only conceptual, but also practical barriers limiting LTER/LTSER in southern South America. We have found a number of existing long-term research sites and platforms throughout the region, but at the same time it has been concluded an agenda is needed to create and implement further training courses for students, postdoctoral fellows and young scientists, particularly in the areas of data and information management systems. Since LTER/LTSER efforts in Chile and Argentina are incipient, instituting such courses now will enhance human and technical capacity of the natural science and resource community to improve the collection, storage, analysis and dissemination of information in emerging LTER/LTSER platforms. In turn, having this capacity, as well as the ongoing formalization of LTER/LTSER programs at national levels, will allow the enhancement of crucial collaborations and comparisons between long-term research programs within the region and between hemispheres and continents. For Spanish version of the entire article, see Online Supporting Information (Appendix S1).Desde 1980, más de cuarenta países han implementado programas de Investigación Ecológica a Largo Plazo (LTER por sus siglas en inglés), los cuales han mostrado su capacidad para influir sobre los avances en las ciencias básicas que permiten entender el mundo natural en escalas temporales y espaciales significativas, y también ayudar a enfocar la investigación hacia estudios socialmente relevantes. Recientemente, gracias a un cambio de paradigma en la disciplina, se integró también la dimensión humana de los ecosistemas, llevándola a un marco conceptual de Investigación Socio-Ecológica a Largo Plazo (LTSER por sus siglas en inglés) para enfrentar los desafíos medio-ambientales del mundo actual. Existe un vacío global en LTER/LTSER en el rango latitudinal de 40–60°S, correspondiente a los biomas templados/subantárticos de Argentina y Chile. Un equipo de investigadores chilenos, argentinos y estadounidenses ha trabajado por varios años para definir cuáles son la barreras que actualmente limitan la creación de una Red de LTER/LTSER en el sur de Sudamérica, no solamente en términos conceptuales, sino también a nivel práctico. Existe un buen número de sitios de investigación a largo plazo en la región, pero también concluimos que es necesario crear e implementar más cursos de capacitación para estudiantes, investigadores post-doctorales y jóvenes científicos, particularmente en las áreas de sistemas de manejo de datos e información. Considerando que los esfuerzos LTER/LTSER en Chile y Argentina son incipientes, este tipo de cursos podría mejorar la capacidad humana y técnica en la comunidad de las ciencias y los recursos naturales, así como mejorar los procesos de recolección, almacenamiento, análisis y difusión de la información. A su vez, la formalización de cursos de programas LTER/LTSER a nivel nacional para adquirir dicha capacidad de manejo de la información, permitirá un fortalecimiento crucial de las colaboraciones y comparaciones entre programas de investigación a largo plazo dentro de la región, y entre hemisferios y continentes. La versión en castellano del artículo se encuentra disponible en forma digital como Online Supporting Information S1.Fil: Anderson, Chistopher B. University of North Texas. Department of Biological Sciences; Estados UnidosFil: Celis-Diez, Juan Luis. Pontificia Universidad Católica de Valparaíso, Escuela de Agronomía; ChileFil: Bond, Barbara J.H.G. Oregon State University. Andrews Forest Long-Term Ecological Research Site. Department of Forest Ecosystems and Society; Estados UnidosFil: Martínez Pastur, Guillermo José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Cientificas; ArgentinaFil: Little, Christian. Universidad Austral de Chile. Facultad de Ciencias. Instituto de Ciencias de la Tierra y Evolución; Chile. Fundación Centro de los Bosques Nativos FORECOS; ChileFil: Armesto, Juan J. Pontificia Universidad Católica de Valparaíso, Escuela de Agronomía; ChileFil: Ghersa, Claudio Marco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Austin, Amy Theresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Schlichter, Tomas Miguel. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche. Grupo de Ecología Forestal; ArgentinaFil: Lara, Antonio. Fundación Centro de los Bosques Nativos FORECOS; Chile. Universidad Austral de Chile. Facultad de Ciencias Forestales y Recursos Naturales. Instituto de Silvicultura; ChileFil: Carmona, Martin. Universidad de Chile. Instituto de Ecologıa y Biodiversidad; ChileFil: Chaneton, Enrique Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomia. Departamento de Recursos Naturales y Ambiente; ArgentinaFil: Gutierrez, Julio R. Universidad de La Serena. Departamento de Biología. Instituto de Ecología y Biodiversidad. Centro de Estudios Avanzados en Zonas Aridas; ChileFil: Rozzi, Ricardo. Universidad de La Serena. Departamento de Biología. Instituto de Ecología y Biodiversidad; ChileFil: Vanderbilt, Kristin University of New Mexico. Department of Biology. Sevilleta Long-Term Ecological Research Site; Estados UnidosFil: Oyarce, Guillermo University of North Texas. Library and Information Sciences; Estados UnidosFil: Fernandez, Roberto J. University of North Texas, Department of Biological Sciences; Estados Unido

The Stars of the HETDEX Survey. I. Radial Velocities and Metal-Poor Stars from Low-Resolution Stellar Spectra

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an unbiased, massively multiplexed spectroscopic survey, designed to measure the expansion history of the universe through low-resolution (R∼750) spectra of Lyman-Alpha Emitters. In its search for these galaxies, HETDEX will also observe a few 105 stars. In this paper, we present the first stellar value-added catalog within the internal second data release of the HETDEX Survey (HDR2). The new catalog contains 120,571 low-resolution spectra for 98,736 unique stars between 10∘) Galactic latitudes. With these spectra, we measure radial velocities (RVs) for ∼42,000 unique FGK-type stars in the catalog and show that the HETDEX spectra are sufficient to constrain these RVs with a 1σ precision of 28.0 km/s and bias of 3.5 km/s with respect to the LAMOST surveys and 1σ precision of 27.5 km/s and bias of 14.0 km/s compared to the SEGUE survey. Since these RVs are for faint (G≥16) stars, they will be complementary to Gaia. Using t-Distributed Stochastic Neighbor Embedding (t-SNE), we also demonstrate that the HETDEX spectra can be used to determine a star's Teff, and log g and its [Fe/H]. With the t-SNE projection of the FGK-type stars with HETDEX spectra we also identify 416 new candidate metal-poor ([Fe/H] <−1~dex) stars for future study. These encouraging results illustrate the utility of future low-resolution stellar spectroscopic surveys

Astronometry with the Hubble Space Telescope : trigonometric parallaxes of planetary nebula nuclei NGC 6853, NGC 7293, Abell 31 and DeHt 5

Original article can be found at: http://www.iop.org/EJ/journal/1538-3881 Copyright American Astronomical Society. DOI: 10.1088/0004-6256/138/6/1969We present absolute parallaxes and relative proper motions for the central stars of the planetary nebulae NGC 6853 (The Dumbbell), NGC 7293 (The Helix), Abell 31, and DeHt 5. This paper details our reduction and analysis using DeHt 5 as an example. We obtain these planetary nebula nuclei (PNNi) parallaxes with astrometric data from Fine Guidance Sensors FGS 1r and FGS 3, white-light interferometers on the Hubble Space Telescope. Proper motions, spectral classifications and VJHKT2M and DDO51 photometry of the stars comprising the astrometric reference frames provide spectrophotometric estimates of reference star absolute parallaxes. Introducing these into our model as observations with error, we determine absolute parallaxes for each PNN. Weighted averaging with previous independent parallax measurements yields an average parallax precision, σπ/π = 5%. Derived distances are: d NGC 6853 = 405+28 –25 pc, d NGC 7293 = 216+14 –12 pc, d Abell 31 = 621+91 –70 pc, and d DeHt 5 = 345+19 –17 pc. These PNNi distances are all smaller than previously derived from spectroscopic analyses of the central stars. To obtain absolute magnitudes from these distances requires estimates of interstellar extinction. We average extinction measurements culled from the literature, from reddening based on PNNi intrinsic colors derived from model SEDs, and an assumption that each PNN experiences the same rate of extinction as a function of distance as do the reference stars nearest (in angular separation) to each central star. We also apply Lutz-Kelker bias corrections. The absolute magnitudes and effective temperatures permit estimates of PNNi radii through both the Stefan-Boltzmann relation and Eddington fluxes. Comparing absolute magnitudes with post-AGB models provides mass estimates. Masses cluster around 0.57 , close to the peak of the white dwarf mass distribution. Adding a few more PNNi with well-determined distances and masses, we compare all the PNNi with cooler white dwarfs of similar mass, and confirm, as expected, that PNNi have larger radii than white dwarfs that have reached their final cooling tracks.Peer reviewe

Right ventricular function declines after cardiac surgery in adult patients with congenital heart disease

Right ventricular function (RVF) is often selectively declined after coronary artery bypass graft surgery. In adult patients with congenital heart disease (CHD) the incidence and persistence of declined RVF after cardiac surgery is unknown. The current study aimed to describe RVF after cardiac surgery in these patients. Adult CHD patients operated between January 2008 and December 2009 in the Academic Medical Centre in Amsterdam were studied. Clinical characteristics, laboratory tests, surgical data and intensive care unit outcome were obtained from medical records. RVF was measured by trans-thoracic echocardiography (TTE) and expressed by tricuspid annular plane systolic excursion (TAPSE), tissue Doppler imaging (RV S’) and myocardial performance index (MPI) pre-operatively and direct, at intermediate and late follow up. Of a total of 185 operated, 86 patients (mean age 39 ± 13 years, 54% male) had echo data available. There was a significant fall in RVF after cardiac surgery. TAPSE and RV S’ were significantly higher and MPI was significantly lower pre-operatively compared to direct post-operative values (TAPSE 22 ± 5 versus 13 ± 3 mm (P < 0.01), RV S’ 11 ± 4 versus 8 ± 2 cm/s (P < 0.01) and MPI 0.36 ± 0.14 vs 0.62 ± 0.25; P < 0.01). There were no significant differences in left ventricular function pre-operatively compared to post-operative values. Right-sided surgery was performed in 33, left-sided surgery in 37 and both sided surgery in 16 patients. Decline in RVF was equal for those groups. Patients with severe decline in RVF, were patients who underwent tricuspid valve surgery. Decline in RVF was associated with post-operative myocardial creatine kinase level and maximal troponin T level. There was no association between decline in RVF and clinical outcome on the intensive care unit. 18 months post-operatively, most RVF parameters had recovered to pre-operative values, but TAPSE which remained still lower (P < 0.01). CHD patients have a decline in RVF directly after cardiac surgery, regardless the side of surgery. Although a gradual improvement was observed, complete recovery was not seen 18 months post-operatively

Identifying patient preferences for communicating risk estimates: A descriptive pilot study

BACKGROUND: Patients increasingly seek more active involvement in health care decisions, but little is known about how to communicate complex risk information to patients. The objective of this study was to elicit patient preferences for the presentation and framing of complex risk information. METHOD: To accomplish this, eight focus group discussions and 15 one-on-one interviews were conducted, where women were presented with risk data in a variety of different graphical formats, metrics, and time horizons. Risk data were based on a hypothetical woman's risk for coronary heart disease, hip fracture, and breast cancer, with and without hormone replacement therapy. Participants' preferences were assessed using likert scales, ranking, and abstractions of focus group discussions. RESULTS: Forty peri- and postmenopausal women were recruited through hospital fliers (n = 25) and a community health fair (n = 15). Mean age was 51 years, 50% were non-Caucasian, and all had completed high school. Bar graphs were preferred by 83% of participants over line graphs, thermometer graphs, 100 representative faces, and survival curves. Lifetime risk estimates were preferred over 10 or 20-year horizons, and absolute risks were preferred over relative risks and number needed to treat. CONCLUSION: Although there are many different formats for presenting and framing risk information, simple bar charts depicting absolute lifetime risk were rated and ranked highest overall for patient preferences for format

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy

Burning in Banksia Woodlands: How Does the Fire-Free Period Influence Reptile Communities?

Fire is an important management tool for both hazard reduction burning and maintenance of biodiversity. The impact of time since last fire on fauna is an important factor to understand as land managers often aim for prescribed burning regimes with specific fire-free intervals. However, our current understanding of the impact of time since last fire on fauna is largely unknown and likely dependent on vegetation type. We examined the responses of reptiles to fire age in banksia woodlands, and the interspersed melaleuca damplands among them, north of Perth, Western Australia, where the current prescribed burning regime is targeting a fire-free period of 8–12 years. The response of reptiles to fire was dependent on vegetation type. Reptiles were generally more abundant (e.g. Lerista elegans and Ctenophorus adelaidensis) and specious in banksia sites. Several species (e.g. Menetia greyii, Cryptoblepharus buchananii) preferred long unburnt melaleuca sites (>16 years since last fire, YSLF) compared to recently burnt sites (<12 YSLF). Several of the small elapids (e.g. the WA priority listed species Neelaps calonotus) were only detected in older-aged banksia sites (>16 YSLF). The terrestrial dragon C. adelaidensis and the skink Morethia obscura displayed a strong response to fire in banksia woodlands only. Highest abundances of the dragon were detected in the recently burnt (<7 YSLF) and long unburnt (>35 YSLF) banksia woodlands, while the skink was more abundant in older sites. Habitats from a range of fire ages are required to support the reptiles we detected, especially the longer unburnt (>16 YSLF) melaleuca habitat. Current burning prescriptions are reducing the availability of these older habitats

Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London