Tree-ring chronologies were examined to investigate the influence of climate on radial growth of Pinus nigra in southeastern Spain. We addressed whether drought differentially affected the ring-widths of dominant and suppressed trees and if our results supported the hypothesis that, in a Mediterranean climate, suppressed conifer trees suffer greater growth reductions than dominant trees. Climate-growth relationships were analyzed using response and correlation functions, whereas the effect of drought on trees growth was approached by superposed epoch analysis in 10 dry years. A cool, wet autumn and spring, and/or mild winter enhanced radial growth. Latewood was the most sensitive ring section in both kinds of trees and it was primarily influenced by current year precipitations. Earlywood was mostly influenced by climatic conditions previous to the growing season. In general, May was the most influential month. Pinus nigra was shown to be very drought sensitive tree in the study area. Tree-rings in suppressed trees showed lower growth reductions caused by drought than those of dominant trees. However, dominant trees recovered normal growth faster. Dominant trees showed a more plastic response, and suppression appeared to reduce the effect of climate on tree radial growth. Some possible causes for these effects are discussed. Our results support the essential role of the balance between light and moisture limitations for plant development during droughts and show that it is not appropriate to generalize about the way in which suppression affects climate-growth relationship in conifers.

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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 1960-2006. Drought, expressed as the standardized precipitationevapotranspiration 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 temperatureprecipitation signal.

-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

Abstract• We present the longest tree-ring chronology (141 y) of Quercus ilex L. (holm oak), and discuss the species climate-growth relationships and the influence of stand density on tree sensitivity to climate.• Similarly to Quercus suber L., the most influential climatic variables upon holm oak growth were late spring and early summer precipitation, which enhanced growth, and high temperatures in the previous August and current July, which negatively affected growth.• High density stands responded to similar climatic factors as low density stands, but their response was generally weaker. Holm oak sensitivity to climate has increased in recent decades, which might be related to increasing temperatures in the region. Sensitivity was higher in low density stands. Additionally, the effect of summer stress on growth seems to have increased during the same period, similarly to other species in the Iberian Peninsula, suggesting that trees are more vulnerable to climatic changes.• Stand density could buffer the response to climate by smoothing climatic extremes. Nevertheless, the effect of competition might reverse this positive effect at the individual tree level. Precautions should be taken before providing management guidelines regarding the effect of climate change and stand density on holm oak. Mots-clés :chêne vert / dendroécologie / changement climatique / réchauffement / dehesas / cernes des arbres Résumé -Variabilité des relations climat-croissance chez Quercus ilex L. dans des peuplements forestiers ouverts de différentes densités dans l'ouest de la péninsule Ibérique.• Nous présentons la plus longue chronologie de cernes (141 ans) de Quercus ilex L. (chêne vert) comme et nous discutons les relations climat-croissance chez cette espèce et l'influence de la densité du peuplement sur la sensibilité des arbres au climat.• De façon similaire à Quercus suber L., les variables climatiques les plus influentes sur la croissance du chêne vert ont été les précipitations de la fin du printemps et du début de l'été, qui ont augmenté la croissance, et les températures élevées d'août de l'année précédente et du mois de juillet de l'année, qui ont affecté négativement la croissance.• Les peuplements de densité élevé ont répondu à des facteurs climatiques similaires que les peuplements de faible densité mais leur réponse a été généralement plus faible. La sensibilité du chêne vert au climat a augmentée au cours des dernières décennies, elle pourrait être liée à l'augmentation des températures dans la région. Cette sensibilité est plus élevée dans les peuplements de faible densité. En outre, le effet du stress estival sur la croissance semble avoir augmenté au cours de la même pé-riode, de la même façon que pour d'autres espèces dans la péninsule Ibérique, ce qui suggère que les arbres sont plus vulnérables aux changements climatiques.• La densité du peuplement pourrait amortir la réponse au climat en lissant les extrêmes climatiques. Néanmoins, les effets de la concurrence pourraient inverser cet effet positif au niveau de...

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