Estudio de la relación entre la selvicultura y la diversidad estructural en los montes Pinar de Valsaín y Pinar de Navafría

El objetivo de la tesis doctoral "Estudio de la relación entre la selvicultura y la diversidad estructural en los montes Pinar de Valsaín y Pinar de Navafría" es estudiar el patrón espacial y la estructura vertical a diferentes escalas para caracterizar la estructura de la masa a lo largo de las distintas etapas de desarrollo en masas regulares de pino silvestre gestionadas. Para analizar el patrón espacial del regenerado y los pies menores se han utilizado el análisis de la varianza en escalas anidadas y técnicas geoestadísticas. El patrón espacial de los pies mayores se ha analizado mediante la función L(d), la función K(d)(ni/A) para cada clase de altura y la función Lrs(d) para analizar la relación espacial entre clases de altura. Para analizar la asociación espacial entre los árboles padre y el regenerado se ha desarrollado una función a partir de la función K(d). La estructura vertical se ha analizado a nivel de microestructura utilizando el índice de diferenciación de Gadow, y a nivel de masa mediante una modificación de la función L(d) y el variograma de la altura dentro de las parcelas experimentales. La estructura a nivel de monte se ha caracterizado utilizando técnicas geoestadísticas. En Valsaín, el aclareo sucesivo se aplica de forma muy gradual, lo que unido a la distribución irregular de los pies de la masa hace que el regenerado y los pies menores presenten patrón espacial agregado en torno a los 15 m, formando bosquetes de diferentes estratos. Este patrón agregado continúa en las primeras etapas de desarrollo, atenuándose con la edad de la masa, aunque todavía se puede observar en la parcela de 100-120 años. La regeneración muestra al comienzo de las cortas de aclareo sucesivo asociación espacial negativa con los pies del estrato superior en distancias superiores a 10 m. Por el contrario, en Navafría, la distribución muy regular de la masa y la rápida puesta en luz al realizar las cortas de regeneración hacen que la regeneración sea muy homogénea, con un rango de autocorrelación inferior a 5 m. El régimen de claras aplicado tiene como resultado un patrón regular, que se extiende a distancias mayores conforme aumenta la edad de la parcela. A nivel de monte, en Valsaín la densidad de pies de las diferentes clases diamétricas, el área basimétrica y el volumen muestran autocorrelación especial, pero la estructura de la masa varía de unos cuarteles a otros. En Navafría una parte importante de la variabilidad de la estructura está vinculada a la división del monte en tramos de corta. Gran parte de la variabilidad de la estructura de las masas de pino silvestre estudiadas tiene lugar entre 25 y 200 m

Characterization of the spatial structure of the canopy in Pinus sylvestris L. stands from hemispherical photographs

The spatial pattern was characterized in five experimental plots of 0.5 ha established in Scots pine stands located in the Central Mountain Range of Spain with different ecological conditions and in which different silvicultural practises are employed. A new method is proposed to asses the spatial pattern from hemispherical photographs, based on the variance between the gap fractions in sky sectors, which was calculated as a function of the angular distance. The results were compared with the spatial pattern analysis based on the second moment measure, and with the analysis of the structure of the tree number semivariogram. The three methods give a very similar scale of the pattern for most of the plots. The mature plot with more intensive silviculture showed a regular pattern at scales below 6 m. The mature plot in which the silviculture was less intensive showed a cluster pattern at scales around 10 m, and clustering at similar scales was detected during regeneration. Cluster patterns at scales around 5 m were found at the upper limit of the altitudinal range of Scots pine as well as at the lower limit, where Pyrenean oak stands merge with the pinewood. The method proposed allows the scale of the pattern of the canopy to be determined from hemispherical photographs, and can be easily implemented in forest inventories

Spatial distribution of the soil carbon pool in a Holm oak dehesa in Spain

Aims Dehesas are agroforestry systems characterized by scattered trees among pastures, crops and/or fallows. A study at a Spanish dehesa has been carried out to estimate the spatial distribution of the soil organic carbon stock and to assess the influence of the tree cover. Methods The soil organic carbon stock was estimated from the five uppermost cm of themineral soil with high spatial resolution at two plots with different grazing intensities. The Universal Kriging technique was used to assess the spatial distribution of the soil organic carbon stocks, using tree coverage within a buffering area as an auxiliary variable. Results A significant positive correlation between tree presence and soil organic carbon stocks up to distances of around 8 m from the trees was found. The tree crown cover within a buffer up to a distance similar to the crown radius around the point absorbed 30 % of the variance in the model for both grazing intensities, but residual variance showed stronger spatial autocorrelation under regular grazing conditions. Conclusions Tree cover increases soil organic carbon stocks, and can be satisfactorily estimated by means of crown parameters. However, other factors are involved in the spatial pattern of the soil organic carbon distribution. Livestock plays an interactive role together with tree presence in soil organic carbon distribution

Comparación de centrales de ciclo combinado hibridadas con energía solar: tecnologías CCP y Fresnel de reflexión

En el presente trabajo se compara la producción, tanto en términos energéticos como económicos, de centrales de ciclo combinado hibridadas con energía solar de concentración según distintas tecnologías. Como se destaca en [1], los ciclos combinados convencionales se prestan muy adecuadamente a la hibridación con sistemas solares de concentración, que aportan la energía térmica producida al ciclo de vapor (centrales denominadas ISCC por sus siglas en inglés, Integrated Solar CombinedCycle). En efecto, durante la producción anual, las condiciones más exigentes para un ciclo combinado (alta temperatura ambiental) se correlacionan con las condiciones óptimas de producción de energía solar térmica de concentración (estación estival), por lo que se producen ciertas sinergias que favorecen el rendimiento conjunto. En trabajos previos [2] se mostró la idoneidad y viabilidad económica de la tecnología ISCC trabajando con un campo de colectores cilindro parabólicos (CCP) y generación directa de vapor (precalentamiento y evaporación) en localizaciones con condiciones atmosféricas muy severas en verano, pero no en ubicaciones de clima más templado. Por otro lado, en [3] se estudian los posibles puntos de aporte de la energía solar sobre el ciclo de vapor, concluyendo que la producción mejora notablemente si el calor se destina exclusivamente a la evaporación en el nivel de alta presión, evitando el precalentamiento del agua y el sobrecalentamiento del vapor. Asimismo, es también previsible la mejora económica en el caso de que se empleen campos de tipo Fresnel de concentración en lugar de CCP. Por ese motivo, se comparan las tecnologías CCP y Fresnel produciendo ambas exclusivamente vapor en el nivel de alta presión del ciclo de vapor. Para ambas configuraciones se procede a la caracterización de las tecnologías y a su posterior simulación para analizar la producción durante un año tipo en dos localizaciones (Almería y Las Vegas).Los autores desean agradecer al Ministerio de Economía y Competitividad la financiación proporcionada al trabajo, a través de los proyectos de Plan nacional de I+D+i ENE2012-37950-C02- 01 y ENE2012-37950-C02-02

A Featured-Based Strategy for Stereovision Matching in Sensors with Fish-Eye Lenses for Forest Environments

This paper describes a novel feature-based stereovision matching process based on a pair of omnidirectional images in forest stands acquired with a stereovision sensor equipped with fish-eye lenses. The stereo analysis problem consists of the following steps: image acquisition, camera modelling, feature extraction, image matching and depth determination. Once the depths of significant points on the trees are obtained, the growing stock volume can be estimated by considering the geometrical camera modelling, which is the final goal. The key steps are feature extraction and image matching. This paper is devoted solely to these two steps. At a first stage a segmentation process extracts the trunks, which are the regions used as features, where each feature is identified through a set of attributes of properties useful for matching. In the second step the features are matched based on the application of the following four well known matching constraints, epipolar, similarity, ordering and uniqueness. The combination of the segmentation and matching processes for this specific kind of sensors make the main contribution of the paper. The method is tested with satisfactory results and compared against the human expert criterion

New tools to study spatio-temporal interactions among species

Las funciones de segundo orden son cada vez más empleadas en el análisis de procesos ecológicos. En este trabajo presentamos dos funciones de 2º orden desarrolladas recientemente que permiten analizar la interacción espacio-temporal entre dos especies o tipos funcionales de individuos. Estas funciones han sido desarrolladas para el estudio de interacciones entre especies en masas forestales a partir de la actual distribución diamétrica de los árboles. La primera de ellas es la función bivariante para procesos de puntos con marca Krsmm, que permite analizar la correlación espacial de una variable entre los individuos pertenecientes a dos especies en función de la distancia. La segunda es la función de reemplazo , que permite analizar la asociación entre los individuos pertenecientes a dos especies en función de la diferencia entre sus diámetros u otra variable asociada a dichos individuos. Para mostrar el comportamiento de ambas funciones en el análisis de sistemas forestales en los que operan diferentes procesos ecológicos se presentan tres casos de estudio: una masa mixta de Pinus pinea L. y Pinus pinaster Ait. en la Meseta Norte, un bosque de niebla de la Región Tropical Andina y el ecotono entre las masas de Quercus pyrenaica Willd. y Pinus sylvestris L. en el Sistema Central, en los que tanto la función Krsmm como la función r se utilizan para analizar la dinámica forestal a partir de parcelas experimentales con todos los árboles localizados y de parcelas de inventario.Second order moment functions are increasingly being used in the study of ecological processes. In this paper, we present two recently developed second order functions that allow us to study the spatio-temporal interactions between individuals belonging to two species or functional types. These functions were developed to study interactions among species in forest stands using the diametric distribution of the trees. The first of these functions is an intertype function, applied to a marked point pattern layer (Krsmm). It allows us to analyze the spatial correlation of a variable related to each individual and between species as a function of the distance. The second function is a replacement species function (r), by which it is possible to analyze the association between individuals belonging to two different species as a function of their diameter size differences or another variable associated with the individuals. In order to determine the behavior of both the Krsmm and the r functions in the analysis of forest systems in which different ecological processes are operating, three case studies are presented here: one in a mixed stand of Pinus pinea L. and Pinus pinaster Ait. in the northern plateau of the Iberian peninsula, another in a cloud forest situated in the tropical Andean region, and finally, one in the ecotone of Pyrenaica Willd. and Pinus sylvestris L in the Central Mountain System of Spain. In these cases, both of the functions proposed are used to study the forest dynamics in experimental plots where all the trees are mapped.Proyectos S2009/AMB-1668 REGENFOR; AGL2010-21153-C02-01 y beca FPI-UPM

Incorporating environmental and geographical information in forest data analysis A new fitting approach for universal kriging

Universal kriging gives the optimal linear model to incorporate auxiliary information in data analysis in the presence of spatial dependence of observations if the underlying variogram is known. However, in practice, the variogram is typically unknown and its estimation constitutes one of the major problems in universal kriging theory. In this paper, a new method is proposed to estimate the variogram and the mean function in universal kriging based on the relationship between the second moments of the variable Z(s) and the auxiliary variables. The performance of the proposed method is analysed in three case studies the prediction of site index in an Italian stone pine (Pinus pinea L.) forest, the estimation of growing stock in a Scots pine (Pinus sylvestris L.) stand, and the assessment of the environmental factors involved in the distribution of a Meliosma species in a tropical montane cloud forest. The results show that the proposed method performs as well as the maximum likelihood and least squares methods in terms of unbiasedness and precision of the kriging predictor and prediction error variance estimation. The proposed method allows the spatial variability linked to environmental and geographical factors to be identified in the analysis of data from forest ecosystems

The spatial relationship between post-crop remaining trees and the establishment of saplings in Pinus sylvestris stands in Spain

Question What is the spatial relationship between remaining trees and the establishment and development of recruited saplings? Location The Pinus sylvestris forest Pinar de Valsaín, in the Sistema mountain range (central Spain). Methods Three 0.5 ha plots have been analysed. The saplings were located in a 2 m × 2 m grid, characterizing their spatial pattern through a nested ANOVA. The spatial pattern of stems was analysed using the L(d) function. To analyse the spatial relationship between stems belonging to different cohorts, the intertype Lrs(d) function was used. Finally a new function Krx(d) is presented as a method to analyse the relationship between the spatial distribution of stems and the sapling density (a sampled continuous variable). Results The mother trees show cluster pattern at scales of ca. 12 m - 22 m, leading to a spatial pattern at 14 m -16 m for the saplings during the regeneration period. At the beginning of the shelter phase, saplings less than 1.30 m in height show spatial repulsion from the old crop at distances above 10 m, whereas taller saplings show repulsion at shorter distances, due to the suppression of sapling development near the mother trees. At the end of the regeneration period, saplings < 1.30 m appear under the last remaining mother tree canopies. Conclusions In the stands analysed, located at the southern limit of Pinus sylvestris distribution, this species behaves as half-shade tolerant. This study shows that the Krx(d) function might be widely applied to analyse the relationship between patterns that occur at different scales or between a point pattern and a continuous variable, being a useful tool for analysing some forest processes. © IAVS; Opulus Press Uppsala

Modelling coarse woody debris dynamics in even-aged Scots pine forests

Coarse woody debris (CWD) has become an important component in the study of forest ecosystems, being a key factor in the nutrient cycle as well as a habitat for many species. CWD dynamics varies greatly from primeval to managed forests. To assess the CWD dynamics, a chronosequence trial was established in two Scots pine forests in the Central mountain range in Spain. Although, the shelterwood system has been applied in both forests, one has received more intensive silviculture, whereas in the other, regeneration has been much more gradual and the thinning regime has not been so intensive. In order to inventory CWD, five decay classes and four categories according to size and CWD type (stumps and fallen logs or branches) were defined. The volume of branches and logs (estimated from length and mean diameter) and the number of stumps by size class and decay class are used to characterise the CWD. The most notable differences between the two silvicultural systems can be appreciated in the graph as peaks for temporary distribution of larger logs and stumps when intensive silviculture is applied. The CWD observed in the forests studied is mainly produced by logging. The maximum volume of logs and branches above 5 cm in diameter is 43.25 m3/ha after regeneration felling in the first forest, whereas in the other, a maximum of 16.30 m3/ha is reached at 60 years, just after thinning. Large stumps (diameter equal or greater than 30 cm) make up an important part of CWD biomass in these forests just after the regeneration felling. A model was developed to predict the changes in CWD quantity and quality distribution over time as well as predicting the effect of different silviculture options on CWD dynamics. The model integrates two different processes the CWD inputs (which may be continuous or instant), and the decay process, modelled through a Richards-Chapman function. The average lifetime of CWD obtained ranges from 30 years for stumps over 30 cm in diameter to 8 years for logs with a diameter less than 10 cm. © 2005 Elsevier B.V. All rights reserved

Leaf area index estimation in mountain even-aged Pinus silvestris L. stands from hemispherical photographs

In this study a stand level approach is proposed for estimating leaf area index (LAI) in even-aged Scots pine stands using gap fraction data derived from hemispherical photographs. The approach includes both the effect of the spatial distribution of the foliage elements as well as the slope of the terrain. Two chronosequences consisting of 11 plots were established in two Scots pine (Pinus sylvestris L.) forests in the Central Mountain Range of Spain. 12 hemispherical photographs were taken in each plot and variables related to the stage of development, density, relative spacing and site index were calculated. The gap frequency Poisson model was used to estimate the leaf area index. A new function is proposed to assess the effect of the foliage inclination on light transmittance for Scots pine, based on the assumption that the foliage elements show circular horizontal cross-sections. A new model was also developed to restrict the clumping effect on the vertical component in the Poisson model. The effect of the slope on LAI estimates was determined and included in the model. The results indicate that both the clumping effect correction and the slope correction improve the fitting of the Poisson model to the gap frequency experimental curves, and that the function proposed for the inclination angle correction may provide an acceptable approach for some coniferous species. The relationship between the parameters of the gap fraction model (the foliage inclination angle and the clumping coefficient) and stand level variables, that is, the stage of development, density, spacing of the stand and the site index, is analysed. © 2007 Elsevier B.V. All rights reserved