I. Martínez

Recruitment in Tropical Tree Species: Revealing Complex Spatial Patterns

Seed dispersal should leave a signature on the spatial distribution of recruits that can be quantified using sophisticated techniques of spatial pattern analysis. Here we study spatial patterns of five frugivore‐dispersed tropical tree species at the Barro Colorado Island forest, Panama, to describe detailed properties of the spatial patterns of recruits and to investigate whether these patterns were produced by temporally consistent mechanisms. Our spatial point pattern analyses detected the existence of surprising spatial structures, such as double‐cluster and superposition patterns, and they allowed for a detailed quantification of their properties. The spatial recruitment patterns were composed of two independent components comprising a random component and a component showing a complex spatial pattern with two critical scales of clustering. The analysis allowed an estimation of the relative contribution of scatter dispersal versus clump dispersal in effective seed dispersal for our study species. Additionally, the cluster characteristics were temporally consistent over 25 years and correlated with several species traits. We are just beginning to discover the richness of spatial patterns found at tropical forests, and we are confident that a combination of advanced point pattern analysis with field data will allow for significant advances in establishing the link between spatial patterns and processes.

Seed dispersal patterns in a temperate forest during a mast event: performance of alternative dispersal kernels

Seed dispersal patterns were studied in a north-western Spain temperate forest community to assess the performances of alternative dispersal kernels during two years with ecologically contrasting scenarios; a non-mast year, and a mast year of the dominant canopy species, beech Fagus sylvatica. Dispersal kernels were fitted under a Bayesian modeling framework. Both simple and mixture kernels were considered for the five more abundant tree species (Corylus avellana, Crataegus monogyna, F. sylvatica, Ilex aquifolium and Taxus baccata). Mixture kernels provided a better fit for almost all species, and the log-normal performed best for T. baccata. No relationship between dispersal syndromes and the best dispersal kernel function emerged. However, we found temporal changes in the shape of the dispersal kernels that seemed to be related to variation in relative fruit production among species and the resulting changes in the responses of dispersal vectors. This reveals a potential role for disperser-mediated indirect effects in terms of introducing temporal variation in species spread. In this sense, our results highlight the need to consider single species seed dispersal as a community process.

Disentangling the formation of contrasting tree line physiognomies combining model selection and Bayesian parameterization for simulation models.

Alpine tree-line ecotones are characterized by marked changes at small spatial scales that may result in a variety of physiognomies. A set of alternative individual-based models was tested with data from four contrasting Pinus uncinata ecotones in the central Spanish Pyrenees to reveal the minimal subset of processes required for tree-line formation. A Bayesian approach combined with Markov chain Monte Carlo methods was employed to obtain the posterior distribution of model parameters, allowing the use of model selection procedures. The main features of real tree lines emerged only in models considering nonlinear responses in individual rates of growth or mortality with respect to the altitudinal gradient. Variation in tree-line physiognomy reflected mainly changes in the relative importance of these nonlinear responses, while other processes, such as dispersal limitation and facilitation, played a secondary role. Different nonlinear responses also determined the presence or absence of krummholz, in agreement with recent findings highlighting a different response of diffuse and abrupt or krummholz tree lines to climate change. The method presented here can be widely applied in individual-based simulation models and will turn model selection and evaluation in this type of models into a more transparent, effective, and efficient exercise.

Back to the Future: The Responses of Alpine Treelines to Climate Warming are Constrained by the Current Ecotone Structure

Alpine treeline ecotones are considered early-warning monitors of the effects of climate change on terrestrial ecosystems, but it is still unclear how accurately treeline dynamics may track the expected temperature rises. Site-specific abiotic constraints, such as topography and demographic trends may make treelines less responsive to environmental fluctuations. A better understanding on how local processes modulate treelines’ response to warming is thus required. We developed a model of treeline dynamics based on individual data of growth, mortality and reproduction. Specifically, we modeled growth patterns, mortality rates and reproductive size thresholds as a function of temperature and stand structure to evaluate the influence of climate- and stand-related processes on treeline dynamics. In this study, we analyze the dynamics of four Pyrenean mountain pine treeline sites with contrasting stand structures, and subjected to differing rates of climate warming. Our models indicate that Pyrenean treelines could reach basal areas and reproductive potentials similar to those currently observed in high-elevation subalpine forest by the mid twenty-first century. The fastest paces of treeline densification are forecasted by the late twenty-first century and are associated with higher warming rates. We found a common densification response of Pyrenean treelines to climate warming, but contrasting paces arise due to current size structures. Treelines characterized by a multistratified stand structure and subjected to lower mean annual temperatures were the most responsive to climate warming. In monostratified stands, tree growth was less sensitive to temperature than in multistratified stands and trees reached their reproductive size threshold later. Therefore, our simulations highlight that stand structure is paramount in modulating treeline responsiveness to ongoing climate warming. Synthesis. Treeline densification over the twenty-first century is likely to occur at different rates contingent on current stand structure and its effects on individual-level tree growth responses to warming. Accurate projections of future treeline dynamics must thus incorporate site-specific factors other than climate, specifically those related to stand structure and its influence on tree growth.

Reinforced Concrete Durability in Marine Environments DURACON Project: Long-Term Exposure

This paper presents the results, after a long-term evaluation in marine environments, from an Ibero-American project called “Effect of the environment on reinforcement durability” (DURACON). This p...

Calcium looping reactor design for fluidized-bed systems

Postcombustion calcium looping (CaL) systems for CO 2 capture require at least two interconnected reactors to operate: a carbonator reactor where CaO particles react with CO 2 (and other impurities like SO 2 ), and a calciner intended to regenerate the CaCO 3 formed in the carbonator and produce CaO in an atmosphere rich in CO 2 . In the most developed process configuration, the calciner is an oxy-fired combustor where coal is burned in O 2 /CO 2 to drive the endothermic calcination reaction. This chapter reviews the basic design methods of these two reactors intended to achieve high gas and solid conversions with meaningful reactor dimensions. Basic models are reviewed together with some emerging CaL systems that integrate further reactors.

Concrete Carbonation in Ibero-American Countries DURACON Project: Six-Year Evaluation

Concrete carbonation data from 16 test sites in 9 countries (Bolivia, Chile, Colombia, Costa Rica, Mexico, Spain, Uruguay, Portugal, and Venezuela) were compared to identify concrete performance du...

Steel Corrosion in a Chloride Contaminated Concrete Pore Solution with Low Oxygen Availability

It is commonly mentioned that in concrete chloride induced corrosion is controlled by the oxygen content in such a manner that in water saturated conditions no oxygen will be present and thus no corrosion can develop. In the present paper, experimentation has been made in low oxygen availability “pore” solutions with several amounts of chlorides. These situations may represent the case of a water saturated concrete. The results indicate that at very low oxygen contents, i.e. almost negligible because complete removal is very difficult, corrosion may develop in presence of chlorides. The presence or absence of corrosion is influenced by the amount of chloride, its corrosion potential and the steel surface condition.

Effect of temperature on corrosion parameters and apparent activation energy measured by embedded sensors in pilot container in El Cabril repository

Abstract In order to study the real on-site aging of concrete and the potential corrosion risk for the reinforcements, Enresa has undertaken a monitoring programme in collaboration with Institute of Construction Science ‘Eduardo Torroja’ (IETcc) by permanently monitoring a pilot nuclear waste container through the installation of sensors. The pilot container of medium and low radioactive waste is buried near the real large concrete cells and has been monitored from 1994. The evolution from 1995 of corrosion parameters (corrosion rate, corrosion potential, electrical resistivity, concrete strains, oxygen availability) obtained is commented in the paper. The results indicate that the parameters evolve with time and the temperature is a very relevant variable influencing the measurements. An attempt to model the effect of temperature has been made by calculating the ‘apparent activation energies’ for the case of the electrical resistivity. Two clear regimes or slopes were found, one below and the other above 20°C, which have been attributed to a change in the state of the water from liquid to vapour although it has not been confirmed. The fact is that the resistivity increase is more pronounced above 20°C than below.

Control of cathodic protection in bridges without disconnecting protection current: passivity verification technique (PVT)

Abstract Standards for monitoring the performance of cathodic protection systems on reinforced concrete structures actually recognised are based on the measurement of the polarised potential of the reinforcement (polarisation/depolarisation, E–log I tests). A new methodology to measure this performance has been developed based on the passivation of the rebar rather than on the level of potential polarisation. This new technique is based on electrochemical impedance spectroscopy measurements using a modulated confinement of the applied current. The results are not quantitative, but properly inform on the passivity of the rebar under protection and its resistance to corrosion. The new technique has been evaluated in the laboratory using sacrificial and impressed current systems. In the present paper results obtained with this technique were compared to results achieved by standard polarisation methods and were found to be in agreement. The new technique is faster than standard methods and does not require interruption of the cathodic protection current.