-This paper presents the growth response of coppice forest of Quercus pyrenaica Willd. to thinnings of different intensities. Four treatments were tested: light, moderate and heavy thinning with respectively 25, 35 and 50% of basal area removed, and no thinning (control). The results obtained show significant differences between treatments for diameter and biomass of the mean tree and for current diameter increment, for the three inventories carried out (1994, 1998, 2002). The largest values for the mean tree were observed with the heaviest thinning treatment. No differences were found between treatments for stand yield (total basal area and biomass). Stand structure appears more regular in thinned plots, reducing the risk of forest fires and increasing the landscape and recreation values and the possibility of silvopastoral use.growth / Mediterranean oak / stand structure / thinning / coppice Résumé -Croissance de taillis de chêne tauzin (Quercus pyrenaica Willd.) soumis à différentes intensités d'éclaircie dans la chaîne montagneuse centrale de l'Espagne. Cet article présente la réponse de taillis de chêne tauzins (Quercus pyrenaica Willd.) à des éclaircies par le bas de différentes intensités. Au total, quatre traitements ont été appliqués: éclaircie faible, moyenne et forte en enlevant respectivement 25, 35 et 50 % de la surface terrière et un traitement sans éclaircie (contrôle). Les résultats ont mis en évidence des écarts significatifs en ce qui concerne le diamètre et la biomasse de l'arbre moyen et l'accroissement courant du diamètre aux trois dates d'inventaires pratiqués (1994, 1998, 2002): à chacun de ces inventaires, des valeurs plus importantes ont été obtenues pour l'arbre moyen lorsque l'intensité d'éclaircie était la plus forte. Aucun écart significatif entre traitements n'a été observé en ce qui concerne la production totale (surface terrière et biomasse). La structure du peuplement est plus régulière dans les parcelles éclaircies, réduisant par là-même les risques d'incendies et augmentant la valeur paysagère et récréative des peuplements ainsi que leur aptitude au sylvo-pastoralisme. croissance / chêne tauzin / éclaircie / structure du peuplement / taillis
-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.thinning / Pinus sylvestris / growth / Mediterranean area / long-term trial Résumé -Intensité d'éclaircie et croissance dans des peuplements de pin sylvestre du sud ouest de l'Europe. L'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.éclaircie / Pinus sylvestris / croissance / région méditerranéenne / essai à long terme
-A dominant height growth model and a site index model were developed for rebollo oak (Quercus pyrenaica Willd.) in northwest Spain. Data from 147 stem analysis in 90 permanent plots, where rebollo oak was the main species, were used for modelling. The plots were selected from the National Forest Inventory at random in proportion to four biogeoclimatic stratums. Different traditional and generalized algebraic difference equations were tested. The evaluation criteria included qualitative and quantitative examinations and a testing with independent data from another region. The generalized algebraic difference equation of Cieszewski based on Bailey equation showed the best results for the four stratums. An analysis of the height growth patterns among ecological stratums was made in order to study the necessity of different site index curves. Results indicated the validity of a common height growth model for the four stratums. In spite of the irregular height growth pattern observed in rebollo oak, probably due to past management, the model obtained allows us to classify and compare correctly rebollo oak stands growing at different sites.growth model / site index / rebollo oak / coppices / algebraic difference equations Résumé -Modèle de croissance en hauteur et qualité de station de chêne tauzin (Quercus pyrenaica Willd.). Les auteurs ont développé un modèle de croissance pour estimer la hauteur dominante et la qualité de station des peuplements de chêne tauzin (Quercus pyrenaica Willd.) dans le NordOuest de l'Espagne. Les données pour établir ce modèle proviennent d'analyse de tiges de 147 arbres dominants de 24 placettes permanentes où l'espèce est la plus représentée. Ces placettes de l'Inventaire Forestier Espagnol ont été proportionnellement réparties dans quatre régions biogéoclimatiques. Huit équations en différences algébriques et huit équations en différences algébriques généralisées ont été essayées pour développer des courbes de croissance. Des analyses numériques, des analyses graphiques et une validation sur un échantillonnage indépendant ont été utilisées pour comparer les différents modèles existants. La fonction de Cieszewski fondée sur l'équation de Bailey avec la méthode des différences algébriques généralisées a donné les meilleurs résultats dans les quatre régions biogéoclimatiques. Les différences des modèles entre écorégions ont été étudiées afin de déterminer si la construction de quatre modèles régionaux différents était nécessaire. Les résultats indiquent qu'un seul modèle commun est utilisable pour toutes les régions étudiées. Malgré une croissance irrégulière en hauteur dominante du chêne tauzin, probablement à cause des gestions antérieures, le modèle recommandé permet de classer et comparer correctement les peuplements de chêne tauzin qui poussent dans différentes régions. modèle de croissance en hauteur / qualité de station / chêne tauzin / taillis / différences algébriques généralisées
Mediterranean dehesas are an archetypal example of high nature value farmland in Europe. To better understand the interactions between trees and grasslands in the conservation and management of the dehesa, we measured, over 3 years, the contribution of scattered trees to the diversity and biomass dry-matter (DM) yield of the herb layer and the relationship between the herb layer (biomass and diversity interaction) and the trees. The study was based on 135 subplots representing four aspects and three distances from fifteen trees selected randomly in a plot within a dehesa in central Spain. The specific questions were the following: (i) To what extent do trees affect biomass of the herbaceous layer? (ii) What is the relationship between herbaceous layer biomass and species diversity under the influence of trees? and (iii) What are the effects of trees and small-scale topography on the herbaceous diversity? Results differed between years depending on water availability. Legume and forb DM yields were highest at the edge of the tree crown and beyond the canopy. Species richness was positively related to legume DM yield, and both were higher at the bottom of the hillside, especially in dry conditions. Given the importance of tree influence on the biomass and diversity of grasslands, maintaining proper agroforestry management practices for trees and grasslands is important for conserving dehesa diversity and productivity under the conditions of high climatic and soil variability in Mediterranean dehesas.
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 the mineral 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.
Acorn production is one of the most important products in silvopastoral systems in the Mediterranean region. In the present study we carried out two preliminary trials to analyze the distribution of production over time and the effect of pruning. The objective was to develop tools to manage this valuable resource within these systems. In the first part of the study, we analyzed the total acorn production of a holm oak stand, and its seasonal distribution (October-January) over two years (1997-1998 and 1998-1999) in five sites in the southwest of Spain. Mean total acorn production ranged from 590 to 830 kg ha -1 . There was considerable variation between the different sites and years studied, as was expected from studies on other oak species. A comparison was also made of acorn production, comparing annual acorn production between 40 pruned and 40 non-pruned trees, for the period 1994-1999. There was an interaction between 'pruning treatment' and 'year'. Pruning, significantly decreased acorn production in all but two years when production was above the average, whereas production was not affected by pruning the three years that acorn yield was below the average. The study of acorn production and the analysis of the effect of pruning, needs to be studied over a longer time period.
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