1,721,112 research outputs found
Coomes, D. A., Burslem, D. F. R. P. & Simonson, W. D. (eds).— Forests and global change. Ecological Reviews, Cambridge University Press, Cambridge & New York, 2014
No full textErard Christian. Coomes, D. A., Burslem, D. F. R. P. & Simonson, W. D. (eds).— Forests and global change. Ecological Reviews, Cambridge University Press, Cambridge & New York, 2014. In: Revue d'Écologie (La Terre et La Vie), tome 70, n°1, 2015. pp. 92-93
Assessing the impacts of fragmentation on plant communities in New Zealand: scaling from survey plots to landscapes
No full textAim Few studies have attempted to assess the overall impact of fragmentation at the landscape scale. We quantify the impacts of fragmentation on plant diversity by assessing patterns of community composition in relation to a range of fragmentation measures.
Location The investigation was undertaken in two regions of New Zealand – a relatively unfragmented area of lowland rain forest in south Westland and a highly fragmented montane forest on the eastern slopes of the Southern Alps.
Methods We calculated an index of community similarity (Bray–Curtis) between forest plots we regarded as potentially affected by fragmentation and control forest plots located deep inside continuous forest areas. Using a multiple nonlinear regression technique that incorporates spatial autocorrelation effects, we analysed plant community composition in relation to measures of fragmentation at the patch and landscape levels. From the resulting regression equation, we predicted community composition for every forest pixel on land-cover maps of the study areas and used these maps to calculate a landscape-level estimate of compositional change, which we term ‘BioFrag’. BioFrag has a value of one if fragmentation has no detectable effect on communities within a landscape, and tends towards zero if fragmentation has a strong effect.
Results We detected a weak, but significant, impact of fragmentation metrics operating at both the patch and landscape levels. Observed values of BioFrag ranged from 0.68 to 0.90, suggesting that patterns of fragmentation have medium to weak impacts on forest plant communities in New Zealand. BioFrag values varied in meaningful ways among landscapes and between the ground-cover and tree and shrub communities.
Main conclusions BioFrag advances methods that describe spatial patterns of forest cover by incorporating the exact spatial patterns of observed species responses to fragmentation operating at multiple spatial scales. BioFrag can be applied to any landscape and ecological community across the globe and represents a significant step towards developing a biologically relevant, landscape-scale index of habitat fragmentation
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
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
Mapping community change in modified landscapes
No full textHabitat loss is not randomly distributed across modified landscapes, yet spatial patterns of habitat cover are not routinely combined with biodiversity data when assessing or predicting the biodiversity impacts of land use change. Here, we convert point observations of more than 28,000 beetles from 851 species into a continuous biodiversity surface representing the similarity of ecological communities relative to that of pristine forest, effectively integrating on-the-ground biodiversity data with remotely sensed land cover data to predict the magnitude of community change in a modified landscape. We generated biodiversity surfaces for both present-day and pre-human landscapes to map spatial patterns of change in a diverse ecological community to calculate the combined biodiversity impacts of habitat loss and fragmentation that accounts for the exact spatial pattern of deforestation. Our spatially-explicit, landscape-scale index of community change shows how the fine-scale configuration of habitat loss sums across a landscape to determine changes in biodiversity at a larger spatial scale. After accounting for naturally occurring within-forest heterogeneity, we estimate that the conversion of 43% of forest to grassland in a 1300 km2 landscape in New Zealand resulted in a 47% change to the beetle community. © 2009 Elsevier Ltd. All rights reserved
Tree-centric mapping of forest carbon density from airborne laser scanning and hyperspectral data
Get PDFAirborne remote sensing is increasingly recognized as an outstanding data source for
high-fidelity mapping of carbon stocks at regional scales. A tree-centric approach to carbon
mapping is developed, based on identifying individual tree crowns (ITCs) from the LiDAR
point cloud and identifying species from airborne hyperspectral data by machine learning.
Using examples from coniferous forest in the Italian Alps, deciduous woodland in Britain,
and lowland tropical forest in Borneo, the tree-centric approach is shown to deliver precise
estimates of individual tree biomass and forest stocks. ITC delineation approaches based
on canopy height models fail to detect subcanopy trees, and a small correction needs to be
made to accommodate these in carbon maps. However, new graph cut approaches using the
entire point cloud can detect individuals beneath the main canopy, provided the LiDAR point
cloud is sufficiently dense. An advantage of the tree-centric approach over existing plot-level
methods is that it is founded on the same principles as field-based inventory approaches,
making it intuitive and transparent to use
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