338 research outputs found

    Interpreting forest diversity-productivity relationships : volume values, disturbance histories and alternative inferences

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    Understanding the relationship between stand-level tree diversity and productivity has the potential to inform the science and management of forests. History shows that plant diversity-productivity relationships are challenging to interpret—and this remains true for the study of forests using non-experimental field data. Here we highlight pitfalls regarding the analyses and interpretation of such studies. We examine three themes: 1) the nature and measurement of ecological productivity and related values; 2) the role of stand history and disturbance in explaining forest characteristics; and 3) the interpretation of any relationship. We show that volume production and true productivity are distinct, and neither is a demonstrated proxy for economic values. Many stand characteristics, including diversity, volume growth and productivity, vary intrinsically with succession and stand history. We should be characterising these relationships rather than ignoring or eliminating them. Failure to do so may lead to misleading conclusions. To illustrate, we examine the study which prompted our concerns —Liang et al. (Science 354:aaf8957, 2016)— which developed a sophisticated global analysis to infer a worldwide positive effect of biodiversity (tree species richness) on “forest productivity” (stand level wood volume production). Existing data should be able to address many of our concerns. Critical evaluations will improve understanding.</p

    Increasing liana abundance and biomass in tropical forests: emerging patterns and putative mechanisms

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    Tropical forests are experiencing large‐scale structural changes, the most apparent of which may be the increase in liana (woody vine) abundance and biomass. Lianas permeate most lowland tropical forests, where they can have a huge effect on tree diversity, recruitment, growth and survival, which, in turn, can alter tree community composition, carbon storage and carbon, nutrient and water fluxes. Consequently, increasing liana abundance and biomass have potentially profound ramifications for tropical forest composition and functioning. Currently, eight studies support the pattern of increasing liana abundance and biomass in American tropical and subtropical forests, whereas two studies, both from Africa, do not. The putative mechanisms to explain increasing lianas include increasing evapotranspirative demand, increasing forest disturbance and turnover, changes in land use and fragmentation and elevated atmospheric CO2. Each of these mechanisms probably contributes to the observed patterns of increasing liana abundance and biomass, and the mechanisms are likely to be interrelated and synergistic. To determine whether liana increases are occurring throughout the tropics and to determine the mechanisms responsible for the observed patterns, a widespread network of large‐scale, long‐term monitoring plots combined with observational and manipulative studies that more directly investigate the putative mechanisms are essential

    Exploring the impact of tenure arrangements and incentives on sustainable forest use:Evidence from a framed-field experiment in Ethiopia

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    The types of tenurial arrangements and incentives appropriate for the sustainable management of common pool resources (CPRs), such as forests, remain a topic of debate. In this study, we aim to (i) investigate the extraction level of forest resources under short and long-term property rights, and (ii) evaluate the effectiveness of introducing mechanisms that leverage reputation and feelings of guilt in promoting cooperation among CPR users with short-term property rights to reduce over-harvesting. We develop a simple theoretical model to predict the optimal extraction level of a shared forest resource and validate the predictions using data from a framed field experiment conducted in rural Ethiopia. Our findings demonstrate that extraction levels under short-term property rights are higher compared to long-term property rights, aligning with the model predictions. Leveraging reputation and feelings of guilt is effective in bridging the gap in extraction intensity between short- and long-term property rights. However, as implementing reputation requires reliable monitoring that can be costly and challenging in the study context, we propose extending the duration of property rights over shared forest resources as a preferred strategy for curtailing over-extraction.</p

    Dry-season retreat and dietary shift of the dart-poison frog Dendrobates tinctorius (Anura: Dendrobatidae)

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    A precipitação sazonal afeta a dinâmica das florestas tropicais e o comportamento das espécies que fazem parte desse ecossistema. A relação positiva entre os padrões de atividade dos anfíbios e a precipitação já foi demonstrada repetidas vezes. Os membros da família Dendrobatidae, um clado de saposvenenodeflecha neotropicais, são bemconhecidos por seu uso de hábitat e comportamento durante a estação chuvosa, mas seu comportamento durante a estação seca tem recebido pouca atenção. Estudamos o uso de hábitat e a dieta do dendrobatídeo Dendrobates tinctorius na Guiana Francesa durante as estações chuvosa e seca. Ao contrário de muitos outros dendrobatídeos, D. tinctorius não mantém territórios ao longo de toda a estação chuvosa. Ambos os sexos colonizam clareiras recentemente abertas e permanecem apenas poucas semanas nessas manchas, onde os animais consomem uma grande variedade de presas, principalmente formigas, besouros, vespas, larvas de insetos e ácaros. Durante a estação seca, os animais movem-se para locais de abrigo na floresta madura, como brácteas de palmeiras e ocos de árvores. Nesse período, são menos ativos e consomem um menor número de itens alimentares; consomem menos vespas e larvas de insetos e mais cupins. Formigas constituem a presa mais comum durante as duas estações. Discutimos os efeitos das mudanças sazonais no uso de hábitat sobre o comportamento territorial dos dendrobatídeos.Seasonal rainfall affects tropical forest dynamics and behavior of species that are part of these ecosystems. The positive correlation between amphibian activity patterns and rainfall has been demonstrated repeatedly. Members of Dendrobatidae, a clade of Neotropical dartpoison frogs, are well known for their habitat use and behavior during the rainy season, but their behavior during the dry season has received little attention. We studied habitat use and diet of the dendrobatid frog Dendrobates tinctorius in French Guiana during the rainy and dry seasons. Unlike many other dendrobatid frogs, D. tinctorius does not maintain territories for the entire rainy season. Both sexes colonize recently formed canopygaps and stay in these forest patches for only a few weeks. The frogs in these patches consume a great diversity of prey, consisting of ants, beetles, wasps, insect larvae, and mites. During the dry season, frogs move to retreat sites in mature forest, such as palm bracts and tree holes. The frogs are less active and consume fewer prey items in the dry season, and they consume fewer wasps and insect larvae, but more termites. Ants are the most common prey items during both the wet and dry seasons. We discuss the effects of shifts in seasonal habitat use on the territorial behavior of dendrobatid frogs

    Arbuscular mycorrhizal fungi improve nutrient status of Commiphora myrrha seedlings under drought

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    In dryland ecosystems, tree and shrub seedling establishment, growth and survival are limited by access to water and nutrients. Arbuscular mycorrhizal fungi (AMF) increase seedling establishment and survival by enhancing nutrient and water acquisition. We executed a fully-factorial greenhouse experiment to determine the interactive effect of AMF (with and without), water deficit (four levels), and soil layer (topsoil and subsoil) on the biomass, growth, nutrient concentrations, and mycorrhizal root colonization of seedlings of Commiphora myrrha, a tree species that dominates large areas of dry forest and woodland in the Horn of Africa. Mycorrhizal seedlings had higher root and shoot biomass than non-mycorrhizal seedlings. They also had higher nutrient concentrations in root and shoot. Plant biomass was higher when plants were grown in topsoil at lower soil moisture levels. Mycorrhizal responsiveness was highest at lower soil moisture. The drought response index was higher for mycorrhizal than for non-mycorrhizal plants, indicating enhanced mycorrhizal benefits at lower water supply. Seedlings grew better in topsoil than in subsoil. Mycorrhizal colonization of roots of C. myrrha seedlings was higher with lower moisture and higher in topsoil than in subsoil. The increased performance of mycorrhizal C. myrrha indicates that mycorrhization is a major component of the adaptive strategy of seedlings of this species, similar to other species in these dryland deciduous ecosystems. We conclude that for restoration purposes with this species, nursery seedlings should be mycorrhized because of their enhanced growth performance

    Changing patterns of home visiting in general practice: an analysis of electronic medical records

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    BACKGROUND: In most European countries and North America the number of home visits carried out by GPs has been decreasing sharply. This has been influenced by non-medical factors such as mobility and pressures on time. The objective of this study was to investigate changes in home visiting rates, looking at the level of diagnoses in1987 and in 2001. METHODS: We analysed routinely collected data on diagnoses in home visits and surgery consultations from electronic medical records by general practitioners. Data were used from 246,738 contacts among 124,791 patients in 103 practices in 1987, and 77,167 contacts among 58,345 patients in 80 practices in 2001. There were 246 diagnoses used. The main outcome measure was the proportion of home visits per diagnosis in 2001. RESULTS: Within the period studied, the proportion of home visits decreased strongly. The size of this decrease varied across diagnoses. The relation between the proportion of home visits for a diagnosis in 1987 and the same proportion in 2001 is curvilinear (J-shaped), indicating that the decrease is weaker at the extreme points and stronger in the middle. CONCLUSION: By comparison with 1987, the proportion of home visits shows a distinct decline. However, the results show that this decline is not necessarily a problem. The finding that this decline varied mainly between diagnoses for which home visits are not always urgent, shows that medical considerations still play an important role in the decision about whether or not to carry out a home visit

    Biodiversity recovery of Neotropical secondary forests

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    Old-growth tropical forests harbor an immense diversity of tree species but are rapidly being cleared, while secondary forests that regrow on abandoned agricultural lands increase in extent. We assess how tree species richness and composition recover during secondary succession across gradients in environmental conditions and anthropogenic disturbance in an unprecedented multisite analysis for the Neotropics. Secondary forests recover remarkably fast in species richness but slowly in species composition. Secondary forests take a median time of ve decades to recover the species richness of old-growth forest (80% recovery after 20 years) based on rarefaction analysis. Full recovery of species composition takes centuries (only 34% recovery after 20 years). A dual strategy that maintains both oldgrowth forests and species-rich secondary forests is therefore crucial for biodiversity conservation in human-modied tropical landscapes

    Strong floristic distinctiveness across Neotropical successional forests

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    Treatment of heart failure in Dutch general practice

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    BACKGROUND: To study the relation between the prescription rates of selected cardiovascular drugs (ACE-inhibitors and Angiotensin receptor blockers, beta-blockers, diuretics, and combinations), sociodemographic factors (age, gender and socioeconomic class) and concomitant diseases (hypertension, coronary heart disease, cerebrovascular accident, heart valve disease, atrial fibrillation, diabetes mellitus and asthma/COPD) among patients with heart failure cared for in general practice. METHODS: Data from the second Dutch National Survey in General Practice, conducted mainly in 2001. In this study the data of 96 practices with a registered patient population of 374.000 were used. Data included diagnosis made during one year by general practitioners, derived from the electronic medical records, prescriptions for medication and sociodemographic characteristics collected via a postal questionnary (response 76%) RESULTS: A diagnosis of HF was found with 2771 patients (7.1 in 1000). Their mean age was 77.7 years, 68% was 75 years or older, 55% of the patients were women. Overall prescription rates for RAAS-I, beta-blockers and diuretics were 50%, 32%, 86%, respectively, whereas a combination of these three drugs was prescribed in 18%. Variations in prescription rates were mainly related to age and concomitant diseases. CONCLUSION: Prescription is not influenced by gender, to a small degree influenced by socioeconomic status and to a large degree by age and concomitant diseases
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