Sonia Roig

Thinning intensity and growth response in SW-European Scots pine stands

The effect of different thinning intensities on growth and yield was studied in Pinus sylvestris L. stands at the south-western limit of its distribution area (Central Spain), using five long-term thinning trials. Data were analysed collectively considering several factors (trial, block, plot and period) as random effects. Total volume and volume increment decreased with thinning intensity, this loss being more significant in the case of moderate and heavy thinning. No difference was found among treatments for total basal area or the increment in basal area. The results revealed an optimum basal area (Assmann’s definition) between 85 and 100% of the basal area in unthinned plots. Volume growth loss associated with heavy thinnings (reduction of 18% in volume increment) was smaller than that reported in Central and Northern European regions (greater than 25%). Height increment was not influenced by thinning, whereas dominant and quadratic mean diameter increments increased with the thinning intensity. The response of diameter growth to thinning was greater at younger ages (less than 50 y) and in medium-sized trees.RésuméL’effet de différentes intensités d’éclaircie sur la croissance et la production de peuplements de Pinus sylvestris L. a été étudié à la limite sud-ouest de sa zone de répartition (centre de l’Espagne), à partir de cinq essais d’éclaircie suivis à long terme. Les données ont été analysées collectivement en prenant en compte différents facteurs (essai, bloc, placeau et période) comme facteurs aléatoires. Le volume total et l’accroissement en volume diminuaient avec l’intensité d’éclaircie, cette perte devenant plus significative dans le cas d’éclaircies modérées et fortes. Aucune différence n’a été trouvée entre traitements pour la surface terrière totale ni pour sa vitesse d’accroissement. Les résultats révèlent un optimum de surface terrière (selon la définition d’Assmann) compris entre 85–100 % de la surface terrière des placeaux non éclaircis. Les pertes de croissance en volume associées aux éclaircies fortes (réduction de 18 %) étaient plus faibles que celles qui sont rapportées pour les régions du Centre et du Nord de l’Europe (supérieures à 25 %). L’accroissement en hauteur n’a pas été influencé par l’éclaircie alors que l’accroissement quadratique moyen en diamètre augmentait avec l’intensité d’éclaircie. La réponse en termes d’accroissement en diamètre à l’éclaircie a été plus forte pour les jeunes arbres (moins de 50 ans) et les arbres de taille moyenne.

Potential productivity of forested areas based on a biophysical model. A case study of a mountainous region in northern Spain

Abstract• Today’s forest managers face a number of important challenges involving an increasing need for precise estimates of forest structure and biomass, potential productivity or forest growth. The objective is to develop a model for potential productivity in a mountainous region of Spain. The model combines climatic, topographic and lithological data using a variant of a traditional biophysical model: the Paterson index.• In a first approach, the climatic productivity is assessed by modelling the required parameters using different geostatistical techniques and software supported by GIS. A second approach includes the correction of the former productivity classes considering the different lithological facies. The potential forest productivity model involves the integration of both models.• Finally, data from the National Forest Inventory (NFI) are used to compare the real and potential yield data within different regions of the studied area.• The results of these analyses demonstrate the usefulness of the model, particularly in mountainous regions, where no significant differences are found between the data from the NFI and the model, but they also show the discrepancies between the estimates and real data when the latter are considered for different tree species, diameter classes or management.Résumé• Les gestionnaires forestiers doivent actuellement faire face à de nombreux défis qui impliquent un besoin croissant d’estimateurs précis de la structure et de la biomasse, de la productivité potentielle et de la croissance des forêts.• L’objectif de ce travail est la modélisation de la productivité potentielle dans une région montagneuse de l’Espagne. Le modèle combine des données climatiques, topographiques et lithologiques et se base sur une variante d’un modèle biophysique classique : l’indice de Paterson.• Dans une première approche, la productivité climatique est estimée en modélisant les paramètres requis grâce à différentes techniques géostatistiques et de logiciels relevant des systèmes d’information géographique (SIG). Une deuxième approche consiste corriger les anciennes classes de productivité en prenant en compte les facies lithologiques. Le modèle de productivité forestière potentielle a été obtenu en combinant ces deux modèles. Finalement, les données de l’Inventaire Forestier National (IFN) sont utilisées pour comparer les rendements réels et potentiels dans les différentes régions de la zone étudiée.• Les résultats de ces analyses ont montré l’utilité du modèle, en particulier dans les régions montagneuses, où aucune différence significative n’a été décelée entre les données IFN et le modèle. Ces résultats ont cependant mis aussi en évidence des divergences entre la productivité potentielle et données réelles lorsque l’on compare différentes espèces, classes de diamètre ou modes de gestion.

Species distribution models applied to plant species selection in forest restoration: are model predictions comparable to expert opinion?

An expert on local flora usually is the best option for plant species selection in most ecological restoration projects; although species selection often needs to be dealt with swiftly as well as on a limited budget, and obtaining the opinion of a local expert may not always be an economically viable alternative. In such cases, species distribution models (SDM) may offer a faster and more cost effective alternative. We asked six experts to rank native tree species according to their suitability at 24 forest sites. The predictive performance of the suitability rankings was evaluated by assessing their ability to discriminate present from absent species in the observed tree assemblages at each evaluation site. We used the area under the receiver operating characteristic curve to calculate the probability that the estimated suitability for a species present at a particular evaluation site is greater than the estimate for an absent species (both picked at random). Suitability rankings were also obtained from the predictions of SDM and the same procedure was used to estimate the predictive performance of the set of models at each site. The experts offered concordant suitability rankings at almost every evaluation site. There were no significant differences in the predictive performance of the SDM and four of the experts, although the SDM performed slightly better than the other two experts. Our results point to the suitability of the proposed species distribution modeling approach to obtain fast and cost effective recommendations for species selection in forest restoration projects.

Changes in livestock footprint and tree layer coverage in Mediterranean dehesas: a six-decade study based on remote sensing

ABSTRACT The decade of the fifties of the twentieth century triggered huge changes in land use and management in ecosystems worldwide, including the iconic Mediterranean ecosystems known as dehesas. In this study, we have quantified the changes in dehesa landscape status within a geographic area of 200,000 km2 covering mainly the Spanish dehesa range over the last 60 years. We focused on changes of two important dehesa elements: tree density and live stocking rates. Tree density and tree cover change were measured via remote sensing in 29 sample plots (16 km2 each) and selected from the plot-monitoring network of Spanish Rural Landscapes (SISPARES). Live stocking (cattle, sheep, and pig) rates data were obtained from the National Statistical Institute of Spain and were used to assess the entire study area. During the 1950–80s, tree density and cover declined significantly (by 18% and 13%, respectively). By the 1960s, sheep was predominant over cattle in all provinces; pigs had higher stocking rates than in the following decades. However, during the 1970–80s, sheep and pig stocking rate declined drastically (by 90% and 70%, respectively) in just 20 years. In contrast, cattle stocking rate increased progressively since the 1960s, reaching a 60% increment by the 2000s. At the municipality level, we observed similar trends. Our multi-scaled analysis explains the impact of social, political, and economic factors on the conservation status of the main dehesa territory within Spain. We conclude that it is necessary to ensure the effectiveness of these systems through sustainable activities to avoid negative consequences of poor management practices which threaten dehesa perpetuation.

Dynamics of ecosystem services in Pinus sylvestris stands under different managements and site quality classes

Timber and biodiversity are considered two antagonistic ecosystem services (ES), largely influenced by silviculture and site ecological conditions. In order to address the trade-offs between these two ES over time, we performed a retrospective study at compartment level in the Pinus sylvestris forests of the Spanish Central Mountain System. Archival data from Management Plans for eight forests with contrasting silvicultural systems (uniform shelterwood system, group shelterwood system, irregular shelterwood system,) and three different site quality classes were analysed. Timber production was assessed through stand volume, harvested timber volume and a stand volume index. Biodiversity was examined through structural diversity (Gini index, Shannon tree size diversity index, Simpson’s reciprocal index and evenness index, all applied to diameter classes) and the abundance of large living trees. For all silvicultural systems investigated, stand volume and harvested timber volume have grown since the beginning of the management plans (beginning of the twentieth century in some forests). The largest yields of timber corresponded to the best quality sites with more intensive silvicultural treatments (uniform and group shelterwood systems). The uniform shelterwood system showed lower figures for structural diversity, though not always significant. The best site qualities maintained notable structural diversity values, even under the most intensive management system. The application of the different management systems over decades has revealed a synergy between timber production and structural diversity, particularly in those systems maintaining more than one age class, although results are conditioned by forest harvesting history. The interaction between historical silvicultural treatment and site quality has been identified as an important source of information to understand forest dynamics and functioning of ES provision.

Climatic Influence on Oak Landscape Distributions

Climate is one determinant of the distribution and structure of California oak woodlands and Spanish dehesas. We summarize studies conducted in the two regions that use different methodologies to investigate the influence of climate on the distribution of oak species in California and on the development of dehesa silvopastoral systems in Spain. Results show some common climatic characteristics, mainly strong summer drought, medium to low overall year rainfall, and high summer temperatures. However, the influence of climate on oak distribution and management differs sharply. Climate strongly influences oak distribution in California. However, it has little effect on whether or not oak forests are managed as dehesa in Spain. Soil characteristics and socioeconomic issues are more important factors than climate for the creation and maintenance of dehesas in Spain.