Isabel Cañellas

Growth response to climate and drought in Pinus nigra Arn. trees of different crown classes

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.

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.

Climate-growth variability in Quercus ilex L. west Iberian open woodlands of different stand density

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.Résumé• 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 période, 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 des arbres individuels. Des précautions doivent être prises avant de fournir, pour le chêne vert, des lignes directrices de gestion concernant les effets du changement climatique et de la densité.

Black pine (Pinus nigra Arn.) growth divergence along a latitudinal gradient in Western Mediterranean mountains

Abstract• Most studies of tree-growth and climate report positive responses to global warming in high latitudes and negative responses at lower ones.• We analyzed tree-ring width of Pinus nigra Arn. along a 500 km latitudinal transect in the Iberian Peninsula to study the temporal trend and climate forcing in tree radial growth during the last century.• Tree growth was enhanced by cool summers and moist cold seasons. Increased moisture stress has decreased tree growth rates. However, we present evidence of growth increases in some trees in all sampled populations after 1980’s. Climate change negatively (positively) affected between 72% (5%) of trees in the southern populations and 40% (25%) in the north Trees with positive growth trends were favored by winter temperatures and their abundance was inversely correlated with forest productivity.• Our findings add evidences of tree growth divergence in the Mediterranean basin and show the gradual transition between forests where positive (temperate and boreal) and negative (Mediterranean) growth trends dominate.Résumé• La plupart des études sur la croissance de l’arbre en relation avec le climat rapportent des réponses positives au réchauffement climatique dans les hautes latitudes et des réponses négatives dans les basses latitudes.• Pour étudier l’évolution temporelle et le forçage climatique dans la croissance radiale des arbres au cours du siècle dernier, nous avons analysé la largeur des cernes chez Pinus nigra Arn. le long d’un transect latitudinal de 500 km dans la Péninsule Ibérique.• La croissance des arbres a été augmentée par des étés frais et des saisons froides humides. L’augmentation du stress hydrique a diminué les taux de croissance des arbres. Cependant, nous présentons la preuve de l’augmentation de la croissance de certains arbres dans toutes les populations échantillonnées après 1980. Le changement climatique a négativement (positivement) affecté entre 72 % (5 %) des arbres dans les populations du Sud et 40 % (25 %) dans les arbres du Nord avec des tendances de croissance positives qui ont été favorisées par les températures hivernales et leur abondance étaient inversement corrélée à la productivité forestière.• Nos résultats ajoutent des preuves de la divergence de croissance des arbres dans le bassin méditerranéen et montrent la transition progressive entre les forêts où les tendances positives (zones tempérées et boréales) et négatives (zone méditerranéenne) de croissance dominent.

Acorn production in Spanish holm oak woodlands

We present a review on the state-of-the-art of fruit prodution in Western Iberia woodlands («dehesas»), and particularly in Q. ilex (holm oak) «dehesas». This threatened ecosystem is of very high ecological and economical importance. Quercus sp. fruits (acorns) are essential for wildlife, and for pig fattening in «dehesas». In the first part of this review we briefly describe the phenology of the holm oak and the factors affecting acorn morphology and chemical composition. In the second half we analyze the main known factors reported in the literature that determine acorn production: pruning, stand characteristics, and site (weather and soil). We make several suggestions to improve future research and detect the existing gaps in the undertanding of acorn production. Fruit production is highly variable, both between and within years and individuals. The mean production in «dehesas» (mean density circa 50 trees/ha) is around 250-600 kg/ha (≈100 g/canopy-m, CV > 100%). Acorn morphology is also very variable, with mean sound acorn size around 3.5 × 1.6 cm, CV ≈ 10% (3.5 g/acorn, CV > 50%). Silviculture plays an essential role in acorn production. Acorn production per tree seems to be negatively related to density. The effect of pruning is less clear: production seems to be reduced in the first and second years after pruning. After the third year it is not possible to discern from the literature whether there is any response to pruning or not. Weather and soil (site) also impact production and their effects should be explored in future management. The influence of genetics is unknown and should also be addressed. Longer data series are necessary. The dasometric features of the stands need to be characterized, in order to better understand production and compare results from different locations. Much research is still required to understand the functioning of fruiting in these woodlands.

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.

Growth and Yield Models for Pinus halepensis Mill

A partir de los datos obtenidos de 72 parcelas instaladas en 1965, en masas repobladas de Pinus halepensis, inventariadas en 1965, 1970, 1975, 1980, 1988 y 1999, se han elaborado modelos de crecimiento y produccion de selvicultura encontrada para cuatro calidades de estacion. Las curvas de calidad se han definido por la altura dominante alcanzada a los 80 anos de edad y se han ajustado por el modelo de Richards, resultando las siguientes curvas: calidad 20, calidad 17, calidad 14 y calidad 11. Posteriormente se han elaborado modelos de produccion de selvicultura variable incluyendo dos regimenes de claras, simulados a traves de la variacion del indice de Hart-Becking, para las calidades 20 y 17, que son las que presenta un mayor interes productivo. Para las calidades 14 y 11 se representan tablas con un unico regimen moderado de claras, como corresponde a su mayor interes protector y su menor interes productivo.

Silviculture and dynamics of Pinus sylvestris L. stands in Spain

En este trabajo se presenta informacion sobre ecologia, tipologia, selvicultura, produccion, dinamica y biodiversidad de los pinares de Pino silvestre en Espana. Inicialmente se realiza una descripcion de la distribucion y tipos de masa de Pino silvestre y de sus aspectos climaticos y edaficos mas importantes. En segundo lugar se presenta una tipologia de las masas naturales en la Peninsula Iberica. Posteriormente se tratan los aspectos mas importantes de la selvicultura de la especie, incluyendo los objetivos de la ordenacion de sus masas en Espana. En el apartado de produccion se aporta informacion relativa de su produccion potencial ademas de una tabla de produccion para las cinco calidades de estacion definidas en Espana. Se tratan las diferentes etapas de sucesion natural de las masas del pinar asi como los tratamientos o practicas selvicolas mas comunes en Espana. Por ultimo se hace una breve referencia de los efectos de la selvicultura aplicada en la biodiversidad de estas masas forestales.

Stand Competition Determines How Different Tree Species Will Cope with a Warming Climate

Plant-plant interactions influence how forests cope with climate and contribute to modulate species response to future climate scenarios. We analysed the functional relationships between growth, climate and competition for Pinus sylvestris, Quercus pyrenaica and Quercus faginea to investigate how stand competition modifies forest sensitivity to climate and simulated how annual growth rates of these species with different drought tolerance would change throughout the 21st century. Dendroecological data from stands subjected to thinning were modelled using a novel multiplicative nonlinear approach to overcome biases related to the general assumption of a linear relationship between covariates and to better mimic the biological relationships involved. Growth always decreased exponentially with increasing competition, which explained more growth variability than climate in Q. faginea and P. sylvestris. The effect of precipitation was asymptotic in all cases, while the relationship between growth and temperature reached an optimum after which growth declined with warmer temperatures. Our growth projections indicate that the less drought-tolerant P. sylvestris would be more negatively affected by climate change than the studied sub-Mediterranean oaks. Q. faginea and P. sylvestris mean growth would decrease under all the climate change scenarios assessed. However, P. sylvestris growth would decline regardless of the competition level, whereas this decrease would be offset by reduced competition in Q. faginea. Conversely, Q. pyrenaica growth would remain similar to current rates, except for the warmest scenario. Our models shed light on the nature of the species-specific interaction between climate and competition and yield important implications for management. Assuming that individual growth is directly related to tree performance, trees under low competition would better withstand the warmer conditions predicted under climate change scenarios but in a variable manner depending on the species. Thinning following an exponential rule may be desirable to ensure long-term conservation of high-density Mediterranean woodlands, particularly in drought-limited sites.

Revisión: Índices de diversidad estructural en masas forestales

La estructura es un buen indicador de la biodiversidad del sistema y es facilmente modif icable a traves de la selvicultura, por lo que su adecuado conocimiento es indispensable para garantizar una gestion sostenible. En este trabajo se presenta una revision sobre el analisis de la diversidad estructural en masas forestales. El estudio de la diversidad estructural de un bosque se puede abordar desde un punto de vista estatico y dinamico. En primer lugar se describen y discuten los principales indices que caracterizan desde un punto de vista estatico los tres aspectos de la estructura de un rodal: distribucion espacial, diversidad y mezcla de especies y diferenciacion. Para cada uno de estos tres aspectos se incluyen indices tanto espaciales como no espaciales. Posteriormente se analizan los indices de diversidad estructural conjunta, que valoran de manera global los tres aspectos de la estructura del rodal antes considerados, incluyendo en algunos casos una estimacion de la madera muerta. Finalmente se revisan los trabajos que realizan un analisis dinamico de la diversidad estructural, generalmente basados en el estudio de la evolucion en el tiempo de los indices estaticos. Se comentan las tres metodologias con las que se puede acometer este estudio: parcelas localizadas en las distintas fases de desarrollo del ciclo de la masa, parcelas permanentes y modelos de crecimiento que simulen la estructura del rodal.