J. Raventós

Age, climate and intra-annual density fluctuations in Pinus halepensis in Spain

Intra-annual density fluctuations (IADFs) in tree rings of Aleppo pine (Pinus halepensis) are considered to be among the most promising wood anatomical features in dendrochronological studies. They provide environmental information in addition to those obtained from tree-ring widths. We used a network of 35 sites in Spain, ranging from nearly desert to temperate climate. We analysed tree-ring series of 529 trees to study IADF frequencies, and their dependence on climatic factors and cambial age. The results showed that IADF frequency is age dependent, with its maximum at the cambial age of 27 years (evaluated at breast height). The frequencies varied across the network and at different sites we recorded that 0.3% to 33% of the analysed tree rings contained IADFs. They were more frequent where and when the temperatures were higher, summer drought was intense and autumn was the main precipitation season. IADF formation was particularly related to high minimum temperatures and wet conditions in late summer and autumn. These results suggest that IADF formation is not related to stressful conditions during summer but to favourable conditions during autumn. These conditions promote cambial reactivation and consequently formation of wider tree rings.

Assessing components of a competition index to predict growth in an even-aged Pinus nigra stand

The relationship between tree growth and competition may depend on some subjective choices that are commonly left to the researcher. Among these are the neighborhood radius, the number of years of growth that are integrated, and tree age. We have evaluated the importance of these factors when relating growth and competition in a forest stand with contrasted densities of the dominant tree species (Pinus nigra) and understory shrub species (Adenocarpus decorticans). Previous to this evaluation we performed a randomization test to assess the relationship between tree growth and neighbors. By using Daniels index of competition we found that the use of a fixed neighborhood radius underestimated the importance of tree competition. The coefficient of determination (r2) of the relationship between tree growth and Daniels index increased asymptotically with the number of years considered. Five years of growth gave high r2 independently of the density of trees and shrubs. The intensity of competition was weakly affected by the characteristics of the plot (tree and shrub densities), and did not change with time. In contrast, the potential growth at equal competition – as represented by constant “a” in the allometric model – changed with time suggesting a gradual decrease in potential tree growth in the plots with higher tree density, and a gradual increase in those plots with high density of shrubs. These results may reflect tree canopy closure and the senescence of Adenocarpus decorticans. A method is suggested to select optimum neighborhood radius and growing period for the calculation of competition indices. By applying this method we were able to explain as much as 79–84% of the variability in tree growth of this stand.

Comparison of sediment ratio curves for plants with different architectures

Abstract We analyzed the empirical relationship between plant coverage and sediment ratio curves (SR) at two semi-arid Mediterranean sites (inland Spain). Comparison of b values in the fitted equation (SR = a * e−b*x), with x as % cover) shows a significant difference (P

Growth dynamics of three tropical savanna grass species: an individual-module model

Abstract We model the dynamics of grass plant growth as a collection of the individual dynamic behavior of shoots and leaves. The model is inspired in data for plants of three species ( Elyonurus adustus , Leptocoryphium lanatum and Andropogon semiberbis ) of common grasses in the Venezuelan savannas that were sampled monthly for 1 year. These species represent different architecture and regeneration response to fire. Modules (shoots and leaves) were counted in each cell of a square grid in each one of several vertical levels. Module density per cell provides the horizontal distribution within a level and is aggregated by level to obtain vertical distribution. Both distributions are simulated by a dynamical model based on shoot emergence and mortality, elongation of shoots and leaves given by Richards’ equation, plus a few simple geometric considerations. For quantitative comparisons of model results to data, the transient and final values for vertical distribution plus two metrics of horizontal distribution at each level, were calculated for the simulation results and the field data. Proportion of occupied cells and maximum distance to the center of growth were the two metrics selected to capture the dispersion and range of the horizontal distribution. The model results indicate predictable final vertical profiles (of proportional density plus the two metrics) similar to the profiles of measured distributions for each species. A reasonable prediction of the transient behavior was also obtained but with larger deviations as evaluated by the root mean square error between model and data. Differences in vertical and horizontal patterns of module density among species are explained by changing a set of parameter values related to growth form and phenology. Thus, the model could be applied to generate plant functional types for analysis of savanna dynamics subject to fire. With modifications, the model is potentially applicable to other grass plants and other grassland ecosystems.

When stable-stage equilibrium is unlikely: integrating transient population dynamics improves asymptotic methods

BACKGROUND AND AIMS Evaluation of population projection matrices (PPMs) that are focused on asymptotically based properties of populations is a commonly used approach to evaluate projected dynamics of managed populations. Recently, a set of tools for evaluating the properties of transient dynamics has been expanded to evaluate PPMs and to consider the dynamics of populations prior to attaining the stable-stage distribution, a state that may never be achieved in disturbed or otherwise ephemeral habitats or persistently small populations. This study re-evaluates data for a tropical orchid and examines the value of including such analyses in an integrative approach. METHODS Six small populations of Lepanthes rubripetala were used as a model system and the R software package popdemo was used to produce estimates of the indices for the asymptotic growth rate (lambda), sensitivities, reactivity, first-time step attenuation, maximum amplification, maximum attenuation, maximal inertia and maximal attenuation. The response in lambda to perturbations of demographic parameters using transfer functions and multiple perturbations on growth, stasis and fecundity were also determined. The results were compared with previously published asymptotic indices. KEY RESULTS It was found that combining asymptotic and transient dynamics expands the understanding of possible population changes. Comparison of the predicted density from reactivity and first-time step attenuation with the observed change in population size in two orchid populations showed that the observed density was within the predicted range. However, transfer function analysis suggests that the traditional approach of measuring perturbation of growth rates and persistence (inertia) may be misleading and is likely to result in erroneous management decisions. CONCLUSIONS Based on the results, an integrative approach is recommended using traditional PPMs (asymptotic processes) with an evaluation of the diversity of dynamics that may arise when populations are not at a stable-stage distribution (transient processes). This method is preferable for designing rapid and efficient interventions after disturbances, and for developing strategies to establish new populations.

Missing Rings in Pinus halepensis - The Missing Link to Relate the Tree-Ring Record to Extreme Climatic Events.

Climate predictions for the Mediterranean Basin include increased temperatures, decreased precipitation, and increased frequency of extreme climatic events (ECE). These conditions are associated with decreased tree growth and increased vulnerability to pests and diseases. The anatomy of tree rings responds to these environmental conditions. Quantitatively, the width of a tree ring is largely determined by the rate and duration of cell division by the vascular cambium. In the Mediterranean climate, this division may occur throughout almost the entire year. Alternatively, cell division may cease during relatively cool and dry winters, only to resume in the same calendar year with milder temperatures and increased availability of water. Under particularly adverse conditions, no xylem may be produced in parts of the stem, resulting in a missing ring (MR). A dendrochronological network of Pinus halepensis was used to determine the relationship of MR to ECE. The network consisted of 113 sites, 1,509 trees, 2,593 cores, and 225,428 tree rings throughout the distribution range of the species. A total of 4,150 MR were identified. Binomial logistic regression analysis determined that MR frequency increased with increased cambial age. Spatial analysis indicated that the geographic areas of south-eastern Spain and northern Algeria contained the greatest frequency of MR. Dendroclimatic regression analysis indicated a non-linear relationship of MR to total monthly precipitation and mean temperature. MR are strongly associated with the combination of monthly mean temperature from previous October till current February and total precipitation from previous September till current May. They are likely to occur with total precipitation lower than 50 mm and temperatures higher than 5°C. This conclusion is global and can be applied to every site across the distribution area. Rather than simply being a complication for dendrochronology, MR formation is a fundamental response of trees to adverse environmental conditions. The demonstrated relationship of MR formation to ECE across this dendrochronological network in the Mediterranean basin shows the potential of MR analysis to reconstruct the history of past climatic extremes and to predict future forest dynamics in a changing climate.

Application of the cross tab analysis to the spatial analysis of climatic tendencies in the eastern sector of Spain

RESUMEN: Proponemos el analisis de las tablas cruzadas (cross-tab analysis) para estudiar el solapamiento y analizar las relaciones espaciales entre las tendencias de diferentes variables del clima. Para ilustrar el metodo se presentan dos ejemplos en los que se comparan las distribuciones espaciales de las tendencias anuales de la precipitacion, del evento diario maximo y de la variabilidad anual. Los ejemplos se desarrollan en la Comunidad Valenciana y el sector central de la Depresion del Ebro. En la Comunidad Valenciana el analisis permite descubrir una relacion doble entre las tendencias de los totales anuales y las del maximo evento diario. Por su parte, en el sector central del valle del Ebro la relacion encontrada entre las tendencias de precipitacion anual y su variabilidad sugiere que los escenarios futuros, si se mantienen las pautas descritas, estaran sometidos a una mayor imprecision y aleatoriedad. ABSTRACT: We suggest cross-tab analysis to study the spatial distribution-overlapping trend between climate elements. We present two examples of such overlapping, in which we compared the spatial distribution of annual rainfall trend with spatial distribution of trend of maximum daily event and spatial distribution of annual rainfall variability. In the first ones (Comunidad de Valencia, E of Spain) we find a complex relationship between annual rainfall trend and daily maximum rainfall trend. In the second ones (Depresion del Ebro, NE inland of Spain) the relationship between annual rainfall trend and annual rainfall variability trend suggest that futures scenarios could be more and more non-predictable.