Marcon, E., & Puech, F. (2010). Measures of the geographic concentration of industries: improving distance-based methods. J. Econ. Geogr., 10(5), 745–762.
Abstract: We discuss a property of distance-based measures that has not been addressed with regard to evaluating the geographic concentration of economic activities. The article focuses on the choice between a probability density function of point-pair distances or a cumulative function. We begin by introducing a new cumulative function, M, for evaluating the relative geographic concentration and the co-location of industries in a non-homogeneous spatial framework. Secondly, some rigorous comparisons are made with the leading probability density function of Duranton and Overman (2005), Kd. The merits of the simultaneous use of Kd and M is proved, underlining the complementary nature of the results they provide.
Keywords: Geographic concentration; distance-based methods; K-density function; Ripley's K function; M function; C40; C60; R12; L60
|
Lebrini, M., Robert, F., Vezin, H., & Roos, C. (2010). Electrochemical and quantum chemical studies of some indole derivatives as corrosion inhibitors for C38 steel in molar hydrochloric acid. Corrosion Sci., 52(10), 3367–3376.
Abstract: A comparative study of 9H-pyrido[3,4-b]indole (norharmane) and 1-methyl-9H-pyrido[3,4-b]indole (harmane) as inhibitors for C38 steel corrosion in 1 M HCl solution at 25 degrees C was carried out. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were applied to study the metal corrosion behavior in the absence and presence of different concentrations of these inhibitors. The OCP as a function of time were also established. Cathodic and anodic polarization curves show that norharmane and harmane are a mixed-type inhibitors. Adsorption of indole derivatives on the C38 steel surface, in 1 M HCl solution, follows the Langmuir adsorption isotherm model. The Delta G degrees(ads) values were calculated and discussed. The potential of zero charge (PZC) of the C38 steel in inhibited solution was studied by the EIS method, and a mechanism for the adsorption process was proposed. Raman spectroscopy confirmed that indole molecules strongly adsorbed onto the steel surface. The electronic properties of indole derivates, obtained using the AM1 semi-empirical quantum chemical approach, were correlated with their experimental efficiencies using the linear resistance model (LR). (C) 2010 Elsevier Ltd. All rights reserved.
Keywords: Steel; EIS; Raman spectroscopy; Polarization; Acid inhibition
|
Herault, B., Beauchene, J., Muller, F., Wagner, F., Baraloto, C., Blanc, L., et al. (2010). Modeling decay rates of dead wood in a neotropical forest. Oecologia, 164(1), 243–251.
Abstract: Variation of dead wood decay rates among tropical trees remains one source of uncertainty in global models of the carbon cycle. Taking advantage of a broad forest plot network surveyed for tree mortality over a 23-year period, we measured the remaining fraction of boles from 367 dead trees from 26 neotropical species widely varying in wood density (0.23-1.24 g cm(-3)) and tree circumference at death time (31.5-272.0 cm). We modeled decay rates within a Bayesian framework assuming a first order differential equation to model the decomposition process and tested for the effects of forest management (selective logging vs. unexploited), of mode of death (standing vs. downed) and of topographical levels (bottomlands vs. hillsides vs. hilltops) on wood decay rates. The general decay model predicts the observed remaining fraction of dead wood (R (2) = 60%) with only two biological predictors: tree circumference at death time and wood specific density. Neither selective logging nor local topography had a differential effect on wood decay rates. Including the mode of death into the model revealed that standing dead trees decomposed faster than downed dead trees, but the gain of model accuracy remains rather marginal. Overall, these results suggest that the release of carbon from tropical dead trees to the atmosphere can be simply estimated using tree circumference at death time and wood density.
Keywords: Amazonia; Carbon cycle; Decomposition; Selective logging; Rainforest; Coarse woody debris
|
Maia, A. C. D., Schlindwein, C., Navarro, D. M. A. F., & Gibernau, M. (2010). Pollination of Philodendron Acutatum (Araceae) in the Atlantic Forest of Northeastern Brazil: A Single Scarab Beetle Species Guarantees High Fruit Set. Int. J. Plant Sci., 171(7), 740–748.
Abstract: Philodendron acutatum (Araceae) is a hemiepiphyte common to the Atlantic Forest of northeastern Brazil. In two localities, we studied the species' breeding system and associations with flower-visiting insects, along with an analysis of its floral scent composition. The fruit set of self-incompatible P. acutatum was high, more than 90%, and inflorescences were exclusively pollinated by one species of scarab beetle, Cyclocephala celata (Scarabaeidae, Dynastinae). Pollinators are drawn toward the inflorescences at dusk by strong floral fragrances given off during the female phase of anthesis, along with endogenous heating of the spadix, whose temperatures were recorded at more than 11 degrees C above ambient air. Two other species of flower-visiting Cyclocephala were also consistently recovered in blacklight trappings during the flowering period of P. acutatum. The fact that only C. celata was found in association with P. acutatum suggests a local reproductive dependence of the plant to this scarab beetle species. Dihydro-beta-ionone and 2-hydroxy-5-methyl-3-hexanone, a rare volatile molecule so far unreported as a floral compound, together accounted for more than 97% of the unique scent composition of P. acutatum and might be involved in specific attraction of C. celata.
Keywords: Cyclocephala; floral volatiles; pollination specificity; reproductive success; thermogenesis
|
Audigeos, D., Buonamici, A., Belkadi, L., Rymer, P., Boshier, D., Scotti-Saintagne, C., et al. (2010). Aquaporins in the wild: natural genetic diversity and selective pressure in the PIP gene family in five Neotropical tree species. BMC Evol. Biol., 10, 18.
Abstract: Background: Tropical trees undergo severe stress through seasonal drought and flooding, and the ability of these species to respond may be a major factor in their survival in tropical ecosystems, particularly in relation to global climate change. Aquaporins are involved in the regulation of water flow and have been shown to be involved in drought response; they may therefore play a major adaptive role in these species. We describe genetic diversity in the PIP sub-family of the widespread gene family of Aquaporins in five Neotropical tree species covering four botanical families. Results: PIP Aquaporin subfamily genes were isolated, and their DNA sequence polymorphisms characterised in natural populations. Sequence data were analysed with statistical tests of standard neutral equilibrium and demographic scenarios simulated to compare with the observed results. Chloroplast SSRs were also used to test demographic transitions. Most gene fragments are highly polymorphic and display signatures of balancing selection or bottlenecks; chloroplast SSR markers have significant statistics that do not conform to expectations for population bottlenecks. Although not incompatible with a purely demographic scenario, the combination of all tests tends to favour a selective interpretation of extant gene diversity. Conclusions: Tropical tree PIP genes may generally undergo balancing selection, which may maintain high levels of genetic diversity at these loci. Genetic variation at PIP genes may represent a response to variable environmental conditions.
|
Bremaud, I., Cabrolier, P., Gril, J., Clair, B., Gerard, J., Minato, K., et al. (2010). Identification of anisotropic vibrational properties of Padauk wood with interlocked grain. Wood Sci. Technol., 44(3), 355–367.
Abstract: Grain deviations and high extractives content are common features of many tropical woods. This study aimed at clarifying their respective impact on vibrational properties, referring to African Padauk (Pterocarpus soyauxii Taub.), a species selected for its interlocked grain, high extractives content and uses in xylophones. Specimens were cut parallel to the trunk axis (L), and local variations in grain angle (GA), microfibril angle (MFA), specific Young's modulus (E' (L) /rho, where rho stands for the density) and damping coefficient (tan delta(L)) were measured. GA dependence was analysed by a mechanical model which allowed to identify the specific Young's modulus (E'(3)/rho) and shear modulus (G'/rho) along the grain (3) as well as their corresponding damping coefficients (tan delta(3), tan delta(G)). This analysis was done for native and then for extracted wood. Interlocked grain resulted in 0-25A degrees GA and in variations of a factor 2 in E'(L)/rho and tan delta(L). Along the grain, Padauk wood was characterized, when compared to typical hardwoods, by a somewhat lower E'(3)/rho and elastic anisotropy (E'/G'), due to a wide microfibril angle plus a small weight effect of extracts, and a very low tan delta(3) and moderate damping anisotropy (tan delta(G)/tan delta(3)). Extraction affected mechanical parameters in the order: tan delta(3) a parts per thousand tan delta(G) > G'/rho > > E'(3)/rho. That is, extractives' effects were nearly isotropic on damping but clearly anisotropic on storage moduli.
|
Castro, H., Fortunel, C., & Freitas, H. (2010). Effects of land abandonment on plant litter decomposition in a Montado system: relation to litter chemistry and community functional parameters. Plant Soil, 333(1-2), 181–190.
Abstract: Changes in land use and subsequent shifts in vegetation can influence decomposition through changes in litter quality (chemistry and structure) and alterations of soil temperature and moisture. Our aim was to study the effects of land abandonment on litter decomposition in a Mediterranean area of Montado, South Portugal. We tested the hypothesis that decomposition tends to slow down with abandonment, as woody species, richer in lignified structures, replace herbaceous species. We assessed the decomposition of community litter in situ using litterbag technique. To test the influence of local conditions, we simultaneously incubated a standard litter in situ. Our results showed that the shift from herbaceous to shrub-dominated communities lead to decreased decomposition rates. Changes in litter decomposition were primarily driven by changes in litter quality, even though the uneven pattern of litter mass loss over the experiment might reveal an effect from possible differences in microclimate. Shrub litter had higher nutrient content than herbaceous litter, which seemed to favour higher initial decomposition rates, but lower decomposition rate in the longer term. Shrubs also contribute to woody litter, richer in lignin, and secondary compounds that retard decomposition, and may play a role in increasing pools of slowly decomposing organic matter.
Keywords: Ecosystem processes; Land use change; Leaf dry matter content; Life form; Litter quality; Mediterranean
|
Phillips, O. L., van der Heijden, G., Lewis, S. L., Lopez-Gonzalez, G., Aragao, L. E. O. C., Lloyd, J., et al. (2010). Drought-mortality relationships for tropical forests. New Phytol., 187(3), 631–646.
Abstract: The rich ecology of tropical forests is intimately tied to their moisture status. Multi-site syntheses can provide a macro-scale view of these linkages and their susceptibility to changing climates. Here, we report pan-tropical and regional-scale analyses of tree vulnerability to drought. We assembled available data on tropical forest tree stem mortality before, during, and after recent drought events, from 119 monitoring plots in 10 countries concentrated in Amazonia and Borneo. In most sites, larger trees are disproportionately at risk. At least within Amazonia, low wood density trees are also at greater risk of drought-associated mortality, independent of size. For comparable drought intensities, trees in Borneo are more vulnerable than trees in the Amazon. There is some evidence for lagged impacts of drought, with mortality rates remaining elevated 2 yr after the meteorological event is over. These findings indicate that repeated droughts would shift the functional composition of tropical forests toward smaller, denser-wooded trees. At very high drought intensities, the linear relationship between tree mortality and moisture stress apparently breaks down, suggesting the existence of moisture stress thresholds beyond which some tropical forests would suffer catastrophic tree mortality.
Keywords: Amazon; Borneo; drought; lags mortality; RAINFOR; trees; tropics
|
Quilichini, A., Macquart, D., Barabe, D., Albre, J., & Gibernau, M. (2010). Reproduction of the West Mediterranean endemic Arum pictum (Araceae) on Corsica. Plant Syst. Evol., 287(3-4), 179–187.
Abstract: Pollination in the genus Arum appears to be in general a complex deceptive pollination process. The genus Arum is composed of 28 species, all belonging to the subgenus Arum, except A. pictum, the only species of the subgenus Gymnomesium, which is basal and sister to all other Arum species. The aim of this paper is to document the pollination ecology of the insular Arum pictum, the only Arum species to flower in autumn, on the island of Corsica (France). The anthesis cycle of A. pictum occurs during the day, attracting sphaerocerid flies and staphylinid beetles early in the morning and late in the afternoon of the first day. The pollen is released from the anthers early in the morning of the second day before the departure of the insects. Its thermogenic cycle matches the anthesis cycle with an original and unique, bimodal temperature pattern of the appendix (morning and afternoon), contrary to the unimodal pattern found in all other studied Arum species. Data from reproductive success and seed sets suggest that sexual reproduction in this species is limited by pollen (e.g. attracting lured insects) rather than by resources. The biology of this Western Mediterranean species appears to be different from other Western European Arum and close to some Eastern Mediterranean species. Further studies are needed to establish whether Arum pictum represents some ancestral stage or whether its peculiar biological traits are adapted to its insular distribution.
Keywords: Floral volatiles; Ocimene; Insect pollination; Reproductive success; Sphaeroceridae; Thermogenesis
|
Rutishauser, E., Wagner, F., Herault, B., Nicolini, E. A., & Blanc, L. (2010). Contrasting above-ground biomass balance in a Neotropical rain forest. J. Veg. Sci., 21(4), 672–682.
Abstract: Question What are the relative roles of tree growth, mortality and recruitment in variations of above-ground biomass in tropical forests? Location Paracou, French Guiana. Methods We quantified the contribution of growth, recruitment and mortality to total biomass of stands (trees DBH >= 10 cm) in six 6.25-ha permanent plots over 16 yr. Live biomass stocks and fluxes were computed for four separate size classes. Results All plots showed increasing biomass stocks over the study period, with an average value of +0.9 Mg ha-1 yr-1. Plots aggrading biomass were characterized by either minor biomass losses due to mortality or substantial increases in the biomass of large trees (DBH >= 60 cm). Conclusions Within the study period, the rarity of mortality events could not counter-balance the slow permanent increase in biomass, resulting in an apparent increase in biomass. Accounting for such rare events results in no net change in biomass balance.
Keywords: Biomass balance; Biomass fluxes; Forest dynamics; Permanent plots; Tropical forests
|