1,720,964 research outputs found
Pith Eccentricity, Basal Area Increments and Disturbances Inferred from Tree-Ring Growth
No full textForest management constantly seeks tools that can optimize the production of goods and services. As natural archives, tree rings have proven to be effective in terms of refining the dynamics of growth on a temporal basis. This study evaluates the application of these tree rings in estimating the effect of pith eccentricity on forest growth, modeling the increase in basal area (BAI) and identifying disturbances in five coexisting species in northern Mexico. A Wilcoxon rank sum test showed significant differences, with higher radial growth in the north direction compared to the other directions. A mixed model analysis revealed two patterns of BAI growth, fast and slow growing. The former includes P. arizonica, P. engel mannii and P. leiophylla, whereas the latter comprises P. durangensis and P. lumholtzii. The fast-growing group shows a higher increment during the sapling stage. However, during subsequent stages, it presents growth rates similar to those of the slow-growing group. Finally, the percentage growth change (PGC) filter approach identified species disturbances with differential species responses, which temporarily cause uneven-aged forest. We conclude that tree rings can provide valuable information for forest management, and their temporal amplitude can be supported with information from permanent plots
Grouping tree species to estimate basal area increment in temperate multispecies forests in Durango, Mexico
No full textMultispecies forests have received increased scientific attention, driven by the hypothesis that biodiversity improves ecological resilience. However, a greater species diversity presents challenges for forest management and research. Our study aims to develop basal area growth models for tree species cohorts. The analysis is based on a dataset of 423 permanent plots (2,500 m2) located in temperate forests in Durango, Mexico. First, we define tree species cohorts based on individual and neighborhood-based variables using a combination of principal component and cluster analyses. Then, we estimate the basal area increment of each cohort through the generalized additive model to describe the effect of tree size, competition, stand density and site quality. The principal component and cluster analyses assign a total of 37 tree species to eight cohorts that differed primarily with regard to the distribution of tree size and vertical position within the community. The generalized additive models provide satisfactory estimates of tree growth for the species cohorts, explaining between 19 and 53 percent of the total variation of basal area increment, and highlight the following results: i) most cohorts show a “rise-and-fall” effect of tree size on tree growth; ii) surprisingly, the competition index “basal area of larger trees” had showed a positive effect in four of the eight cohorts; iii) stand density had a negative effect on basal area increment, though the effect was minor in medium- and high-density stands, and iv) basal area growth was positively correlated with site quality except for an oak cohort. The developed species cohorts and growth models provide insight into their particular ecological features and growth patterns that may support the development of sustainable management strategies for temperate multispecies forests.Open-Access-Publikationsfonds 202
Spatial variation of the relative importance of the soil loss drivers in a watershed of northern Mexico: a geographically weighted regression approach
No full textSpatial assessing of the soil loss drivers provides information to prioritize the soil conservation areas. In this study, the Universal Soil Loss Equation (USLE) and Geographically Weighted Regression (GWR) were combined to estimate the spatial variation of the relative importance of soil loss drivers, in the Nazas-Rodeo watershed of northern Mexico. Also, the improvements in the GWR model compared to the Ordinary Least Square (OLS) were evaluated. The results indicated that 61.58% of the watershed surface it has a potential for soil loss greater than the tolerance value (T value). Besides, there is a significant amount of surface classified between the categories of considerable to extreme erosion (36,435.89 ha). Regarding the regression analysis, the GWR model showed improvements in the explanation of the variation and the reduction of the error compared to the OLS model. An F-test also indicated that the reduction of the residual sum of squares between the OLS and GWR was significant (p < 0.05). The GWR coefficients showed spatial non-stationarity (i.e. they varied across space) and indicated that the K-factor is the one with the greatest relative importance, followed by the C-factor, the LS-factor, and the R-factor. These results will allow the development of strategies focused on reducing and managing the drivers of soil loss of greater relative importance, facilitating the understanding of the causes and mechanisms of soil loss across space
Patterns of Density and Production in the Community Forests of the Sierra Madre Occidental, Mexico
No full textThe Mexican Sierra Madre Occidental (SMO) represents a region where hundreds of plant species reach the limits of their northern or southern range. The SMO also features a unique cultural diversity, and many communities living within the forest or in its close vicinity depend on the products and services that these forests provide. Our study was based on a large set of remeasured field plots placed in the forests of Durango which are part of the SMO. Using hierarchical clustering, three distinctly different forest types were identified based on structural differences and the relation between stem density and basal area. Maximum forest densities were estimated using a 0.975th quantile regression. Forest production (expressed as current periodic volume increment per unit of area and time) was estimated based on number of stems, forest density, mean height, and forest diversity. Forest density is the principal factors affecting periodic volume production. The discussion presented recommendations for the sustainable use of this unique natural resource. Maintaining minimum levels of residual density is key to ensuring the continued viability of the forests of the Mexican SMO. Future research is needed to identify optimum residual structures, productive residual densities, and desirable levels of biodiversity
Tamaño de sitio de muestreo para inventarios forestales en una selva baja caducifolia de la costa de Jalisco
No full textEfecto de cuatro tratamientos silvícolas en la producción maderable en un Bosque de Durango
No full textEl manejo forestal a través de la aplicación de tratamientos silvícolas adecuados permite lograr la persistencia, el rendimiento sostenido y la máxima producción de los bosques. El objetivo de este trabajo fue evaluar el incremento en volumen fustal de árboles de Pinus durangensis, a partir del análisis de los anillos de crecimiento mediante la técnica del análisis troncal en rodales sometidos a cuatro tratamientos silvícolas; los cuales fueron cortas de regeneración con árboles Padre (realizada en 2007), matarrasa, selección y de aclareo aplicados en el año 2010. Se estudiaron 16 árboles muestra de Pinus durangensis recolectados en sitios de 100 m2, distribuidos al azar por cada tratamiento. Para el análisis troncal, por individuo se obtuvo una rodaja a la base, otra a 1.3 m sobre el nivel del suelo y posteriormente cada metro hasta llegar a la punta. Se estimó el diámetro y la altura de los árboles cada dos anillos de crecimiento y se estimó el volumen, para finalmente conocer los incrementos (ICA e IMA) en intervalos de dos años. Los resultados de la prueba no paramétrica de Kruskal Wallis mostraron diferencias significativas (p < 0.05) en el ICA e IMA en la mayoría de los tratamientos silvícolas evaluados. La matarrasa resultó ser la práctica con los mayores valores de ICA e IMA para todas las edades estudiadas
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
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