1,721,158 research outputs found
Context dependent effects of nitrogen deposition on forest understory plant communities
No full textUnderstory communities can dominate forest plant diversity and strongly affect forest ecosystem structure and function. Understories often respond sensitively but inconsistently to nitrogen (N) deposition, varying greatly among species, functional groups and forest types. Here, we characterize such context dependency as driven by differences in the amounts and forms of deposited N, cumulative deposition, the filtering of N by overstories, and available plant species pools. All else being equal, the effects of N deposition on understory trajectories can also vary due to differences in surrounding landscape conditions, ambient browsing pressure, soils and geology, other environmental factors controlling plant growth and historical and current disturbance/management regimes. The number of these factors and their potentially complex interactions complicate our efforts to make simple predictions about how N deposition affects forest understories. Based on a literature review, we summarize evidence for context dependency in the effects of N deposition on forest understories. Our review reaffirms that historical management, and site conditions, such as light and pH-fertility gradients, significantly affect how understory communities respond to N deposition. We conclude that plant species’ and communities’ responses to N deposition vary greatly depending on environmental contexts, implying context dependent values of critical loads for N deposition, and complicating efforts to predict how N deposition will affect forest understories. We need a better understanding of the relationship between the effect of N deposition on an understory community with environmental conditions, including habitat structure and key site historical information. Ideally, this requires a sufficient observational survey, experimental and modeling evidence base in order to make quantified predictions of effects in relation to broad N deposition. In some regions (e.g., temperate forests in Europe and northeastern US), researchers also need to understand context dependency in understory community dynamics in forest ecosystems experiencing lower levels of N deposition than in the recent past
Monitoring nitrogen deposition in global forests
No full textMonitoring the status of nitrogen (N) deposition is a prerequisite for evaluating its ecological and environmental impacts. This chapter reviews the monitoring strategies to measure N deposition to forest ecosystems in six different regions (Europe, North America, East Asia, South Asia, Africa, Central and South America). The current status of monitoring is at very different stages for these regions, ranging from sophisticated and coordinated monitoring networks devoted to the quantification of fluxes to both forested and non-forested sites to sparse intensive studies with variations in methodologies and limited quality assurance protocols. Methods for routine measurements and inferential estimates are described and include: (1) wet and dry deposition, (2) throughfall, stemflow, and bulk deposition, and (3) biomonitoring of lichens and mosses. Key uncertainties and limitations to the routine monitoring methods are described. Low total N deposition rates (20 kg N ha−1 yr−1) to forests occurred in East Asia, parts of the western U.S., central and western Europe, and areas of Africa influenced by biomass burning. Throughfall studies in forests in China reported a substantial increase in N deposition with closer distance to urban areas.
Globally, the monitoring of N deposition to forests is limited and current methods are subject to large uncertainty. Suggestions are made to improve the amount of monitoring sites, the accuracy and the standardization of the monitoring methods, and the accessibility and standardization of the monitoring data. An improved connection between forest monitoring and deposition model development is also needed to improve the utilization of existing monitoring data, along with the coupling of new technologies (e.g., satellite data, measurement model fusion) that can be complementary to monitoring strategies
Contribution of nitrogen deposition to global forest carbon sequestration
No full textHuman activities have drastically increased inputs of reactive nitrogen globally. Increased deposition of N onto forests may alleviate N limitation and thereby stimulated productivity and carbon (C) sequestration in forest aboveground woody biomass (AGWB), a stable C pool with long turn-over times. The associated reduction in atmospheric CO2 concentrations use represents a cooling effect of human N use that may partly offsets the warming effect of human-induced N2O emissions.
The accompanying datasets give information on global spatial variation in the contribution of atmospherically deposited nitrogen (N) to carbon (C) sequestration in forest aboveground woody biomass, as well as the net climatic footprint of human N use resulting from the warming effect of N-induced direct and indirect N2O emissions on the one hand, and the cooling effect of N-induced C sequestration in forest aboveground woody biomass on the other
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Dynamic geochemical models to assess deposition impacts of metals for soils and surface waters
No full textThis chapter describes the use of geochemical models to assess the impacts of the deposition of metals on the concentrations of metals in soils and surface waters. We describe three dynamic models: SMART2-metals, SMARTml and CHUM-AM, each with their specific purpose and geographical scale of application. All three models include the most relevant metal fluxes and soil chemical processes, but with various level of detail related to their specific aim and scale. The ability of the models to simulate the long-term trends of metal fate was assessed by comparing model results and observations of either the present metal status, using hind cast simulations with historical deposition trends, or metal pools in chronosequences of afforested agricultural land of different stand age, or metal concentrations observed in a long-term monitoring study. The model simulations show the long times needed to approach equilibrium concentrations of metals due to changes in the atmospheric deposition of metals, sulphur and nitrogen. Dynamic models are therefore indispensable tools for the assessment of metal concentrations at changing levels of metal inputs to soil-water system
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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