1,720,979 research outputs found
Grouping Forest Tree Species on the Sierra Madre Occidental, Mexico
No full textThe Sierra Madre Occidental in the Mexican State of Durango, is home to about five million ha of species-rich forest ecosystems. Many people live in or near these forests and depend on them for their livelihood. The preservation of the species richness of this unique resource requires improved understanding of individual species functioning, effective modeling and advanced methods of monitoring. Identifying similarities and differences between individual tree species is a key to achieving these aims. Accordingly, the purpose of this study is to define species cohorts based on Durango's extensive network of permanent observational studies. We review different approaches of simplifying speciesrich forest communities. A simple height-growth ordenation, that had been used in several previous studies, provided the motivation for an improved new method of species grouping. The new approach is based on the differentiation between canopy species and permanent subcanopy species. The canopy group is further subdivided into mature and immature individuals using the relationship between diameters and heights within a bivariate mixed normal distribution. The main contribution of this work is the specific approach of vertical stratification based on height/diameter ratios and bivariate clusters. This, to our knowledge, is new and potentially important for developing more advanced methods of harvest control in the forests of the Sierra Madre Occidental, and perhaps also in other multi-species forests that are subject to management
Density and Production in the Natural Forests of Durango/Mexico
No full textMulti-species natural forests, representing more than 90 percent of the total forest area of the world, are a huge resource which can deliver many products and se-vices, in addition to timber. Prominent examples of such natural ecosystems are the communal forests on the Mexican Sierra Madre Occidental, covering approximately 14 million ha. Based on evidence gathered in long-term observational studies in Durango (Mexico), this study presents estimates of forest production in response to specific residual levels of forest density. These estimates permit an evaluation of production losses due to reduced stocking levels in the municipios: Santiago Papasquiaro, San Dimas and Pueblo Nuevo. The available observations show a linear response of forest production to forest density in the communal forests on the Mexican Sierra Madre Occidental, irrespective of site quality, species mixing effects and other variables. Potential production gains are illustrated for the Ejido San Diego de Tezains where detailed compartment data are available. The results regarding potential production gains provide a new basis for improved control of residual forest structures in the natural forests of the Sierra Madre Occidental. However, further studies are needed regarding the response to species diversity and mixing effects as well as specific site variables, as soon as such observations are available.Mexican Comision Nacional Forestal (CONAFOR
Density and Production in the Natural Forests of Durango/Mexico
No full textMulti-species natural forests, representing more than 90 percent of the total forest area of the world, are a huge resource which can deliver many products and se-vices, in addition to timber. Prominent examples of such natural ecosystems are the communal forests on the Mexican Sierra Madre Occidental, covering approximately 14 million ha. Based on evidence gathered in long-term observational studies in Durango (Mexico), this study presents estimates of forest production in response to specific residual levels of forest density. These estimates permit an evaluation of production losses due to reduced stocking levels in the municipios: Santiago Papasquiaro, San Dimas and Pueblo Nuevo. The available observations show a linear response of forest production to forest density in the communal forests on the Mexican Sierra Madre Occidental, irrespective of site quality, species mixing effects and other variables. Potential production gains are illustrated for the Ejido San Diego de Tezains where detailed compartment data are available. The results regarding potential production gains provide a new basis for improved control of residual forest structures in the natural forests of the Sierra Madre Occidental. However, further studies are needed regarding the response to species diversity and mixing effects as well as specific site variables, as soon as such observations are available.Mexican Comision Nacional Forestal (CONAFOR
Assessing biological dissimilarities between five forest communities
Full text linkCITATION: Hao, M., et al. 2019. Assessing biological dissimilarities between five forest communities. Forest Ecosystems, 6:30, doi:10.1186/s40663-019-0188-9The original publication is available at https://forestecosyst.springeropen.comBackground: Dissimilarity in community composition is one of the most fundamental and conspicuous features by
which different forest ecosystems may be distinguished. Traditional estimates of community dissimilarity are based
on differences in species incidence or abundance (e.g. the Jaccard, Sørensen, and Bray-Curtis dissimilarity indices).
However, community dissimilarity is not only affected by differences in species incidence or abundance, but also by
biological heterogeneities among species.
Methods: The objective of this study is to present a new measure of dissimilarity involving the biological
heterogeneity among species. The “discriminating Avalanche” introduced in this study, is based on the taxonomic
dissimilarity between tree species. The application is demonstrated using observations from five stem-mapped
forest plots in China and Mexico. We compared three traditional community dissimilarity indices (Jaccard, Sørensen,
and Bray-Curtis) with the “discriminating Avalanche” index, which incorporates information, not only about species
frequencies, but also about their taxonomic hierarchies.
Results: Different patterns emerged for different measures of community dissimilarity. Compared with the
traditional approaches, the discriminating Avalanche values showed a more realistic estimate of community
dissimilarities, indicating a greater similarity among communities when species were closely related.
Conclusions: Traditional approaches for assessing community dissimilarity disregard the taxonomic hierarchy. In
the traditional analysis, the dissimilarity between Pinus cooperi and Pinus durangensis would be the same as the
dissimilarity between P. cooperi and Arbutus arizonica. The dissimilarity Avalanche dissimilarity between P. cooperi
and P. durangensis is considerably lower than the dissimilarity between P. cooperi and A. arizonica, because the
taxonomic hierarchies are incorporated. Therefore, the discriminating Avalanche is a more realistic measure of
community dissimilarity. This main result of our study may contribute to improved characterization of community
dissimilarities.https://forestecosyst.springeropen.com/articles/10.1186/s40663-019-0188-9Publisher's versio
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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