Influence of drought on tree rings and tracheid features of Pinus nigra and Pinus sylvestris in a mesic Mediterranean forest

We investigated the influence of climate on the ring width and xylem anatomy of two co-occurring pines (Pinus nigra Arn. and P. sylvestris L.) in the mountains of east-central Spain in order to test their utility for dendroclimatic reconstructions. We developed chronologies of ring width, mean lumen diameter and mean cell-wall thickness (in the earlywood, latewood, and the total annual ring) and the number of cells between 1960 and 2006. Drought, expressed as the standardized precipitation-evapotranspiration index (SPEI), was the main climatic driver of tree radial growth, although trees were also sensitive to temperature (negative effect in previous autumn and current summer) and precipitation (with a general positive effect). P. sylvestris response was stronger to climate of the current year, whereas the effect of previous-year climate was more important for P. nigra. Warm and dry summers reduced ring width, tracheid lumen, and wall thickness in both species, whereas warm winter-spring temperatures had the opposite effect, primarily for P. sylvestris. Previous-year or early-season conditions mainly affected earlywood features, whereas latewood was more responsive to summer climate. Overall, climate appeared to be a stronger limiting factor for P. sylvestris. During periods of drought, cell-wall thickness was reduced while lumen width increased in the latewood of P. sylvestris. This could compromise its hydraulic safety against drought-induced cavitation as our site was close to the southern and dry edge of the species distribution area. Our results suggest that anatomical variables record different and stronger climate information than ring width variables, especially in P. sylvestris. Reconstruction models for SPEI at the 3-month scale were developed for July–August and September– October using principal components regression. The best models included anatomical and width variables of both pine species suggesting that tracheid chronologies can be useful for drought reconstructions especially at mesic sites or with species that encode a mixed drought and temperature-precipitation signal

Presentation of the Special Section Agro-silvo-pastoral Systems

The special section includes selected presentations given at the World Congress Silvo-Pastoral Systems 2016 , held in Universidade de Évora, Portugal from 27th to 30th September, 2016, in the frame of the working group “Forest management and modeling: silviculture, tree management and planning”. The aim of this special section is to give a comprehensive view of latest research developed in the frame of planning and management of agro-silvo-pastoral systems in several countries, with a climate characterized by two seasons, respectively dry and wet, and thus with drought as a limiting factor

Fruticeticultura. Gestión de arbustedos y matorrales

Los arbustos, o frútices, son vegetales leñosos de menos de 5 m de altura sin un tronco preponderante, porque se ramifican a partir de la base. Los arbustos de menor altura, de un metro a lo sumo o poco más, se llaman matas o matillas; sin embargo, el término sufrútice se aplica a plantas semejantes a arbustos, generalmente pequeñas y sólo lignificadas en la base (FONT QUER, 1989). Como consecuencia de esas definiciones, generalmente aceptadas, un matorral (suffruticetum) es una comunidad vegetal dominada por matas, mientras que si el dominio corresponde a arbustos, debe recibir la denominación de arbustedo (fruticetum). La técnica correspondiente a la gestión de los arbustedos y matorrales no ha recibido ningún nombre oficial, o al menos aceptado con generalidad, pero, por similitud con los términos selvicultura (o silvicultura) y pascicultura, debiera denominarse fruticeticultura. Por ello, ese será el término que utilizaremos como título para este trabajo preliminar, dedicado a resumir la tipología general de los arbustedos y matorrales de la Península Ibérica, su significación ecológica, sus características esenciales y sus técnicas de utilización. Esperamos que este trabajo sirva de base e introducción para uno más extenso y profundo que analice la situación de los matorrales y arbustedos españoles con una escala sintaxonómica mucho más detallada

A new method for the identification of old-growth trees in National Forest Inventories: Application to Pinus halepensis Mill. stands in Spain

Old-growth trees play a very important role in the maintenance of biodiversity in forests. However, no clear definition is yet available to help identify them since tree age is usually not recorded in National Forest Inventories. To develop and test a new method to identify old-growth trees using a species-specific threshold for tree diameter in National Forest Inventories. Different nonlinear mixed models for diameter ? age were generated using data from the Spanish Forest Inventory in order to identify the most appropriate one for Aleppo pine in its South-western distribution area. The asymptote of the optimal model indicates the threshold diameter for defining an old-growth tree. Additionally, five site index curves were examined to analyze the influence of site quality on these models

Growth trends and sensitivity to climate of declining Mediterranean open woodlands exhibiting widespread mortality in Southern Spain

We present two chronologies of dead and weakened Quercus ilex trees from declining open woodlands of Southern Andalusia and discuss climate's implication in the current widespread mortality in these ecosystems. Basal area increments were used to find out periods of growth decline preceding death. Absent rings became frequent since the 1970s, coinciding with increasing drought. Negative pointer years matched dry years and became more pronounced in the last decades. Growth was correlated with the annual Palmer Drought Severity Index and precipitations from previous October to May. Mean sensitivity increased recently, ranging between high values (0.35-0.5). Correlations with spring temperatures turned from positive to negative, positive correlations with current autumn precipitation arose whereas significant positive correlations with summer precipitations were no longer observed. These changes could suggest modifications on tree phenology. Intensively-used Mediterranean open woodlands of Southern Andalusia are vulnerable and the current dying process suggests that they are unlikely to overcome increasing stress climatic conditions

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

Modelo dinámico de crecimiento en altura para monte alcornocal (Quercus suber L.) españoles y tunecinos

Seven simple and advanced dynamic polymorphic functions were considered to develop a dominant height growth model for Spanish and Tunisian cork oak forests. Data from 115 stem analyses performed in two regions in each country were used to fit the equations. Parameter estimates were obtained using the Dummy variable method. Both numerical, graphical and biological consistency were used to compare alternative models. The dynamic equation finally selected was derived from the Hossfeld model by considering the shape parameter to be related to site productivity. An analysis of the dominant height growth patterns between the two countries indicated that the same dominant height growth model was valid for both countries. This dominant height growth model allows estimation of dominant height with a level of reliability of at least 83% from an age of 15 years for a prediction interval of less than 40 years.Para desarrollar un modelo de crecimiento en altura dominante para monte alcornocal en España y Túnez se han probado siete funciones polimórficas simples y dinámicas. Para ello se han utilizado datos procedentes de 115 análisis de troncos realizados en dos regiones distintas de cada país. Para estimar los parámetros se utilizó el método de las variables ficticias. Los modelos fueron comparados de forma numérica y gráfica. La ecuación dinámica finalmente seleccionada fue derivada a partir de la ecuación de crecimiento de Hossfeld considerando el parámetro de forma como relacionado con la productividad de la estación. El análisis del patrón que sigue el crecimiento en altura dominante en ambos países indica que el mismo modelo de crecimiento en altura dominante es valido para ambos países. Este modelo de crecimiento en altura dominante nos permite estimar la altura dominante con una fiabilidad de más de un 83% a partir de los 15 años para un periodo de predicción menor de 40 años

Modeling sapling distribution over time using a functional predictor in a generalized additive model

[Key message], The effect of adult trees on sapling density distribution during the regeneration fellings is determined in a Pinus sylvestris L. Mediterranean forest using generalized additive models. [Context], Spatial pattern of adult trees determines the number of new individuals after regeneration fellings, which modify the light and air temperature under tree canopy. [Aims], We proposed a novel spatiotemporal model with a functional predictor in a generalized additive model framework to describe nonlinear relationships between the size of the adult trees and the number of saplings of P. sylvestris and to determine if the spatial pattern of the number of saplings remained constant or changed in time. [Methods], In 2001, two plots (0.5 ha) were set up in two phases of regeneration fellings under the group shelterwood method. We mapped the trees and saplings and measured their diameter and height. The inventories were repeated in 2006, 2010, and 2014. [Results], We found a negative association between the diameter of adult trees and number of saplings up to 7–8 m. Beyond these distances, the diameter of adult trees was not associated with the number of saplings. Our results indicate that the spatial pattern of the number of saplings remained quite constant in time. [Conclusion ], The generalized additive models are a flexible tool to determine the distance range of inhibition of saplings by adult trees

Carbon Sequestration in Medlterranean Oak Forests

The objective of this chapter is to present sorne of the studies currently being carried out in Spain and Portugal which are concerned with the possibility of estimating the amount of carbon flxed by two of the main oak species in the lberian Peninsula; rebollo oak (Quercus pyrenaica Willd.) and cork oak (Quercus suber L.). Three different methodological approaches have been used. The first approach is to use growth models to evaluate the carbon sequestration in both cork and wood over the life of a cork oak plantation.This approach has been applied both for Spain and Portugal. The second approach involves using a yield table as a tool to estímate the carbon sequestration in Quercus pyrenaica forests based on Spanish National Forest lnventories. In a third approach, data from a network of plots is used to estímate the carbon sequestration in pure and mixed Quercus pyrenaica forests. The application of these different methodologies would allow us to forecast and improve the carbon sequestration in lberian oak forests as well as increase our understanding of their dynamics.Instituto Universitario de Gestión Forestal Sostenibl