In this paper, we evaluated how well-selected distance-dependent and distance-independent competition indices explain individual tree basal area growth of trees, growing in mature and even-aged stands of Pinus cooperi Blanco. A total of 18 competition measures were analyzed of which six do not need tree location (distance-independent) and 12 that utilize tree location (distance-dependent). The competition situation of a stand and/or an individual tree was studied using 11 different competitor selection methods. The mean square error reduction relative to no-competition was used to judge the performance of each competition index. It was found that the best distance-independent competition indices performed as well as the best distance-dependent competition indices. It was concluded that the BAL-MOD-index would be a good competition index to be incorporated into further individual tree basal area growth models for the study area.

ResumenLa presencia de especies vegetales está en función de la altitud, por lo que, el propósito de este estudio fue estimar y comparar la diversidad arbórea sobre un gradiente altitudinal entre los 1 500 a los 3 000 m de la región de El Salto, Durango, que fue dividido en cinco intervalos de 300 m cada uno. Se seleccionaron doce comunidades forestales, y se ubicaron 268 sitios circulares de 0.1 ha de manera aleatoria, distribuidos de forma proporcional por cada intervalo, dentro del cual se estimó la riqueza de especies (S), los índices de diversidad proporcional de Shannon-Wiener (H') y Simpson (l), los de equidad de Pielou (J') y de dominancia de Simpson (E l ). La comparación de la diversidad arbórea entre altitudes se hizo sobre el índice de Shannon-Wiener mediante la prueba de t de Hutcheson. La riqueza de especies varió de 14 a 25 taxa, el índice de Shannon de 1.94 a 2.67 y el de Simpson de 0.09 a 0.18. Los de equidad y dominancia de Pielou y Simpson sugieren que la abundancia de las especies tiende a ser heterogénea. La prueba de t de Hutcheson demostró que existen diferencias significativas en la diversidad de especies entre los intervalos altitudinales.Palabras clave: Diversidad arbórea, gradiente altitudinal, índice de Pielou, índice de Shannon-Wiener, índice de Simpson, riqueza de especies. AbstractThe presence of plant species is a function of altitude; therefore, the purpose of this study was to estimate and compare tree diversity on the altitudinal gradient of the El Salto, Durango region. Twelve forest communities were selected from between 1 500 and 3 000 m, which was divided into five intervals of 300 m each. A total of 268 circular sites of 0.1 ha were randomly distributed proportionally for each interval, where species richness (S), proportional diversity indexes of Shannon-Wiener (H') and Simpson (l), of Pielou's equity (J') and dominance of Simpson (E l ) were determined. Comparison of tree diversity between altitudes was made on the Shannon-Wiener index using the Hutcheson t-test. Species richness varied from 14 to 25 taxa, the Shannon-Wiener index from 1.94 to 2.67 and Simpson's 0.09 to 0.18. Equity and dominance by Pielou and Simpson suggest that species abundance tends to be heterogeneous. The Hutcheson t test showed that there are significant differences in species diversity between altitudinal intervals.

Background Studies on the relationship between biodiversity and ecosystem productivity have suggested that species richness and functional diversity are the main drivers of ecosystem processes. Several patterns on this relationship have been found, including positive, unimodal, negative, and neutral trends, keeping the issue controversial. In this study, taxonomic diversity and functional diversity as drivers of above-ground biomass (AGB) were compared, and the mechanisms that influence biomass production were investigated by testing the complementarity and the mass-ratio hypotheses. Methods Using data from 414 permanent sample plots, covering 23% of temperate forest in the Sierra Madre Oriental (México), we estimated the above-gound biomass (AGB), taxonomic and functional diversity indices, as well as community weighted mean values (CWM) for three functional traits (maximum height, leaf size and wood density) for trees ≥7.5 cm DBH, in managed and unmanaged stands. To compare taxonomic diversity differences between managed and unmanaged stands we carried out a rarefaction analysis. Furthermore, we evaluated the relationship between AGB and taxonomic and functional diversity metrics, as well as CWM traits throught spatial autoregressive models. Results We found a hump-shaped relationship between AGB and species richness in managed and unmanaged forests. CMW of maximum height was the most important predictor of AGB in both stands, which suggested that the mechanism underlaying the AGB-diversity relationship is the dominance of some highly productive species, supporting the mass-ratio hypothesis. Above-ground biomass was significantly correlated with three of the five functional diversity metrics, CWM maximum height and species richness. Our results show the importance of taking into account spatial autocorrelation in the construction of predictive models to avoid spurious patterns in the AGB-diversity relationship. Conclusion Species richness, maximum height, functional richness, functional dispersion and RaoQ indices relate with above-ground biomass production in temperate mixed-species and uneven-aged forests of northern Mexico. These forests show a hump-shaped AGB-species richness relationship. Functional diversity explains better AGB production than classical taxonomic diversity. Community weighted mean traits provide key information to explain stand biomass in these forests, where maximum tree height seems to be a more suitable trait for understanding the biomass accumulation process in these ecosystems. Although the impact of forest management on biodiversity is still debated, it has not changed the AGB-diversity relationships in the forests of the Sierra Madre Occidental, Mexico.

T he aim of this study was to determine the site quality of juniper (Juniperus deppeana Steud.) in the San Dimas region of the state of Durango, Mexico, using the site index method. The database comes from stem analysis of 43 trees felled in harvesting activities. The Chapman-Richards and Schumacher models, by means of the algebraic difference and generalized algebraic difference approaches, were tested to determine the site index; in addition, the error structure was modeled with a second-order autoregressive model to remedy the dependency of existing longitudinal errors. The results showed that the Chapman-Richards model in generalized algebraic difference form provided the best fit according to the adjusted coefficient of determination (R 2 adj = 0.98) and root mean square error (RMSE = 0.46 m). Plotting of the quality curves generated with this model, superimposed on the observed heights, corroborated the goodness of fit of the model selected. The equation obtained with the generalized algebraic difference approach directly estimates the dominant height and site index at any height and base age.Resumen E l objetivo de este trabajo fue determinar la calidad de estación de táscate (Juniperus deppeana Steud.), a través del método de índice de sitio, en la región de San Dimas, Durango. La base de datos proviene de 43 análisis troncales de árboles derribados en actividades de aprovechamiento. Los modelos de Chapman-Richards y de Schumacher, mediante los procedimientos de diferencias algebraicas y diferencias algebraicas generalizadas, se probaron para determinar el índice de sitio; además, se modeló la estructura del error con un modelo autorregresivo de segundo orden para corregir la dependencia de errores longitudinales presentes. Los resultados mostraron que el modelo de ChapmanRichards en diferencias algebraicas generalizadas presentó el mejor ajuste de acuerdo con el coeficiente de determinación ajustado (R 2 adj = 0.98) y la raíz del cuadrado medio del error (RCME = 0.46 m). La representación gráfica de las curvas de calidad generadas con este modelo, sobrepuestas a las alturas observadas, corroboraron la bondad de ajuste del modelo seleccionado. La ecuación obtenida con la metodología de diferencias algebraicas generalizadas estima directamente la altura dominante y el índice de sitio a cualquier altura y edad de referencia.