Miren del Río

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.

Analysis of diameter-density relationships and self-thinning in non-thinned even-aged Scots pine stands

Abstract Self-thinning and size–density relationships in non-thinned even-aged Scots pine stands in Spain were studied. Data from nine thinning experimental areas located in natural and artificial stands were used with a total of 23 untreated or control permanent plots. Three different diameter–density expressions were fitted and compared: the Reineke’s equation, the modification of this expressions proposed by Zeide [Zeide, B., 1995. For. Ecol. Manage. 72, 265–272], and the self-thinning model developed by Tang et al. [Tang S., Meng, C.H., Wang, Y.H., 1994. For. Ecol. Manage. 70, 67–73]. Results indicate that self-thinning in Pinus sylvestris L. follows a concave down line whose slope increases with stand density until it takes as its asymptote the straight line of maximum density. The slope of this straight line obtained for Scots pine stands in Spain is −1.75.

Comparing volume growth in pure and mixed stands of Pinus sylvestris and Quercus pyrenaica

Abstract• In Mediterranean forestry, it is important to improve knowledge about mixed stands dynamics, including their productivity. Previous studies have focused on the interactions between different species (competition, reduction of competition and facilitation) depending on site, species composition and structure.• At the centre of this research are the possible differences between pure and mixed stands of Pinus sylvestris and Quercus pyrenaica in terms of density-growth relationships and volume growth per species.• Using data from the second and third Spanish National Forest Inventory (606 plots), volume increment models for these species were fitted. Both species displayed a similar density-growth pattern for pure and mixed stands, with a maximum volume growth at maximum density. Volume increment per occupied area was also found to be greater in mixed stands as opposed to pure stands, suggesting a species interaction with reduced levels of competition in the former. However, the total volume growth was generally lower in mixed stands since the growth rate of oak is much lower.• The results highlight the expedience of favouring P. sylvestris-Q. pyrenaica mixed stands with higher proportions of pine trees in order to gain the benefits of a more complex forest whilst retaining an acceptable level of wood production.Résumé• Dans la foresterie méditerranéenne, il est important d’améliorer les connaissances sur la dynamique des peuplements mixtes, y compris sur leur productivité. Des études antérieures ont mis l’accent sur les interactions entre espèces différentes (concurrence, réduction de la concurrence et facilitation), selon la station, la composition des essences et la structure.• Cette recherche porte sur les différences possibles entre les peuplements purs et les peuplements mixtes de Pinus sylvestris et Quercus pyrenaica en termes de relation densité-croissance et croissance en volume par espèce.• À partir des données du deuxième et du troisième Inventaire Forestier National Espagnol (606 placettes), des modèles d’accroissement en volume pour ces espèces ont été ajustés. Les deux espèces ont affiché un modèle densité-croissance similaire pour les peuplements purs et les peuplements mixtes, avec un volume maximum de croissance à une densité maximale. L’accroissement de volume par zone occupée a également été trouvé plus important dans les peuplements mixtes plutôt que dans les peuplements purs, ce qui suggère une interaction entre espèces avec réduction des niveaux de concurrence dans celui-là. Toutefois, la croissance totale en volume a été généralement plus faible dans les peuplements mixtes puisque le taux de croissance du chêne est beaucoup plus faible.• Les résultats soulignent l’opportunité de favoriser les peuplements mixtes P. sylvestris-Q. pyrenaica avec une proportion plus élevée de pins afin d’obtenir les avantages d’une forêt plus complexe, tout en conservant un niveau acceptable de production de bois.

Temporal variation of competition and facilitation in mixed species forests in Central Europe

Facilitation, reduced competition or increased competition can arise in mixed stands and become essential to the performance of these stands when compared to pure stands. Facilitation and over-yielding are widely held to prevail on poor sites, whereas neutral interactions or competition, leading to under-yielding of mixed versus pure stands, can occur on fertile sites. While previous studies have focused on the spatial variation of mixing effects, we examine the temporal variation of facilitation and competition and its effect on growth. The study is based on tree ring measurement on cores from increment borings from 559 trees of Norway spruce (Picea abies [L.] Karst.), European beech (Fagus sylvatica [L.]) and sessile oak (Quercus petraea (Matt.) Liebl.) in southern Germany, half of which were in pure stands and half in adjacent mixed stands. Mean basal area growth indices were calculated from tree ring measurements for pure and mixed stands for every species and site. The temporal variation, with positive correlations between species-specific growth indices during periods of low growth and neutral or negative correlations during periods of high growth, is more distinct in mixed than in neighbouring pure stands. We provide evidence that years with low growth trigger over-yielding of trees in mixed as opposed to pure stands, while years with high growth lead to under-yielding. We discuss the relevance of the results in terms of advancing our understanding and modelling of mixed stands, extension of the stress gradient hypothesis, and the performance of mixed versus pure stands in the face of climate change.

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.

Characterization of the structure, dynamics, and productivity of mixed-species stands: review and perspectives

The growth and yield of mixed-species stands has become an important topic of research since there are certain advantages of this type of forest as regards functions and services. However, the concepts and methods used to characterize mixed stands need to be understood, as well as harmonized and standardized. In this review we have compiled a set of measures, indices, and methods at stand level to characterize the structure, dynamics, and productivity of mixed stands, and we discuss the pros and cons of their application in growth and yield studies. Parameters for the characterization of mixed stand structure such as stand density, species composition, horizontal (intermingling) and vertical tree distribution pattern, tree size distribution, and age composition are described, detailing the potential as well as the constraints of these parameters for understanding resource capture, use, and efficiency in mixed stands. Furthermore, a set of stand-level parameters was evaluated to characterize the dynamics of mixed stands, e.g. height growth and space partitioning, self- and alien-thinning, and growth partitioning among trees. The deviations and changes in the behaviour of the analysed parameters in comparison with pure stand conditions due to inter-specific interactions are of particular interest. As regards stand productivity, we reviewed site productivity indices, the growth–density relationship in mixed stands as well as methods to compare productivity in mixed versus monospecific stands. Finally, we discuss the main problems associated with the methodology such as up-scaling from tree to stand level as well as the relevance of standardized measures and methods for improving forest growth and yield research in mixed stands. The main challenges are also outlined, especially the need for qualitatively sound data.

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.

Climate modifies tree interactions in terms of basal area growth and mortality in monospecific and mixed Fagus sylvatica and Pinus sylvestris forests

Abstract Net interactions between trees vary depending on environmental conditions and other factors such as stand density, age, or between-species complementarity and/or facilitation. According to the stress gradient hypothesis, positive or facilitative interactions are more frequent in high-stress environments whereas negative or competitive interactions occur in benign environments, although recent studies highlight the influence of species composition, type of stress, ontogeny, etc. on the interaction–stress gradient pattern. The aim of this paper is to analyze whether site climatic variables are a key factor in tree interactions in mixed stands of beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.). To test how site climatic conditions modify the effect of inter-specific competition on tree basal area growth and tree mortality, growth and mortality models were fitted using monospecific and mixed sample plots located in matching site conditions selected from the Spanish National Forest Inventory in the Navarra Province. Tree competition status was broken down into four terms according to size-symmetry (size-symmetric vs. size-asymmetric) and species identity (intra-specific vs. inter-specific). The results showed that the size-symmetric inter-specific component was non-significant on beech basal area growth and had a negative effect on pine growth. The effect of size-asymmetric inter-specific competition was always non-significant, resulting in a higher basal area growth when the admixed species are of a larger size. The interaction between annual precipitation and this inter-specific competition effect was much more pronounced on beech than on pine. Inter-specific competition had a negative effect on pine growth under better climatic conditions and a positive effect at dryer sites, while beech always benefited from the presence of pine, although the benefit was greater where climatic site conditions were better. In tree mortality models, pine mortality increased with the proportion of beech, while beech mortality was lower as the proportion of pine increased. Precipitation modified the inter-specific competition effect on tree mortality although the site influence was less relevant than on tree growth. For pine mortality, the negative effect of beech admixture was stronger at lower mean annual precipitation, while in the case of beech the positive effect of pine increased at higher levels of precipitation. The influence of climate on the effect of competition, the variation in their strength depending on the mode of competition (size-symmetric or size-asymmetric), along with the inter-specific competition component, highlight the importance of considering the effect of site conditions on between-species interactions when modeling tree growth and mortality. The species-specific patterns of variation in tree interactions along climatic gradients and the differences in tree growth and mortality corroborate the need to consider the nature of stress-limiting factors and species composition and the importance of analyzing both dynamic processes simultaneously.

Regional changes of Pinus pinaster site index in Spain using a climate-based dominant height model.

This study compares two site index estimations for Mediterranean maritime pine (Pinus pinaster Ait.) stands in the Iberian Peninsula. The first prediction was performed under the assumption of cons...

Modeling individual-tree mortality in Pyrenean oak (Quercus pyrenaica Willd.) stands

Abstract• Tree mortality is an important process in forest ecosystem dynamics and is one of the least understood phenomena, because of the complex interactions between different environmental stresses, minimal understanding of whole-plant mortality processes, and a chronic shortage of data.• A multilevel logistic regression model was developed for predicting the probability of mortality in individual trees with the objective of improving long-term planning in Spanish pyrenean oak forests. The data came from one 10-year re-measurement of the permanent plot network belonging to the Spanish National Forest Inventory distributed throughout north-west Spain.• The probability of mortality decreased with increasing individual diameter at breast height and increasing ratio of the height of subject tree to the dominant height of the sample plot. The resulting mortality model was evaluated using an independent data set from a region close to the study area.• The regeneration of pyrenean oak generally takes place through stump and/or root sprouting; so stand dynamics differ from those of others species. The model developed is expected to improve the accuracy of stand forecasts in northwest Spain.