Felipe Bravo

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.

Growth response of Pinus pinaster Ait. to climatic variables in central Spanish forests

Abstract• The effect of climatic variables (temperature and precipitation) on radial growth of the Mediterranean Maritime pine (Pinus pinaster Ait.) was studied using dendrochronological techniques in the Iberian Peninsula.• Ten tree-ring width chronologies, along the central distribution area of the species, were built. Chronology variability was analysed using Principal Component Analysis (PCA) for the period 1952–2005.• The first principal component (PC1) explained 56% of tree-growth variability. Tree-growth association with climate was analysed at regional and local scales using correlation coefficient and bootstrapped response functions.• Radial growth at both scales was positively correlated with rainfall during and prior to the growing season at all sites, and with summer rainfall before the growing season at five sites. Mean temperature effect changed according to the sampling site, from non-significant at the highest sites to significant (positive relationship in winter) at the lowest sites. Growth season temperature also had a negative effect.• The Kalman filter was applied to estimate changing association between growth and climate over-time. Results suggested a change in association, initiated in the 80s, from non-significant to significant (*p < 0.05) at six of the sampling sites.• Pinus pinaster is an accurate species for analysing tree-growth association with climate and for studying plant behaviour under global change conditions.Résumé• L’influence des variables climatiques (températures et précipitations) sur la croissance radiale du pin maritime (Pinus pinaster Ait.) a été étudiée en utilisant des techniques dendrochronologiques dans la péninsule Ibérique.• Dix chronologies de largeur de cerne ont été établies tout au long de la zone centrale de distribution de l’espèce. La variabilité des chronologies a été étudiée par une Analyse en Composantes Principales (PCA) pour la période 1952–2005.• La première composante principale (PC1) a expliqué 56 % de la variabilité de la croissance des arbres. L’association entre la croissance des arbres et le climat a été analysée à l’échelle locale et régionale en utilisant un coefficient de corrélation et une méthode de rééchantillonnage.• La croissance radiale à ces deux échelles a montré une corrélation positive avec les précipitations survenues pendant et avant la saison de croissance dans tous les sites et avec les précipitations estivales survenues avant la saison de croissance dans cinq sites. L’effet de la température moyenne a varié en fonction de l’altitude des sites, en étant non significatif dans les sites les plus élevés et positivement significatif en hiver dans les sites les plus bas. La température de la saison de croissance a également eu un effet négatif.• On a appliqué le filtre de Kalman pour estimer les variations temporelles de l’association variable entre la croissance et le climat. Les résultats ont suggéré que cette association est passée, dans les années 80, de non significative à significative (*p < 0, 05) dans six sites d’échantillonnage.• Pinus pinaster est une espèce adéquate pour analyser l’association entre la croissance des arbres et le climat, et pour étudier le comportement de l’espèce dans des conditions de changement global.

Carbon sequestration in Spanish Mediterranean forests under two management alternatives: a modeling approach

Management implications associated with two different silvicultural strategies in two Spanish pine forests (Scots pine stands in northern Spain and Mediterranean Maritime pine stands in Central Spain) were explored. Whole-stand yield, growth models and individual tree equations were used to estimate carbon stock in forests under different silvicultural alternatives and site indexes. Each alternative was evaluated on the basis of the land expectation value (LEV). Results reveal the appropriateness of implementing carbon payments, because it can clearly complement traditional management objectives in economic terms. Longer rotations on the poorest sites result in a positive economic return by introducing carbon output. The proportion of carbon stock in the final harvest relative to total fixed carbon is always higher in long rotation scenarios. However, short rotation systems produce the highest values of carbon MAI regardless of site index. The impact of carbon price is higher on the Maritime pine stands than on Scots pine stands. For both the species, changes in the discount rate have a minor impact on Carbon LEV. Notwithstanding, the proportion of total LEV due to carbon is greater when the discount rate increases.

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.

Effects of shrub and canopy cover on the relative growth rate of Pinus pinaster Ait. seedlings of different sizes

Abstract• IntroductionShrubs are recognized as important tree regeneration niches. In this study, we experimentally analysed the effects of shrub presence, canopy cover (closed cover and open cover-gaps), and seedling size on Pinus pinaster growth.• ObjectiveWe expected that (1) seedling–shrub interaction would depend on seedling size and would shift from positive to negative with increasing size; (2) overstorey canopy would affect seedling–shrub interaction, with stronger and positive interactions in gaps, and (3) microsite factors would be affected by vegetation. Social status and plant size appeared to determine the post-shrub-treatment growth response.• ResultsThe effect of shrub on seedling growth varied with the canopy cover. Under closed canopy, there was a shift from a positive net effect on smaller seedlings to a negative net effect on mid-size seedlings, and then back to a positive net effect on larger seedling response. Under open canopy, a negative net effect was observed, with no change in the sign of the interaction as seedling size increased. Microenvironmental conditions varied in relation to overstorey and understorey vegetation, while soil conditions varied in relation to overstorey. The seedling–shrub interaction had both positive and negative net effects, which could help define the natural regeneration dynamic of P. pinaster.

Climatic variability and other site factor influences on natural regeneration of Pinus pinaster Ait. in Mediterranean forests

BackgroundHow environmental factors affect forest regeneration is relevant for systems that depend partially or fully on natural regeneration.MethodsP. pinaster post-disturbance regeneration and its relationship to environmental factors was studied in five P. pinaster forest populations of central Spain. We expected that: 1) different harvesting methods or wildfire would promote natural regeneration in all populations, but with local and regional variations,or 2) alternatively, different site-dependent stand factors would affect natural regeneration, although generalized climate effects would be seen. Analysis of variance and multivariate analysis were used to test differences, to classify ecological variations, and to search for the most important factors affecting regeneration.ResultsThe results suggest that the recovery of P. pinaster forest in burnt stands, and stand replacement in harvested stands, can be achieved soon after disturbance if climatic conditions and other local-site factors (e.g., soil and overstory structure in harvested stands, cone bank in burnt stands) make the stand suitable for natural regeneration. Heterogeneous regeneration can be expected in all cases. The time of precipitation strongly influenced seedling density and successive regeneration development stages.ConclusionEdaphic properties, combined with water availability from precipitation, can seriously limit the natural establishment of P. pinaster in xeric systems or during years of intense drought. Although many factors contribute to high variability, natural regeneration has been very effective (successful) in P. pinaster forests, which contributes to the generalization that natural regeneration is a viable forestry option in many forest types.

Carbon in heartwood, sapwood and bark along the stem profile in three Mediterranean Pinus species

Abstract• ContextUnderstanding biological processes in forests is necessary to orientate ecosystem management towards potential C sequestration. To achieve this, information is required about changes in forest biomass C pools, including the stem components (bark, sapwood and heartwood).• AimsThis study aimed to determine whether there are differences in C concentration in axial and radial directions within stem biomass in Pinus nigra, Pinus pinaster and Pinus sylvestris.• MethodsWood samples from a permanent plantation in northern Spain were examined for C concentration and wood bulk density. • Results The results showed that C concentration was higher in heartwood than in sapwood in the three species. Pinus spp. sapwood C concentration increased along the stem, while the C concentration in heartwood tissue showed the opposite behavior. In bark, Pinus pinaster showed a decreasing trend, in contrast to Pinus nigra and Pinus sylvestris, where higher values were found at the base and top of the stem. Finally, wood bulk density decreased in heartwood, sapwood and bark areas when stem height increased. Estimating C content taking into account different anatomical parts and heights is important in considering the specificity of the different parts because of their potential commercial or ecological use in forest ecosystems.

Carbon sequestration in Mediterranean pine forests

Management objectives and techniques in woodlands dominated by Quercus species have changed dramatically over the last few decades, especially in the case of coppices. The fact that these stands are of little economic importance today is in part compensated by their value, for example, as carbon sinks. The identification of this important role of Quercus woodlands allows us to contemplate the development of specific silviculture and to promote investment in the stands. It is also important, in the context of global change, to analyze the dynamics involved in the transformation of Quercus woodlands from carbon sinks to emitters.

Variation in carbon concentration and basic density along stems of sessile oak (Quercus petraea (Matt.) Liebl.) and Pyrenean oak (Quercus pyrenaica Willd.) in the Cantabrian Range (NW Spain)

ContextInformation about variations in basic density (BD) and carbon content (%C) along tree stems is key to assessing forest carbon sinks.AimsThe aim of the study was to determine any differences in %C and BD between different woody tissues (bark, sapwood and heartwood) in two widespread European oak species (Quercus pyrenaica and Quercus petraea).MethodsTwenty trees were felled in northern Spain, and 317 discs cut from the trees were dried and analysed to determine %C and BD.ResultsThere were significant differences in %C between bark, heartwood and sapwood, and between species. There were also significant differences in BD between the tissues (heartwood > sapwood > bark), and the BD was higher in Q. petraea than in Q. pyrenaica. Both %C and BD varied along the stem.ConclusionMore accurate estimates of carbon contents were obtained by using specific values for different heights and anatomical parts, than by using single values.

CLIMATE CHANGE, TREE-RING WIDTH AND WOOD DENSITY OF PINES IN MEDITERRANEAN ENVIRONMENTS

During the second half of the 20th century, the Mediterranean area has experienced an increase in temperature, and a decrease in precipitation leading to a higher frequency of severe droughts. Consequently, widespread Mediterranean pine species suffered a shift in their climate-growth relationships that might lead to detrimental consequences. Wood features such as wood density are also affected by recent climatic changes producing an effect on wood structure and quality. Tree-ring anatomy was analyzed in three species (Pinus halepensis, P. pinaster and P. sylvestris), the three main pine species in Spain, in order to understand the relationships between tree-ring width and wood density as well as the influence of the climatic variations on these variables. Precipitation influenced tree radial growth and wood density for the three species, but at different times of the growth period. Mean and maximum density followed different patterns for the three species, decreasing with time in P. pinaster and increasing in P. halepensis and P. sylvestris. Growth and mean density trends were followed by a 5-year moving average with low variability in the three species. However, a high variability was observed in the inter-annual trends during the most recent years presumably related to climate. These climate-triggered modifications could adversely effect wood properties and wood quality.